Describe the micturition reflex. What is the name of the muscle that contracts as part of the micturition reflex? What is the name of the involuntary urethral sphincter? What is the name of the voluntary urethral sphincter?
The Correct Answer and Explanation is:
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Correct Answer:
The micturition reflex is a spinal reflex that controls the process of urination. The detrusor muscle contracts as part of the micturition reflex. The internal urethral sphincter is the involuntary sphincter, while the external urethral sphincter is the voluntary one.
Explanation
Micturition, commonly known as urination, is the process by which urine is expelled from the bladder. This process is regulated by a complex reflex known as the micturition reflex, which involves the coordination of the nervous system and the muscles of the urinary tract. The bladder stores urine until stretch receptors in its walls are activated due to increased urine volume. Once the bladder reaches a certain threshold, these stretch receptors send signals to the spinal cord, particularly to the sacral region.
In response, parasympathetic nerve fibers trigger the contraction of the detrusor muscle, a smooth muscle that forms the bladder wall. This contraction increases bladder pressure and encourages urine flow. Simultaneously, the internal urethral sphincter, composed of smooth muscle and located at the junction of the bladder and urethra, relaxes involuntarily to allow urine to pass into the urethra.
To prevent premature urination, the external urethral sphincter, made of skeletal muscle and under voluntary control, remains contracted. This sphincter is controlled by the pudendal nerve and allows conscious regulation of urination. When appropriate, the brain sends signals to relax this voluntary sphincter, completing the process of micturition.
In infants or individuals with spinal cord injuries, the reflex operates without voluntary control. In healthy adults, higher brain centers, such as the pons and cerebral cortex, can inhibit or facilitate the reflex, allowing urination to be postponed or initiated at will. This integration of autonomic and somatic control ensures that urination occurs at socially acceptable times and places, maintaining homeostasis and hygiene.
