Question

The external urethral sphincter of the urinary bladder is under the voluntary control of the perineal branch of which nerve?

a) Femoral nerve
b) Pudendal nerve
c) Sciatic nerve
d) Obturator nerve

Answer 1

The perineal branch of the pudendal nerve controls the external urethral sphincter, allowing for voluntary urination. It emerges from the S2-S4 nerves of the sacral plexus in the sacral region of the spinal cord.

Step-by-step explanation:

The external urethral sphincter, which allows for voluntary urination, is controlled by the pudendal nerve. This nerve comes from the sacral region of the spinal cord, through the S2-S4 nerves of the sacral plexus, and gives voluntary control of the external urethral sphincter through its perineal branch. The pudendal nerve's role is crucial because, without an intact spinal cord and a functional pudendal nerve, voluntary micturition would not be possible. As the bladder fills, this voluntary control allows the sphincter to maintain contraction and ensure continence. When urination is initiated, somatic motor neurons that innervate the sphincter must be inhibited to allow the sphincter to relax and for urination to occur.