A technique for demonstrating the nerve supply of whole larynges

Evaluation of nerve innervation distribution of orbicularis oculi muscle for botulinum neurotoxin application using Sihler's method

BACKGROUND

Blepharospasm is the involuntary and forced closure of the eyelids due to spasm-like contraction of the orbicularis oculi muscle around the eye. The study aimed to reveal the nerve innervation of the orbicularis oculi muscle for Botulinum neurotoxin (BoNT) treatment of blepharospasm by Sihler's staining technique.

METHODS

This study used six cephalus (12 orbicularis oculi muscles) with an average age of 69,6 (62-88) years. Then, the orbicularis oculi muscles were removed by dissection, and Sihler's staining technique was applied to the muscles. The limit for dissection of the muscle is the orbital opening level, where the nerves enter the muscle, and the muscle attaches to the bone.

RESULTS

In the region above the palpebral fissure, the nerves entering the muscle were densely located in the superolateral quadrant between 9 and 12 o'clock in the right eye and between 12 and 3 o'clock in the left eye. In the region under the palpebral fissure, the nerves' density in the orbicularis oculi muscle was higher between 4 and 7 o'clock in the right eye and between 5 and 8 o'clock in the left eye.

CONCLUSION

This study unveiled the nerve branches associated with the orbicularis oculi muscle. It pinpointed precise crossing points of these nerve branches, which can be targeted for applying BoNT in treating blepharospasm. Consequently, by utilizing minimal BoNT, it is anticipated that the quantity of toxin administered will decrease, leading to more efficient outcomes and reduced expenses. Furthermore, this approach can aid in averting potential undesired complications during BoNT administration.

Intramuscular Nerves of the Inferior Rectus Muscle: Distribution and Characteristics

PURPOSE

Knowledge of the distribution of intramuscular nerves of the extraocular muscles is crucial for understanding their function. The purpose of this study was to elucidate the intramuscular distribution of the oculomotor nerve within the inferior rectus muscle (IRM) using Sihler's staining.

METHOD

Ninety-three IRM from 50 formalin-embalmed cadavers were investigated. The IRM including its branches of the oculomotor nerve was finely dissected from its origin to the point where it inserted into the sclera. The intramuscular nerve course was investigated after performing Sihler's whole-mount nerve staining technique that stains the nerves while rendering other soft tissues either translucent or transparent.

RESULTS

The oculomotor nerve enters the IRM around the distal one-fourth of the muscle and then divides into multiple smaller branches. The intramuscular nerve course finishes around the distal three-fifth of the IRM in gross observations. The types of branching patterns of the IRM could be divided into two subcategories based on whether or not topographic segregation was present: (1) no significant compartmental segregation (55.9% of cases) and (2) a several-zone pattern with possible segregation (44.1% of cases). Possible compartmentalization was less clear for the IRM, which contained overlapping mixed branches between different trunks.

CONCLUSION

Sihler's staining is a useful technique for visualizing the gross nerve distribution of the IRM. The new information about the nerve distribution and morphological features provided by this study will improve the understanding of the biomechanics of the IRM, and could be useful for strabismus surgery.

Intramuscular innervation of plantaris muscle evaluated using a modified Sihler's staining protocol - Proposal for a new classification

PURPOSE

The plantaris muscle is a morphologically variable structure with regard to both its origin and insertion, and the course of the tendon. We here determined the pattern of branching and distribution of intramuscular nerves of the plantaris muscle to determine its usability for autologous transplantation. No information exists on the innervation of the plantaris muscle using Sihler's staining technique, and hence its intramuscular nerves. The main purpose of the work is to determine the pattern of branching and distribution of the intramuscular nerves of the plantaris muscle. Is the plantaris muscle a good transplant candidate?

MATERIALS AND METHODS

Eighty lower limbs from cadavers (40 left, 40 right, 40 male, 40 female, age range 41-94 years) were fixed in 10% formalin solution and examined macroscopically as well as morphometrically with regard to the innervation pattern of the respective plantaris muscle. Afterwards Sihler's staining was used in all 80 plantaris muscles to identify the exact distribution of the muscular branch originating from the main nerve trunk in the muscle belly.

RESULTS

Two patterns of branching and nerve distribution could be intensified in the plantaris muscle: Type I, with a single pattern entire up to the muscle and then divided into superior and inferior intramuscular branches.; type II with a double innervation pattern (superior and inferior). The superior and inferior pattern were not connected to each other.

CONCLUSION

The plantaris muscle reveals variability with two different innervation patterns. Type II is ideally suited for autologous transplantation. New classifications of innervation are desirable for individual muscles rather than a generalized approach.

Intramuscular Nerve Distribution of the Inferior Oblique Muscle

Purpose: The intramuscular nerve distribution in the extraocular muscles is important for understanding their function. This study aimed to determine the intramuscular nerve distribution of the oculomotor nerve within the inferior oblique muscle (IO) using Sihler's staining.Method: Seventy-two IOs from 50 formalin-embalmed cadavers were investigated. The IO including its branch of the oculomotor nerve was finely dissected from its origin to its insertion point into the sclera. The total length of the muscle and its width were measured. The intramuscular nerve course was investigated after performing Sihler's staining, which is a whole-mount nerve-staining technique that stains the nerves while rendering other soft tissues either translucent or transparent.Results: The total length of the muscle and muscle width were 30.0 ± 2.8 mm (mean±standard deviation), 8.8 ± 1.2 mm, respectively. The oculomotor nerve enters the IO around the middle of the muscle and then divides into multiple smaller branches without distinct subdivisions. The intramuscular nerve distribution within the IO has a root-like arborization and supplies the entire width of the muscle. The Sihler's stained intramuscular nerve course (covering a length of 7.6 ± 1.2 mm) finishes around the distal one-third of the IO in gross observations.Conclusion: Sihler's staining is a useful technique for visualizing the gross nerve distribution of the IO. This new information about the nerve distribution and morphological features will improve the understanding of the biomechanics of the IO.

Detailed anatomy of the trochlear nerve in the superior oblique muscle

PURPOSE

The purpose of this study was to elucidate the detailed anatomy of the trochlear nerve in the superior oblique muscle (SOM) and the intramuscular innervation pattern using Sihler staining.

METHODS

SOMs were dissected from their origin to the insertion in 28 eyes of 14 cadavers. The following distances were determined: from the SOM insertion to the trochlear, from the trochlear to the entry site of the anterior branch or posterior branch, and the widths of the main trunk and anterior and posterior branches. Sihler staining was then performed.

RESULTS

The trochlear nerve traveled straight ahead medially and divided. Eighteen of 28 (64.3%) orbits showed two anterior and posterior branches, six (21.4%) showed three branches, and four (14.3%) showed no branching. The most distally located intramuscular nerve ending was observed at 62.4 ± 2.4% of the length of each muscle (35.8 mm from insertion when considering that the length of the SOM was 57.4 mm) and at 29.9 ± 3.2% of the length of each muscle (17.2 mm from the trochlear). Additionally, the length of the intramuscular arborization part was 9.4 ± 1.1% of the length of the SOM (5.4 mm when considering that the length of the SOM was 57.4 mm). Nonoverlap between two intramuscular arborizations of the nerve was detected in 20 of 28 cases (71.4%). Eight cases (28.6%) showed a definite overlap of two zones.

CONCLUSIONS

This study provided a good understanding of the anatomy of the trochlear nerve in the SOM.

Intramuscular Nerve Distribution in the Medial Rectus Muscle and Its Clinical Implications

PURPOSE

The intramuscular nerve distribution in the extraocular muscles may be crucial for understanding their physiological and pathological responses. This study aimed to determine the oculomotor nerve distribution in the medial rectus muscle (MR) using Sihler's staining.

METHOD

Thirty-seven MRs from 23 cadavers were investigated. The MR including the oculomotor nerve was finely dissected from its origin to its insertion point into the sclera. The total length of the muscle-belly, tendon length and maximum width of the muscle were measured. We evaluated the pattern of distribution and the length of the intramuscular nerve distribution by gross observation after performing Sihler's staining, which is a method for visualizing the distribution of nerve fibers without alteration of the nerve.

RESULTS

The total length of the muscle-belly, tendon length, and muscle width were 37.6 ± 4.6 mm, 4.4 ± 1.9 mm, and 10 ± 1.8 mm, respectively. The oculomotor nerve enters the MR at a mean of two-fifths along the muscle (24 ± 2.0 mm posterior to the insertion point) and then typically divides into a few branches (mean of 2.1). The intramuscular nerve distribution showed a Y-shaped ramification, forming the terminal nerve plexus, and its course typically finished at around 17 ± 1.5 mm posterior to the muscle insertion point by gross observation. The nerve plexus in the upper part generally coursed more distally than the lower part.

CONCLUSION

This new information regarding the nerve distribution pattern of MR will be helpful for understanding MR function and the diverse pathophysiology of strabismus.

Intramuscular Distribution of the Abducens Nerve in the Lateral Rectus Muscle for the Management of Strabismus

AIMS

To elucidate the intramuscular distribution and branching patterns of the abducens nerve in the lateral rectus (LR) muscle so as to provide anatomical confirmation of the presence of compartmentalization, including for use in clinical applications such as botulinum toxin injections.

METHODS

Thirty whole-mount human cadaver specimens were dissected and then Sihler's stain was applied. The basic dimensions of the LR and its intramuscular nerve distribution were investigated. The distances from the muscle insertion to the point at which the abducens nerve enters the LR and to the terminal nerve plexus were also measured.

RESULTS

The LR was 46.0 mm long. The abducens nerve enters the muscle on the posterior one-third of the LR and then typically divides into a few branches (average of 1.8). This supports a segregated abducens nerve selectively innervating compartments of the LR. The intramuscular nerve distribution showed a Y-shaped ramification with root-like arborization. The intramuscular nerve course finished around the middle of the LR (24.8 mm posterior to the insertion point) to form the terminal nerve plexus. This region should be considered the optimal target site for botulinum toxin injections. We have also identified the presence of an overlapping zone and communicating nerve branches between the neighboring LR compartments.

CONCLUSION

Sihler's staining is a useful technique for visualizing the entire nerve network of the LR. Improving the knowledge of the nerve distribution patterns is important not only for researchers but also clinicians to understand the functions of the LR and the diverse pathophysiology of strabismus.

Method to test the long-term stability of functional electrical stimulation via multichannel electrodes (e.g., applicable for laryngeal pacing) and to define best points for stimulation: in vivo animal analysis

The study aim was to identify and analyze intramuscular electrically sensitive points. Electrically sensitive points are herein defined as positions, which allow muscles stimulation with a minimum possible fatigue for a maximum amount of time. A multichannel array electrode was used which could be interesting to retain the function of larynx muscle after paralysis. Eight array electrodes were implanted in the triceps brachii muscle of four rats. While being under anesthesia, the animals were intramuscularly stimulated at 16 different positions. Sihler's staining technique was used to make visible the nerves routes and the intramuscular position of the individual electrode plate. The positions of the motor end plates were determined by means of multichannel-electromyography. The positions that allow longest stimulation periods are located close to the points where the nerves enter the muscle. Stimulation at the position of the motor end plates does not result in stimulation periods above average. Locations initially causing strong muscle contractions are not necessarily identical to the ones allowing long stimulation periods. The animal model identified the stimulation points for minimal possible muscle fatigue stimulation as being located close to the points of entrance of the nerve into the muscle. Stimulation causing an initially strong contraction response is no indication of optimal location of the stimulation electrode in terms of chronic stimulation. The array electrode of this study could be interesting as a stimulation electrode for a larynx pacemaker.

Is There a Double Innervation of the Tensor Tympani Muscle in Humans?

The middle ear muscles and their function have not yet been fully explored. The statement of Lawrence, for example, that the tensor tympani muscle of humans might have a dual innervation has never been proven or disproven. The question is of great interest; in our opinion, it represents one of the key questions in the putative afferent feedback loop of the middle ear muscles in humans. A light microscopic study was performed on 16 tensor tympani muscles taken from 11 cadavers. Six muscles were taken out in toto and stained according to the modified method of Sihler. The remaining 10 muscles were dehydrated and embedded in paraffin. In 5 of these muscles, complete transverse serial sections were made on a microtome at 7 microm and alternately stained by silver impregnation, S-100 protein immunohistochemistry, and ferric oxide. In the remaining 5 muscles, complete longitudinal serial sections were made at 10 microm. These sections were alternately stained by the methods of Cason and Maskar. Neither the surgical microscopic investigation nor the light microscopic investigation revealed any innervation to the human tensor tympani muscle other than the one arising from the mandibular branch of the trigeminal nerve. Our findings, apart from the fact that they clearly refute an unproven hypothesis, might represent another small step toward understanding the innervation of the tensor tympani muscle.

Intramuscular innervations of lower leg skeletal muscles: applications in their clinical use in functional muscular transfer

PURPOSE

This study aims to investigate nerve distribution patterns of human lower leg skeletal muscles using a modified Sihler's staining method.

METHODS

Sixteen lower leg from eight fresh adult cadavers were used in this study and all the skeletal muscles were dissected. The muscle specimens were classified according to Lim's classification. The specimens were then stained by further modified Sihler's staining technique. Data were analyzed according to research results.

RESULTS

After the staining, we found four patterns of nerve distribution in human lower leg muscles: (1) Type 1: single nerve pattern in which the nerve branches into two either running parallel to each other or radiating in a spray pattern (such as the extensor digitorum longus, extensor hallucis longus, fibularis brevis and flexor hallucis longus). (2) Type 2: double nerve pattern, one being proximal and the other being distal (such as the extensor digitorum longus, flexor digitorum longus, flexor hallucis longus). (3) Type 3: multiple branch pattern (such as the tibialis anterior, fibularis longus, gastrocnemius, soleus, tibialis anterior and popliteus).

CONCLUSION

Our modified Sihler's staining method is useful for research of large muscles and intramuscular nerves in human. These findings might provide guidance for clinicians for muscle reconstruction surgery.

Determination of injection site in flexor digitorum longus for effective and safe botulinum toxin injection

OBJECTIVE

To determine the optimal injection site in the flexor digitorum longus (FDL) muscle for effective botulinum toxin injection.

METHODS

Fourteen specimens from eight adult Korean cadavers were used in this study. The most proximal medial point of the tibia plateau was defined as the proximal reference point; the most distal tip of the medial malleolus was defined as the distal reference point. The distance of a line connecting the proximal and distal reference points was defined as the reference length. The X-coordinate was the distance from the proximal reference point to the intramuscular motor endpoint (IME), or motor entry point (MEP) on the reference line, and the Y-coordinate was the distance from the nearest point from MEP on the medial border of the tibia to the MEP. IME and MEP distances from the proximal reference point were evaluated using the raw value and the X-coordinate to reference length ratio was determined as a percentage.

RESULTS

The majority of IMEs were located within 30%-60% of the reference length from the proximal reference point. The majority of the MEPs were located within 40%-60% of the reference length from the proximal reference point.

CONCLUSION

We recommend the anatomical site for a botulinum toxin injection in the FDL to be within a region 30%-60% of the reference length from the proximal reference point.

Human tongue neuroanatomy: Nerve supply and motor endplates

The human tongue has a critical role in speech, swallowing, and respiration, however, its motor control is poorly understood. Fundamental gaps include detailed information on the course of the hypoglossal (XII) nerve within the tongue, the branches of the XII nerve within each tongue muscle, and the type and arrangement of motor endplates (MEP) within each muscle. In this study, five adult human tongues were processed with Sihler's stain, a whole-mount nerve staining technique, to map out the entire intra-lingual course of the XII nerve and its branches. An additional five specimens were microdissected into individual muscles and stained with acetylcholinesterase and silver staining to study their MEP morphology and banding patterns. Using these techniques the course of the entire XII nerve was mapped from the main nerve to the smallest intramuscular branches. It was found that the human tongue innervation is extremely dense and complex. Although the basic mammalian pattern of XII is conserved in humans, there are notable differences. In addition, many muscle fibers contained multiple en grappe MEP, suggesting that they are some variant of the highly specialized slow tonic muscle fiber type. The transverse muscle group that comprises the core of the tongue appears to have the most complex innervation and has the highest percentage of en grappe MEP. In summary, the innervation of the human tongue has specializations not reported in other mammalian tongues, including nonhuman primates. These specializations appear to allow for fine motor control of tongue shape.

Investigation of the nerve distribution pattern of leg muscles in rat

Information about the distribution of intramuscular nerve fibres within the skeletal muscles will enhance the understanding of their morphological structure and functions. This study was designed to examine the entire intramuscular nerve distribution pattern in rat leg muscles. The tibialis cranialis, tibialis caudalis, extensor digitorum longus, flexor digitorum longus, gastrocnemius, peroneus longus and brevis muscles were dissected from origo and insertion points under a surgical microscope in seven rats. These skeletal muscles from right hindlimbs were stained with Sihler's stain. The diameter of extramuscular and major nerve branches, number of major and minor nerve branches and anastomoses were measured and photographed under a stereomicroscope. In addition, serial sections were obtained from the left hindlimb muscles with S100 immunohistochemical staining and transferred to the computer to reconstruct images. A significant difference was found between the gastrocnemius and tibialis caudalis (p < 0.001), flexor digitorum longus and tibialis caudalis (p < 0.003), and peroneus longus and tibialis caudalis (p < 0.049) with regard to the diameter of major branches. The gastrocnemius was significantly different from the flexor digitorum longus, peroneus longus, extensor digitorum longus, tibialis caudalis and tibialis cranialis with regard to the number of minor nerve branches (p < 0.001). Knowledge of the branching pattern and some key landmarks, such as the number and diameter of major and minor nerve branches and the number of anastomoses between the nerve branches of skeletal muscles, is helpful in surgical or therapeutic interventions and botulinum toxin injections in areas of high extramuscular and intramuscular nerve density.

Intramuscular distribution of the phrenic nerve in human diaphragm as shown by Sihler staining

INTRODUCTION

Intramuscular innervation of the human diaphragm has not been well described. The goal of this study was to elucidate the detailed intramuscular distribution of the phrenic nerve in the human diaphragm.

METHODS

Fifteen human diaphragms were visualized using modified Sihler staining, and the detailed intramuscular phrenic nerve distribution was photographed and recorded.

RESULTS

Three types of primary phrenic nerve branches were noted. Each type of primary branch innervated a confined muscular subvolume of the diaphragm, and the intramuscular branches in each subvolume anastomosed largely with one another and formed a characteristic "net" of nerve branches. A few small nerve filaments were seen entering the peripheral diaphragm. The directions and locations of nerve branches innervating the hiatal diaphragm were not symmetrical between sides.

CONCLUSION

These findings may offer useful information for anatomists, physiologists, and clinicians.

Clinical and anatomical approach using Sihler's staining technique (whole mount nerve stain)

Sihler's staining allows visualization of the nerve distribution within soft tissues without extensive dissection and does not require slide preparation, unlike traditional approaches. This technique can be applied to the mucosa, muscle, and organs that contain myelinated nerve fibers. In particular, Sihler's technique may be considered the best tool for observing nerve distribution within skeletal muscles. The intramuscular distribution pattern of nerves is difficult to observe through manual manipulation due to the gradual tapering of nerves toward the terminal end of muscles, so it should be accompanied by histological studies to establish the finer branches therein. This method provides useful information not only for anatomists but also for physiologists and clinicians. Advanced knowledge of the nerve distribution patterns will be useful for developing guidelines for clinicians who perform operations such as muscle resection, tendon transplantation, and botulinum toxin injection. Furthermore, it is a useful technique to develop neurosurgical techniques and perform electrophysiological experiments. In this review, Sihler's staining technique is described in detail, covering its history, staining protocol, advantages, disadvantages, and possible applications. The application of this technique for determining the arterial distribution pattern is also described additionally in this study.

Sihler's whole mount nerve staining technique: a review

Sihler's stain is a whole mount nerve staining technique that renders other soft tissue translucent or transparent while staining the nerves. It permits mapping of entire nerve supply patterns of organs, skeletal muscles, mucosa, skin, and other structures after the specimens are fixed in neutralized formalin, macerated in potassium hydroxide, decalcified in acetic acid, stained in Ehrlich's hematoxylin, destained in acetic acid, and cleared in glycerin. The unique advantage of Sihler's stain over other anatomical methods is that all the nerves within the stained specimen can be visualized in their three-dimensional positions. To date, Sihler's stain is the best tool for demonstrating the precise intramuscular branching and distribution patterns of skeletal muscles, which are important not only for anatomists, but also for physiologists and clinicians. Advanced knowledge of the neural structures within mammalian skeletal muscles is critical for understanding muscle functions, performing electrophysiological experiments and developing novel neurosurgical techniques. In this review, Sihler's stain is described in detail and its use in nerve mapping is surveyed. Special emphasis is placed on staining procedures and troubleshooting, strengths and limitations, applications, major contributions to neuroscience, physiological and clinical significance, and areas for further technical improvement that deserve future research.

Extra- and intramuscular nerves distributions of the triceps surae muscle as a basis for muscle resection and botulinum toxin injections

PURPOSE

To compare the distribution of extramuscular nerve branches with their intramuscular ramifications in the triceps surae muscle, thus providing anatomical substantiation for the topography of muscle resection and botulinum toxin injections.

METHODS

Dissection and modified Sihler's staining of 18 whole-mount human cadaveric specimens.

RESULTS

The distance between the areas with the highest extramuscular branch density and the area of densest intramuscular arborization in gastrocnemius and soleus muscles is approximately 10% of the calf length. This finding should be taken into consideration during nerve blocking and botulinum toxin injections for the treatment of spasticity. Intramuscular nerve arborization patterns make it possible to outline neuromuscular segments in the gastrocnemius and soleus muscles.

CONCLUSIONS

Surgical or therapeutic interventions in areas of high extramuscular and intramuscular nerve density can increase the efficacy and safety of botulinum toxin injections and neurotomy. Intramuscular nerve branching patterns should be taken into consideration during triceps surae resection.

The internal innervation and morphology of the human female levator ani muscle

OBJECTIVE

The purpose of this study was to describe the microinnervation of the human the female levator ani muscle complex.

STUDY DESIGN

Detailed microdissection of 10 fresh female levator ani muscles was performed. Specimens were processed by modified Sihler's staining technique. A composite drawing of the levator ani nerve (LAN) distribution was created.

RESULTS

Six hemi-levator ani muscles were stained and digitally reconstructed. The LAN traveled perpendicular to major muscular bundles while progressively branching into finer nerves that eventually entered single muscle fascicles. The LAN continued its course through the iliococcygeous muscle to innervate the puborectalis, puboperinealis, and puboanalis muscles. There was no distinct separation between pubovisceralis and iliococcygeous fibers. There were muscle fibers that could be best described as coccygeoperinealis.

CONCLUSION

The utilized staining technique enabled us to visualize the LAN microinnervation of the levator ani muscle that extends to puboperinealis and puboanalis muscles. A blueprint for LAN and levator ani morphology was created.

Neuroanatomy of the equine dorsal cricoarytenoid muscle: surgical implications

REASON FOR PERFORMING STUDY

Studies are required to define more accurately and completely the neuroanatomy of the equine dorsal cricoarytenoid muscle as a prerequisite for developing a neuroprosthesis for recurrent laryngeal neuropathy.

OBJECTIVES

To describe the anatomy, innervation, fibre types and function of the equine dorsal cricoarytenoid muscle.

METHODS

Thirty-one larynges were collected at necropsy from horses with no history of upper airway disease and 25 subjected to gross dissection. Thereafter, the following preparations were made on a subset of larynges: histochemical staining (n = 5), Sihler's and acetylcholinesterase staining for motor endplates (n = 2). An additional 6 larynges were collected and used for a muscle stimulation study.

RESULTS

Two neuromuscular compartments (NMC), each innervated by a primary nerve branch of the recurrent laryngeal nerve, were identified in all larynges. Stimulation of the lateral NMC produced more lateral displacement of the arytenoid cartilage than the medial NMC (P<0.05). The medial NMC tended to rotate the arytenoid cartilage dorsally. Motor endplates were identified at the junction of the middle and caudal thirds of each NMC. If fibre type grouping was present it was always present in both NMCs.

CONCLUSIONS

The equine dorsal cricoarytenoid muscle has 2 distinct muscle NMCs with discrete innervation and lines of action. The lateral NMC appears to have a larger role in increasing cross-sectional area of the rima glottidis.

POTENTIAL RELEVANCE

This information should assist in planning surgical reinnervation procedures and development of a neuroprosthesis for recurrent laryngeal neuropathy.

Anatomical localization of motor endplate bands in the human biceps brachii

OBJECTIVES

: Botulinum neurotoxin (BoNT) reduces disabling muscle contraction in numerous disorders with muscle overactivity. While motor endplates are the primary site of action for BoNT, their location is unknown in most human muscles. This study localized the motor endplate bands (MEB) within human biceps brachii (BB) muscles in relation to external landmarks.

METHODS

: Five human BB muscles were obtained from autopsy. Three muscles were processed for Sihler's stain, a nerve staining technique, and 2 were processed by whole-mount acetylcholinesterase stain.

RESULTS

: The major MEB in BB is an inverted V-shaped band, 1 cm in width, located 7 cm superior to the olecranon laterally, 11 cm superior to the olecranon in the middle, and 8 cm above the olecranon medially. The ratio of MEB location to total olecranon-acromion length is 0.25 at the lateral edge, 0.39 in the midline, and 0.28 at the medial edge.

CONCLUSIONS

: This study localized MEB in human BB in reference to external landmarks. This data should improve the feasibility of endplate targeting when injecting BoNT in BB, which might enhance the clinical efficacy of these injections.

Qualitative comparison of anatomical microdissection, Sihler's staining and computerized reconstruction methods for visualizing intramuscular nerve branches

STATING BACKGROUND: This study was designed to examine the entire intramuscular nerve distribution pattern of various human skeletal muscles in fetuses.

METHODS

In the present study rhomboid major, trapezius, long head of the biceps femoris and masseter muscles were investigated in five 18 weeks old fetal cadavers. Anatomical microdissection was applied to one fetal cadaver. In two fetuses, the extramuscular (main), major and minor nerve branches, and anastomosis were examined using Sihler's staining and labeling. In the remaining two fetuses, consecutive slices with 0.5 mm interval and 5 microm thickness were obtained from each skeletal muscle. These slices were stained with S100 for the demonstration of the nerve fibers and thereafter 3D reconstruction images were constituted using PC software.

RESULTS

Anatomical microdissection, Sihler's staining and computerized reconstruction methods were compared to demonstrate the intramuscular nerve distribution pattern. Demonstration of the intramuscular minor nerve branches and anastomosis showed difficulties in anatomical dissected specimens when compared with three-dimensionally reconstructed images and specimens obtained with Sihler's staining technique. Nevertheless, anatomical dissection is a simple method whereas Sihler's technique and computer aided 3D reconstruction are complex methods and take a long time to complete.

CONCLUSION

The obtained information exposed that staining technique and the 3D reconstructions appeared to provide better results than did anatomical dissection.

Phrenic nerve distribution in the rabbit diaphragm and morphometric analysis of nerve branches

The best method to evaluate the pathogenesis of diaphragmatic disorders is to demonstrate the distribution pattern of the phrenic nerve in the diaphragm. For this purpose the branching pattern and the microanatomic features of the phrenic nerve were observed in six rabbits. All diaphragms were stained by using Sihler's stain method. The phrenic nerve divided into three to four branches when entering the diaphragm. These branches were classified as sternal, anterolateral, posterolateral and crural. The crural branches were the thickest whereas the anterolateral branches were the thinnest. Knowledge about the distribution pattern of the phrenic nerve may be important in surgical approach to the diaphragm.

Observation of the relationship between the shape of skeletal muscles and their nerve distribution patterns: a transparent and microanatomic study

BACKGROUND

There are many gaps in the understanding of the neuroanatomy of skeletal muscles with regards to the nerve distribution pattern and shape of the muscles. This study was designed to examine the entire intramuscular nerve-distribution patterns of various human skeletal muscles.

METHODS

The relationships among nine skeletal muscles with various architecture (rhomboid major, biceps brachii, flexor pollicis longus, rectus femoris, sternohyoid, trapezius, masseter, digastric muscles) and their nerve-distribution patterns were investigated in four fetal cadavers using the Sihler staining method. The diameter and number of extramuscular (main) and major nerve branches, the number of minor nerve branches, and anastomoses were examined and evaluated statistically.

RESULTS

With regards to the number of extramuscular (main) nerve branches, the rhomboid major muscle resembled the flexor pollicis longus, trapezius, masseter, and sternohyoid muscles, and the anterior belly of the digastricus muscle (p > 0.05), whereas it was significantly different from the rectus femoris, the posterior belly of digastricus, and the long and short heads of the biceps brachii (p < 0.05). Trapezius and masseter muscles were different from all of the skeletal muscles that were studied with regards to the diameter of main branches (p < 0.05). The masseter muscle had the largest diameter (p < 0.05). With regards to the number of minor nerve branches, the sternohyoid muscle was significantly different from all the skeletal muscles that were studied (p < 0.05) except the short head of the biceps brachii, rectus femoris, and the posterior belly of digastricus (p > 0.05). As for the number of neural anastomoses, the sternohyoid muscle was statistically different from all skeletal muscles that were studied (p < 0.05) except the masseter and trapezius muscles (p > 0.005).

CONCLUSIONS

A surgeon's thorough knowledge of the relationship between the shape and nerve distribution pattern of skeletal muscles is important in successful reinnervation and regeneration of these muscles. It might also be useful in the field of muscle transplantation.

[The epiglottis, a glosso-laryngeal structure: an anatomic study of its innervation]

The epiglottis is known as a laryngeal structure. The authors studied the innervation of epiglottis using the Sihler method on six human epiglottises. Innervation of the epiglottis depended on the rami from the vagus, glossopharyngeal and hypoglossal nerves. By its innervation, epiglottis seems to be a glosso-laryngeal structure, as is confirmed by embryology, histology and clinical applications.

Intrinsic muscles and distribution of the recurrent laryngeal nerve in the pig larynx

To use the pig larynx in studies of laryngeal reinnervation, it is essential to have a clear understanding of its anatomy. We aimed to define the macroscopic anatomy of the intrinsic muscles and the course of the recurrent laryngeal nerve (RLN) in the pig larynx. Twelve large white pig larynges were used. Five larynges were preserved in formalin, then dissected to study the anatomy of the intrinsic muscles. Seven larynges were stained using the modified Sihler's staining technique, which results in nerves being stained dark purple while the remainder of the larynx is rendered translucent. The intrinsic muscles of the pig larynx were similar to those in the human. The RLN gives off a branch that enters the posterior cricoarytenoid muscle (PCA) on its deep surface and supplies the entire muscle, although the branching pattern of the nerve within the muscle varies considerably. These results facilitate detailed reinnervation studies in the pig laryngeal transplant model.

Clearing and embedding in polyester resin for demonstrating the nerve distribution pattern of skeletal muscles

The preservation of many stained gross specimens in solution creates some difficulties. It is convenient and effective to preserve material in polyester resin instead of glycerol. The aim of this study was to determine the usefulness of clearing and embedding using polyester resin. The samples consisted of the nerve distribution patterns of skeletal muscles stained using Sihler's method. The muscles were cleared more successfully and the intramuscular nerve distributions were demonstrated better in polyester than in glycerol. The method presented here eliminates not only the storage and handling problems of specimens, but also problems such as pale stains and the molding of preparations. Furthermore, it is more convenient to examine and to photograph specimens cleared and embedded in polyester than those stored in glycerol.

Distribution pattern of the human lingual nerve

The tongue is an intricate organ with many functions. Despite the knowledge of the presence of muscular and neural connections in the tongue, a detailed neuroanatomical depiction of the nerves' topography in the tongue has not been demonstrated. The topography, branching patterns and neuronal interconnections of the lingual nerve were studied in five postmortem human tongues. They were stained with Sihler's stain, a technique that renders most of the tongue tissue translucent while counterstaining nerves. The lingual nerve reaches the tongue posterolaterally. There are two main branches off of the main trunk: the medial branch sends 2-4 small branches to the medial part of the ventrolateral tongue and the lateral branch runs along the lateral tongue border and sends 3-4 large branches to the anterior tip of tongue. Each subdivision gives off 2-5 distal branches. Both medial and lateral branches have interconnections with the proximal part of the hypoglossal nerve. One of the unexpected discoveries in this study was the high density of nervous fibers in the lateral aspect of the tongue as compared to the midline region. The average diameter of the main trunk of the lingual nerve is 3.5 mm. The medial and lateral branches average 1 mm in diameter, the more distal subdivisions measure 0.5-0.75 mm, and the lingual-hypoglossal interconnections measure 0.125-0.250 mm. In summary, this study provides the first detailed depiction of the topography of the human lingual nerve and its branches in situ, confirmation of lingual-hypoglossal nerve connection, and the first depiction of the high density of lingual nerve innervation in the lateral tongue.

Intralaryngeal neuroanatomy of the recurrent laryngeal nerve of the rabbit

We undertook this study to determine the detailed neuroanatomy of the terminal branches of the recurrent laryngeal nerve (RLN) in the rabbit to facilitate future neurophysiological recordings from identified branches of this nerve. The whole larynx was isolated post mortem in 17 adult New Zealand White rabbits and prepared using a modified Sihler's technique, which stains axons and renders other tissues transparent so that nerve branches can be seen in whole mount preparations. Of the 34 hemi-laryngeal preparations processed, 28 stained well and these were dissected and used to characterize the neuroanatomy of the RLN. In most cases (23/28) the posterior cricoarytenoid muscle (PCA) was supplied by a single branch arising from the RLN, though in five PCA specimens there were two or three separate branches to the PCA. The interarytenoid muscle (IA) was supplied by two parallel filaments arising from the main trunk of the RLN rostral to the branch(es) to the PCA. The lateral cricoarytenoid muscle (LCA) commonly received innervation from two fine twigs branching from the RLN main trunk and travelling laterally towards the LCA. The remaining fibres of the RLN innervated the thyroarytenoid muscle (TA) and comprised two distinct branches, one supplying the pars vocalis and the other branching extensively to supply the remainder of the TA. No communicating anastomosis between the RLN and superior laryngeal nerve within the larynx was found. Our results suggest it is feasible to make electrophysiological recordings from identified terminal branches of the RLN supplying laryngeal adductor muscles separate from the branch or branches to the PCA. However, the very small size of the motor nerves to the IA and LCA suggests that it would be very difficult to record selectively from the nerve supply to individual laryngeal adductor muscles.

Demonstration of the nerve distribution of the extraocular muscles in rabbits (Oryctolagus cuniculus)

PURPOSE

The intramuscular nerve distribution of the extraocular muscles may be of utmost importance for better understanding of their physiologic and pathologic reactions. The aim of this study was to determine the entire intramuscular nerve distribution pattern of rabbit extraocular muscles by utilizing Sihler's staining technique.

METHODS

Six New Zealand rabbits were used in order to demonstrate the intramuscular nerve distribution of the extraocular muscles by using Sihler's staining method.

RESULTS

The number of extramuscular and intramuscular major nerve branches were higher in the inferior oblique muscle while the number of intramuscular minor nerve branches were higher in the superior oblique muscle when compared with the other extraocular muscles. The smallest number of extramuscular branch and intramuscular both major and minor branches were found in the medial rectus muscle. More complex anastomoses and a branching pattern were observed in the superior oblique and superior rectus muscle. The anastomosing nerve branches were observed to run in a "Y", "I" or "U"-shaped pattern in all of the extraocular muscles. Of all the extraocular muscles, the longest major nerve branches were observed in the retractor bulbi muscles. However, these branches had the smallest diameter. No morphological difference was observed between the two sides with regard to all the characteristics of the extraocular muscles.

CONCLUSION

Sihler's neural staining technique could be quite useful in the demonstration of the intramuscular nerve distribution of extraocular muscles.

Demonstration of the nerve distribution of the masticatory muscles in rabbits (Oryctolagus cuniculus)

Two methods can be used in order to demonstrate the nerve distribution of an organ. One is the three-dimensional reconstruction of the innervation pattern of the organ by tracing images of that organ from serial histological sections. The other is the in toto staining of the organ with subsequent clearing of the muscles. In the present study, in order to visualize the nerve distribution of the organ, that organ was completely cleared and the nerve fibres were stained. Detailed morphological structure of the intramuscular nerve distribution of a certain region and its functions are of importance not only for anatomists and physiologists but also for clinicians. In this study eight New Zealand rabbits were used to visualize the intramuscular nerve distribution of the muscles involved in mastication (temporalis m., pterygoideus medialis m., digastricus m., retractor mandibulae m. and masseter m.). The main nerve bundle was observed entering into the muscle as a single trunk and dividing into three branches in the muscle. These branches were also observed dividing into several subbranches while going to the periphery. When the samples were examined under a stereomicroscope, 'Y'-, 'I'- and 'O'-shaped communications between those branches were observed.

Sensory nerve supply of the human oro- and laryngopharynx: a preliminary study

To date, the details of human sensory innervation to the pharynx and upper airway have not been demonstrated. In this study, a single human oro- and laryngopharynx obtained from autopsy was processed with a whole-mount nerve staining technique, Sihler's stain, to determine its entire sensory nerve supply. The Sihler's stain rendered all mucosa and soft tissue translucent while counterstaining nerves. The stained specimen was then dissected and the nerves were traced from their origins to the terminal branches. It was found that the sensory innervation of the human pharynx is organized into discrete primary branches that innervate specific areas, although these areas are often connected by small neural anastomoses. The density of innervation varied, with some areas receiving almost no identifiable nerve supply (e.g., posterior wall of the hypopharynx) and certain areas contained much higher density of sensory nerves: the posterior tonsillar pillars; the laryngeal surface of the epiglottis; and the postcricoid and arytenoid regions. The posterior tonsillar pillar was innervated by a dense plexus formed by the pharyngeal branches of the IX and X nerves. The epiglottis was densely innervated by the internal superior laryngeal nerve (ISLN) and IX nerve. Finally, the arytenoid and postcricoid regions were innervated by the ISLN. The postcricoid region had higher density of innervation than the arytenoid area. The use of the Sihler's stain allowed the entire sensory nerve supply of the pharyngeal areas in a human to be demonstrated for the first time. The areas of dense sensory innervation are the same areas that are known to be the most sensitive for triggering reflex swallowing or glottic protection. The data would be useful for further understanding swallowing reflex and guiding sensory reinnervation of the pharynx to treat neurogenic dysphagia and aspiration disorders.

Neuromuscular organization of the canine tongue

The tongue manipulates food while chewing and swallowing, dilates the airway during inspiration, and shapes the sounds of speech in humans. While performing these functions the tongue morphs through many complex shapes. At present it is not known how the muscles of the tongue perform these complex shape changes. The difficulty in understanding tongue biomechanics is partly due to gaps in our knowledge regarding the complex neuromuscular anatomy of the tongue. In this study the motor and sensory nerve anatomy of four canine tongues was studied with Sihler's stain, a technique that renders most of the tongue tissue translucent while counterstaining nerves. An additional tongue specimen was serially sectioned to provide a reference for the muscle structure of the tongue. The hypoglossal nerve (XII) has approximately 50 primary nerve branches that innervate all intrinsic and extrinsic tongue muscles. Two extrinsic muscles, the styloglossus and hyoglossus, are innervated by about three to four branches from the lateral division of the XII. The third extrinsic muscle, the genioglossus, is composed of oblique and horizontal compartments, which receive about ten nerve branches from the medial division of the XII. The intrinsic muscles are composed of many neuromuscular compartments. On each side, the superior longitudinal muscle had an average of 40 distinct muscle fascicles that spanned the length of the tongue. Each of the fascicles is supplied by a nerve branch. The inferior longitudinal muscle had a similar organization. Each of the transverse and vertical muscles is composed of over 140 separate muscle sheets, and every sheet is innervated by a separate terminal nerve. The muscle sheets from the vertical and transverse alternate their orientation 90 degrees throughout the length of the tongue. It is concluded that the intrinsic canine tongue muscles are actually composed of groups of neuromuscular compartments that are arranged in parallel (longitudinal muscles) or in a precise alternating sequence (transverse and vertical muscles). This arrangement suggests that the compartments from the different tongue muscles could cooperate to control the three-dimensional contractile state of their local area. This hypothesis could explain how many different tongue shapes are formed, and is supported by physiologic evidence.

Neuromuscular specializations of the pharyngeal dilator muscles: I. Compartments of the canine geniohyoid muscle

BACKGROUND

Little is known about the structure and innervation of the geniohyoid muscle (GH), which is an important pharyngeal dilator muscle activated in swallowing and respiration.

METHODS

The neuromuscular specializations of the canine GH were studied in detail by using a combination of histological, histochemical, and anatomical techniques. First, hematoxylin and eosin staining, Gomori's rapid one-step trichrome stain, and silver impregnation were used to determine the terminations of muscle fibers and existence of fibrous septa within the muscle (n = 8). Second, myofibrillar ATPase staining was employed to document the muscle fiber type distribution (n = 8). Finally, Sihler's stain (n = 10) and wholemount acetylcholinesterase staining (n = 8) were used to examine the distribution of the nerve supply within the muscle.

RESULTS

The canine GH is divided into rostral and caudal compartments, which are arranged in series and separated by a transverse fibrous septum. Each compartment receives its own primary nerve branch, which supplies a separate motor endplate zone. The rostral compartment is innervated bilaterally, whereas the caudal compartment is innervated ipsilaterally. The rostral compartment was composed of significantly more type I (slow twitch) muscle fibers (56%) than the caudal compartment (25%).

CONCLUSIONS

The canine GH is composed of two in-series neuromuscular compartments rather than a single muscle as traditionally believed. This anatomical finding suggests that these two compartments may function independently under different physiological conditions.

Respiratory activity of the rat posterior cricoarytenoid muscle

An anatomic and electrophysiological study of the rat posterior cricoarytenoid (PCA) muscle is described. The intramuscular nerve distribution of the PCA branch of the recurrent laryngeal nerve was demonstrated by a modified Sihler's stain. The nerve to the PCA was found to terminate in superior and inferior branches with a distribution that appeared to be confined to the PCA muscle. Electromyography (EMG) recordings of PCA muscle activity in anesthetized rats were obtained under stereotaxic control together with measurement of phrenic nerve discharge. A total of 151 recordings were made in 7 PCA muscles from 4 rats. Phasic inspiratory activity with a waveform similar to that of phrenic nerve discharge was found in 134 recordings, while a biphasic pattern with both inspiratory and post-inspiratory peaks was recorded from random sites within the PCA muscle on 17 occasions. The PCA EMG activity commenced 24.6 +/- 2.2 milliseconds (p < .0001) before phrenic nerve discharge. The results are in accord with findings of earlier studies that show that PCA muscle activity commences prior to inspiratory airflow and diaphragmatic muscle activity. The data suggest that PCA and diaphragm motoneurons share common or similar medullary pre-motoneurons. The earlier onset of PCA muscle activity may indicate a role for medullary pre-inspiratory neurons in initiating PCA activity.

Subglottic branch of the superior laryngeal nerve in the dog penetrates the cricoid cartilage

The topographic anatomical study on the distribution pattern of the superior laryngeal nerve (SLN) in the larynx was studied in thirteen adult dogs. The ramus posterior of the SLN divides into two branches; the interarytenoid branch (IA) and the pharyngoesophageal branch (PE). The IA on both sides connect to the cricoid ganglion (CG) in the midline at the cranial border of the cricoid cartilage. Posterior glottic branches arise from the IA, run over the cricoid cartilage, and distribute fibers to the posterior wall of the glottis. Every specimen observed in the present study possessed the CG and the posterior glottic branches. The subglottic branch derives from the IA near the cricoid ganglion, and passes through the cricoid foramen (CF) (Yoshida, 1986). The subglottic branch distributes fibers to the subglottic mucous membrane covering the cricothyreoid ligament. The CF and the subglottic branch were observed on both sides of seven specimens out of thirteen dogs. They were also observed on only one side in three specimens, and were not detectable on either side in the three remaining specimens. The silver impregnation applied in the semimicroscopic dissection facilitated identification of the precise localization and the topographic arrangement of ganglia and nerve bundles.

Modified Sihler's technique for studying the distribution of intramuscular nerve branches in mammalian skeletal muscle

BACKGROUND

A largely forgotten technique initially designed by Sihler for staining nerve tissue has not been fully explored for staining intramuscular nerve branches in skeletal muscles.

METHODS

Fresh, long heads of triceps from locally bred New Zealand white rabbits were used for this study. Immediately after their removal, the muscles with their motor nerve branches from the radial nerve were fixed in 10% unneutralized formalin, followed by maceration and depigmentation in 3% aqueous potassium hydroxide, decalcification in Sihler's solution I, micro-dissection, staining in Sihler's solution II, destaining in Sihler's solution I, neutralization in 0.05% lithium carbonate, and clearance in increasing concentrations of glycerin.

RESULTS

A clear three-dimensional orientation of the distribution of the intramuscular nerve branches within the muscle belly was visualized. It was found in all specimens that the long head of triceps in the rabbit was constantly innervated by three main intramuscular nerve branches and each of them supplied different amounts of muscle fibers with some variation.

CONCLUSION

The Sihler's neural staining technique can be applied to the study of the distribution of intramuscular nerve branches in limb skeletal muscles. Extension of the technique may be utilised in the identification of neuromuscular compartments in skeletal muscles. Such information may be usefully applied in free muscle transfer of segments of skeletal muscle.

The innervation of the human upper esophageal sphincter

The neuroanatomy and physiology of the human upper esophageal sphincter (UES) has long been controversial. As a result, there has been little progress in diagnosing and treating dysphagias involving this area. In this study, three specimens of the UES obtained from human autopsies were examined by Sihler's stain. This stain clears soft tissue while counterstaining the nerves, thereby allowing nerve supply to each muscle of the UES to be demonstrated. It was found that the nerve supply to each component of the UES is substantially different. The inferior pharyngeal constrictor (IPC) is supplied by a dense linear plexus which is about 1.0-1.5 cm wide and 10 cm long and located about 1.5 cm lateral to the attachment of the IPC on the thyroid lamina. The cricopharyngeal (CP) muscle receives its innervation from below via the recurrent laryngeal nerve (RLN) and from above via the pharyngeal plexus. Neural connections between the RLN and the pharyngeal plexus were observed. Finally, the upper esophagus (UE) is innervated by the RLN. The innervation pattern of each component of the UES suggests functional differences between these muscles. These observations help clarify the innervation of the UES. Accurate knowledge of the neuroanatomy of the UES is necessary for advances in diagnosis and treatment of pharyngeal dysphagia.

The intramuscular nerve supply of the human lateral cricoarytenoid muscle

The lateral cricoarytenoid (LCA) muscle is one of the adductors of the vocal cords; however, some investigators believe that the lateral edge of the muscle may be involved in abduction. The possibility of functionally distinct compartments within the LCA was investigated by observing the pattern of the intramuscular nerve supply. This technique has previously clearly demonstrated neural compartments in the posterior cricoarytenoid, thyroarytenoid and cricothyroid muscles. Five adult human larynges were processed by the Sihler's stain which clears all soft tissue while counterstaining the nerves. The results of our study showed that the innervation pattern of the human LCA muscle is composed of a homogenous nerve plexus localized to the middle region of the muscle. This pattern correlates with the location of motor endplates described by prior investigators. The consistent neural pattern suggests that the LCA is composed of a single neuromuscular compartment.

A technique for displaying the entire nerve branching pattern of a whole muscle: results in 10 canine posterior cricoarytenoid muscles

There is anatomical and histological evidence for three functionally distinct muscle bellies in the canine posterior cricoarytenoid (PCA) muscle. This study attempted to define the exact nerve branching pattern to each muscle belly in 10 dogs using a modification of Sihler's neural staining technique. The results are presented here as photographs and schematic nerve maps which illustrate the following points. 1. the final terminal branches within the PCA do correspond to the three bellies of the PCA; 2. the initial nerve branch to the PCA is usually composed of multiple fascicles which rearrange before their final branching to the three bellies; 3. there is tremendous variability of the nerve branching patterns including bilateral asymmetry within the same animal; 4. the terminal branching within each belly can be surprisingly complex and contain multiple anastomoses; 5. the fast- and slow-twitch bellies of the PCA have different terminal branching patterns. These results support the functional subdivision of the canine PCA into three distinct neuromuscular compartments. This microanatomical technique appears useful for studying the basic neuromuscular organization of laryngeal muscles and their developmental and pathological changes.