**3. Physiology and pathophysiology of the lower gastrointestinal tract**

The enteric nervous system plays the most important role in regulating the peristaltic reflex of the lower gastrointestinal tract20. Two types of myoelectrical activity or pressure changes in the colon are documented. Slow phasic pressure waves are the most common manometric phenomenon26, and in humans are measured as spontaneous phasic rectal contraction9,22. The peristaltic reflex can be evoked by surface stroking or by circumferential stretching.20 The reflex consists of two components: ascending contraction (mediated by cholinergic fibers) oral to the stimulus site, and descending relaxation (mediated by non-adrenergic, non-cholinergic fibers) caudal to the stimulus site2.

Sphincter EMG for Diagnosing MSA and Related Disorders 291

waves and giant motor complexes is thought to promote bowel transport, which in humans is measured by colonic transit time4. The strength of cholinergic transmission in the enteric nervous system is thought to be regulated by opposing receptors; serotonin 5-HT4 receptor-

Whereas the rostral lower gastrointestinal tract is innervated by the vagus nerves originating in the medulla, extra-enteric innervation of the caudal lower gastrointestinal tract primarily shares the innervation of the lower urinary tract **(Fig. 2)**12,22. The lower urinary tract and lower gastrointestinal tracts perform similar functions of storage and emptying. However, they differ profoundly with regard to anatomy (closed bag versus open-ended tube, respectively), luminal contents (liquid versus half-solid), and physiology (dysfunctional transport, rare ureter versus common bowel; smooth muscle contraction, bladder contraction only on emptying versus persistent spontaneous phasic rectal contraction; abdominal strain, minimal on urination versus strong on defecation)22. In addition, while the lower urinary tract requires an intact neuraxis for storage and emptying12, it has not been entirely clear to what extent the lower gastrointestinal tract

Constipation in MSA most probably results from slow colonic transit, decreased phasic rectal contraction, and weak abdominal strain.58 Some patients also have paradoxical sphincter contraction on defecation (PSCD).58 The sites responsible for this dysfunction seem to be both the central and peripheral nervous systems, which regulate the lower gastrointestinal tract. Slow colonic transit and decreased phasic rectal contraction most probably reflect peripheral enteric nervous system lesions, whereas weak abdominal strain and PSCD may reflect central lesions.61 In contrast, fecal incontinence results mostly from a

The genital organ primarily shares lumbosacral innervation with the lower urinary tract. Erection is a vascular event3; occurring secondarily after dilatation of the cavernous helical artery and compression of the cavernous vein to the tunica albuginea3. Helical artery dilatation is brought about by activation of cholinergic and nitrergic nerves; this activation facilitates nitric oxide secretion from the vascular endothelium. Ejaculation is brought about by contraction of the vas deferens and the bladder neck, in order to prevent retrograde ejaculation, by activation of adrenergic nerves **(Fig. 3)**. Sacral Onuf's nucleus innervates the bulbocavernosus muscle; and is thought to participate in erection and ejaculation. Sexual intercourse in healthy men can be divided into 3 phases65: a) desire (libido), b) excitement and erection, and c) orgasm, seminal emission from the vas deferens, and ejaculation from the penis. Erection can be further classified into 3 types by the relevant stimulation: 1) psychogenic erection (by audiovisual stimulation), 2) reflexive erection (by somatosensory stimulation), and 3) nocturnal penile tumescence (NPT) (associated with rapid eye movement [REM]-sleep). 'Morning erection' is considered the last NPT in the nighttime.

mediating excitation31,73 and dopamine D2 receptor-mediating inhibition76.

needs the extra-enteric nervous system.

weak anal sphincter due to denervation.58

**4. Physiology and pathophysiology of the genital organ** 

The function of the lower gastrointestinal tract is thought to depend on the brain and spinal cord, although less significantly than the lower urinary tract (LUT) does. Whereas the small intestine and ascending colon are innervated by the vagus nerves originating in the medulla, the descending colon, sigmoid colon, and rectum primarily share sacral innervation of the LUT (Figure 1). Both the sacral cord and the vagus nuclei receive projecting fibers from Barrington's nucleus (the pontine micturition/defecation center). Bowel function seems to be modulated by the higher brain structures, including the frontal lobe, the hypothalamus, and the basal ganglia; the main action of the latter on the bowel seems to be inhibitory.

NBM: nucleus basalis Meynert, Ch: cholinergic, PVN: paraventricular nucleus, MPOA: medial preoptic area, ZI: zona incerta, A: adrenergic/noradrenergic, VTA: ventral tegmental area, SNC: substantia nigra pars compacta, LC: locus ceruleus, DLTN: dorsolateral tegmental nucleus, PBN: parabrachial nucleus, PAG: periaqueductal gray, IML: IML cell column, GABA: γ-aminobutyric acid, T: thoracic, L: lumbar, S: sacral (cited from ref. 41)

**Figure 2.** Neural circuitry relevant to defecation.

Other types of pressure changes in the colon include giant motor complexes20. A giant motor complex is a cyclic contractile activity with a periodicity of 20 to 30 min, and is perhaps analogous to the migrating motor complex of the small intestine26. A combination of slow waves and giant motor complexes is thought to promote bowel transport, which in humans is measured by colonic transit time4. The strength of cholinergic transmission in the enteric nervous system is thought to be regulated by opposing receptors; serotonin 5-HT4 receptormediating excitation31,73 and dopamine D2 receptor-mediating inhibition76.

Computational Intelligence in Electromyography Analysis – 290 A Perspective on Current Applications and Future Challenges

non-cholinergic fibers) caudal to the stimulus site2.

the bowel seems to be inhibitory.

(cited from ref. 41)

column, GABA: γ-aminobutyric acid, T: thoracic, L: lumbar, S: sacral

**Figure 2.** Neural circuitry relevant to defecation.

phenomenon26, and in humans are measured as spontaneous phasic rectal contraction9,22. The peristaltic reflex can be evoked by surface stroking or by circumferential stretching.20 The reflex consists of two components: ascending contraction (mediated by cholinergic fibers) oral to the stimulus site, and descending relaxation (mediated by non-adrenergic,

The function of the lower gastrointestinal tract is thought to depend on the brain and spinal cord, although less significantly than the lower urinary tract (LUT) does. Whereas the small intestine and ascending colon are innervated by the vagus nerves originating in the medulla, the descending colon, sigmoid colon, and rectum primarily share sacral innervation of the LUT (Figure 1). Both the sacral cord and the vagus nuclei receive projecting fibers from Barrington's nucleus (the pontine micturition/defecation center). Bowel function seems to be modulated by the higher brain structures, including the frontal lobe, the hypothalamus, and the basal ganglia; the main action of the latter on

NBM: nucleus basalis Meynert, Ch: cholinergic, PVN: paraventricular nucleus, MPOA: medial preoptic area, ZI: zona incerta, A: adrenergic/noradrenergic, VTA: ventral tegmental area, SNC: substantia nigra pars compacta, LC: locus ceruleus, DLTN: dorsolateral tegmental nucleus, PBN: parabrachial nucleus, PAG: periaqueductal gray, IML: IML cell

Other types of pressure changes in the colon include giant motor complexes20. A giant motor complex is a cyclic contractile activity with a periodicity of 20 to 30 min, and is perhaps analogous to the migrating motor complex of the small intestine26. A combination of slow Whereas the rostral lower gastrointestinal tract is innervated by the vagus nerves originating in the medulla, extra-enteric innervation of the caudal lower gastrointestinal tract primarily shares the innervation of the lower urinary tract **(Fig. 2)**12,22. The lower urinary tract and lower gastrointestinal tracts perform similar functions of storage and emptying. However, they differ profoundly with regard to anatomy (closed bag versus open-ended tube, respectively), luminal contents (liquid versus half-solid), and physiology (dysfunctional transport, rare ureter versus common bowel; smooth muscle contraction, bladder contraction only on emptying versus persistent spontaneous phasic rectal contraction; abdominal strain, minimal on urination versus strong on defecation)22. In addition, while the lower urinary tract requires an intact neuraxis for storage and emptying12, it has not been entirely clear to what extent the lower gastrointestinal tract needs the extra-enteric nervous system.

Constipation in MSA most probably results from slow colonic transit, decreased phasic rectal contraction, and weak abdominal strain.58 Some patients also have paradoxical sphincter contraction on defecation (PSCD).58 The sites responsible for this dysfunction seem to be both the central and peripheral nervous systems, which regulate the lower gastrointestinal tract. Slow colonic transit and decreased phasic rectal contraction most probably reflect peripheral enteric nervous system lesions, whereas weak abdominal strain and PSCD may reflect central lesions.61 In contrast, fecal incontinence results mostly from a weak anal sphincter due to denervation.58
