Describe micturition in an adult and baby. Include the following in your answer : parasympathetic neurons, external urethral sphincter, and internal urethral sphincter
What will be an ideal response?
When the bladder begins to fill with urine, stretch receptors in the bladder's wall initiate nerve impulses that travel to the spinal cord and then back to the bladder through parasympathetic neurons. As a result, the bladder contracts and mechanically opens the internal urethral sphincter. In addition, some of the impulses from the stretch receptors inhibit the motor neurons that normally keep the external urethral sphincter contracted. As a result, the external sphincter relaxes and micturition occurs. Adults have a perception of bladder fullness, however, before the external sphincter reflexively relaxes, warning that micturition is approaching. This allows the person to keep the external sphincter closed voluntarily until an appropriate time for micturition is possible. In babies, as soon as the bladder fills enough to trigger the reflex, micturition occurs.
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