Neural Control of Micturition

• The external urethral sphincter is under voluntary (somatic) control, and muscle fiber contraction causes closure of the sphincter.
• Activation of S2-S4 α-motor neurons causing contraction of the external urethral sphincter striated muscle fibers

• A full bladder sends afferent signals causing inhibition of sympathetic tone and an increase in parasympathetic activity to the bladder through the pelvic splanchnic nerves.
• The parasympathetic activity relaxes the internal urethral sphincter and induces bladder contraction.