Micturition, or the process of urination, is a complex body function. It require
ID: 3522738 • Letter: M
Question
Micturition, or the process of urination, is a complex body function. It requires control and integration of both voluntary and involuntary nervous system components. The process of voiding urine begins if the voluntary relaxation of this muscle, ________________, occurs.
internal sphincter muscle of the bladder
urethra
external sphincter muscle of the bladder
emptying reflex muscle
a.internal sphincter muscle of the bladder
b.urethra
c.external sphincter muscle of the bladder
d.emptying reflex muscle
Explanation / Answer
Micturition is a regulated voluntary physiological action of release of urine from bladder. In infant and elderly people, however this process is involuntary. Urinary bladder and urethra are the two main organs associated with this process. Micturition has two specific phases:
The whole process is controlled by central and peripheral nervous system and conducted by muscles contraction and relaxation. The bladder is constructed of detrusor (smooth muscle system) which is linned with both Sympathetic and Parasympathetic nervous system from lumbar spinal cord and sacral spinal cord respectively. Upper part of the Urethra is encircled by internal urethral sphincter and the lower portion is enclosed by external urethral sphincter muscle.The external sphincter is controlled by Somatic Pudendal nerve fibre coming from sacral cord. The most important nerve of bladder is the Pelvic Nerve fibre (parasympathetic nerve) and Hypogastric nerve fibre (sympathetic nerve).
When the bladdder is empty the afferent stimulus from bladder is at minimal. In this relaxed state the bladder starts to filled up. The detrusor muscle of bladder remains relaxed to allow more urine to be filled; at the same time the sphincter muscles are excited which prevents urine to flow out. The afferent signal runs through the spinal cord and to the pontine micturition center of the central nervous system. The CNS prevents the urge to urinate during this filling stage.
Once the bladder is saturated, the afferent stimulations are at maximal which creates the urge to urinate. When the voluntary signal of emptying the bladder initiates it creates the Micturition reflex, begining of the voiding stage. Neurons of Pontine micturition center of CNS gives strong signal through the pelvic nerve which causes bladder muscles to contract. At the same time pontine micturition also inhibits Onuf's nucleus (located at sacral spinal cord, prevents relaxation of sphincter muscles) so that external sphincter muscle can relax and let urine flow out. During this, micturinition reflex creates waves of contraction to bladder muscle until the bladder is empty. When urination is complete the relax stage begins again.
So in conclusion the answer is C. external sphincter muscle of the bladder; relaxation of which initiates the voiding of bladder.