Architectural design, fiber-type composition, and innervation of the rat rectus abdominis muscle.

The rectus abdominis muscle is architecturally compartmentalized by tendinous intersections and is supplied by multiple thoracic nerves. In this study, the rectus abdominis of the rat has been qualitatively and quantitatively examined with regard to muscle dimensions, fiber organization, fiber-type composition, and innervation. The muscle exhibits architectural heterogeneity and different patterns of innervation among its thoracic, epigastric, and hypogastric parts. The epigastric part, adherent to the rectus sheath via tendinous intersections, represents relatively simple design. It is formed by serially arranged compartments with shorter fibers, compared with the other parts. These compartments are segmentally supplied by thoracic nerves. The hypogastric part is more complex, forms an interdigitation of muscular slips, and has segmental distribution of thoracic nerves in mediolateral direction. The thoracic part much differs from the other parts. It has smaller cross-sectional areas, compartments composed of abundant nonspanning fibers with intrafascicular termination, and non-segmental distribution of thoracic nerves. In addition to these craniocaudal specializations among the three parts, the muscle exhibits mediolateral differences in fiber-type composition. Slow-twitch oxidative fibers are more densely distributed in the medial half region than the lateral, whereas fast-twitch glycolytic fibers follow an inverse pattern. The mediolateral differences in fiber-type composition as well as the craniocaudal specializations in architectural design and innervation imply regionally differentiated recruitments of the muscle in various behaviors.     

Architectural design,fiber-type composition,and innervation of the rat rectus abdominis muscle

The rectus abdominis muscle is architecturally compartmentalized by tendinous intersections and is supplied by multiple thoracic nerves. In this study, the rectus abdominis of the rat has been qualitatively and quantitatively examined with regard to muscle dimensions, fiber organization, fiber-type composition, and innervation. The muscle exhibits architectural heterogeneity and different patterns of innervation among its thoracic, epigastric, and hypogastric parts. The epigastric part, adherent to the rectus sheath via tendinous intersections, represents relatively simple design. It is formed by serially arranged compartments with shorter fibers, compared with the other parts. These compartments are segmentally supplied by thoracic nerves. The hypogastric part is more complex, forms an interdigitation of muscular slips, and has segmental distribution of thoracic nerves in mediolateral direction. The thoracic part much differs from the other parts. It has smaller cross-sectional areas, compartments composed of abundant nonspanning fibers with intrafascicular termination, and non-segmental distribution of thoracic nerves. In addition to these craniocaudal specializations among the three parts, the muscle exhibits mediolateral differences in fiber-type composition. Slow-twitch oxidative fibers are more densely distributed in the medial half region than the lateral, whereas fast-twitch glycolytic fibers follow an inverse pattern. The mediolateral differences in fiber-type composition as well as the craniocaudal specializations in architectural design and innervation imply regionally differentiated recruitments of the muscle in various behaviors.© Willey-Liss, Inc.     

Proportions of slow-twitch and fast-twitch extrafusal fibers in receptive fields of tendon organs in chicken leg muscles

Golgi tendon organs are mechanoreceptors that monitor the contractile force produced by motor units. Receptors are most responsive to contractions of extrafusal muscle fibers that terminate closest to them and on them. Three anterior and four posterior chicken leg muscles were examined. Proportions of immunohistochemically identified slow-twitch extrafusal fibers and fast-twitch extrafusal fibers were calculated for 374 tendon organ receptive fields. Tendon organs were observed in muscle regions occupied either by slow-twitch fibers or fast-twitch fibers only, but most were found in regions that contained both slow-twitch and fast-twitch extrafusal fibers. The frequency with which each fiber type occurred near tendon organs approached the frequency with which it occurred in more inclusive regions. In receptive fields with mixed fiber populations, fast-twitch fibers were the predominant type, especially in the anterior leg muscles. Distribution patterns of extrafusal fiber types adjacent to and farther removed from tendon organs suggest that afferent discharges from tendon organs are by and large unbiased measures of the contractile activity of the extrafusal fiber population of the muscle portion in which the tendon organs are located. In mixed muscle regions, slow-twitch fibers and fast-twitch fibers attach on given tendon organs, enabling them to monitor forces produced by slow motor units and by fast motor units. Most tendon organs are situated in mixed extrafusal fiber fields with high fast-twitch fiber content, indicating that in chicken leg muscles sensory feedback from tendon organs is largely one from fast motor units. Anat. Rec. 252:34–40, 1998. © 1998 Wiley-Liss, Inc.     

环杓后肌神经的显微外科解剖

本文借助SXP-Ⅰ型手术显微镜观察了30例成人喉返神经终末支支配环杓后肌的分支,并用改良的karnovsky-Roots AchE染色方法鉴定了喉返神经终末分支的性质。结果表明,喉返神经以前、后二终支入喉,前支是运动支,后支为感觉支;环杓后肌神经来自前支和前支的分支——杓间肌支,支数多,长度短。组织学研究表明,前支内,环杓后肌神经纤维和其它神经纤维随机分布在一起,未形成一个独立的神经束。     

Visualization and Quantification of Digitally Dissected Muscle Fascicles in the Masticatory Muscles of Callithrix jacchus Using Nondestructive DiceCT

The organization and length of a muscle's fascicles imparts its contractile properties. Longer fascicles permit increased muscle excursion, whereas changes in fascicle orientation relate to the overall vector of contractile force. Collecting data on fascicle architecture has traditionally involved destructive and irreversible gross dissection. In recent years, however, new imaging modalities have permitted muscles and their fascicles to be visualized nondestructively. Here, we present data from a primate (Callithrix jacchus), in which, for the first time, individual muscle fascicles are digitally “dissected” (segmented and reconstructed) using nondestructive, high-resolution diffusible iodine-based contrast-enhanced computed tomography (DiceCT) techniques. We also present quantitative data on the length and orientation of these fascicles within 10 muscle divisions of the jaw adductor and abductor musculature (superficial, deep, and zygomatic portions of temporalis and masseter; medial and lateral pterygoid; anterior and posterior digastric) and compare these digitally measured lengths to fascicular lengths measured using traditional gross and chemical dissection. Digitally derived fascicle lengths correspond well to their dissection-derived counterparts. Moreover, our analyses of changes in fascicle orientation across the adductor complex enable us to visualize previously uncharacterized levels of detail and highlight significant variation between adjacent muscle layers within muscle groups (e.g., between superficial, deep, and zygomatic portions of masseter and temporalis). We conclude that this technique offers great potential to future research, particularly for questions centered around the visualization and quantification of obscured and often-overlooked muscles such as the pterygoid and digastric muscles, and for deriving more accurate models of the masticatory system as a whole. Anat Rec, 302:1891–1900, 2019. © 2019 American Association for Anatomy     

Formation and distribution of the sural nerve based on nerve fascicle and nerve fiber analyses

The formation and distribution of the sural nerve are presented on the basis of an investigation of 31 legs of Japanese cadavers using nerve fascicle and fiber analyses. Nerve fibers constituting the medial sural cutaneous nerve were designated as 'T', whereas those constituting the peroneal communicating branch were designated as 'F'. In 74.2% of cases (23/31), the T and F fibers joined each other in the leg, whereas in 9.7% of cases (3/31) they descended separately. In 16.1% of cases (5/31), the sural nerve was formed of only the T fibers. The sural nerve gave off lateral calcaneal branches and medial and lateral branches at the ankle. The lateral calcaneal branches always contained T fibers. The medial branches consisted of only T fibers, whereas most of the lateral branches consisted of only F fibers (71.0%; 22/31). In addition to the T and F fibers, P fibers, which derived from the superficial and deep peroneal nerves, formed the dorsal digital nerves. The P fibers were entirely supplied to the medial four and one-half toes. However, they were gradually replaced by the T and F fibers in the lateral direction. The 10th proper dorsal digital nerve consisted of T fibers only (38.7%; 12/31), of F fibers only (19.4%; 6/31) or of both T and F fibers (38.7%; 12/31). These findings suggest that the T fibers are essential nerve components for the skin and deep structures of the ankle and heel rather than the skin of the lateral side of the fifth toe. The designation of the medial sural cutaneous nerve should be avoided and only the T fibers are appropriate components for naming as the sural nerve.     

Muscle length affects the architecture and pattern of innervation differently in leg muscles of mouse, guinea pig, and rabbit compared to those of human and monkey muscles

The innervation pattern and fascicular anatomy of muscles of different lengths in mouse, guinea pig, rabbit, macaque monkey and human legs were analyzed. Neuromuscular junctions, muscle tendon junctions and ends of intrafascicularly terminating fibers were stained for acetylcholinesterase, and fascicle lengths measured. A high correlation between increasing fascicle length and increasing number of neuromuscular junctions was found, with non-primate (mouse, guinea pig, rabbit) and primate (macaque monkey, human) muscles forming two discrete groups. In non-primates, muscles with a single endplate band, fascicles were always shorter than 35 mm, fixing the limit of fiber length served by one neuromuscular junction. Muscles with fascicles longer than this had multiple discrete bands of motor endplates crossing their width at regular intervals. An increase in muscle length across or within species corresponded to an equivalent, standard increase of 10-12 mm fascicle length per motor endplate band. All human and monkey leg muscles, with the exception of gracilis and sartorius, were singly innervated and all muscle fibers ran the full distance from tendon to tendon. Singly innervated primate muscle fibers were up to 140 mm long whereas the mean distance between endplate bands in the two multiply innervated muscles was also considerably greater than in non-primates. These data indicate that allometric effects of increasing fascicle length, are distinct in common laboratory animals and two primates, when architecture and pattern of innervation are compared.     

Proportion of muscles spindles supplied by skeletofusimotor axons (beta-axons) in peroneus brevis muscle of the cat.

Of 32 cat peroneus brevis spindles, 23 (72%) were found to be supplied by a least 1 skeletofusimotor or beta-axon. A motor axon was identified as skeletofusimotor when repetitive stimulation of it elicited both the contraction of extrafusal muscle fibers and as acceleration of the discharge of primary ending, which persisted after selective block of the neuromuscular junctions of extrafusal muscle fibers. The block was obtained by stimulating single axons at 400-500/s for a few seconds. Of 135 axons supplying extrafusal muscle fibers, 24 (18%) were shown to be beta-axons; 22 beta-axons had conduction velocities ranging from 45 to 75 m/s. All but three beta-axons increased the dynamic sensitivity of primary endings. Beta-innervated spindles may also be supplied by dynamic gamma-axons.     

Functional morphology of the maxillomandibular apparatus in the mini-Lewe minipig. 6. Intramuscular nerve ramifications in the masticatory muscles of adult animals

The masseter muscle is innervated by branches of 3 nerves. The zygomaticomandibular muscle must be regarded as part of the masseter as it is supplied by 2 branches of the massetericus nerve. Two branches of the medial pterygoid nerve enter the medial pterygoid muscle medially. The lateral pterygoid muscle is supplied by the lateral pterygoid nerve, which enters the muscle dorsally perpendicular to the muscle fibres. Five branches of the profound temporal nerves enter the temporal muscle from the ventral and medial sides. The branches of all nerves proceed parallel to each other in the dorsal direction towards the origin of the muscle.     

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.     

前锯肌及其神经支配的解剖学研究

在100侧成人标本上,研究了前锯肌及其神经支配。支配前锯肌的肌支除传统报道的胸长神经外,尚有肋间神经肌支支配。用 AchE 组织化学方法,证明肋间神经分到前锯肌的神经含有运动束。对颈5、6、7神经根损伤后,为什么常不出现“翼状肩胛”的现象进行分析讨论。     

Application of the modified Sihler's stain technique to cadaveric peripheral nerves after medical students' dissection course

The exact ramification and distribution pattern of the peripheral nerves is one of the most important information for anatomists and clinicians. However, it is very difficult to pursue perfectly all of the fine twigs of nerve branches even if we use a stereoscopic microscope. Recently, Liu et al. (Anat. Rec., 247: 137, 1997) applied a modified Sihler's stain technique to study the distribution of intramuscular nerve branches in mammalian skeletal muscles. Then, we attempted to apply this technique to plantar nerves of human foot removed from cadavers which were used for ordinary dissection practices at the School of Medicine. Intrinsic muscles of the foot with motor and sensory nerve branches were removed en bloc from bones of the foot. They were macerated and depigmented in 3% aqueous potassium hydroxide, decalcified in Sihler's solution 1. Then, after staining in Sihler's solution II, they were destained in Sihler's solution I, neutralized in 0.05% lithium carbonate, and cleared in increasing concentrations of glycerin. As a result, each nerve fascicle, which are bundles of nerve fibers invested by the perineurium, was very clearly visualized, since only nerve fibers were stained deep blue-purple, while muscles, the epineurium and the perineurium were made transparent in glycerin. We found an anastomosis between a deep branch of the lateral plantar nerve and the medial plantar nerve, composed of several nerve fascicles. Therefore, the modified Sihler's stain technique can be applied to cadaveric peripheral nerves after medical students' dissection course.     

The medial branch of the lateral branch of the posterior ramus of the spinal nerve

In the needle insertion of epidural anesthesia with the paramedian approach, the needle can pass through the longissimus muscle in the dorsum of the patients. When the needle touches a nerve in the muscles, the patients may experience pain in the back. Obviously, the needle should avoid the nerve tract. To provide better anesthetic service, analysis of the structure and where the concerned nerves lie in that region is inevitable. Material and method: We studied five cadavers in this study. Two cadavers were fixed with Thiel’s method. With these cadavers, we studied the nerve running of the posterior rami of the spinal nerve from the nerve root to the distal portion. Three of them were used for the study of transparent specimen, with which we studied the course and size of the nerve inside the longissimus muscle. Results: We observed there were three branches at the stem of the posterior rami of the spinal nerves between the body segment T3 and L5, i.e. medial branch, medial branch of the lateral branch and lateral branch of the lateral branch. The medial branch of the lateral branch supplied to the longissimus muscle. With the transparent specimen, we found that there were different nerve layouts between the upper thoracic, lower thoracic, upper lumbar, and lower lumbar segments in the medial branch of the lateral branch in the longissimus muscle. In the lower thoracic and upper lumbar segments, the medial branch of the lateral branch of the upper lumbar segments produced layers nerve network in the longissimus muscle. L1 and L2 nerves were large in size in the muscle. Conclusion: In the upper lumbar segments the medial branch of the lateral branch of the posterior rami of the spinal nerve produced dense network in the longissimus muscle, where the epidural needle has high possibility to touch the nerve. Anesthetists have to consider the existence of the medial branch of the lateral branch of the posterior rami of the spinal nerve when they insert the needle in the paramedical approach to the spinal column.     

The facial nucleus of the rat: representation of facial muscles revealed by retrograde transport of horseradish peroxidase

The representation of facial muscle groups in the facial nucleus of rat was examined by retrograde transport of HRP. Motoneurons supplying muscle groups are arranged in longitudinal columns. Those supplying nasolabial muscles are located in the lateral and ventral intermediate segments, posterior auricular muscles in a medial column, platysma in an intermediate column; the lower lip and ocular muscles are in the ventral and dorsal segments respectively of the intermediate column. The posterior belly of the digastric muscle is supplied by motoneurons extending from the dorsal aspect of the facial nucleus to the caudal pole of the trigeminal motor nucleus.     

Superfluousness of motor innervation for the formation of muscle spindles in neonatal rats

Summary Muscle spindles form de novo in reinnervated muscles of neonatal rats treated with nerve growth factor. Whether the spindles can also form in muscle reinnervated only by afferents was investigated by removing the lumbosacral segment of the spinal cord immediately after crushing the nerve to the medial gastrocnemius muscle at birth, and administering nerve growth factor for 10 days afterwards. As predicted, the medial gastrocnemius muscles were reinnervated by afferents, but not efferents. No motor endplates were visible on any muscle fibers, and extrafusal fibers were atrophied. The reinnervated muscles contained spindle-like encapsulations of one to four fibers at 5, 7, 9 and 30 days after the nerve crush. The number of spindles as well as encapsulated fibers exceeded that of normal medial gastrocnemius muscles. The encapsulated fibers resembled typical intrafusal fibers. They had normal sensory-muscle contacts, but no motor endings. The fibers displayed equatorial clusters of myonuclei and expressed the spindle-specific slow-tonic myosin heavy chain isoform at postnatal day 30. Thus, efferents are not essential for the formation and differentiation of muscle spindles in reinnervated muscles of neonatal rats.     

Segmental reflex inputs to motoneurons innervating dorsal neck musculature in the cat

Summary The responses to Stimulation of upper cervical muscle and cutaneous afferents were studied in motoneurons innervating splenius, complexus, and biventer cervicis dorsal neck muscles of cats. Motoneurons innervating complexus and biventer cervicis fibers, which are in the deeper, longitudinally oriented muscles, were monosynaptically excited by ipsilateral Group I afferents from each of these muscles, but they did not receive significant input from splenius Group I afferents. Likewise, splenius motoneurons were not monosynaptically excited by ipsilateral afferents from complexus and biventer cervicis. Stimulation of ipsilateral cutaneous afferents produced predominant excitation in splenius motoneurons, predominant inhibition in biventer cervicis motoneurons, and inhibition or mixed responses in complexus motoneurons.None of the neck motoneurons studied showed postsynaptic potentials following single or multiple shock stimulation of contralateral muscle nerves at stimulus intensities expected to excite exclusively Group I afferents. Higher intensity stimulation of contralateral muscle afferents, as well as fibers in the greater auricular nerves, produced predominant inhibition in all three neck motoneuron pools.Segmentally-excited afferents to neck motoneurons, like those from supraspinal systems, appear to evoke different patterns of synaptic responses in splenius motoneurons than they do in motoneurons innervating fibers in the deeper, longitudinally oriented complexus and biventer cervicis muscles.     

Preliminary observations on the microarchitecture of the human abdominal muscles

Precise knowledge of muscle architecture and innervation patterns is essential for the development of accurate clinical and biomechanical models. Although the gross anatomy of the human abdominal muscles has been investigated, the finer details of their microanatomy are not well described. Fascicles were systematically sampled from each of the human abdominal muscles, and small fiber bundles from selected fascicles stained with acetylcholinesterase to determine the location of motor endplate bands, myomyonal junctions, and myotendinous junctions. Statistical analysis was used to ascertain the association between fascicular length and number of endplate bands. The number of endplate bands along a fascicle was variable between different portions of each muscle, but was strongly correlated with fascicular length (r = 0.814). In fascicles less than 50 millimeters (mm) in length, only a single endplate band was generally present, while multiple endplate bands (usually two or three) were found in fascicles longer than 50 mm. The presence of myomyonal junctions throughout the longer (>50 mm) fascicles verified that they were composed of short, intrafascicularly terminating fibers, while shorter fascicles comprised fibers spanning the entire fascicular length. This preliminary study provides evidence that multiple endplate bands are contained in some regions of the abdominal muscles, an arrangement that differs from most human appendicular muscles. It is not clear whether the variations in the described fine architectural features reflect regional differences in muscle function.