Ruby is 77 years old and can no longer control her urination. What changed in the reflex pathway that used to control her urination?
What will be an ideal response?
Micturition normally occurs when stretch receptors in the bladder wall are stimulated by distension due to the
accumulation of urine. The stretch receptors project to an integration center in the spinal cord, which stimulates
parasympathetic neurons of the bladder wall, which stimulates bladder contraction, forcing the internal urethral
sphincter to open. At the same time, the spinal control center inhibits somatic motor neurons that control the
external urethral sphincter, which relaxes in response, so that urine can flow out. The spinal reflex is normally
overridden by descending control from the brain stem and cerebral cortex. The brain inhibits the parasympathetic
output to the bladder and stimulates the somatic motor output to the external urethral sphincter, thus preventing
urination until a convenient time. It is likely that Ruby's descending control is what is no longer working properly;
thus she is not able to suppress the urge until she can get to a toilet.
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