Preganglionic parasympathetic neurons are in the brainstem and in lower levels of the spinal cord, and usually send long axons through cranial or spinal nerves to synapse in distant ganglia. Postganglionic parasympathetic neurons then usually send short axons to reach their target cells. Parasympathetic activation usually causes body responses appropriate for “rest and digest” activities, including diverting blood from skeletal muscle to the intestine (smooth muscle cells of blood vessels), decreasing cardiac output (cardiac muscle cells of the heart), and salivating (salivary gland cells). All of these changes allow for the conservation and storage of energy when there are no immediate threats to deal with.

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Level 3 Unit 2 Part 38: Urination, defecation, and genital function