Up and down the spinal cord: afferent and efferent innervation of the human external anal sphincter (original) (raw)
Related papers
Journal of The Neurological Sciences, 1997
Electrophysiological activation of the motor pathways can be obtained by electrical or magnetic stimulation. The latter has the great advantage of being painful and able to stimulate deeply situated nervous structures. Only a few reports describe responses obtained from pelvic floor muscles and external anal sphincter (EAS) by transcranial and lumbo-sacral magnetic stimulation. Our purpose is to present normative data of motor evoked responses from EAS in a group of healthy subjects (age range 19-80 years) using a standardized protocol of magnetic stimulation. Nine females and 7 males, with a mean age of 52.63 years, were included in this study. They had no known neurological and gastrointestinal disease. Magnetic shocks were delivered by a Magstim 200 (Novametrix) and a circular coil, centered on the vertex and on the lumbo-sacral region. Electromyographic recordings were taken from EAS using needle electrodes. The cortical magnetic stimulation was performed in two conditions: at rest and during a mild contraction of pelvic floor muscles. The mean values of motor evoked potentials (MEPs) latencies after cortical stimulation were 26.9263.01 ms at rest and 23.3162.70 ms during facilitation. Motor latency after lumbo-sacral root stimulation was 6.0961.43 ms. The MEPs from EAS are easily obtained and stably reproducible in normal subjects. It can be suggested also as a useful adjunct in the assessment of faecal incontinence. © 1997 Elsevier Science B. V.
British Journal of Surgery, 2011
Background: Sacral and posterior tibial nerve stimulation may be used to treat faecal incontinence; however, the mechanism of action is unknown. The aim of this study was to establish whether sensory activation of the cerebral cortex by anal canal stimulation was increased by peripheral neuromodulation. Methods: A multielectrode array was positioned over the right primary somatosensory cortex of anaesthetized rats. A brief burst of electrical stimulation was applied to either the left sacral root or the left posterior tibial nerve, and evoked potentials from anal canal stimulation were signal-averaged at intervals over 1 h. At the end of the experiment, the cerebral cortex was removed and probed for polysialylated neural cell adhesion molecule (PSA-NCAM).
Cerebral Activation during Anal and Rectal Stimulation
Neuroimage, 2001
While the rectum is innervated by visceral afferents, the anal canal is innervated by the somatosensory pudendal nerve. The representation of these two central domains of intestinal sensations in the human brain is largely unknown. Nonpainful pneumatic stimulation of the anal canal and the distal rectum using event-related functional magnetic resonance imaging (fMRI) was performed in eight healthy subjects. Subjective scaling of sensations revealed no differences in unpleasantness and pain during both stimuli. Both types of stimuli revealed fMRI activation in secondary somatosensory, insula, cingular gyrus, left inferior parietal, and right orbitofrontal cortex. Anal stimulation resulted in additional activation of primary sensory and motor cortex, supplementary motor area, and left cerebellum. We concluded that viscerorectal and somatosensory anal stimulation predominantly differ in their primary sensory activation and additional activation in motor areas. This motor response following aversive somatosensory stimuli may be caused by a reflexive avoidance reaction which is not observed after the more diffuse experienced visceral stimulation.
Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section, 1998
The aim of this study is to localize the primary sensory cortex of urogenital organs in the human brain. Using a newly developed MRIlinked magnetoencephalography system, we measured somatosensory evoked magnetic fields (SEFs) for unilateral stimuli on the dorsal penile nerve (DPN), posterior tibial nerve (PTN) and median nerve (MN). In five healthy male subjects, SEFs were clearly observed. Peak latencty of the first cortical components were 63.8 ± 9.2 ms for DPN, 39.8 ± 3.0 ms for PTN and 20.7 ± 0.7 ms for MN stimuli. Peak amplitude of the first cortical components were 63.1 ± 10.8 fT for DPN, 160.2 ± 50.1 fT for PTN and 335.2 ± 70.3 fT for MN stimuli. Isofield map for the peak latencies indicated a single dipolar pattern for DPN as well as for PTN and MN stimuli. Using a single current dipole model, all SEF sources were localized on the contralateral central sulcus to the stimuli, indicating the primary sensory cortex. The DPN sources were localized on the interhemispheric surfaces, corresponding to previous speculations by direct cerebral stimulation. This non-invasive SEF technique promises further brain functional mapping for the urogenital organs.
Anal sphincter responses after perianal electrical stimulation
Journal of Neurology, Neurosurgery & Psychiatry, 1982
By perianal electrical stimulation and EMG recording from the external anal sphincter three responses were found with latencies of 2-8, 13-18 and 30-60 ms, respectively. The two first responses were recorded in most cases. They were characterised by constant latency and uniform pattern, were not fatigued by repeated stimulation, were most dependent on placement of stimulating and recording electrodes, and always had a higher threshold than the third response. The third response was constantly present in normal subjects. It had the longest EMG response and the latency decreased with increasing stimulation to a minimum of 30-60 ms. This response represented the clinical observable spinal reflex, "the classical anal reflex". The latencies of the two first responses were so short that they probably do not represent spinal reflexes. This was further supported by the effect of epidural anaesthesia which left the first responses unaffected but abolished the classical anal reflex. The origin of the two first responses is discussed and models involving antidromal impulse propagation in the efferent fibre as the afferent limbs of the responses are proposed.
External anal sphincter responses after S3 spinal root surface electrical stimulation
Neurourology and Urodynamics - NEUROUROL URODYNAM, 2006
AimsThe aim of this study is to present the normative data of direct and reflex motor anal sphincter responses, simultaneously evoked by S3 surface electrical stimulation. By this method, it is possible to test the functional integrity of the nervous pathways activated during sacral neuromodulation (SNM).The aim of this study is to present the normative data of direct and reflex motor anal sphincter responses, simultaneously evoked by S3 surface electrical stimulation. By this method, it is possible to test the functional integrity of the nervous pathways activated during sacral neuromodulation (SNM).MethodsTwenty healthy subjects were studied. Motor-evoked potentials (MEPs) were recorded by concentric needle electrode from external anal sphincter (EAS). Electrical stimulation was applied by means of a bipolar surface electrode over the S3 right or left sacral foramina.Twenty healthy subjects were studied. Motor-evoked potentials (MEPs) were recorded by concentric needle electrode from external anal sphincter (EAS). Electrical stimulation was applied by means of a bipolar surface electrode over the S3 right or left sacral foramina.ResultsDirect (R1) and reflex responses (R2 and R3) were found at latencies of 6.98, 25.12, and 50.31 msec, respectively. The two first responses were recorded in all the cases; the last response is steadily recorded in 17 out of 20 subjects.Direct (R1) and reflex responses (R2 and R3) were found at latencies of 6.98, 25.12, and 50.31 msec, respectively. The two first responses were recorded in all the cases; the last response is steadily recorded in 17 out of 20 subjects.ConclusionsOur data can serve as reference values for future study in patients with pelvic floor dysfunction. EAS responses following S3 percutaneous electrical stimulation can represent a useful aid in the selection of candidates to SNM. Neurourol. Urodynam. 25:788–791, 2006. © 2006 Wiley-Liss, Inc.Our data can serve as reference values for future study in patients with pelvic floor dysfunction. EAS responses following S3 percutaneous electrical stimulation can represent a useful aid in the selection of candidates to SNM. Neurourol. Urodynam. 25:788–791, 2006. © 2006 Wiley-Liss, Inc.
The external anal sphincter and the role of surface electromyography
Neurogastroenterology and Motility, 2005
Assessment of the neuronal control of the external anal sphincter (EAS) has long been restricted to investigating patients with defecation disorders by invasive tools such as needle electromyography (EMG), while less invasive techniques have been regarded as non-suitable for diagnostic purposes. Multichannel surface EMG by means of electrode arrays applied to anal sphincter muscle records and identifies individual motor unit action potentials, their place of origin along the circumference, their repetitive firing frequency, and their progression along the muscle fibres at different levels within the anal canal. These data shed doubts on conventional knowledge about the anatomy of the EAS muscle, and confirms new concepts of anatomical differences between gender. This may eventually be transferred to a new understanding of the role of symmetry and asymmetry of pelvic floor innervation and its role in the pathogenesis of fecal incontinence.
Innervation Zones of the External Anal Sphincter in Healthy Male and Female Subjects
Digestion, 2004
Objectives: The objective of this work was to investigate the distribution of the innervation zones of the motor units that make up the external anal sphincter (EAS) in healthy males and females. Methods: A cylindrical probe carrying a circumferential array of 16 electrodes was used to detect the generation, propagation and extinction of individual motor unit action potentials (MUAPs) at 1, 2, and 3 cm depth from the orifice of the anal canal during maximal voluntary contractions of the EAS. Fifteen healthy males and 37 healthy nulliparous females were investigated. Results: IZs could be detected in all males and in 34 out of 37 females. In the males, the IZs are scattered in the right and left hemisphincter at each of the three levels and their distribution is not affected by depth. In the females, the distribution is also concentrated in the right and left hemisphincter at depth 1 cm but is more uniform at depth 2 cm and more concentrated in the dorsal and ventral regions at depth...
Colorectal Disease, 2004
Background: Control of defaecation and continence may be lost in patients with spinal cord injury. Electrical stimulation of sacral nerve roots to promote defaecation simultaneously activates both the rectum and the external anal sphincter (EAS), and may actually obstruct defaecation. The aim of this study was to investigate whether the EAS could be blocked selectively by selective stimulation of the ventral sacral nerve roots, and whether activation of the rectum without activation of the EAS could be obtained by stimulation of the ventral sacral nerve roots. Methods: Selective electrical stimulation was performed using anodal blocking, a tripolar cuff electrode and monophasic rectangular current pulses applied to the sacral nerve roots in nine Göttingen minipigs. Results: Simultaneous responses in the rectum and the anal canal were observed in five animals, whereas only anal responses were noted in four. Variations in cross-sectional area and an increase in rectal pressure seemed to facilitate defaecation. Without blocking, the increase in anal canal pressure was 16-45 cmH 2 O. With blocking, this increase was abolished in seven and reduced to 3-6 cmH 2 O in two animals. Conclusion: Selective activation of the rectum is possible using an anodal block of somatic motor fibres. This technique holds promise in further development of electro-defaecation.