In this module, we will consider how sympathetic innervation reaches various structures and regions within the body, and we will look at the general scheme of the parasympathetic nervous system.

Postsynaptic sympathetic fibers need to reach the neck, body wall and limbs to provide sympathetic innervation to the peripheral blood vessels, arrector pili muscles, and sweat glands in these areas. Remember that the sympathetic nervous system acts to constrict peripheral blood vessels, increase secretion from sweat glands and contract the arrector pili muscles. These are all responses that promote survival in times of distress.

To reach these structures in the neck, body wall and limbs, postsynaptic fibers exit the sympathetic trunk via gray rami communicantes, then enter the spinal nerves to be passed to the ventral primary rami and dorsal primary rami for distribution to the periphery.