What is the micturition reflex?
The act of voiding is controlled by a delicate balance between reflexive actions and cortical control.
Bilateral projections originating from cortical (frontal) and pontine micturition centers descend in the spinal cord just medial to the corticospinal tracts and synapse with preganglionic parasympathetic neurons in the S2, S3, and S4 regions.
These fibers then travel out the ventral roots of S2, S3, and S4 to synapse at postganglionic parasympathetic ganglia near the bladder to innervate the detrusor muscle.
Muscle spindles located in the detrusor muscle are stretched when the bladder is filled, increasing their firing rate.
This signal change increases the firing rate of the preganglionic parasympathetic fibers of S2, S3, and S4, resulting in detrusor muscle contraction, and thus voiding of the bladder.
This reflex is normally under the voluntary control of descending inputs from the cortex.
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