Anatomical study of the masseteric and obturator nerves: Application to face transplant and reanimation procedures.

The masseteric nerve (MN) and the anterior branch of the obturator nerve (ON) that innervate the transferred gracilis muscle have proved highly efficient for reanimating paralyzed facial muscles when muscle transfer is required. Previous researchers have published the total axonal load for myelinated fibers in both nerves. However, the real motor axonal load has not been established. We performed the study on 20 MN and 13 ON. The segments of the MN and the ON were embedded in paraffin, sectioned at 10 µm, and stained following a standard immunohistochemical procedure using anti-choline acetyltransferase to visualize the motor fibers. The MN has a higher axonal load than the ON. There were statistically significant differences between the axonal load of the proximal segment of the MN and the ON. These findings confirm that end-to-end anastomoses between the MN and the ON should preferably use the proximal segment. However, MN neurotomy should ideally be performed between the proximal and distal segments, preserving innervation to the deep fascicles. Our results show that the MN is ideal as a donor motor nerve for reinnervating transplanted muscle for dynamic reanimation of the paralyzed face. The neurotomy should ideally be performed between the first and second collateral branches of the MN. Clin. Anat. 32:612-617, 2019. © 2019 Wiley Periodicals, Inc.

Which is the function of a martin-gruber connection?

Clinical and diagnostic variations may occur due to the variable presence of a connection between the median and ulnar nerves in the forearm (Martin-Gruber anastomosis). This incidence has a wide range at 7%-40%. Most commonly, the connection between the nerves is considered to be composed of motor fibers; although, a sensory role has also been described. It is important to note that the number of axons, or the nature of the fibers in this connection, have not yet been elucidated. Fifty upper limbs were examined evaluating morphometric characteristics of the Martin Gruber connection, dissected out, sectioned, and immunohistochemically stained for choline acetyltransferase (ChAT) and analyzed with ImageJ© . The connection was observed in 32% of all cases (16/50). The nerve connections were identified as those in Pattern 1 group (12%-type 1b, 19%-type 1a, and 69%-type 1c) and contained motor (ChAT positive) fibers (40.42 ± 10.5% per connection) with three to four fascicles in each. No statistically significant differences were found according to sex, side, or laterality. There were statistically significant differences in the percentages of ChAT positive fibers; however, this was dependent on the distribution being greater in those not distributed zonally. The presence of this connection is prevalent in almost a third of the cadavers dissected; the understanding of this complex composition in sensory and motor fibers allows for the optimization of diagnosis and treatment of certain median-ulnar nerve injuries. Clin. Anat. 32:501-508, 2019. © 2019 Wiley Periodicals, Inc.

Fascicular Topography of the Human Median Nerve for Neuroprosthetic Surgery.

One of the most sought-after applications of neuroengineering is the communication between the arm and an artificial prosthetic device for the replacement of an amputated hand or the treatment of peripheral nerve injuries. For that, an electrode is placed around or inside the median nerve to serve as interface for recording and stimulation of nerve signals coming from the fascicles that innervate the muscles responsible for hand movements. Due to the lack of a standard procedure, the electrode implantation by the surgeon is strongly based on intuition, which may result in poor performance of the neuroprosthesis because of the suboptimal location of the neural interface. To provide morphological data that can aid the neuroprosthetic surgeon with this procedure, we investigated the fascicular topography of the human median nerve along the forearm and upper arm. We first performed a description of the fascicular content and branching patterns along the length of the arm. Next we built a 3D reconstruction of the median nerve so we could analyze the fascicle morphological features in relation to the arm level. Finally, we characterized the motor content of the median nerve fascicles in the upper arm. Collectively, these results indicate that fascicular organization occurs in a short segment distal to the epicondyles and remains unaltered until the muscular branches leave the main trunk. Based on our results, overall recommendations based on electrode type and implant location can be drawn to help and aid the neuroprosthetic procedure. Invasive interfaces would be more convenient for the upper arm and the most proximal third of the forearm. Epineural electrodes seem to be most suitable for the forearm segment after fascicles have been divided from the main trunk.

Are the interarytenoid muscles supplied by branches of both the recurrent and superior laryngeal nerves?

OBJECTIVES/HYPOTHESIS: It has been generally accepted that the branches of the internal branch of the superior laryngeal nerve to the interarytenoid muscle are exclusively sensory. However, some experimental studies have suggested that these branches may contain motor axons, and therefore that the interarytenoid muscle is supplied by both the superior and recurrent laryngeal nerves. The aim of this work was to determine whether motor axons to the interarytenoid muscles are present in both laryngeal nerves. STUDY DESIGN: Basic research. METHODS: Twelve human internal branches of the superior laryngeal nerve were dissected, and its branches to the interarytenoid muscle were removed and processed for choline-acetyltransferase immunohistochemistry, a method not used previously in studying the nerve fiber composition of the laryngeal nerves. RESULTS: The internal branch of the superior laryngeal nerve divided into two to five branches to the interarytenoid muscle. All branches contained motor axons, with the proportion of motor axons varying from 6% to 31%. CONCLUSION: The present study confirms that the internal branch of the superior laryngeal nerve provides a motor innervation to the interarytenoid muscles. LEVEL OF EVIDENCE: N/A. Laryngoscope, 126:1117-1122, 2016.

Guides and protocols for a good practice. I. Act of donation and donation card

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Guides and protocols for a good practice. Ii. Traceability of the cadaver: from reception to removal

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Guides and protocols for a good practice. III. The dissection

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Guides and protocols for a good practice. IV. Postgraduate and continuing professional development

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Somatotopic changes in the nucleus ambiguus after section and regeneration of the recurrent laryngeal nerve of the rat.

Changes in motoneurons innervating laryngeal muscles after section and regeneration of the recurrent laryngeal nerve (RLN) are far from being understood. Here, we report the somatotopic changes within the nucleus ambiguus (Amb) after the nerve injury and relates it to the resulting laryngeal fold impairment. The left RLN of each animal was transected and the stumps were glued together using surgical fibrin glue. After several survival periods (1, 2, 4, 8, 12, 16 weeks; at least six rats at each time point) the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were injected with fluorescent-conjugated cholera toxin and the motility of the vocal folds evaluated. After section and subsequent repair of the RLN, no movement of the vocal folds could be detected at any of the survival times studied and the somatotopy and the number of labeled motoneurons changed. From 4 wpi award, the somatotopy was significantly disorganized, with the PCA motoneurons being located rostrally relative to their normal location. A rostrocaudal overlap between the two pools of motoneurons supplying the PCA and TA muscles was observed from 2 wpi onwards. Hardly any labeled neurons were found in the contralateral Amb in any of the experimental groups. An injury of the RLN leads to a reinnervation of the denervated motor endplates of PCA and TA. However, misdirected axons sprout and regrowth from the proximal stump to the larynx. As a result, misplaced innervation of muscles results in a lack of functional recovery of the laryngeal folds movement following a RLN injury.

Reorganization of laryngeal motoneurons after crush injury in the recurrent laryngeal nerve of the rat.

Motoneurons innervating laryngeal muscles are located in the nucleus ambiguus (Amb), but there is no general agreement on the somatotopic representation and even less is known on how an injury in the recurrent laryngeal nerve (RLN) affects this pattern. This study analyzes the normal somatotopy of those motoneurons and describes its changes over time after a crush injury to the RLN. In the control group (control group 1, n = 9 rats), the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) muscles were injected with cholera toxin-B. In the experimental groups the left RLN of each animal was crushed with a fine tip forceps and, after several survival periods (1, 2, 4, 8, 12 weeks; minimum six rats per time), the PCA and TA muscles were injected as described above. After each surgery, the motility of the vocal folds was evaluated. Additional control experiments were performed; the second control experiment (control group 2, n = 6 rats) was performed labeling the TA and PCA immediately prior to the section of the superior laryngeal nerve (SLN), in order to eliminate the possibility of accidental labeling of the cricothyroid (CT) muscle by spread from the injection site. The third control group (control group 3, n = 5 rats) was included to determine if there is some sprouting from the SLN into the territories of the RLN after a crush of this last nerve. One week after the crush injury of the RLN, the PCA and TA muscles were injected immediately before the section of the SLN. The results show that a single population of neurons represents each muscle with the PCA in the most rostral position followed caudalwards by the TA. One week post-RLN injury, both the somatotopy and the number of labeled motoneurons changed, where the labeled neurons were distributed randomly; in addition, an area of topographical overlap of the two populations was observed and vocal fold mobility was lost. In the rest of the survival periods, the overlapping area is larger, but the movement of the vocal folds tends to recover. After 12 weeks of survival, the disorganization within the Amb is the largest, but the number of motoneurons is similar to control, and all animals recovered the movement of the left vocal fold. Our additional controls indicate that no tracer spread to the CT muscle occurred, and that many of the labeled motoneurons from the PCA after 1 week post-RLN injury correspond to motoneurons whose axons travel in the SLN. Therefore, it seems that after RLN injury there is a collateral sprouting and collateral innervation. Although the somatotopic organization of the Amb is lost after a crush injury of the RLN and does not recover in the times studied here, the movement of the vocal folds as well as the number of neurons that supply the TA and the PCA muscles recovered within 8 weeks, indicating that the central nervous system of the rat has a great capacity of plasticity.

Somatotopy of the neurons innervating the cricothyroid, posterior cricoarytenoid, and thyroarytenoid muscles of the rat's larynx.

Neurons innervating the intrinsic muscles of the larynx are located within the nucleus ambiguus but the precise distribution of the neurons for each muscle is still a matter for debate. The purpose of this study was to finely determine the position and the number of the neurons innervating the intrinsic laryngeal muscles cricothyroid, posterior cricoarytenoid, and thyroarytenoid in the rat. The study was carried out in a total of 28 Sprague Dawley rats. The B subunit of the cholera toxin was employed as a retrograde tracer to determine the locations, within the nucleus ambiguus, of the neurons of these intrinsic laryngeal muscles following intramuscular injection. The labelled neurons were found ipsilaterally in the nucleus ambiguus grouped in discrete populations with reproducible rostrocaudal and dorsoventral locations among the sample of animals. Neurons innervating the cricothyroid muscle were located the most rostral of the three populations, neurons innervating the posterior cricoarytenoid were found more caudal, though there was a region of rostrocaudal overlap between these two populations. The most caudal were the neurons innervating the thyroarytenoid muscle, presenting a variable degree of overlap with the posterior cricoarytenoid muscle. The mean number (±SD) of labelled neurons was found to be 41 ± 9 for the cricothyroid, 39 ± 10 for the posterior cricoarytenoid and 33 ± 12 for the thyroarytenoid.

Ulnar nerve innervation of the triceps muscle: real or apparent? An anatomic study.

BACKGROUND: Since the 18th century, the existence of ulnar nerve innervation of the medial head of the triceps brachii muscle has been controversial. The evidence for or against such innervation has been based on macroscopic dissection, an unsuitable method for studying intraneural topography or intramuscular branching. The study of smaller specimens (embryos or fetuses) by means of serial histologic sections may resolve the controversy. QUESTIONS/PURPOSES: Using fetal specimens and histology we determined the contributions of the ulnar and radial nerves to innervation of the triceps brachii muscle. METHODS: We histologically examined 15 embryonic and fetal arms. Radial nerve branches obtained from six adult arms were analyzed immunohistochemically to determine motor fiber content. RESULTS: The medial head of the triceps brachii muscle was always innervated by the radial nerve (ulnar collateral branch). The branches seeming to leave the ulnar nerve at elbow level were the continuation of the radial nerve that had joined the ulnar nerve sheath via a connection in the axillary region. Immunohistochemistry revealed motor and nonmotor fibers in this radial nerve branch. CONCLUSIONS: A connection between the radial and ulnar nerves sometimes may exist, resulting in an apparent ulnar nerve origin of muscular branches to the medial head of the triceps, even though in all our specimens the fibers could be traced back to the radial nerve. CLINICAL RELEVANCE: Before performing or suggesting new muscle and nerve transpositions using this apparent ulnar innervation, the real origin should be confirmed to avoid failure.

Morphogenesis of the human laryngeal ventricles.

BACKGROUND: Two theories explain the origin of human laryngeal ventricles: (1) ventricles derive from the fifth pharyngeal pouches; (2) development independent from the pouches. METHODS: In all, there were 21 serially sectioned human embryos from stages 15 to 23, and 11 fetuses of 9 to 18 weeks. Computer-aided 3-dimentional reconstructions were made. RESULTS: The cranial part of the laryngeal sulcus and future vestibule expands from the pharyngeal floor between the third and fourth pharyngeal pouches during stages 15 and 16 (33-37 days). The primordia of the ventricles appeared at stage 18 (44 days) as 2 lateral swellings in the caudal end of the future vestibule, limited by the third pharyngeal pouches. Active epithelial expansion and subsequent canalization during late embryonic and early fetal periods finalizes their development. CONCLUSIONS: The laryngeal ventricles do not derive from the pharyngeal pouches but the median region of the pharyngeal floor between the third and fourth pharyngeal pouches and arches at the caudal end of the future vestibule.

Recurrent laryngeal nerve landmarks revisited.

BACKGROUND: The aim of this work was to evaluate, to prove their reliability, the different surgical landmarks previously proposed as a mean to locate the recurrent laryngeal nerve (RLN). METHODS: The necks of 143 (68 male and 76 female) human adult embalmed cadavers were examined. RLN origin and length and its relationship to different landmarks were recorded and results compared with those previously reported. Statistical comparisons were performed using the chi-square test (significance, p ≤ .05). RESULTS: Mostly, RLN is located anterior to the tracheoesophageal sulcus (41.6%), posterior to the inferior thyroid artery (35.8%), lateral to Berry's ligament (88.1%), below the inferior rim of the inferior constrictor muscle (90.4%), and entering the larynx before its terminal division (54.6%). CONCLUSIONS: The position of the RLN in relation to those structures classically considered as landmarks is highly variable. The most reliable relationships are those with Berry's ligament or the inferior constrictor muscle.

Functional role of human laryngeal nerve connections.

OBJECTIVES/HYPOTHESIS: Current knowledge of the functional role of human laryngeal nerves is based on traditional laryngeal neuroanatomic descriptions or contradictory electromyographic studies. The aim of this study was to clarify the functional role of neural connections between laryngeal nerves by correlating the different electromyographic patterns observed after laryngeal stimulation and the existence of different neural connections. STUDY DESIGN: Descriptive. METHODS: Electromyographic and morphologic study in 13 patients during total laryngectomy procedure. RESULTS: Seven patients showed an additional evoked response from the cricothyroid muscle after recurrent laryngeal nerve stimulation. External laryngeal nerve stimulation resulted in additional responses from the posterior cricoarytenoid muscle in three cases and from the arytenoid muscle in one. The presence of a neural connection was confirmed in all patients who showed an unexpected electromyographic response. CONCLUSIONS: The different connections between laryngeal nerves are at least partially of motor nature and play a role in the mobility of vocal folds.

The central projections of the laryngeal nerves in the rat.

The larynx serves respiratory, protective, and phonatory functions. The motor and sensory innervation to the larynx controlling these functions is provided by the superior laryngeal nerve (SLN) and the recurrent laryngeal nerve (RLN). Classical studies state that the SLN innervates the cricothyroid muscle and provides sensory innervation to the supraglottic cavity, whereas the RLN supplies motor innervation to the remaining intrinsic laryngeal muscles and sensory innervation to the infraglottic cavity, but recent data suggest a more complex anatomical and functional organisation. The current neuroanatomical tracing study was undertaken to provide a comprehensive description of the central brainstem connections of the axons within the SLN and the RLN, including those neurons that innervate the larynx. The study has been carried out in 41 adult male Sprague-Dawley rats. The central projections of the laryngeal nerves were labelled following application of biotinylated dextran amines onto the SLN, the RLN or both. The most remarkable result of the study is that in the rat the RLN does not contain any afferent axons from the larynx, in contrast to the pattern observed in many other species including man. The RLN supplied only special visceromotor innervation to the intrinsic muscles of the larynx from motoneurons in the nucleus ambiguus (Amb). All the afferent axons innervating the larynx are contained within the SLN, and reach the nucleus of the solitary tract. The SLN also contained secretomotor efferents originating from motoneurons in the dorsal motor nucleus of the vagus, and special visceral efferent fibres from the Amb. In conclusion, the present study shows that in the rat the innervation of the larynx differs in significant ways from that described in other species.

Biocompatibility of chronically implanted transverse intrafascicular multichannel electrode (TIME) in the rat sciatic nerve.

The transverse intrafascicular multichannel electrode (TIME) is intended to be transversally implanted in the peripheral nerve and to selectively interface subsets of axons in different fascicles within the same nerve. Two versions of TIME (TIME-2, TIME-3) were designed and tested for biocompatibility and safety in the sciatic nerve of the rat. TIME-2 was implanted in two groups: one group had only an acute implant and the second group had chronic implantation for 2 months; a third group was also chronically implanted with the TIME-3 version, designed to avoid the mechanical traction produced by muscles motion. We evaluated the functional and morphological effects of either TIME-2 or TIME-3 implanted in the rat sciatic nerve for 2 months. The results of the study indicate that implantation of the TIME-2 and TIME-3 devices in the rat sciatic nerve did not cause significant axonal loss or demyelination, as evidenced by the functional and histological results. The results of this study indicate that the TIME-2 and TIME-3 designs are biocompatible and safe after chronic implantation in a small peripheral nerve, such as the rat sciatic nerve.

Immunohistochemical study of the astrocytes of the adult rat cochlear nuclei

Astrocytes play crucial roles in the organization, function and maintenance of neurons and neuronal circuits. Apart from reports on reactive gliosis after auditory/vestibular injuries, few authors have focused their attention on the astroglial cytoarchytecture of the cochlear nuclei (CN). In this qualitative immunohistochemical study, we analyse the distribution of the astrocytic markers glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and S-100 protein (S-100) in the adult CN of twelve young adult male rats (AU)

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The clinical interest of the ary-thyro-cricoid fascicle.

The aim of this work was to study the prevalence and form of the ary-thyro-cricoid (ATC) muscular fascicle, a variable muscular slip connecting the oblique and/or transverse arytenoid muscles with the thyroarytenoid (TA) and/or lateral cricoarytenoid (LCA) muscles resembling a sphincter encircling the glottis. Thirty larynges obtained from necropsies of individuals with no known laryngeal pathology were dissected. The ATC fascicle was observed in 96.7% of the larynges. It appeared bilaterally in 60% of subjects and unilaterally in 36.7%. The posterior attachment of the muscular slip was observed to be in common with either the transverse arytenoid (34%), or the oblique arytenoid (28%) or both muscles (38%). Its fibers terminated by intermingling with either those of the LCA muscle (10.6%), or the TA muscle (38.3%) or both (51.1%). These variable attachments mean that there are nine possible variants of this muscular fascicle. The ATC fascicle was supplied by branches originating bilaterally from the recurrent laryngeal (RLN) and internal laryngeal nerves. The existence of this ATC fascicle could explain the variable position (intermediate, paramedian or lateral) adopted by the vocal folds after lesion of the RLN. The bilateral disposition and innervation of the fascicle could also complicate the interpretation of electromyographic techniques used for testing laryngeal nerve function.

Sigma receptor agonist 2-(4-morpholinethyl)1 phenylcyclohexanecarboxylate (Pre084) increases GDNF and BiP expression and promotes neuroprotection after root avulsion injury.

Spinal root avulsion leads to a progressive loss of axotomized motoneurons (MNs). Nowadays, there is no effective treatment to prolong MN survival that could permit recovery as a result of delayed surgical repair. Administration of Sigma-1 receptor (Sig-1R) ligands has been reported to promote beneficial effects after several types of neural injury. In order to shed light of whether Sig-1R ligands could promote MN survival after root avulsion, L4-L5 spinal roots were unilaterally avulsed in adult rats and the Sig-1R agonist Pre084 was administered at different doses. The ventral spinal cords of the animals were studied from 3 to 21 days post-operation (DPO) by using histological, immunohistochemical, and Western blot techniques. Daily treatment with 0.25 mg/kg Pre084 significantly promoted MN survival (68% vs 43% in untreated rats) at 21 DPO, an effect that was antagonized by coadministration of BD1063, an antagonist of Sig-1R. There was a reduction in astroglial- associated immunoreactivity in rats treated with Pre084. Moreover, Pre084 produced an increase in the Sig-1R co-chaperone BiP within MNs, and an increase of GDNF expression by astrocytes in the ventral horn early after injury. Although the mechanisms promoting MN survival by Pre084 remain unclear, we hypothesize that it is mediated at least in part through the increase in these cytoprotective factors. Therefore, early application of Sig-1R agonist appears to be a promising therapy to improve MN survival after root avulsion.