The innervation of the external urethral sphincter muscle

Innervation of external urethral sphincter muscle was examined in 100 human fetuses and 10 adults of both sexes. Examined nerves take place from deep perineal nerve (branch of pudendal nerve) and, probably, from pelvic splanchnic nerves (via inferior hypogastric plexus). However, this supposition needs further microscopic research. It is also concluded that pelvic splanchnic nerves and pudendal nerve arise from the same ventral branches of spinal nerves (S2-S4).     

Innervation of the anterior perineal muscles and its morphological consideration

3 male and 3 female pelvic-halves were dissected carefully under a stereomicroscope in order to obtain more detailed data on the nerve supply to the anterior perineal muscles. At its origin from the pudendal plexus, the perineal nerve has a close relationship with the dorsal nerve of the penis or clitoris, while it tends to be separate from the inferior rectal nerve. The ischiocavernosus and the transversus perinei profundus are in general supplied by a common branch which arises from the perineal nerve at the posterior part of the ischiorectal fossa and takes a more lateral course, independent of the cutaneous branches. The bulbospongiosus and the transversus perinei superficialis receive several twigs from the medial and intermediate cutaneous branches of the perineal nerve. From the view point of nerve supply, the anterior perineal muscles may be classified into 2 groups: the lateral group comprising the ischiocavernosus and the transversus perinei profundus, the medial group comprising the bulbospongiosus and the transversus perinei superficialis.     

The nerve branches to the external anal sphincter: the macroscopic supply and microscopic structure

The study was performed using 45 pelvic half section specimens (41 fetal ones and four adults). The macroscopic dissection followed the nerve branches from their spinal roots up to the external anal sphincter. Three nerve branches were found: the anterior ramus arising from the external perineal nerve, the inferior rectal nerve and an independent posterior branch. The anterior and the inferior rectal nerve branches always emerged from the pudendal plexus. The posterior branch arising either from S4 or from the inferior rectal nerve was only found in (31%) of our cases. Five anatomical distributions are described, percentages of every type notified. The fibre content of these nerve bundle branches was evaluated through histological sections using Heidenhain's azan stain and Luxol fast blue. The branches consisted of 2,896 to 2,137 fibres, 20% of them being unmyelinated and 80% containing various myelinated fibres. The nomenclature of these nerve branches has to be debated. The terms of anterior, middle and posterior anal nerves seem more suitable.     

男性盆腔内脏神经的解剖学研究及其临床意义

男性盆腔内脏神经与盆筋膜及盆内脏器的毗邻关系复杂,且个体形态学差异大,临床上涉及肛肠外科、泌尿外科、男科等多个学科,应用甚广。近年来,对内脏神经的术中保护越来越受到重视。男性盆腔内脏神经主要包括上腹下丛、腹下神经、下腹下丛(即盆丛)、盆内脏神经、膀胱丛、前列腺丛、直肠丛及其分支等。现已证明盆腔内脏神经的损伤会给患者的排便、排尿及阴茎勃起等造成功能障碍。熟悉男性盆腔内脏神经及其分支的形态特点及其与周围结构的关系,能降低手术并发症,提高患者术后生活质量。     

Extrinsic innervation of the pelvic organs in the lesser pelvis of human embryos

Realistic models to understand the developmental appearance of the pelvic nervous system in mammals are scarce. We visualized the development of the inferior hypogastric plexus and its preganglionic connections in human embryos at 4–8 weeks post-fertilization, using Amira 3D reconstruction and Cinema 4D-remodelling software. We defined the embryonic lesser pelvis as the pelvic area caudal to both umbilical arteries and containing the hindgut. Neural crest cells (NCCs) appeared dorsolateral to the median sacral artery near vertebra S1 at ~5 weeks and had extended to vertebra S5 1 day later. Once para-arterial, NCCs either formed sympathetic ganglia or continued to migrate ventrally to the pre-arterial region, where they formed large bilateral inferior hypogastric ganglionic cell clusters (IHGCs). Unlike more cranial pre-aortic plexuses, both IHGCs did not merge because the 'pelvic pouch', a temporary caudal extension of the peritoneal cavity, interposed. Although NCCs in the sacral area started to migrate later, they reached their pre-arterial position simultaneously with the NCCs in the thoracolumbar regions. Accordingly, the superior hypogastric nerve, a caudal extension of the lumbar splanchnic nerves along the superior rectal artery, contacted the IHGCs only 1 day later than the lumbar splanchnic nerves contacted the inferior mesenteric ganglion. The superior hypogastric nerve subsequently splits to become the superior hypogastric plexus. The IHGCs had two additional sources of preganglionic innervation, of which the pelvic splanchnic nerves arrived at ~6.5 weeks and the sacral splanchnic nerves only at ~8 weeks. After all preganglionic connections had formed, separate parts of the inferior hypogastric plexus formed at the bladder neck and distal hindgut.     

Anatomical study of the pudendal nerve adjacent to the sacrospinous ligament

The pudendal nerve (S3-S5) is a major branch of the sacral plexus. After branching from the sacral plexus, the pudendal nerve travels through three main regions: the gluteal region, the pudendal canal, and the perineum. In the gluteal region, the pudendal nerve lies posterior to the sacrospinous ligament. The relationship of the pudendal nerve to the sacrospinous ligament has important clinical ramifications, but there is a lack of literature examining the variations in pudendal nerve anatomy in the gluteal region. This study investigates the pudendal nerve trunking in relation to the sacrospinous ligament in 37 cadavers (73 sides of pelves) of 21 males and 16 females, ranging from 18-83 years of age. Pudendal nerve trunking could be grouped into five types: Type I is defined as one-trunked (41/73; 56.2%), Type II is two-trunked (8/73; 11%), Type III is two-trunked with one trunk as an inferior rectal nerve piercing through the sacrospinous ligament (8/73; 11%), Type IV is two-trunked with one as an inferior rectal nerve not piercing through the sacrospinous ligament (7/73; 9.5%), and Type V is three-trunked (9/73; 12.3%). In summary, 56.2% of pudendal nerves adjacent to the sacrospinous ligament were one-trunked, 31.5% were two-trunked and 12.3% were three-trunked. Fifteen inferior rectal nerves originated independently from the S4 root and never joined the main pudendal nerve. Eight of fifteen inferior rectal nerves pierced through the sacrospinous ligament, perhaps making it prone for entrapment. We measured the average diameter of the main trunk of the pudendal nerve to be 4.67 +/- 1.17 mm. We also measured the average length of the pudendal nerve trunks before terminal branching to be 25.14 +/- 10.29 mm. There was no significant statistical difference in the average length, average diameter, number of trunks, and pudendal nerve variations between male and female or right or left sides of the pelves. A detailed study of pudendal nerve trunking in relationship to the sacrospinous ligament would be useful for instruction in basic anatomy courses and in relevant clinical settings as well.     

The origins of the adrenergic fibres which innervate the internal anal sphincter, the rectum, and other tissues of the pelvic region in the guinea-pig

Summary The adrenergic innervation of the pelvic viscera was examined by the fluorescence histochemical technique, applied to tissue from untreated guinea-pigs and from guinea-pigs in which nerve pathways had been interrupted at operation. It was found that adrenergic neurons in the inferior mesenteric ganglia give rise to axons which run in the colonic nerves and end in the myenteric and submucous plexuses and around the arteries of the distal colon. In the rectum, part of the innervation of the myenteric plexus and all of the innervation of the submucous plexus comes from the inferior mesenteric ganglia. The rest of the adrenergic innervation of the myenteric plexus comes from the posterior pelvic ganglia or the sacral sympathetic chains. The innervation of the blood vessels of the rectum is from the posterior pelvic ganglia. Adrenergic nerves run from the sacral sympathetic chains and pass via nerves accompanying the rectal arteries to the internal anal sphincter. Other adrenergic fibres to the internal anal sphincter either arise in, or pass through, the posterior pelvic plexuses. The anal accessory muscle is innervated by adrenergic axons arising in the posterior pelvic plexuses. Adrenergic nerves which run in the pudendal nerves, probably from the sacral sympathetic chains, innervate the erectile tissue of the penis.This work was supported by grants from the Australian Research Grants Committee and the National Health and Medical Research Council. We thank Professor G. Burnstock for his generous support.     

盆腔内筋膜的解剖结构及神经走形：避免修复中的损伤

背景：盆腔内走行着大量支配泌尿生殖等系统脏器的神经,包括内脏神经和脊神经两种,每一种均由运动神经和感觉神经两种成分组成。其中内脏神经的核心为盆丛。1982年,Heald提出的全直肠系膜切除已经成为直肠癌诊疗的“金标准”。但术中极易损伤神经,导致术后出现尿潴留、性功能障碍等并发症。目的：综述前人的研究,以明确盆腔内筋膜的解剖结构和神经走形。方法：以“splanchnic nerves,superior hypogastric plexus,pelvic plexus,pelvic splanchnic nerve,total mesorectal excision(TME),clinical anatomy”为关键词,检索2000年1月至2015年1月PubMed数据库中关于盆腔内神经及相关脊神经的走形和成分、盆腔内神经节及相关脏器反射等研究,以盆腔内的神经为主。结果与结论：盆腔内的主要内脏神经丛为：①上腹下丛：主体位于由左、右髂总动脉和骶岬围成的髂间三角内,左髂总静脉和第5腰椎前面。②盆丛：腹下神经、盆内脏神经、骶内脏神经在直肠侧面的后下方1/3处汇合形成神经丛,也称下腹下丛,位于输尿管后下方、膀胱及精囊腺的背侧。由内脏神经丛发出的神经包含交感神经、副交感神经及感觉神经3种成分,走行分布在盆腔各脏器表面,支配其运动与感觉功能。明确的盆腔内筋膜的解剖结构和神经走形是全直肠系膜切除成功的关键,可在手术中最大程度避免神经损伤,提高患者预后及生活质量。中国组织工程研究杂志出版内容重点：组织构建;骨细胞;软骨细胞;细胞培养;成纤维细胞;血管内皮细胞;骨质疏松;组织工程     

Coexistence of adrenergic and cholinergic nerves in the inferior hypogastric plexus: anatomical and immunohistochemical study with 3D reconstruction in human male fetus

Classic anatomical methods have failed to determine the precise location, origin and nature of nerve fibres in the inferior hypogastric plexus (IHP). The purpose of this study was to identify the location and nature (adrenergic and/or cholinergic) of IHP nerve fibres and to provide a three-dimensional (3D) representation of pelvic nerves and their relationship to other anatomical structures. Serial transverse sections of the pelvic portion of two human male fetuses (16 and 17 weeks' gestation) were studied histologically and immunohistochemically, digitized and reconstructed three-dimensionally. 3D reconstruction allowed a 'computer-assisted dissection', identifying the precise location and distribution of the pelvic nerve elements. Proximal (supra-levator) and distal (infra-levator) communications between the pudendal nerve and IHP were observed. By determining the nature of the nerve fibres using immunostaining, we were able to demonstrate that the hypogastric nerves and pelvic splanchnic nerves, which are classically considered purely sympathetic and parasympathetic, respectively, contain both adrenergic and cholinergic nerve fibres. The pelvic autonomic nervous system is more complex than previously thought, as adrenergic and cholinergic fibres were found to co-exist in both 'sympathetic' and 'parasympathetic' nerves. This study is the first step to a 3D cartography of neurotransmitter distribution which could help in the selection of molecules to be used in the treatment of incontinence, erectile dysfunction and ejaculatory disorders.     

全直肠系膜切除相关盆自主神经的解剖学观察

目的：阐述全直肠系膜切除术相关盆自主神经的局部解剖学特点，探讨盆自主神经保留的部位和对策。方法：对20具男性盆腔固定标本进行解剖观察。结果：腹主动脉丛远离肠系膜下动脉起点；上腹下丛贴近骶岬表面；腹下神经部分毗邻输尿管；盆内脏神经伴行直肠中动脉外侧部；下腹下丛位于直肠系膜后外侧；其直肠侧支走行于直肠侧韧带内，直肠前支向前穿过Denonvilliers筋膜后叶；勃起神经位于Denonvilliers筋膜前叶外侧部。结论：盆自主神经保留的部位是：离断肠系膜下血管时的腹主动脉丛左干，直肠后分离时的上腹下丛和腹下神经，直肠侧面分离时的下腹下丛和盆内脏神经，直肠前分离时的勃起神经。共同原则是：在直肠后间隙中贴近直肠系膜操作；直视下操作；避免过度牵引直肠系膜。     

Perineal pain and inferior cluneal nerves: anatomy and surgery

Neuropathic perineal pains are generally linked to suffering of the pudendal nerve. But some patients present pains described as a type of burning sensation located more laterally on the anal margin and on areas including the scrotum or the labiae majorae, the caudal and medial parts of the buttock and the upper part of the thigh. These pains extend beyond the territory of the pudendal nerve. It is interesting to note that the inferior cluneal nerves are responsible for the cutaneous sensitivity in the inferior part of the buttock. We wanted to check if these nerves, or some of their branches, could be responsible for such pains. An anatomic study, containing six dissections on corpse, has been conducted. The inferior cluneal nerves, emerging from the posterior femoral cutaneous nerve have some branches joining the perineum, especially by a perineal ramus. However, two conflict areas have been identified on the path of these nerves and on the perineal ramus: one at the level of the sacrotuberal ligament, and the other being the passage under the ischium. Two surgical approaches have been established from these observations with the aim of suppressing the conflicts.     

Alpha-adrenoceptor-mediated penile erection in dogs: in vivo and in vitro observations.

We have evaluated the role of adrenergic components in the pelvic splanchnic nerve on the erectile function in the dog. Electrical stimulation of pelvic splanchnic nerves increased blood flow in the internal pudendal artery and also elevated the cavernous pressure. These increases were blocked in part by phentolamine or methylene blue, but not by propranolol or atropine. The effects of cholinergic and adrenergic agonists and antagonists on mechanical responses were also examined in muscle strips obtained from various arteries in the intrapelvic region including the internal pudendal artery. Norepinephrine induced contraction in the iliac artery and relaxation in the internal pudendal artery, and both the contraction and relaxation responses were blocked by phentolamine but not by propranolol. These findings suggest that in the dog, alpha-adrenergic components projected through the pelvic splanchnic nerve may contribute to penile erection, together with cyclic GMP-mediated mechanisms.     

Mechanism of the reflex inhibition of micturition contractions of the urinary bladder elicited by acupuncture-like stimulation in anesthetized rats.

The effects of acupuncture-like stimulation of various segmental areas on the rhythmic micturition contractions (RMCs) of the urinary bladder were examined in anesthetized rats. The urinary bladder was cannulated via the urethra and expanded by infusing saline until the urinary bladder produced micturition contractions rhythmically as a consequence of the rhythmic burst discharges of the vesical pelvic efferent nerves. An acupuncture needle, having a diameter of either 160 or 340 microns, was inserted to a depth of about 4-5 mm into the skin and underlying muscles at various segmental areas, rostrally from the face then caudally to the hindlimb. Once being inserted, the needle was twisted left and right with the fingers about once every second for 1 min. (1) Acupuncture-like stimulation applied to the perineal area inhibited both the RMCs and the rhythmic burst discharges of vesical pelvic efferent nerves without any significant changes in the hypogastric efferent nerve activity. By contrast, stimulation applied to the face, neck, forelimb, chest, abdomen, back, and hindlimb areas was ineffective. (2) After surgically separating the perineal skin from the underlying muscles with the main cutaneous nerve branches intact, stimulation of either the perineal skin or the perineal muscles inhibited the RMCs. Stimulation of the perineal muscles produced a stronger inhibition of the RMCs than that of the perineal skin. (3) Stimulation of the perineal area increased afferent nerve activity, either recorded from the pudendal nerve branches innervating the perineal skin or underlying muscles, or recorded from the pelvic nerve branches innervating the perineal muscles. (4) The stimulation-induced inhibition of the RMCs was abolished after surgically severing both pudendal and pelvic nerve branches that innervated the perineal skin and underlying muscles. (5) The present findings indicate that the inhibition of the RMCs following acupuncture-like stimulation of the perineal area is a reflex response characterized by segmental organization. The afferent arcs of the reflex are both pelvic and pudendal nerve branches innervating the perineal skin and underlying muscles, while the efferent arcs are pelvic nerve branches innervating the urinary bladder.     

Stratificational relationship among the main nerves from the dorsal division of the sacral plexus and the innervation of the piriformis.

In order to comprehend more completely the morphology of the nerves to the piriformis, it is necessary to obtain a detailed understanding of the relationship of the origin and the course of these nerves from the dorsal division of the sacral plexus, with reference to the superior and inferior gluteal nerves. Twelve of seven human pelvic halves were carefully dissected in order to examine the origins of the nerves from the dorsal division of the sacral plexus. Six of these pelvic halves were further dissected under a stereomicroscope to examine the nerves to the piriformis. 1. The origin of the superior gluteal nerve was more proximal and dorsal in the sacral plexus than that of the inferior gluteal nerve. 2. The superior gluteal nerve consisted of a thick cranial part and a thin caudal part; the former continued as the inferior branch of the nerve, and the latter, the superior branch. The cranial and caudal parts crossed before reaching the glutei medius and minimus. 3. The nerves to the piriformis arose from three main nerves from the dorsal division of the sacral plexus: 1) the caudalmost root of the superior gluteal nerve, 2) the caudal roots of the inferior gluteal nerve and 3) the common peroneal nerve. Considering the stratificational relationship among the main nerves from the dorsal division of the sacral plexus, the piriformis appears to be composed of parts from different muscle layers.     

Nerve contributions to the pelvic plexus and the umbilical cord

Serial sections of human embryos and fetuses reveal that the sacral nerves which contribute fibers to the pelvic plexus often have dorsal, ventral, and oblique communicating rami. The ventral rami resemble the white rami of upper thoracic nerves and some of their fibers pass close by or through the chain ganglia and into the pelvic plexus. The sizes of the ventral rami are often in inverse proportion to that of the pelvic splanchnic nerves. That is, when the pelvic splanchnic nerves are poorly developed, the ventral rami are large, and conversely, when the pelvic splanchnic nevers are well developed, these rami are small. The pelvic plexus was found to receive fibers from the sympathetic trunk and its ganglia in addition to those from the hypogastric plexus and the pelvic splanchnic nerves. Analysis of the observations made in this study together with a review of the literature in light of the present day classification of nerve fibers raises serious doubts concerning the limits set for the outflow of preganglionic nerve fibers from the spinal cord and the distribution of gray and white rami as described in recent textbooks in terms of their histological and physiological significance. Nerve fibers from the pelvic plexus can be traced along the walls of the bladder and the urachus and along the umbilical arteries into the umbilical cord. In embryos, only a few scattered nerve fibers were found distal to the umbilicus, but in fetuses at term, distinct nerve bundles were identified in the cord. These bundles sent branches to the walls of the umbilical arteries; other branches terminated as “end-nets” in Wharton's jelly. These nets appeared as fine fibers with nodular swellings at irregular intervals. Innervation of the umbilical arteries was richest within the first few inches of the cord. Beyond this region, the nerves rapidly decreased in number. “End-nets” were present as far as four inches from the umbilicus. Granular cells resembling Langerhans' cells were found in the cord. Often these cells were closely associated with fine nerve fibers.     

Origins and courses of the nervous branches to the male urethral sphincter

The striated sphincter of the male urethra, the so-called rhabdosphincter, contributes significantly to urethral closure pressure. It is generally agreed that the somatic nerve fibers from the pudendal nerve innervate the rhabdosphincter, and the autonomic nerve fibers innervate the smooth muscle of the urethra. Although it is difficult to clearly identify the rhabdosphincter macroscopically, we minutely investigated the nerve branches to the urethral sphincter muscle region in 10 male pelvic halves. In addition, the origins and courses of the pudendal plexus in 88 male pelvic halves were investigated. To this region were given branches of the pudendal nerve and the pelvic plexus. The branches from the pelvic plexus to the region generally originated from S4 as the lowest branch of the pelvic splanchnic nerve, and ran along the rectal attachment of the levator ani. The caudal root of the pelvic splanchnic nerve formed a common trunk with the nerve to the levator ani (94%). Various connections were sometimes observed between the pudendal nerve and the branches medial to the levator ani. It is suggested that the somatic nerve fibers from the nerve to the levator ani or from the pudendal nerve might also join the nerve branches to the region from the pelvic plexus.

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Origine et trajet des branches nerveuses destinées au sphincter uréthral de l'homme

Résumé Le sphincter strié de l'urètre de l'homme, aussi appelé rhabdosphincter, contribue significativement a la pression de clôture de l'urètre. Il est généralement admis que les fibres somatiques du nerf pudendal innervent le sphincter strié, et que les fibres nerveuses autonomes innervent le muscle lisse de l'urètre. Ben qu'il soit difficile d'identifier macroscopiquement le sphincter strié, nous avons observé microscopiquement les branches nerveuses destinées aux muscle sphincter urétral sur dix hémi-pelvis masculins. De plus, l'origine et le trajet du plexus pudendal ont été explorés sur 88 hémi-pelvis masculins. Cette région recevait des branches du nerf pudendal et du plexus pelvien. Les branches du plexus pelvien pour cette zone provenaient en général de S4, sous la forme de la branche la plus distale du nerf splanchnique pelvien, et cheminaient le long de l'insertion rectale du muscle élévateur de l'anus. La racine caudale du nerf splanchnique pelvien formait un tronc commun avec le nerf du muscle élévateur de l'anus (94%). Des connexions variables ont parfois été observées entre le nerf pudendal et les branches médiales au muscle élévateur de l'anus. Ceci suggère que les fibres nerveuses somatiques du nerf du muscle élévateur de l'anus ou du nerf pudendal puissent rejoindre les branches nerveuses provenant du plexus pelvien.

     

Stratificational relationship among the main nerves from the dorsal division of the sacral plexus and the innervation of the piriformis

In order to comprehend more completely the morphology of the nerves to the piriformis, it is necessary to obtain a detailed understanding of the relationship of the origin and the course of these nerves from the dorsal division of the sacral plexus, with reference to the superior and inferior gluteal nerves. Twelve of seven human pelvic halves were carefully dissected in order to examine the origins of the nerves from the dorsal division of the sacral plexus. Six of these pelvic halves were further dissected under a stereomicroscope to examine the nerves to the piriformis.

• 1 The origin of the superior gluteal nerve was more proximal and dorsal in the sacral plexus than that of the inferior gluteal nerve.
• 2 The superior gluteal nerve consisted of a thick cranial part and a thin caudal part; the former continued as the inferior branch of the nerve, and the latter, the superior branch. The cranial and caudal parts crossed before reaching the glutei medius and minimus.
• 3 The nerves to the piriformis arose from three main nerves from the dorsal division of the sacral plexus: (1) the caudalmost root of the superior gluteal nerve, (2) the caudal roots of the inferior gluteal nerve and (3) the common peroneal nerve. Considering the stratificational relationship among the main nerves from the dorsal division of the sacral plexus, the piriformis appears to be composed of parts from different muscle layers. © 1992 Wiley-Liss, Inc.

     

Caverno-pudendal nervous communicating branches in the penile hilum

Classically, the peripheral neural pathways for erection are proerectile, issuing from the parasympathetic sacral fibres, and antierectile from the thoracolumbar sympathetic trunk. The cavernous nerves as terminal branches of the pelvic plexus convey the parasympathetic fibres to the penis. The pudendal nerve conveys sensory fibres from the penis and somatic fibres to the bulbospongiosus and ischiocavernosus striated mm. In animals, it has been demonstrated that the dorsal nerve of the penis contains sympathetic fibres. These findings suggest that communicating branches exist between the cavernous nerves and the dorsal nerve. Our aim in this study was to demonstrate the presence of such connections in man. We dissected 20 fresh male cadavers. The pelvic plexus and pudendal nerves were dissected to identify their terminal branches and connections. Histologic study was performed. Our results showed evidence of communicating nervous branches between the cavernous nerves and the dorsal nerve of the penis. Several variants existed concerning the number and type of connections. The presence of such communicating branches proves that the supralevator and infralevator neural pathways communicate and suggest the possibility of a kind of plasticity of the nervous supply of penile erection. Further studies are needed to identify the nature of these communicating branches.     

Nerves in the intersphincteric space of the human anal canal with special reference to their continuation to the enteric nerve plexus of the rectum

In the intersphincteric space of the anal canal, nerves are thought to “change” from autonomic to somatic at the level of the squamous‐columnar epithelial junction of the anal canal. To compare the nerve configuration in the intersphincteric space with the configuration in adjacent areas of the human rectum, we immunohistochemically assessed tissue samples from 12 donated cadavers, using antibodies to S100, neuronal nitric oxide synthase (nNOS), and tyrosine hydroxylase (TH). Antibody to S100 revealed a clear difference in intramuscular nerve distribution patterns between the circular and longitudinal muscle layers of the most inferior part of the rectum, with the former having a plexus‐like configuration, while the latter contained short, longitudinally running nerves. Most of the intramural ganglion cells in the anal canal were restricted to above the epithelial junction, but some were located just below that level. Near or at the level of the epithelial junction, the nerves along the rectal adventitia and Auerbach's nerve plexus joined to form intersphincteric nerves, with all these nerves containing both nNOS‐positive parasympathetic and TH‐positive sympathetic nerve fibers. Thus, it was histologically difficult to distinguish somatic intersphincteric nerves from the autonomic Auerbach's plexus. In the intersphincteric space, the autonomic nerve elements with intrapelvic courses seemed to “borrow” a nerve pathway in the peripheral branches of the pudendal nerve. Injury to the intersphincteric nerve during surgery may result in loss of innervation in the major part of the internal anal sphincter. Clin. Anat. 26:843–854, 2013. © 2013 Wiley Periodicals, Inc.