Autonomic nervous system lesion syndromes

Neurogenic defecation and urination disorders

The physiological processes of rectal and urinary bladder emptying have much in common. Normally, the initiation of peristalsis and relaxation of the internal sphincters are stimulated by the parasympathetic nervous system (segments S2–S4), whereas the suppression of peristalsis and contraction of the internal sphincter are mediated by the sympathetic system (L1–L2). Voluntary control over the external sphincters (striated muscle) is exerted by the somatic nervous system, specifically the pudendal nerve.

Nerve structure damage leads to characteristic disorders:

• Constipation. Occurs when the spinal cord is damaged above the thoracolumbar defecation centers. The afferent link is interrupted (information regarding rectal ampulla filling does not reach higher centers) along with descending motor fibers (impairing the ability to strain). Inadequate sphincter contraction due to spastic paresis frequently develops.
• Fecal incontinence. Results from lesions of the sacral segments S2–S4. The anal reflex is lost, making fecal retention impossible.
• Dysfunction of the external urethral sphincter. Frequently causes obstructive voiding dysfunction in young women (the sphincter fails to relax adequately). Diagnosed via ENMG, which reveals changes resembling myotonic discharges.
• Enuresis. Involuntary urination during sleep in individuals over 4 years of age. By definition, it is not associated with structural nervous system damage; however, it requires mandatory differential diagnosis with epilepsy and spina bifida occulta.

Male genital innervation disorders

Sexual function is under the higher control of the hypothalamus (via reticulospinal nerve fibers and hormonal regulation). At the spinal cord level, innervation is strictly segregated:

1. Erection is triggered by parasympathetic fibers from segments S2–S4, which travel within the pelvic splanchnic nerves to the corpora cavernosa, inducing vasodilation.
2. Ejaculation is mediated by sympathetic fibers from the upper lumbar segments (L1) via the hypogastric plexus to the seminal vesicles, prostate, and vas deferens.

The clinical presentation of sexual dysfunction is strictly dependent on the level of the lesion:

• Thoracic spinal cord: causes erectile dysfunction. Paraplegia may be accompanied by testicular atrophy; reflex priapism and periodic ejaculation may occur.
• Sacral region (S2–S4): complete impotence occurs, with a total absence of erection and ejaculation.

Mechanisms of visceral and referred pain

Most autonomic impulses originating from internal organs do not reach consciousness. However, individuals are capable of perceiving pain during significant distension of hollow organs, ischemia (e.g., angina pectoris), inflammation, or wall irritation causing reflex smooth muscle spasm (renal or biliary colic). Visceral pain is invariably diffuse and poorly localized.

The phenomenon of referred pain is based on an anatomical feature—pathway convergence:

• Afferent autonomic fibers from internal organs (enterotome) and somatic afferent fibers from the skin (dermatome) and muscles (myotome) enter the spinal cord together.
• They converge on a single common sensory neuron located in the dorsal horn of the spinal cord.
• Subsequently, the combined signal ascends to the brain via fibers of the lateral spinothalamic tract (tractus spinothalamicus lateralis).

As a result, the central nervous system may mistakenly interpret pain signals primarily originating in internal organs as impulses arriving from the corresponding skin areas. This bidirectional viscero-cutaneous connection also explains the therapeutic effect of counter-irritation procedures (warming, rubbing): superficial skin stimulation can alleviate visceral pain.

Topography of Zakharyin-Head zones

Zakharyin-Head zones are specific areas of cutaneous hyperesthesia where reflex pain occurs during pathology of specific internal organs. Knowledge of these zones is critical for the topical diagnosis of internal diseases.

• Diaphragm: segment C4.
• Heart: segments Th3–Th4 (explaining left arm pain during myocardial ischemia).
• Esophagus: segments Th4–Th5.
• Stomach: segments Th6–Th9.
• Liver, gallbladder: segments Th8–Th11.
• Small intestine: segments Th10–L1.
• Large intestine: segments Th11–L1.
• Kidneys, testes/ovaries: segments Th10–L1.
• Urinary bladder: segments Th11–L1.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathogenesis and surgical treatment of conus medullaris tethering anomalies.
• Differential diagnosis of enuresis (organic causes, occult spina bifida, developmental malformations).
• ENMG criteria for external urethral sphincter dysfunction in women.
• The role of the cerebral cortex and pontine reticular formation in the control of pelvic functions.

Other topics in the section "DeMyer's The Neurologic Examination" / "Duus' Topical Diagnosis in Neurology"

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