Reflex arc allows movement without conscious sensation

Steps:

• Pinprick activates sensory neuron, sending impulse to spinal cord.
• In spinal cord, sensory neuron synapses with motor neuron, triggering leg movement via reflex.
• Sensory impulse also travels via ascending pathway to brain for conscious feeling.
• Block at Z interrupts only the ascending pathway to brain, preserving reflex.

Why C is correct:

• Block at Z severs the sensory pathway to the brain after spinal reflex connection, allowing motor response but blocking pain perception.

Why the others are wrong:

• A: Block at X halts all sensory input, preventing both movement and sensation.
• B: Block at Y disrupts motor output, stopping leg movement while allowing sensation to reach brain.
• D: No block means full sensory and motor function, so both movement and feeling occur.

Final answer: C