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Anatomy · Neuroanatomy: neurogenic bladder after cord injury
Sample itemA man with a cervical cord injury regains reflex bladder emptying, but the detrusor and the external sphincter contract at the same time, leaving a large residual volume. What explains this dyssynergia?
Original practice item, not a recalled exam question. Nothing here is recorded.
The answer and the reasoning
C. Cord lesion interrupts pathways from the pontine micturition centre to the sacral cord
The pontine micturition centre coordinates detrusor contraction with sphincter relaxation through descending fibres to the sacral cord. A suprasacral lesion leaves the sacral reflex arc intact but removes this coordination, giving detrusor-sphincter dyssynergia.
Option by option
A. Destruction of the sacral parasympathetic nucleus
Sacral nucleus destruction would give an areflexic, flaccid bladder with overflow.
B. Injury to the pudendal nerve
Pudendal injury paralyses the external sphincter, causing incontinence rather than simultaneous contraction.
C. Cord lesion interrupts pathways from the pontine micturition centre to the sacral cord (correct)
Correct. Loss of pontine coordination while the sacral reflex remains produces detrusor-sphincter dyssynergia.
D. Damage to the hypogastric plexus
Hypogastric plexus injury impairs sympathetic storage and bladder neck closure, not this dyssynergia.
Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.
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