1
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Raikova R, Krutki P, Celichowski J. Skeletal muscle models composed of motor units: A review. J Electromyogr Kinesiol 2023; 70:102774. [PMID: 37099899 DOI: 10.1016/j.jelekin.2023.102774] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Revised: 04/06/2023] [Accepted: 04/09/2023] [Indexed: 04/28/2023] Open
Abstract
The mathematical muscle models should include several aspects of muscle structure and physiology. First, muscle force is the sum of forces of multiple motor units (MUs), which have different contractile properties and play different roles in generating muscle force. Second, whole muscle activity is an effect of net excitatory inputs to a pool of motoneurons innervating the muscle, which have different excitability, influencing MU recruitment. In this review, we compare various methods for modeling MU twitch and tetanic forces and then discuss muscle models composed of different MU types and number. We first present four different analytical functions used for twitch modeling and show limitations related to the number of twitch describing parameters. We also show that a nonlinear summation of twitches should be considered in modeling tetanic contractions. We then compare different muscle models, most of which are variations of Fuglevand's model, adopting a common drive hypothesis and the size principle. We pay attention to integrating previously developed models into a consensus model based on physiological data from in vivo experiments on the rat medial gastrocnemius muscle and its respective motoneurons. Finally, we discuss the shortcomings of existing models and potential applications for studying MU synchronization, potentiation, and fatigue.
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Affiliation(s)
- Rositsa Raikova
- Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, Bulgaria.
| | - Piotr Krutki
- Department of Neurobiology, Poznan University of Physical Education, Poland
| | - Jan Celichowski
- Department of Neurobiology, Poznan University of Physical Education, Poland
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2
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Lulic-Kuryllo T, Greig Inglis J. Sex differences in motor unit behaviour: A review. J Electromyogr Kinesiol 2022; 66:102689. [DOI: 10.1016/j.jelekin.2022.102689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 10/15/2022] Open
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3
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Glass TJ, Figueroa JE, Russell JA, Krekeler BN, Connor NP. Progressive Protrusive Tongue Exercise Does Not Alter Aging Effects in Retrusive Tongue Muscles. Front Physiol 2021; 12:740876. [PMID: 34744782 PMCID: PMC8567011 DOI: 10.3389/fphys.2021.740876] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 09/27/2021] [Indexed: 12/02/2022] Open
Abstract
Purpose: Exercise-based treatment approaches for dysphagia may improve swallow function in part by inducing adaptive changes to muscles involved in swallowing and deglutition. We have previously shown that both aging and progressive resistance tongue exercise, in a rat model, can induce biological changes in the genioglossus (GG); a muscle that elevates and protrudes the tongue. However, the impacts of progressive resistance tongue exercise on the retrusive muscles (styloglossus, SG; hyoglossus, HG) of the tongue are unknown. The purpose of this study was to examine the impact of a progressive resistance tongue exercise regimen on the retrusive tongue musculature in the context of aging. Given that aging alters retrusive tongue muscles to more slowly contracting fiber types, we hypothesized that these biological changes may be mitigated by tongue exercise. Methods: Hyoglossus (HG) and styloglossus (SG) muscles of male Fischer 344/Brown Norway rats were assayed in age groups of young (9 months old, n = 24), middle-aged (24 months old, n = 23), and old (32 months old, n = 26), after receiving an 8-week period of either progressive resistance protrusive tongue exercise, or sham exercise conditions. Following exercise, HG and SG tongue muscle contractile properties were assessed in vivo. HG and SG muscles were then isolated and assayed to determine myosin heavy chain isoform (MyHC) composition. Results: Both retrusive tongue muscle contractile properties and MyHC profiles of the HG and SG muscles were significantly impacted by age, but were not significantly impacted by tongue exercise. Old rats had significantly longer retrusive tongue contraction times and longer decay times than young rats. Additionally, HG and SG muscles showed significant MyHC profile changes with age, in that old groups had slower MyHC profiles as compared to young groups. However, the exercise condition did not induce significant effects in any of the biological outcome measures. Conclusion: In a rat model of protrusive tongue exercise, aging induced significant changes in retrusive tongue muscles, and these age-induced changes were unaffected by the tongue exercise regimen. Collectively, results are compatible with the interpretation that protrusive tongue exercise does not induce changes to retrusive tongue muscle function.
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Affiliation(s)
- Tiffany J Glass
- Department of Surgery-Otolaryngology, University of Wisconsin-Madison, Madison, WI, United States
| | | | - John A Russell
- Department of Surgery-Otolaryngology, University of Wisconsin-Madison, Madison, WI, United States
| | - Brittany N Krekeler
- Department of Surgery-Otolaryngology, University of Wisconsin-Madison, Madison, WI, United States.,Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL, United States
| | - Nadine P Connor
- Department of Surgery-Otolaryngology, University of Wisconsin-Madison, Madison, WI, United States.,Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Madison, WI, United States
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4
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Maghsoudipour M, Nokes B, Bosompra NO, Jen R, Li Y, Moore S, DeYoung PN, Fine J, Edwards BA, Gilbertson D, Owens R, Morgan T, Malhotra A. A Pilot Randomized Controlled Trial of Effect of Genioglossus Muscle Strengthening on Obstructive Sleep Apnea Outcomes. J Clin Med 2021; 10:jcm10194554. [PMID: 34640575 PMCID: PMC8509668 DOI: 10.3390/jcm10194554] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Revised: 09/27/2021] [Accepted: 09/29/2021] [Indexed: 12/19/2022] Open
Abstract
The genioglossus is a major upper airway dilator muscle. Our goal was to assess the efficacy of upper airway muscle training on Obstructive Sleep Apnea (OSA) as an adjunct treatment. Sixty-eight participants with OSA (AHI > 10/h) were recruited from our clinic. They fall into the following categories: (a) Treated with Automatic Positive Airway Pressure (APAP), (n = 21), (b) Previously failed APAP therapy (Untreated), (n = 25), (c) Treated with Mandibular Advancement Splint (MAS), (n = 22). All subjects were given a custom-made tongue strengthening device. We conducted a prospective, randomized, controlled study examining the effect of upper airway muscle training. In each subgroup, subjects were randomized to muscle training (volitional protrusion against resistance) or sham group (negligible resistance), with a 1:1 ratio over 3 months of treatment. In the baseline and the final visit, subjects completed home sleep apnea testing, Epworth Sleepiness Scale (ESS), Pittsburgh Sleep Quality Index (PSQI), SF-36 (36-Item Short Form Survey), and Psychomotor Vigilance Test (PVT). Intervention (muscle training) did not affect the AHI (Apnea-Hypopnea Index), (p-values > 0.05). Based on PSQI, ESS, SF-36 scores, and PVT parameters, the changes between the intervention and sham groups were not significant, and the changes were not associated with the type of treatment (p-value > 0.05). The effectiveness of upper airway muscle training exercise as an adjunct treatment requires further study.
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Affiliation(s)
- Maryam Maghsoudipour
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Brandon Nokes
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Naa-Oye Bosompra
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Rachel Jen
- Department of Medicine, University of British Columbia, Vancouver, BC V6T 1Z4, Canada;
| | - Yanru Li
- Department of Otorhinolaryngology Head and Neck Surgery, Beijing Tongren Hospital, Capital Medical University, Beijing 100730, China;
| | - Stacie Moore
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Pamela N. DeYoung
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Janelle Fine
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Bradley A. Edwards
- Department of Physiology, School of Biomedical Sciences and Biomedical Discovery Institute, Monash University, Melbourne, VIC 3800, Australia;
- Turner Institute for Brain and Mental Health, Monash University, Melbourne, VIC 3800, Australia
| | - Dillon Gilbertson
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Robert Owens
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
| | - Todd Morgan
- Department of Dentistry, Scripps Encinitas Hospital, Encinitas, CA 92024, USA;
| | - Atul Malhotra
- Department of Medicine, University of California, La Jolla, San Diego, CA 92161, USA; (M.M.); (B.N.); (N.-O.B.); (S.M.); (P.N.D.); (J.F.); (D.G.); (R.O.)
- Correspondence:
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5
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Luu BL, Saboisky JP, McBain RA, Trinder JA, White DP, Taylor JL, Gandevia SC, Butler JE. Genioglossus motor unit activity in supine and upright postures in obstructive sleep apnea. Sleep 2020; 43:5686881. [PMID: 31875918 DOI: 10.1093/sleep/zsz316] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2019] [Revised: 10/03/2019] [Indexed: 11/14/2022] Open
Abstract
This study investigated whether a change in posture affected the activity of the upper-airway dilator muscle genioglossus in participants with and without obstructive sleep apnea (OSA). During wakefulness, a monopolar needle electrode was used to record single motor unit activity in genioglossus in supine and upright positions to alter the gravitational load that causes narrowing of the upper airway. Activity from 472 motor units was recorded during quiet breathing in 17 males, nine of whom had OSA. The mean number of motor units for each participant was 11.8 (SD 3.4) in the upright and 16.0 (SD 4.2) in the supine posture. For respiratory-modulated motor units, there were no significant differences in discharge frequencies between healthy controls and participants with OSA. Within each breath, genioglossus activity increased through the recruitment of phasic motor units and an increase in firing rate, with an overall increase of ~6 Hz (50%) across both postures and participant groups. However, the supine posture did not lead to compensatory increases in the peak discharge frequencies of inspiratory and expiratory motor units, despite the increase in gravitational load on the upper airway. Posture also had no significant effect on the discharge frequency of motor units that showed no respiratory modulation during quiet breathing. We postulate that, in wakefulness, any increase in genioglossus activity to compensate for the gravitational effects on the upper airway is achieved primarily through the recruitment of additional motor units in both healthy controls and participants with OSA.
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Affiliation(s)
- Billy L Luu
- Neuroscience Research Australia, Randwick, NSW, Australia
| | - Julian P Saboisky
- Neuroscience Research Australia, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | - Rachel A McBain
- Neuroscience Research Australia, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | | | - David P White
- Sleep Disorders Research Program, Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA
| | - Janet L Taylor
- Neuroscience Research Australia, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia.,Edith Cowan University, Joondalup, WA, Australia
| | - Simon C Gandevia
- Neuroscience Research Australia, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
| | - Jane E Butler
- Neuroscience Research Australia, Randwick, NSW, Australia.,University of New South Wales, Sydney, NSW, Australia
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6
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Krekeler BN, Weycker JM, Connor NP. Effects of Tongue Exercise Frequency on Tongue Muscle Biology and Swallowing Physiology in a Rat Model. Dysphagia 2020; 35:918-934. [PMID: 32130514 DOI: 10.1007/s00455-020-10105-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2019] [Accepted: 02/25/2020] [Indexed: 11/28/2022]
Abstract
Age-related changes in muscle composition and function are often treated using exercise, including muscles of the tongue to treat swallowing impairments (dysphagia). Although tongue exercise is commonly prescribed, optimal tongue exercise doses have not been determined. The purpose of this study was to evaluate effects of varying tongue exercise frequency on tongue force, genioglossus muscle fiber size, composition and metabolism, and swallowing in a rat model. We randomized 41 old and 40 young adult Fischer 344/Brown Norway rats into one of four tongue exercise groups: 5 days/week; 3 days/week; 1 day/week; or sham. Tongue force was higher following all exercise conditions (vs sham); the 5 day/week group had the greatest change in tongue force (p < 0.001). There were no exercise effects on genioglossus (GG) fiber size or MyHC composition (p > 0.05). Significant main effects for age showed a greater proportion of Type I fibers in (p < 0.0001) and increased fiber size of IIa fibers (p = 0.026) in old. There were no significant effects of citrate synthase activity or PGC-1α expression. Significant differences were found in bolus speed and area (size), but findings were potentially influenced by variability. Our findings suggest that tongue force is influenced by exercise frequency; however, these changes were not reflected in characteristics of the GG muscle assayed in this study. Informed by findings of this study, future work in tongue dose optimization will be required to provide better scientific premise for clinical treatments in humans.
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Affiliation(s)
- Brittany N Krekeler
- Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Goodnight Hall, 1300 University Ave, Madison, WI, 53706, USA. .,Department of Surgery-Otolaryngology, Clinical Science Center, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI, 53792-7375, USA. .,Department of Communication Sciences and Disorders, Northwestern University, Swallowing Cross-Systems Collaborative, 2240 Campus Drive, Evanston, IL, 60208, USA.
| | - Jacqueline M Weycker
- Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Goodnight Hall, 1300 University Ave, Madison, WI, 53706, USA.,Department of Surgery-Otolaryngology, Clinical Science Center, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI, 53792-7375, USA
| | - Nadine P Connor
- Department of Communication Sciences and Disorders, University of Wisconsin-Madison, Goodnight Hall, 1300 University Ave, Madison, WI, 53706, USA.,Department of Surgery-Otolaryngology, Clinical Science Center, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI, 53792-7375, USA
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7
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Measurement and State-Dependent Modulation of Hypoglossal Motor Excitability and Responsivity In-Vivo. Sci Rep 2020; 10:550. [PMID: 31953471 PMCID: PMC6969049 DOI: 10.1038/s41598-019-57328-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Accepted: 12/19/2019] [Indexed: 12/17/2022] Open
Abstract
Motoneurons are the final output pathway for the brain’s influence on behavior. Here we identify properties of hypoglossal motor output to the tongue musculature. Tongue motor control is critical to the pathogenesis of obstructive sleep apnea, a common and serious sleep-related breathing disorder. Studies were performed on mice expressing a light sensitive cation channel exclusively on cholinergic neurons (ChAT-ChR2(H134R)-EYFP). Discrete photostimulations under isoflurane-induced anesthesia from an optical probe positioned above the medullary surface and hypoglossal motor nucleus elicited discrete increases in tongue motor output, with the magnitude of responses dependent on stimulation power (P < 0.001, n = 7) and frequency (P = 0.002, n = 8, with responses to 10 Hz stimulation greater than for 15–25 Hz, P < 0.022). Stimulations during REM sleep elicited significantly reduced responses at powers 3–20 mW compared to non-rapid eye movement (non-REM) sleep and wakefulness (each P < 0.05, n = 7). Response thresholds were also greater in REM sleep (10 mW) compared to non-REM and waking (3 to 5 mW, P < 0.05), and the slopes of the regressions between input photostimulation powers and output motor responses were specifically reduced in REM sleep (P < 0.001). This study identifies that variations in photostimulation input produce tunable changes in hypoglossal motor output in-vivo and identifies REM sleep specific suppression of net motor excitability and responsivity.
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8
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Kirk EA, Gilmore KJ, Stashuk DW, Doherty TJ, Rice CL. Human motor unit characteristics of the superior trapezius muscle with age-related comparisons. J Neurophysiol 2019; 122:823-832. [PMID: 31242057 DOI: 10.1152/jn.00138.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Current understanding of human motor unit (MU) control and aging is mostly derived from hand and limb muscles that have spinal motor neuron innervations. The aim here was to characterize and test whether a muscle with a shared innervation supply from brainstem and spinal MU populations would demonstrate similar age-related adaptations as those reported for other muscles. In humans, the superior trapezius (ST) muscle acts to elevate and stabilize the scapula and has primary efferent supply from the spinal accessory nerve (cranial nerve XI) located in the brainstem. We compared electrophysiological properties obtained from intramuscular and surface recordings between 10 young (22-33 yr) and 10 old (77-88 yr) men at a range of voluntary isometric contraction intensities (from 15 to 100% of maximal efforts). The old group was 41% weaker with 43% lower MU discharge frequencies compared with the young (47.2 ± 9.6 Hz young and 26.7 ± 5.8 Hz old, P < 0.05) during maximal efforts. There was no difference in MU number estimation between age groups (228 ± 105 young and 209 ± 89 old, P = 0.33). Furthermore, there were no differences in needle detected near fiber (NF) stability parameters of jitter or jiggle. The old group had lower amplitude and smaller area of the stimulated compound muscle action potential and smaller NF MU potential area with higher NF counts. Thus, despite age-related ST weakness and lower MU discharge rates, there was minimal evidence of MU loss or compensatory reinnervation.NEW & NOTEWORTHY The human superior trapezius (ST) has shared spinal and brainstem motor neuron innervation providing a unique model to explore the impact of aging on motor unit (MU) properties. Although the ST showed higher MU discharge rates compared with most spinally innervated muscles, voluntary strength and mean MU rates were lower in old compared with young at all contraction intensities. There was no age-related difference in MU number estimates with minimal electrophysiological evidence of collateral reinnervation.
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Affiliation(s)
- Eric A Kirk
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada
| | - Kevin J Gilmore
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Ontario, Canada
| | - Timothy J Doherty
- Department of Clinical Neurological Sciences, The University of Western Ontario, London, Ontario, Canada.,Department of Physical Medicine and Rehabilitation, The University of Western Ontario, London, Ontario, Canada
| | - Charles L Rice
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.,Department of Anatomy and Cell Biology, The University of Western Ontario, London, Ontario, Canada
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Moritaka H, Mineki M, Kobayashi M, Ono T, Hori K. Effect of carrot puree in vegetable juice on linguapalatal swallowing pressure. J Texture Stud 2017; 49:240-246. [PMID: 29226954 DOI: 10.1111/jtxs.12315] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 11/07/2017] [Accepted: 12/05/2017] [Indexed: 11/28/2022]
Abstract
This study aimed to ascertain the influence of various amounts (0-30%) of carrot puree (CP) in vegetable juice on linguapalatal swallowing pressure in healthy volunteers. Twenty healthy women (age range: 20-22 years) swallowed a 17-ml drink in a natural state, and linguapalatal swallowing pressure was measured using a special sensor sheet. Peak magnitude (maximum pressure of the tongue pushing on the hard palate), integrated values of linguapalatal swallowing pressure on the waveform, and duration of linguapalatal swallowing pressure were increased with increases in CP concentrations. The total integrated value for 30% CP vegetable juice was larger than that of vegetable juice with no CP. The apparent viscosity of the vegetable juice with a low CP concentration was smaller than that with a high CP concentration at the same shear rate. These results suggest that vegetable juice containing CP affects mechanoreceptor activity in the mouth and generates a neuromotor response. PRACTICAL APPLICATIONS This study aimed to ascertain the influence of various amounts of carrot puree (CP) in vegetable juice on linguapalatal swallowing pressure measured by using a special sensor sheet in healthy volunteers. Obtained results of this study clearly showed that vegetable juice containing CP affects the movement of the tongue in maneuvering the bolus. Moreover, the results demonstrated that this effect depended on the concentration of CP in the vegetable juice. These findings are expected to provide clinically valuable data on the effect of mechanical stimulation during the oral stage of swallowing.
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Affiliation(s)
- Hatsue Moritaka
- Institute of Women's Health Sciences, Showa Women's University, Meguro-ku, Tokyo, Japan
| | - Machiko Mineki
- Graduate School of Human Life Science, Tokyo Kasei University, Itabashi-ku, Tokyo, Japan
| | - Makoto Kobayashi
- Central Research Institute, ITO EN LTD., Makinohara, Shizuoka, Japan
| | - Takahiro Ono
- Graduate School of Medical and Dental Sciences, Niigata University, Chuo-ku, Niigata, Japan
| | - Kazuhiro Hori
- Graduate School of Medical and Dental Sciences, Niigata University, Chuo-ku, Niigata, Japan
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10
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Enoka RM, Duchateau J. Rate Coding and the Control of Muscle Force. Cold Spring Harb Perspect Med 2017; 7:cshperspect.a029702. [PMID: 28348173 DOI: 10.1101/cshperspect.a029702] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The force exerted by a muscle during a voluntary contraction depends on the number of motor units recruited for the action and the rates at which they discharge action potentials (rate coding). Over most of the operating range of a muscle, the nervous system controls muscle force by varying both motor unit recruitment and rate coding. Except at relatively low forces, however, the control of muscle force depends primarily on rate coding, especially during fast contractions. This review provides five examples of how the modulation of rate coding influences the force exerted by muscle during voluntary actions. The five examples comprise fast contractions, lengthening and shortening contractions, steady isometric contractions, fatiguing contractions, and contractions performed after a change in the daily level of physical activity.
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Affiliation(s)
- Roger M Enoka
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado 80309-0354
| | - Jacques Duchateau
- Laboratory of Applied Biology and Neurophysiology, Neuroscience Institute, Université Libre de Bruxelles, 1070 Brussels, Belgium
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11
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LaCross A, Watson PJ, Bailey EF. Association between Laryngeal Airway Aperture and the Discharge Rates of Genioglossus Motor Units. Front Physiol 2017; 8:27. [PMID: 28179887 PMCID: PMC5263150 DOI: 10.3389/fphys.2017.00027] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2016] [Accepted: 01/11/2017] [Indexed: 11/13/2022] Open
Abstract
We know very little about how muscles and motor units in one region of the upper airway are impacted by adjustments in an adjacent airway region. In this case, the focus is on regulation of the expiratory airstream by the larynx and how changes in laryngeal aperture impact muscle motor unit activities downstream in the pharynx. We selected sound production as a framework for study as it requires (i) sustained expiratory airflow, (ii) laryngeal airway regulation for production of whisper and voice, and (iii) pharyngeal airway regulation for production of different vowel sounds. We used these features as the means of manipulating expiratory airflow, pharyngeal, and laryngeal airway opening to compare the effect of each on the activation of genioglossus (GG) muscle motor units in the pharynx. We show that some GG muscle motor units (a) discharge stably on expiration associated with production of vowel sounds, (b) are exquisitely sensitive to subtle alterations in laryngeal airflow, and (c) discharge at higher firing rates in high flow vs. low flow conditions even when producing the same vowel sound. Our results reveal subtle changes in GG motor unit discharge rates that correlate with changes imposed at the larynx, and which may contribute to the regulation of the expiratory airstream.
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Affiliation(s)
- Amy LaCross
- Department of Physiology, College of Medicine, University of Arizona Tucson, AZ, USA
| | - Peter J Watson
- Department of Speech, Language, and Hearing Science, College of Liberal Arts, University of Minnesota Minneapolis, MN, USA
| | - E Fiona Bailey
- Department of Physiology, College of Medicine, University of Arizona Tucson, AZ, USA
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12
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Piotrkiewicz M, Türker KS. Onion Skin or Common Drive? Front Cell Neurosci 2017; 11:2. [PMID: 28154526 PMCID: PMC5243795 DOI: 10.3389/fncel.2017.00002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 01/05/2017] [Indexed: 11/13/2022] Open
Affiliation(s)
- Maria Piotrkiewicz
- Department of Engineering of Nervous and Muscular System, Nalecz Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences Warsaw, Poland
| | - Kemal S Türker
- Laboratory of Neuromuscular Research, Koç University School of Medicine Istanbul, Turkey
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13
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Revill AL, Fuglevand AJ. Inhibition linearizes firing rate responses in human motor units: implications for the role of persistent inward currents. J Physiol 2017; 595:179-191. [PMID: 27470946 PMCID: PMC5199728 DOI: 10.1113/jp272823] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2016] [Accepted: 07/21/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Motor neurons are the output neurons of the central nervous system and are responsible for controlling muscle contraction. When initially activated during voluntary contraction, firing rates of motor neurons increase steeply but then level out at modest rates. Activation of an intrinsic source of excitatory current at recruitment onset may underlie the initial steep increase in firing rate in motor neurons. We attempted to disable this intrinsic excitatory current by artificially activating an inhibitory reflex. When motor neuron activity was recorded while the inhibitory reflex was engaged, firing rates no longer increased steeply, suggesting that the intrinsic excitatory current was probably responsible for the initial sharp rise in motor neuron firing rate. ABSTRACT During graded isometric contractions, motor unit (MU) firing rates increase steeply upon recruitment but then level off at modest rates even though muscle force continues to increase. The mechanisms underlying such firing behaviour are not known although activation of persistent inward currents (PICs) might be involved. PICs are intrinsic, voltage-dependent currents that activate strongly when motor neurons (MNs) are first recruited. Such activation might cause a sharp escalation in depolarizing current and underlie the steep initial rise in MU firing rate. Because PICs can be disabled with synaptic inhibition, we hypothesized that artificial activation of an inhibitory pathway might curb this initial steep rise in firing rate. To test this, human subjects performed slow triangular ramp contractions of the ankle dorsiflexors in the absence and presence of tonic synaptic inhibition delivered to tibialis anterior (TA) MNs by sural nerve stimulation. Firing rate profiles (expressed as a function of contraction force) of TA MUs recorded during these tasks were compared for control and stimulation conditions. Under control conditions, during the ascending phase of the triangular contractions, 93% of the firing rate profiles were best fitted by rising exponential functions. With stimulation, however, firing rate profiles were best fitted with linear functions or with less steeply rising exponentials. Firing rate profiles for the descending phases of the contractions were best fitted with linear functions for both control and stimulation conditions. These results seem consistent with the idea that PICs contribute to non-linear firing rate profiles during ascending but not descending phases of contractions.
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Affiliation(s)
- Ann L. Revill
- Department of PhysiologyCollege of MedicineUniversity of ArizonaTucsonAZUSA
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Tadros MA, Fuglevand AJ, Brichta AM, Callister RJ. Intrinsic excitability differs between murine hypoglossal and spinal motoneurons. J Neurophysiol 2016; 115:2672-80. [PMID: 26936988 DOI: 10.1152/jn.01114.2015] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 02/29/2016] [Indexed: 12/12/2022] Open
Abstract
Motoneurons differ in the behaviors they control and their vulnerability to disease and aging. For example, brain stem motoneurons such as hypoglossal motoneurons (HMs) are involved in licking, suckling, swallowing, respiration, and vocalization. In contrast, spinal motoneurons (SMs) innervating the limbs are involved in postural and locomotor tasks requiring higher loads and lower movement velocities. Surprisingly, the properties of these two motoneuron pools have not been directly compared, even though studies on HMs predominate in the literature compared with SMs, especially for adult animals. Here we used whole cell patch-clamp recording to compare the electrophysiological properties of HMs and SMs in age-matched neonatal mice (P7-P10). Passive membrane properties were remarkably similar in HMs and SMs, and afterhyperpolarization properties did not differ markedly between the two populations. HMs had narrower action potentials (APs) and a faster upstroke on their APs compared with SMs. Furthermore, HMs discharged APs at higher frequencies in response to both step and ramp current injection than SMs. Therefore, while HMs and SMs have similar passive properties, they differ in their response to similar levels of depolarizing current. This suggests that each population possesses differing suites of ion channels that allow them to discharge at rates matched to the different mechanical properties of the muscle fibers that drive their distinct motor functions.
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Affiliation(s)
- M A Tadros
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and
| | - A J Fuglevand
- Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona
| | - A M Brichta
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and
| | - R J Callister
- School of Biomedical Sciences and Pharmacy, Faculty of Health and Hunter Medical Research Institute, The University of Newcastle, Callaghan, New South Wales, Australia; and
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15
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Wakefield HE, Fregosi RF, Fuglevand AJ. Current injection and receptor-mediated excitation produce similar maximal firing rates in hypoglossal motoneurons. J Neurophysiol 2016; 115:1307-13. [PMID: 26745245 PMCID: PMC4808106 DOI: 10.1152/jn.00848.2015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 12/21/2015] [Indexed: 11/22/2022] Open
Abstract
The maximum firing rates of motoneurons (MNs), activated in response to synaptic drive, appear to be much lower than that elicited by current injection. It could be that the decrease in input resistance associated with increased synaptic activity (but not current injection) might blunt overall changes in membrane depolarization and thereby limit spike-frequency output. To test this idea, we recorded, in the same cells, maximal firing responses to current injection and to synaptic activation. We prepared 300 μm medullary slices in neonatal rats that contained hypoglossal MNs and used whole-cell patch-clamp electrophysiology to record their maximum firing rates in response to triangular-ramp current injections and to glutamate receptor-mediated excitation. Brief pressure pulses of high-concentration glutamate led to significant depolarization, high firing rates, and temporary cessation of spiking due to spike inactivation. In the same cells, we applied current clamp protocols that approximated the time course of membrane potential change associated with glutamate application and with peak current levels large enough to cause spike inactivation. Means (SD) of maximum firing rates obtained in response to glutamate application were nearly identical to those obtained in response to ramp current injection [glutamate 47.1 ± 12.0 impulses (imp)/s, current injection 47.5 ± 11.2 imp/s], even though input resistance was 40% less during glutamate application compared with current injection. Therefore, these data suggest that the reduction in input resistance associated with receptor-mediated excitation does not, by itself, limit the maximal firing rate responses in MNs.
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Affiliation(s)
- Hilary E Wakefield
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and
| | - Ralph F Fregosi
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and Department of Neuroscience, University of Arizona, Tucson, Arizona
| | - Andrew J Fuglevand
- Department of Physiology, College of Medicine, Arizona Health Sciences Center, University of Arizona, Tucson, Arizona; and Department of Neuroscience, University of Arizona, Tucson, Arizona
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16
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Dotan Y, Pillar G, Schwartz AR, Oliven A. Asynchrony of lingual muscle recruitment during sleep in obstructive sleep apnea. J Appl Physiol (1985) 2015; 118:1516-24. [DOI: 10.1152/japplphysiol.00937.2014] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 03/25/2015] [Indexed: 11/22/2022] Open
Abstract
Pharyngeal collapsibility during sleep increases primarily due to decline in dilator muscle activity. However, genioglossus EMG is known to increase during apneas and hypopneas, usually without reversing upper airway obstruction or inspiratory flow limitation. The present study was undertaken to test the hypothesis that intense activation of the genioglossus fails to prevent pharyngeal obstruction during sleep, and to evaluate if sleep-induced changes in tongue muscle coordination may be responsible for this phenomenon. We compared genioglossus and tongue retractors EMG activity in 13 obstructive sleep apnea (OSA) patients during wakefulness, while breathing through inspiratory resistors, to the activity observed at the end of apneas and hypopneas after 25 mg of brotizolam, before arousal, at equal esophageal pressure. During wakefulness, resistive breathing triggered increases in both genioglossus and retractor EMG. Activation of agonist tongue muscles differed considerably from that of the arm, as both genioglossus and retractors were activated similarly during all tongue movements. During sleep, flow limitation triggered increases in genioglossal EMG that could reach more than twofold the level observed while awake. In contrast, EMGs of the retractors reached less than half the wakefulness level. In sleeping OSA patients, genioglossal activity may increase during obstructed breathing to levels that exceed substantially those required to prevent pharyngeal collapse during wakefulness. In contrast, coactivation of retractors is deficient during sleep. These findings suggest that sleep-induced alteration in tongue muscle coordination may be responsible for the failure of high genioglossal EMG activity to alleviate flow limitation.
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Affiliation(s)
| | - Giora Pillar
- Rappaport School of Medicine, Technion Israel Institute of Technology, Haifa, Israel
- Carmel Medical Centre, Haifa, Israel
- Sleep Laboratory, Technion, Haifa, Israel; and
| | - Alan R. Schwartz
- Sleep Disorders Center, Johns Hopkins School of Medicine, Baltimore, Maryland
| | - Arie Oliven
- Bnai-Zion Medical Centre, Haifa, Israel
- Rappaport School of Medicine, Technion Israel Institute of Technology, Haifa, Israel
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Shumway KR, Porfirio DJ, Bailey EF. Phonation-related rate coding and recruitment in the genioglossus muscle. Exp Brain Res 2015; 233:2133-40. [PMID: 25899868 DOI: 10.1007/s00221-015-4284-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Accepted: 04/10/2015] [Indexed: 11/26/2022]
Abstract
Motor unit recruitment was assessed in two muscles with similar muscle fiber-type compositions and that participate in skilled movements: the tongue muscle, genioglossus (GG), and the hand muscle, first dorsal interosseous (FDI). Our primary objectives were to determine in the framework of a voluntary movement whether muscle force is regulated in tongue as it is in limb, i.e., via processes of rate coding and recruitment. Recruitment in the two muscles was assessed within each subject in the context of ramp force (FDI) and in the tongue (GG) during vowel production and specifically, in the context of ramp increases in loudness, and subsequently expressed relative to the maximal. The principle findings of the study are that the general rules of recruitment and rate coding hold true for both GG and FDI, and second, that average firing rates, firing rates at recruitment and peak firing rates in GG are significantly higher than for FDI (P < 0.001) despite tasks performed across comparable force ranges (~2-40 % of max). The higher firing rates observed in the tongue within the context of phonation may be a function of that muscle's dual role as (prime) mover and hydrostatic support element.
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Affiliation(s)
- K R Shumway
- Department of Physiology, College of Medicine, The University of Arizona, Tucson, AZ, 85721-0093, USA
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18
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Fuglevand AJ, Lester RA, Johns RK. Distinguishing intrinsic from extrinsic factors underlying firing rate saturation in human motor units. J Neurophysiol 2015; 113:1310-22. [PMID: 25475356 PMCID: PMC4346713 DOI: 10.1152/jn.00777.2014] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 12/01/2014] [Indexed: 11/22/2022] Open
Abstract
During voluntary contraction, firing rates of individual motor units (MUs) increase modestly over a narrow force range beyond which little additional increase in firing rate is seen. Such saturation of MU discharge may be a consequence of extrinsic factors that limit net synaptic excitation acting on motor neurons (MNs) or may be due to intrinsic properties of the MNs. Two sets of experiments involving recording of human biceps brachii MUs were carried out to evaluate saturation. In the first set, the extent of saturation was quantified for 136 low-threshold MUs during isometric ramp contractions. Firing rate-force data were best fit by a saturating function for 90% of MUs recorded with a maximum rate of 14.8 ± 2.0 impulses/s. In the second set of experiments, to distinguish extrinsic from intrinsic factors underlying saturation, we artificially augmented descending excitatory drive to biceps MNs by activation of muscle spindle afferents through tendon vibration. We examined the change in firing rate caused by tendon vibration in 96 MUs that were voluntarily activated at rates below and at saturation. Vibration had little effect on the discharge of MUs that were firing at saturation frequencies but strongly increased firing rates of the same units when active at lower frequencies. These results indicate that saturation is likely caused by intrinsic mechanisms that prevent further increases in firing rate in the presence of increasing synaptic excitation. Possible intrinsic cellular mechanisms that limit firing rates of motor units during voluntary effort are discussed.
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Affiliation(s)
- Andrew J Fuglevand
- Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona
| | - Rosemary A Lester
- Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona
| | - Richard K Johns
- Department of Physiology, College of Medicine, University of Arizona, Tucson, Arizona
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Zhou L, Wang ZY, Lian H, Song HY, Zhang YM, Zhang XL, Fan RF, Zheng LF, Zhu JX. Altered expression of dopamine receptors in cholinergic motoneurons of the hypoglossal nucleus in a 6-OHDA-induced Parkinson’s disease rat model. Biochem Biophys Res Commun 2014; 452:560-6. [DOI: 10.1016/j.bbrc.2014.08.104] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Accepted: 08/21/2014] [Indexed: 02/06/2023]
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20
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Mottram CJ, Heckman CJ, Powers RK, Rymer WZ, Suresh NL. Disturbances of motor unit rate modulation are prevalent in muscles of spastic-paretic stroke survivors. J Neurophysiol 2014; 111:2017-28. [PMID: 24572092 DOI: 10.1152/jn.00389.2013] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Stroke survivors often exhibit abnormally low motor unit firing rates during voluntary muscle activation. Our purpose was to assess the prevalence of saturation in motor unit firing rates in the spastic-paretic biceps brachii muscle of stroke survivors. To achieve this objective, we recorded the incidence and duration of impaired lower- and higher-threshold motor unit firing rate modulation in spastic-paretic, contralateral, and healthy control muscle during increases in isometric force generated by the elbow flexor muscles. Impaired firing was considered to have occurred when firing rate became constant (i.e., saturated), despite increasing force. The duration of impaired firing rate modulation in the lower-threshold unit was longer for spastic-paretic (3.9 ± 2.2 s) than for contralateral (1.4 ± 0.9 s; P < 0.001) and control (1.1 ± 1.0 s; P = 0.005) muscles. The duration of impaired firing rate modulation in the higher-threshold unit was also longer for the spastic-paretic (1.7 ± 1.6 s) than contralateral (0.3 ± 0.3 s; P = 0.007) and control (0.1 ± 0.2 s; P = 0.009) muscles. This impaired firing rate of the lower-threshold unit arose, despite an increase in the overall descending command, as shown by the recruitment of the higher-threshold unit during the time that the lower-threshold unit was saturating, and by the continuous increase in averages of the rectified EMG of the biceps brachii muscle throughout the rising phase of the contraction. These results suggest that impairments in firing rate modulation are prevalent in motor units of spastic-paretic muscle, even when the overall descending command to the muscle is increasing.
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Affiliation(s)
- C J Mottram
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois;
| | - C J Heckman
- Departments of Physiology, Physical Medicine and Rehabilitation, and Physical Therapy and Human Movement Sciences, Northwestern University Feinberg School of Medicine, Chicago, Illinois
| | - R K Powers
- Department of Physiology & Biophysics, University of Washington, Seattle, Washington; and
| | - W Z Rymer
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois; Department of Physical Medicine and Rehabilitation, Northwestern University, Feinberg School of Medicine, Chicago, Illinois
| | - N L Suresh
- Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois
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21
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Butler JE, Hudson AL, Gandevia SC. The Neural Control of Human Inspiratory Muscles. PROGRESS IN BRAIN RESEARCH 2014; 209:295-308. [DOI: 10.1016/b978-0-444-63274-6.00015-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Moritaka H, Kitade M, Sawamura SI, Takihara T, Awano I, Ono T, Tamine K, Hori K. Effect of Carbon Dioxide in Carbonated Drinks on Linguapalatal Swallowing Pressure. Chem Senses 2013; 39:133-42. [DOI: 10.1093/chemse/bjt062] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Abstract
Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.
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Affiliation(s)
- C J Heckman
- Northwestern University, Evanston, Illinois, USA.
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24
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Horner RL. Neural control of the upper airway: integrative physiological mechanisms and relevance for sleep disordered breathing. Compr Physiol 2013; 2:479-535. [PMID: 23728986 DOI: 10.1002/cphy.c110023] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The various neural mechanisms affecting the control of the upper airway muscles are discussed in this review, with particular emphasis on structure-function relationships and integrative physiological motor-control processes. Particular foci of attention include the respiratory function of the upper airway muscles, and the various reflex mechanisms underlying their control, specifically the reflex responses to changes in airway pressure, reflexes from pulmonary receptors, chemoreceptor and baroreceptor reflexes, and postural effects on upper airway motor control. This article also addresses the determinants of upper airway collapsibility and the influence of neural drive to the upper airway muscles, and the influence of common drugs such as ethanol, sedative hypnotics, and opioids on upper airway motor control. In addition to an examination of these basic physiological mechanisms, consideration is given throughout this review as to how these mechanisms relate to integrative function in the intact normal upper airway in wakefulness and sleep, and how they may be involved in the pathogenesis of clinical problems such obstructive sleep apnea hypopnea.
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25
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Fregosi RF, Ludlow CL. Activation of upper airway muscles during breathing and swallowing. J Appl Physiol (1985) 2013; 116:291-301. [PMID: 24092695 DOI: 10.1152/japplphysiol.00670.2013] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The upper airway is a complex muscular tube that is used by the respiratory and digestive systems. The upper airway is invested with several small and anatomically peculiar muscles. The muscle fiber orientations and their nervous innervation are both extremely complex, and how the activity of the muscles is initiated and adjusted during complex behaviors is poorly understood. The bulk of the evidence suggests that the entire assembly of tongue and laryngeal muscles operate together but differently during breathing and swallowing, like a ballet rather than a solo performance. Here we review the functional anatomy of the tongue and laryngeal muscles, and their neural innervation. We also consider how muscular activity is altered as respiratory drive changes, and briefly address upper airway muscle control during swallowing.
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Affiliation(s)
- Ralph F Fregosi
- Department of Physiology, University of Arizona, Tucson, Arizona
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Walls CE, Laine CM, Kidder IJ, Bailey EF. Human hypoglossal motor unit activities in exercise. J Physiol 2013; 591:3579-90. [PMID: 23690561 DOI: 10.1113/jphysiol.2013.252452] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The genioglossus (GG) muscle is considered the principal protruder muscle of the tongue that dilates and stiffens the pharyngeal airway. We recorded whole muscle and single motor unit (MU) activities in healthy adults performing progressive intensity exercise on a cycle ergometer. Tungsten microelectrodes were inserted percutaneously into the GG of 11 subjects (20-40 years) to record electromyographic (EMG) activities and pulmonary ventilation (VI) at rest and at workload increments up to 300 W. Increases in respiratory drive were associated with increases in VI, mean inspiratory flow (Vt/Ti) and tonic and phasic components of the GG EMG activity. In contrast, individual MUs typically showed expiration-related decreases in firing as exercise intensity increased. We suggest the decrease in MU activity may occur secondary to afferent feedback from lungs/chest wall and that compensation for more negative inspiratory airway pressures generated during heavy exercise occurs primarily via recruitment of previously silent MUs.
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Affiliation(s)
- Clinton E Walls
- Department of Physiology, College of Medicine, The University of Arizona, Tucson, AZ 85721-0093, USA
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Kletzien H, Russell JA, Leverson GE, Connor NP. Differential effects of targeted tongue exercise and treadmill running on aging tongue muscle structure and contractile properties. J Appl Physiol (1985) 2012; 114:472-81. [PMID: 23264540 DOI: 10.1152/japplphysiol.01370.2012] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Age-associated changes in tongue muscle structure and strength may contribute to dysphagia in elderly people. Tongue exercise is a current treatment option. We hypothesized that targeted tongue exercise and nontargeted exercise that activates tongue muscles as a consequence of increased respiratory drive, such as treadmill running, are associated with different patterns of tongue muscle contraction and genioglossus (GG) muscle biochemistry. Thirty-one young adult, 34 middle-aged, and 37 old Fischer 344/Brown Norway rats received either targeted tongue exercise, treadmill running, or no exercise (5 days/wk for 8 wk). Protrusive tongue muscle contractile properties and myosin heavy chain (MHC) composition in the GG were examined at the end of 8 wk across groups. Significant age effects were found for maximal twitch and tetanic tension (greatest in young adult rats), MHCIIb (highest proportion in young adult rats), MHCIIx (highest proportion in middle-aged and old rats), and MHCI (highest proportion in old rats). The targeted tongue exercise group had the greatest maximal twitch tension and the highest proportion of MHCI. The treadmill running group had the shortest half-decay time, the lowest proportion of MHCIIa, and the highest proportion of MHCIIb. Fatigue was significantly less in the young adult treadmill running group and the old targeted tongue exercise group than in other groups. Thus, tongue muscle structure and contractile properties were affected by both targeted tongue exercise and treadmill running, but in different ways. Studies geared toward optimizing dose and manner of providing targeted and generalized tongue exercise may lead to alternative tongue exercise delivery strategies.
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Affiliation(s)
- Heidi Kletzien
- Department of Surgery, Otolaryngology-Head and Neck Surgery, University of Wisconsin, Madison, Wisconsin, USA
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Stepp CE. Surface electromyography for speech and swallowing systems: measurement, analysis, and interpretation. JOURNAL OF SPEECH, LANGUAGE, AND HEARING RESEARCH : JSLHR 2012; 55:1232-1246. [PMID: 22232412 DOI: 10.1044/1092-4388(2011/11-0214)] [Citation(s) in RCA: 66] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
PURPOSE Applying surface electromyography (sEMG) to the study of voice, speech, and swallowing is becoming increasingly popular. An improved understanding of sEMG and building a consensus as to appropriate methodology will improve future research and clinical applications. METHOD An updated review of the theory behind recording sEMG for the speech and swallowing systems is provided. Several factors that are known to affect the content of the sEMG signal are discussed, and practical guidelines for sEMG recording and analysis are presented, focusing on special considerations within the context of the speech and swallowing anatomy. RESULTS Unique challenges are seen in application of sEMG to the speech and swallowing musculature owing to the small size of the muscles in relation to the sEMG detection volume and the present lack of knowledge about innervation zone locations. CONCLUSIONS Despite the challenges discussed, application of sEMG to speech and swallowing has potential as a clinical and research tool when used correctly and is specifically suited to noninvasive clinical studies using between-condition or between-group comparisons for which detection of specific isolated muscle activities is not necessary.
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Saboisky JP, Butler JE, Gandevia SC, Eckert DJ. Functional role of neural injury in obstructive sleep apnea. Front Neurol 2012; 3:95. [PMID: 22715333 PMCID: PMC3375463 DOI: 10.3389/fneur.2012.00095] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2012] [Accepted: 05/28/2012] [Indexed: 12/31/2022] Open
Abstract
The causes of obstructive sleep apnea (OSA) are multifactorial. Neural injury affecting the upper airway muscles due to repetitive exposure to intermittent hypoxia and/or mechanical strain resulting from snoring and recurrent upper airway closure have been proposed to contribute to OSA disease progression. Multiple studies have demonstrated altered sensory and motor function in patients with OSA using a variety of neurophysiological and histological approaches. However, the extent to which the alterations contribute to impairments in upper airway muscle function, and thus OSA disease progression, remains uncertain. This brief review, primarily focused on data in humans, summarizes: (1) the evidence for upper airway sensorimotor injury in OSA and (2) current understanding of how these changes affect upper airway function and their potential to change OSA progression. Some unresolved questions including possible treatment targets are noted.
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30
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Nicholas CL, Jordan AS, Heckel L, Worsnop C, Bei B, Saboisky JP, Eckert DJ, White DP, Malhotra A, Trinder J. Discharge patterns of human tensor palatini motor units during sleep onset. Sleep 2012; 35:699-707. [PMID: 22547896 PMCID: PMC3321429 DOI: 10.5665/sleep.1834] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
STUDY OBJECTIVES Upper airway muscles such as genioglossus (GG) and tensor palatini (TP) reduce activity at sleep onset. In GG reduced muscle activity is primarily due to inspiratory modulated motor units becoming silent, suggesting reduced respiratory pattern generator (RPG) output. However, unlike GG, TP shows minimal respiratory modulation and presumably has few inspiratory modulated motor units and minimal input from the RPG. Thus, we investigated the mechanism by which TP reduces activity at sleep onset. DESIGN The activity of TP motor units were studied during relaxed wakefulness and over the transition from wakefulness to sleep. SETTING Sleep laboratory. PARTICIPANTS Nine young (21.4 ± 3.4 years) males were studied on a total of 11 nights. INTERVENTION Sleep onset. MEASUREMENTS AND RESULTS Two TP EMGs (thin, hooked wire electrodes), and sleep and respiratory measures were recorded. One hundred twenty-one sleep onsets were identified (13.4 ± 7.2/subject), resulting in 128 motor units (14.3 ± 13.0/subject); 29% of units were tonic, 43% inspiratory modulated (inspiratory phasic 18%, inspiratory tonic 25%), and 28% expiratory modulated (expiratory phasic 21%, expiratory tonic 7%). There was a reduction in both expiratory and inspiratory modulated units, but not tonic units, at sleep onset. Reduced TP activity was almost entirely due to de-recruitment. CONCLUSIONS TP showed a similar distribution of motor units as other airway muscles. However, a greater proportion of expiratory modulated motor units were active in TP and these expiratory units, along with inspiratory units, tended to become silent over sleep onset. The data suggest that both expiratory and inspiratory drive components from the RPG are reduced at sleep onset in TP.
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Affiliation(s)
| | - Amy S. Jordan
- School of Psychological Science, University of Melbourne, Parkville, Australia
| | - Leila Heckel
- School of Psychological Science, University of Melbourne, Parkville, Australia
| | - Christopher Worsnop
- School of Psychological Science, University of Melbourne, Parkville, Australia
| | - Bei Bei
- School of Psychological Science, University of Melbourne, Parkville, Australia
| | - Julian P. Saboisky
- Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston MA
| | - Danny J. Eckert
- Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston MA
| | - David P. White
- Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston MA
| | - Atul Malhotra
- Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston MA
| | - John Trinder
- School of Psychological Science, University of Melbourne, Parkville, Australia
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Daugherty M, Luo Q, Sokoloff AJ. Myosin heavy chain composition of the human genioglossus muscle. JOURNAL OF SPEECH, LANGUAGE, AND HEARING RESEARCH : JSLHR 2012; 55:609-25. [PMID: 22337492 PMCID: PMC3816748 DOI: 10.1044/1092-4388(2011/10-0287)] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/13/2023]
Abstract
BACKGROUND The human tongue muscle genioglossus (GG) is active in speech, swallowing, respiration, and oral transport, behaviors encompassing a wide range of tongue shapes and movement speeds. Studies demonstrate substantial diversity in patterns of human GG motor unit activation, but whether this is accompanied by complex expression of muscle contractile proteins is not known. PURPOSE The authors tested for conventional myosin heavy chain (MHC) MHCI, MHCIIA, MHCIIX, developmental MHCembryonic and MHCneonatal and unconventional MHCαcardiac, MHCextraocular, and MHCslow tonic in antero-superior (GG-A) and posterior (GG-P) adult human GG. METHOD SDS-PAGE, Western blot, and immunohistochemistry were used to describe MHC composition of GG-A and GG-P and the prevalence of muscle fiber MHC phenotypes in GG-A. RESULTS By SDS-PAGE, only conventional MHC are present with ranking from most to least prevalent MHCIIA > MHCI > MHCIIX in GG-A and MHCI > MHCIIA > MHCIIX in GG-P. By immunohistochemistry, many muscle fibers contain MHCI, MHCIIA, and MHCIIX, but few contain developmental or unconventional MHC. GG-A is composed of 5 phenotypes (MHCIIA > MHCI-IIX > MHCI > MHCI-IIA > MHCIIX). Phenotypes MHCI, MHCIIA, and MHCI-IIX account for 96% of muscle fibers. CONCLUSIONS Despite activation of GG during kinematically diverse behaviors and complex patterns of GG motor unit activity, the human GG is composed of conventional MHC isoforms and 3 primary MHC phenotypes.
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Johnson AN, Huo X, Ghovanloo M, Shinohara M. Dual-task motor performance with a tongue-operated assistive technology compared with hand operations. J Neuroeng Rehabil 2012; 9:1. [PMID: 22244362 PMCID: PMC3287148 DOI: 10.1186/1743-0003-9-1] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2011] [Accepted: 01/13/2012] [Indexed: 01/09/2023] Open
Abstract
Background To provide an alternative motor modality for control, navigation, and communication in individuals suffering from impairment or disability in hand functions, a Tongue Drive System (TDS) has been developed that allows for real time tracking of tongue motion in an unobtrusive, wireless, and wearable device that utilizes the magnetic field generated by a miniature disk shaped magnetic tracer attached to the tip of the tongue. The purpose of the study was to compare the influence of a concurrent motor or cognitive task on various aspects of simple movement control between hand and tongue using the TDS technology. Methods Thirteen young able-bodied adults performed rapid and slow goal-directed movements of hand and tongue (with TDS) with and without a concurrent motor (hand or tongue) or cognitive (arithmetic and memory) task. Changes in reaction time, completion time, speed, correctness, accuracy, variability of displacement, and variability of time due to the addition of a concurrent task were compared between hand and tongue. Results The influence of an additional concurrent task on motor performance was similar between the hand and tongue for slow movement in controlling their displacement. In rapid movement with a concurrent motor task, most aspects of motor performance were degraded in hand, while tongue speed during rapid continuous task was maintained. With a concurrent cognitive task, most aspects of motor performance were degraded in tongue, while hand accuracy during the rapid discrete task and hand speed during the rapid continuous task were maintained. Conclusion Rapid goal-directed hand and tongue movements were more consistently susceptible to interference from concurrent motor and cognitive tasks, respectively, compared with the other movement.
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Affiliation(s)
- Ashley N Johnson
- School of Applied Physiology, Georgia Institute of Technology, Atlanta, GA, USA
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Hudson AL, Gandevia SC, Butler JE. Control of human inspiratory motoneurones during voluntary and involuntary contractions. Respir Physiol Neurobiol 2011; 179:23-33. [DOI: 10.1016/j.resp.2011.06.010] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Revised: 06/14/2011] [Accepted: 06/14/2011] [Indexed: 11/17/2022]
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Krival K, Bates C. Effects of club soda and ginger brew on linguapalatal pressures in healthy swallowing. Dysphagia 2011; 27:228-39. [PMID: 21811834 DOI: 10.1007/s00455-011-9358-9] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 05/06/2011] [Indexed: 11/27/2022]
Abstract
Oral chemesthesis is the detection of chemicals that activate temperature and pain receptors in the oral mucosa. Presentation of orally chemesthetic input has been theorized to stimulate a faster, stronger swallow. We measured differences in peak linguapalatal swallowing pressures, pressure durations, and pressure adjustments in response to two volumes of water and carbonation (in Schweppes® Club Soda) and carbonation + gingerol (in Reed's Extra Ginger Brew) in 20 young adult women. There was a main effect of stimulus on linguapalatal swallowing pressure, F(6,74) = 6.247, p = 0.000, hp(2) = 0.536 (Reed's Extra Ginger Brew > Schweppes Club Soda > water). Rising and releasing linguapalatal pressure durations were greater for carbonation + gingerol and carbonation than for water. Our results add to the evidence that orally chemesthetic beverages influence greater neuromotor activity compared to water during the oral stage of swallowing. Our findings also suggest that there may be some benefit to the cumulative addition of chemosensory agents in a beverage. Clinically, this provides a theoretical basis for considering the use of these or chemically similar beverages as facilitating stimuli in patients who aspirate thin liquids.
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Affiliation(s)
- Kate Krival
- Kent State University, 1325 Theater Drive, Kent, OH 44242, USA.
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Bailey EF. Activities of human genioglossus motor units. Respir Physiol Neurobiol 2011; 179:14-22. [PMID: 21558022 DOI: 10.1016/j.resp.2011.04.018] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Revised: 04/14/2011] [Accepted: 04/17/2011] [Indexed: 01/13/2023]
Abstract
Upper airway muscles play an important role in regulating airway lumen and in increasing the ability of the pharynx to remain patent in the face of subatmospheric intraluminal pressures produced during inspiration. Due to the considerable technical challenges associated with recording from muscles of the upper airway, much of the experimental work conducted in human subjects has centered on recording respiratory-related activities of the extrinsic tongue protudor muscle, the genioglossus (GG). The GG is one of eight muscles that invest the human tongue (Abd-El-Malek, 1939). All eight muscles are innervated by the hypoglossal nerve (cranial nerve XII) the cell bodies of which are located in the hypoglossal motor nucleus (HMN) of the caudal medulla. Much of the earlier work on the respiratory-related activity of XII motoneurons was based on recordings obtained from single motor axons dissected from the whole XII nerve or from whole muscle GG EMG recordings. Detailed information regarding respiratory-related GG motor unit activities was lacking until as recently as 2006. This paper examines key findings that have emerged from the last decade of work conducted in human subjects. Wherever appropriate, these results are compared with results obtained from in vitro and in vivo studies conducted in non-human mammals. The review is written with the objective of facilitating some discussion and some new thoughts regarding future research directions. The material is framed around four topics: (a) motor unit type, (b) rate coding and recruitment, (c) motor unit activity patterns, and (d) a compartment based view of pharyngeal airway control.
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Affiliation(s)
- E Fiona Bailey
- Department of Physiology, College of Medicine, The University of Arizona, Tucson, AZ 85721-0093, USA.
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Kollewe K, Münte TF, Samii A, Dengler R, Petri S, Mohammadi B. Patterns of cortical activity differ in ALS patients with limb and/or bulbar involvement depending on motor tasks. J Neurol 2010; 258:804-10. [DOI: 10.1007/s00415-010-5842-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Revised: 11/15/2010] [Accepted: 11/17/2010] [Indexed: 11/24/2022]
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Nicholas CL, DPsych BB, Worsnop C, Malhotra A, Jordan AS, Saboisky JP, Chan JKM, Duckworth E, White DP, Trinder J. Motor Unit Recruitment in Human Genioglossus Muscle in Response to Hypercapnia. Sleep 2010. [DOI: 10.1093/sleep/33.5.1529] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Richardson PA, Bailey EF. Tonically discharging genioglossus motor units show no evidence of rate coding with hypercapnia. J Neurophysiol 2010; 103:1315-21. [PMID: 20053847 DOI: 10.1152/jn.00686.2009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The genioglossus (GG) is considered the principle protrudor muscle of the human tongue. Unlike most skeletal muscles, GG electromyographic (EMG) activities are robustly preserved in sleep and thus may fulfill a critical role in preserving airway patency. Previous studies in human subjects also confirm that the GG EMG increases in response to chemoreceptor and mechanoreceptor stimulation. This increase occurs secondary to the recruitment of previously inactive motor units (MUs) and/or an increase in firing rate of already active MUs. Which strategy the nervous system uses when the synaptic drive onto GG motoneurons increases is not known. Here we report on GG whole muscle and tonic MU activities under conditions that mimic sleep, i.e., mild-moderate elevations in CO(2) (3% inspired CO(2) or the addition of a 1.0 l dead space) and elevated airway resistance. Based on previous work in rat, we hypothesized that mild hypercapnia would increase the firing rates of tonic MUs and that these effects would be further potentiated by a modest increase in airway resistance. Fine wire and tungsten microelectrodes were inserted into the GG to record whole muscle and single MU activities in 21 subjects (13 women, 8 men; 20-55 yr). Either 3% inspired CO(2) or added dead space resulted in a 200-300% increase in the amplitude of both tonic and phasic components of the whole muscle GG EMG and a doubling of minute ventilation. Despite these changes, recordings obtained from a total of 84 tonically discharging GG single MUs provide no evidence of a change in firing rate under any of the conditions. On this basis we conclude that in healthy adults, the increase in the tonic component of the whole muscle GG EMG secondary to mild hypercapnia is due almost exclusively to the recruitment of previously inactive MUs.
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Affiliation(s)
- Patrick A Richardson
- Dept. of Physiology, College of Medicine, The University of Arizona, Tucson, AZ 85721-0093, USA
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39
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Saboisky JP, Chamberlin NL, Malhotra A. Potential therapeutic targets in obstructive sleep apnoea. Expert Opin Ther Targets 2009; 13:795-809. [PMID: 19530985 DOI: 10.1517/14728220903005608] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Obstructive sleep apnoea (OSA) is a disease of ever-increasing importance due to its association with multiple impairments and rising prevalence in an increasingly susceptible demographic. The syndrome is linked with loud snoring, disrupted sleep and observed apnoeas. Serious co-morbidities associated with OSA appear to be reversed by continuous positive airway pressure (CPAP) treatment; however, CPAP is variably tolerated leaving many patients untreated and emphasising the need for alternative treatments. Virtually all OSA patients have airways that are anatomically vulnerable to collapse, but numerous pathophysiological factors underlie when and how OSA is manifested. This review describes how the complexity of OSA requires multiple treatment approaches that are individually targeted. This approach may take the form of more specific diagnoses in terms of the mechanisms underlying OSA as well as rational pharmacological treatment directed toward such disparate ends as arousal threshold and ventilatory control/chemosensitivity, and mechanical treatment in the form of surgery and augmentation of lung volumes.
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Affiliation(s)
- Julian P Saboisky
- Brigham and Women's Hospital, Harvard Medical School, Division of Sleep Medicine, 221 Longwood Avenue, Boston, Massachusetts 02115, USA.
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Abstract
PURPOSE OF REVIEW This review presents a current synopsis of newer research in cortical control of swallowing and its relationship to advancing knowledge in the field of human swallowing neurophysiology. The intent is to highlight recent findings and to stimulate potential research questions not yet investigated. RECENT FINDINGS Advances in human brain imaging have led to a wealth of newer insights into the cortical and subcortical control of human swallowing. This includes a better understanding of the hemispheric contributions to swallowing control and the mechanisms that underlie recovery or compensation after neurological injury. SUMMARY Through advances in imaging and neuroimaging techniques, our knowledge of the neuroanatomy and physiology of swallowing has increased dramatically over the last decade. Integration and interconnection of the diverse swallowing cortical network and how sensory input influences swallowing cortical activation has started to provide a better understanding of the physiological mechanisms that underpin this exquisite yet fundamental sensorimotor function. Experimental paradigms for swallowing neural reorganization have begun to provide evidence for their translation into clinical practice for dysphagia rehabilitation.
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Skelly JR, Bradford A, Jones JFX, O'Halloran KD. Superoxide scavengers improve rat pharyngeal dilator muscle performance. Am J Respir Cell Mol Biol 2009; 42:725-31. [PMID: 19635929 DOI: 10.1165/rcmb.2009-0160oc] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Obstructive sleep apnea is a common disorder associated with upper airway muscle dysfunction. Agents that improve respiratory muscle performance may be useful as an adjunct therapy. The aim of this study was to examine the effects of antioxidants on rat pharyngeal dilator muscle performance. Adult male Wistar rats were killed humanely and isometric contractile properties of isolated sternohyoid muscle strips were examined in physiological salt solution at 35 degrees C in vitro. Muscle strips were incubated in tissue baths under hyperoxic (95%O(2)/5%CO(2)) or hypoxic (95%N(2)/5%CO(2)) conditions in the absence (control) or presence of the antioxidants: N-acetylcysteine (10 mM), Tiron (10 mM), or Tempol (10 mM). Force-frequency relationship was determined in response to supramaximal stimulation (10-100 Hz in increments of 10-20 Hz, train duration: 300 ms). Isometric force was also recorded during repetitive muscle stimulation (40 Hz, 300 ms every 2 s for 2 min). Under hyperoxic conditions, Tiron and Tempol, but not N-acetylcysteine, significantly increased sternohyoid muscle force and caused a left-shift in the force-frequency relationship. In addition, Tempol had a significant positive inotropic effect over the initial 90 seconds of repeated muscle activation. Hypoxia caused a significant decrease in sternohyoid muscle force. Under hypoxic conditions, Tempol-incubated muscles generated significantly higher forces compared with control muscles and showed improved performance in the early phase of the fatigue trial. This study illustrates that superoxide scavengers increase upper airway muscle force and that this effect persists under hypoxic conditions. We conclude that antioxidant treatment may be beneficial as a therapy in obstructive sleep apnea.
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Affiliation(s)
- J Richard Skelly
- UCD School of Medicine and Medical Science, Room C228, Health Sciences Centre, University College Dublin, Belfield, Dublin 4, Ireland
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42
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Lu JW, Kubin L. Electromyographic activity at the base and tip of the tongue across sleep-wake states in rats. Respir Physiol Neurobiol 2009; 167:307-15. [PMID: 19539786 DOI: 10.1016/j.resp.2009.06.004] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 05/19/2009] [Accepted: 06/09/2009] [Indexed: 11/19/2022]
Abstract
Obstructive sleep apnea (OSA) patients have elevated tonic and phasic inspiratory activity in the genioglossus and other upper airway muscles during wakefulness; this protects their upper airway from collapse. In this group, sleep-related decrements of upper airway motor tone result in sleep-related upper airway obstructions. We previously reported that in the rat, a species widely used to study the neural mechanisms of both sleep and breathing, lingual electromyographic activity (EMG) is minimal or absent during slow-wave sleep (SWS) and then gradually increases after the onset of rapid eye movement sleep (REMS) due to the appearance of large phasic bursts. Here, we investigated whether sleep-wake patterns and respiratory modulation of lingual EMG depend on the site of EMG recording within the tongue. In nine chronically instrumented rats, we recorded from 17 sites within the tongue and from the diaphragm across sleep-wake states. We quantified lingual EMG in successive 10s intervals of continuous 2h recordings (1-3 p.m.). We found that sleep-wake patterns of lingual EMG did not differ between the base and tip of the tongue, and that respiratory modulation was extremely rare regardless of the recording site. We also determined that the often rhythmic lingual bursts during REMS do not occur with respiratory rhythmicity. This pattern differs from that in OSA subjects who, unlike rats, have collapsible upper airway, exhibit prominent respiratory modulation of upper airway motor tone during quiet wakefulness, retain considerable tonic and inspiratory phasic activity during SWS, and show nadirs of activity during REMS.
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Affiliation(s)
- Jackie W Lu
- Department of Animal Biology 209E/VET, School of Veterinary Medicine and Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104-6046, USA
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43
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Mohammadi B, Kollewe K, Samii A, Krampfl K, Dengler R, Münte TF. Decreased brain activation to tongue movements in amyotrophic lateral sclerosis with bulbar involvement but not Kennedy syndrome. J Neurol 2009; 256:1263-9. [DOI: 10.1007/s00415-009-5112-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2008] [Revised: 02/17/2009] [Accepted: 03/17/2009] [Indexed: 11/30/2022]
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Farina D, Falla D. Discharge Rate of Sternohyoid Motor Units Activated With Surface EMG Feedback. J Neurophysiol 2009; 101:624-32. [DOI: 10.1152/jn.90901.2008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We analyzed individual motor units of the sternohyoid muscle with the aim of characterizing their minimum and maximum discharge rates and their variability in discharge during voluntary contractions. Surface EMG signals were recorded with an array of eight electrodes from the sternohyoid muscle of seven healthy men (age: 30.2 ± 3.5 yr). The multichannel surface EMG signals were displayed as feedback for the subjects who identified and modulated the activity of one target motor unit in 30-s contractions during which the discharge rate was increased from minimum to maximum (ramp contraction), sustained at maximum level (sustained), or increased in brief bursts (burst). During the ramp contractions, the minimum average discharge rate over epochs of 1 s was 11.6 ± 1.5 pulses per second (pps) and the maximum 57.0 ± 5.7 pps ( P < 0.001). During the sustained contractions, the motor unit discharge rate decreased from 65.5 ± 8.4 pps at the beginning to 52.9 ± 7.6 pps at the end of the contraction ( P < 0.05). The coefficient of variation for the interspike interval during the sustained contractions was 40.2 ± 9.8% and a large percentage of discharges had instantaneous rates >50 pps (52.2 ± 12.5%) and >100 pps (8.0 ± 1.2%), with peak values >150 pps. During the burst contractions, the instantaneous discharge rate reached average maximum values of 97.6 ± 36.8 pps. The observed discharge rates and their variability are higher than those reported for limb muscles, which may be due to large synaptic input and noise received by these motor neurons.
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Pittman LJ, Bailey EF. Genioglossus and intrinsic electromyographic activities in impeded and unimpeded protrusion tasks. J Neurophysiol 2008; 101:276-82. [PMID: 18987117 DOI: 10.1152/jn.91065.2008] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Eight muscles invest the human tongue: four extrinsic muscles have external origins and insert into the tongue body and four intrinsic muscles originate and terminate within the tongue. Previously, we noted minimal activation of the genioglossus tongue muscle during impeded protrusion tasks (i.e., having subjects push the tongue against a force transducer), suggesting that other muscles play a role in the production of tongue force. Accordingly, we sought to characterize genioglossus tongue muscle activities during impeded and unimpeded protrusion tasks (i.e., having subjects slowly and smoothly move the tongue out of their mouth). Electromyographic (EMG) and single motor-unit potentials of the extrinsic genioglossus muscle were recorded with tungsten microelectrodes and EMG activities of intrinsic tongue muscles were recorded with hook-wire electrodes inserted into the anterior tongue body. Tongue position was detected by an isotonic transducer coupled to the tongue tip. Protrusive force was detected by a force transducer attached to a rigid bar. Genioglossus and intrinsic tongue muscles were simultaneously active in both impeded and unimpeded protrusion tasks. Genioglossus whole muscle EMG and single motor-unit activities changed faithfully as a function of tongue position, with increased discharge associated with protrusion and decreased discharge associated with retraction back to the rest position. In contrast, during the impeded protrusion task drive the genioglossus muscle remained constant as protrusion force increased. Conversely, intrinsic tongue muscle activities appropriately followed changes in both tongue position and force. Importantly, we observed significantly higher levels of intrinsic muscle activity in the impeded protrusion task. These observations suggest that protrusion of the human tongue requires activation of the genioglossus and intrinsic protrudor muscles, with the former more important for establishing anterior-posterior tongue location and the latter playing a greater role in the generation of protrusive force. A biomechanical model of these actions is provided and discussed.
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Affiliation(s)
- Lora J Pittman
- Department of Physiology, College of Medicine, The University of Arizona, Tucson, AZ 85721-0093, USA
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Wilkinson V, Malhotra A, Nicholas CL, Worsnop C, Jordan AS, Butler JE, Saboisky JP, Gandevia SC, White DP, Trinder J. Discharge patterns of human genioglossus motor units during sleep onset. Sleep 2008; 31:525-33. [PMID: 18457240 DOI: 10.1093/sleep/31.4.525] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
STUDY OBJECTIVES Multiunit electromyogram recordings of genioglossus have demonstrated an abrupt reduction in the muscle's activity at sleep onset. Recent evidence from single motor unit recordings indicates that the human genioglossus muscle consists of motor units with a variety of discharge patterns. The aim of the present study was to determine the effect of sleep onset on the activity of individual motor units as a function of their particular discharge pattern. DESIGN Genioglossus activity was assessed using intramuscular fine-wire electrodes via a percutaneous approach. Sleep onsets (alpha-to-theta transitions) were identified and the genioglossus electromyogram recordings analyzed for single motor unit activity. SETTING Sleep research laboratory. PARTICIPANTS Sleep and respiratory data were collected in 8 healthy subjects (6 men). MEASUREMENTS AND RESULTS One hundred twenty-seven motor units were identified: 23% inspiratory phasic, 45% inspiratory tonic, 4% expiratory phasic, 9% expiratory tonic, 16% tonic, and 3% other. Approximately 50% of inspiratory units (phasic and tonic) ceased activity entirely at sleep onset, whereas those inspiratory units that continued to be active showed a reduction in the proportion of each breath over which they were active. However, the rate of discharge of inspiratory units during the period they did fire was not altered. In contrast, tonic and expiratory units were unaffected by sleep onset, maintaining their discharge pattern over the alpha-to-theta transition. CONCLUSIONS Central control of inspiratory motoneuron output differs from that of tonic and expiratory units during sleep onset, suggesting that the maintenance of airway patency during sleep may become more reliant on the stiffening properties of tonic and expiratory modulated motor units.
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Affiliation(s)
- Vanessa Wilkinson
- Department of Psychology, University of Melbourne, Parkville, Australia
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Abstract
Obstructive sleep apnea (OSA) is a common disorder characterized by repetitive narrowing or collapse of the pharyngeal airway during sleep. The disorder is associated with major comorbidities including excessive daytime sleepiness and increased risk of cardiovascular disease. The underlying pathophysiology is multifactorial and may vary considerably between individuals. Important risk factors include obesity, male sex, and aging. However, the physiological mechanisms underlying these risk factors are not clearly understood. This brief review summarizes the current understanding of OSA pathophysiology in adults and highlights the potential mechanisms underlying the principal risk factors. In addition, some of the pathophysiological characteristics associated with OSA that may modulate disease severity are illustrated. Finally, the potential for novel treatment strategies, based on an improved understanding of the underlying pathophysiology, is also discussed with the ultimate aim of stimulating research ideas in areas where knowledge is lacking.
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48
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Saboisky JP, Butler JE, McKenzie DK, Gorman RB, Trinder JA, White DP, Gandevia SC. Neural drive to human genioglossus in obstructive sleep apnoea. J Physiol 2007; 585:135-46. [PMID: 17916615 DOI: 10.1113/jphysiol.2007.139584] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
One postulated mechanism for obstructive sleep apnoea (OSA) is insufficient drive to the upper-airway musculature during sleep, with increased (compensatory) drive during wakefulness. This generates more electromyographic activity in upper airway muscles including genioglossus. To understand drives to upper airway muscles, we recorded single motor unit activity from genioglossus in male groups of control (n = 7, 7 +/- 2 events h(-1)) and severe OSA (n = 9, 54 +/- 4 events h(-1)) subjects. One hundred and seventy-eight genioglossus units were recorded using monopolar electrodes. Subjects were awake, supine and breathing through a nasal mask. The distribution of the six types of motor unit activity in genioglossus (Inspiratory Phasic, Inspiratory Tonic, Expiratory Phasic, Expiratory Tonic, Tonic and Tonic Other) was identical in both groups. Single unit action potentials in OSA were larger in area (by 34%, P < 0.05) and longer in duration (by 23%, P < 0.05). Inspiratory units were recruited earlier in OSA than control subjects. In control subjects, Inspiratory Tonic units peaked earlier than Inspiratory Phasic units, while in OSA subjects, Inspiratory Tonic and Phasic units peaked simultaneously. Onset frequencies did not differ between groups, but the peak discharge frequency for Inspiratory Phasic units was higher in OSA (22 +/- 1 Hz) than control subjects (19 +/- 1 Hz, P = 0.003), but conversely, the peak discharge frequency of Inspiratory Tonic units was higher in control subjects (28 +/- 1 Hz versus 25 +/- 1 Hz, P < 0.05). Increased motor unit action potential area indicates that neurogenic changes have occurred in OSA. In addition, the differences in the timing and firing frequency of the inspiratory classes of genioglossus motor units indicate that the output of the hypoglossal nucleus may have changed.
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Affiliation(s)
- Julian P Saboisky
- Prince of Wales Medical Research Institute, Barker Street, Randwick, NSW, 2031, Australia
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