Chapter 15: The Autonomic Nervous System

Author's Commentary

In the CNS, the autonomic nervous system is primarily regulated by the hypothalamus and functions to control:

  1. Respiration
  2. Cardiac parameters
  3. Vasomotor activity
  4. Brain stem reflexes

Peripherally, it innervates smooth muscles and glands. It functions unconsciously.

Excerpts From Chapter 15

General Inspection

The skin frequently reflects autonomic dysregulation. Livido reticularis (a blue lacy pattern), dusky cyanosis and poor capillary refill tell the examiner that capillary circulation of the extremity is not regulated properly. There is a delicate interplay between sympathetic vasoconstriction and the release of vasoactive neuropeptides in the skin. The tips of the fingers and toes are important for thermoregulation and have a high blood flow. The deep circulation to muscles, adventitial tissues and bone is the core of the nutritive blood supply. Dysfunction of the sympathetic nervous system at this level causes the atrophy and dystrophy of chronic regional pain syndrome (CRPS). The peripheral nerves carry sympathetic fibers to the extremities and all components of their tissue. Almost all peripheral neuropathies, particularly the small fiber axonal ones, are associated with cold extremities. Sympathetic tone increases and decreases minute by minute. Large dilated veins on an extremity that do not vary in diameter during the day suggest loss of this tone. An flushed warm extremity suggests loss of sympathetic tone. Inspiration blocks cutaneous thermoregulatory blood flow. Extremely red ears and facial flushing are manifestations of sympathetic paralysis and the release of vasoactive neuropeptides on the corresponding blood vessels (neurogenic edema). These neuropeptides paralyze smooth muscle and increase capillary leakage.

Complete sympathetic lesions result in absence of sweating, while irritative lesions may increase sweating. There is no denervation hypersensitivity, with resulting hyperhidrosis after sympathetic denervation. Excessive hyperhidrosis has a central nervous system origin and may be seen after a cortical or posterior hypothalamic stroke.

A peripheral Horner's syndrome is seen from loss of sympathetic innervation that derives from the C8–T1 dermatome and follows the internal carotid artery to the eye. The T2 sympathetic dermatome selectively innervates the arm.