Mechanism of normal Micturation at a glance

Urinary Bladder innervated by three types of neurons .Parasympathetic, sympathetic & Somatic. Parasympathetics derive from Sacral _{2, 3 & 4} via pelvic nerve &, sympathetic Derive from lumber_1,2  via hypogastric nerve .On the other hands Somatic nerve derive from Sacral_{2,3 & 4}  via pudendal nerve.

In general there is no effect of sensory nerve on micturation . Somatic nerve controls the external sphincter and Parasympathetic nerve control the internal sphincter. Parasympathetic nerve also causes contraction of Detrusore muscle of bladder.

When bladder fills with urine, it’s become distended and the stretch receptors presents in the wall of the bladder are stimulated. Afferent stimulation or impulses from the bladder wall reaches to the spinal cord centre via the pelvic & hypogastric nerve. Then the impulse reach in the sensory cortex of the brain via the lateral spinothalamic tract of thalamus and the person become aware about the fullness of bladder. Therefore the motor drive from the motor centre of the brain sends efferent impulse to the spinal cord center of micturation via descending autonomic fibers .After that impulse from spinal cord centre causes contraction of Detrusor muscle and relaxation of internal urethral sphincter by parasympathetic nerve (hypogastric).Micturation Reflex occurs. At the same time if person desire to micturate he / she voluntarery inhabit external urethral sphincter by somatic (pudendal) nerve and the Micturation is initiated.




Collected & Concise only for postgraduate student