Neural Control of Micturition

• 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.

• 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
  • Allows for the voluntary retention of urine once a full bladder has induced an increase in bladder parasympathetic tone

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  Autonomic (sympathetic and parasympathetic) and somatic innervation of the lower urinary tract. ACh, Acetylcholine.

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  Parasympathetic innervation of the bladder.

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  Sympathetic innervation of the bladder.

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  Pudendal innervation of the urethra and pelvic floor.