Autonomic Division of Peripheral Nervous System

Description

The autonomic division of the nervous system consists of two parts: sympathetic nerves and parasympathetic nerves. These nerves exist and operate on a largely subconscious level and are involved in maintaining body homeostasis.

The sympathetic and parasympathetic nerves are efferent, or motor, nerves traveling to and innervating peripheral structures such as the viscera, smooth muscle, and glandular tissues of the body. Typically, these two types of nerves have opposing functions, such as increasing heart rate (sympathetic) or decreasing heart rate (parasympathetic).

It is important to note that visceral, or afferent, sensory neurons accompany the nerve fibers of the autonomic division; however, they are not considered part of the autonomic nervous system. This visceral component provides feedback from the viscera and internal tissues of the body to the central nervous system. This system operates at a largely subconscious level and is essential for the maintenance of homeostasis. Functions include monitoring vascular pressure, chemosensation, and stretch. Visceral sensory neurons also convey information from nociceptors in visceral organs and tissues. However, these pain fibers are not perceived in the same way as somatic pain sensations and conscious perception of visceral pain is often diffuse or interpreted as referred pain (Sikandar and Dickenson, 2012).

Unlike the two-neuron pathways that mediate sympathetic and parasympathetic components of the autonomic division, the visceral part of the autonomic division is mediated by single neurons whose cell bodies are located in dorsal root ganglia, glossopharyngeal ganglia, or the inferior ganglion of the vagus nerve (Standring, 2016). Visceral axons travel through mixed plexuses and along spinal nerves, splanchnic nerves, or cranial nerves to reach the central nervous system. Thus, no named nerves or plexuses are strictly visceral in nature.