Autonomic Reflexes Summary
The function of somatic reflexes, which have a single motor neuron, is to safely control skeletal muscle reflexes. The role of visceral reflexes (with two motor neurons) is to maintain a balance of function in the organ systems of the body. The two divisions of the autonomic system each play a role in affecting change, usually in competing directions, called dual innervation. The sympathetic system increases heart rate, whereas the parasympathetic system decreases heart rate. The sympathetic system dilates the pupil of the eye, whereas the parasympathetic system constricts the pupil. The competing inputs can contribute to the resting tone of the organ system. Heart rate is normally under parasympathetic tone, whereas blood pressure is normally under sympathetic tone. The heart rate is slowed by the autonomic system at rest, whereas blood vessels retain a slight constriction at rest.
