The figure schematically illustrates the somatic (voluntary) and autonomic innervation of the urinary bladder. The autonomic nervous system facilitates both the filling and emptying of the bladder. As with other organs, the bladder is controlled by both sympathetic and parasympathetic efferents, which exert opposing actions. Although you may not have studied the physiology of the bladder in depth, you should already know all you will need to answer this question. For example, the effects and mechanisms of sympathetic neurotransmitters on bladder smooth muscle are the same as on vascular smooth muscle.
During early filling of the bladder, afferents carry information indicating the bladder walls are not stretched, and sympathetic efferent innervation of the internal sphincter is increased which causes contraction of the sphincter and holds the urine in the bladder. As the filling proceeds and the walls of the bladder stretch, an emptying reflex can be initiated in which parasympathetic efferents are activated, conveying information to contract the smooth muscle in the walls of the bladder (which increases the pressure inside and forces urine out through the sphincters and urethra.
Withdrawal of all autonomic and voluntary neural input to the bladder, as would occur in spinal shock, is characterized by:
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