Question

when the urinary bladder fills to about 250 ml with urine,
__________ send sensory nerve signals to the
__________ .

motor nerve signals from the ________ and ________
regions of the spinal cord cause the urinary bladder to contract and
the __________ to relax so that urination is possible

Explanation:

First Blank (Sensory Signals):

When the urinary bladder fills, stretch receptors in the bladder wall detect the stretch (due to urine accumulation) and send sensory nerve signals. The target of these sensory signals in the reflex arc (for micturition) is the spinal cord (specifically the sacral region initially, but the first part of the pathway is stretch receptors sending to spinal cord).

Second Blank (Sensory Target):

Stretch receptors send signals to the spinal cord (the sacral spinal cord, but the general structure here is spinal cord as the integration center for the reflex).

Motor Nerve Signals Blanks:

• The sacral region of the spinal cord is involved in the micturition reflex for bladder contraction. The lumbar region can also be involved in motor control, and the sphincters (specifically the internal urethral sphincter, controlled by autonomic nerves, and external by somatic, but in the reflex, the signals from sacral and lumbar (for some aspects) cause bladder contraction and sphincter relaxation. So motor signals from sacral and lumbar regions of the spinal cord cause the bladder to contract and the sphincters (or specifically the internal sphincter, but the option is sphincters) to relax.

Filling the Blanks:

1. First sentence: "When the urinary bladder fills to about 250 ml with urine, stretch receptors send sensory nerve signals to the spinal cord."
2. Second sentence: "Motor nerve signals from the sacral and lumbar regions of the spinal cord cause the urinary bladder to contract and the sphincters to relax so that urination is possible." (Note: The brain is involved in voluntary control, but the reflex is spinal - mediated initially, with sacral and lumbar for motor output to bladder and sphincters.)

Answer:

First sentence blanks: stretch receptors; spinal cord
Second sentence blanks: sacral; lumbar; sphincters

(Note: The options are used as per the blue boxes: stretch receptors, spinal cord, sacral, lumbar, sphincters fit the physiological micturition reflex pathway. The cervical is related to neck, brain is for higher control (not primary in the reflex arc's motor output for contraction/relaxation here), so the correct fills are as above.)