The Visceral Receptors The fourth subsystem, which provides the deepest level of interoception, derives from our viscera and blood vessels. In Chapter 6 I described the vagus nerve, which connects the brain stem to most of our internal organs. This massive nerve is second only to the spinal cord in total number of neurons. Over 90% of these nerve fibers are afferent: that is, the vagus nerve’s main function is to relay information from our guts upward to our brains.
