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MCAT

Unit 4: Lesson 1

Foundations of behavior passages

Spinal nerves and Guillain-Barre syndrome

Problem

Unlike many better-known nervous system disorders, Guillain-Barre syndrome (GBS) is a polyneuropathy that affects only the peripheral nervous system (PNS). GBS is an autoimmune disease, most often triggered by a specific bacterial infection whose surface proteins mimic the cell surface molecules of the nervous system. This tricks the immune system into attacking host cells in addition to the bacteria. Patients present with progressive weakness or numbness in their limbs, and symptoms often progress very quickly. Left untreated, GBS can lead to paralysis or death.
The PNS is composed of the nerves and ganglia found outside the brain and spinal cord. It is the PNS that innervates the body and transmits messages to and from the brain. The point of contact between the PNS and the central nervous system (CNS) is the spinal cord from which exit the spinal nerves (Figure 1).
There are two major nerve classifications – somatic or visceral, and afferent or efferent. The word “somatic” shares a root with the word “soma”, which means cell bodies. Somatic refers to nerves that go to the body wall and limbs. “Visceral” is the terms used for nerves that innervate the organs, or viscera.
Afferent nerves bring signals from the body to the CNS. These nerves connect to the spinal cord at the dorsal root. Efferent nerves, on the other hand, send signals from the CNS to the rest of the body. They exit the spinal column at the ventral root, and meet with the afferent nerves to create a spinal nerve.
Figure 1. Spinal nerve. Attribution: adapted from Tristanb, CC-BY-SA 3.0.
Which of the following signals would be transmitted through a visceral efferent nerve?
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