Reflex arc allows movement without conscious sensation to brain

Steps:

• Pinprick stimulates sensory receptors, sending signals via afferent neurons to spinal cord for reflex.
• Reflex arc in spinal cord triggers motor neurons for leg movement without brain involvement.
• Conscious feeling requires sensory signals to ascend to brain via specific tracts.
• Drug block at Z interrupts ascending sensory tract post-reflex, preserving movement but blocking sensation.

Why C is correct:

• Block at Z severs ascending sensory pathway to brain (per spinal cord anatomy), allowing spinal reflex movement but preventing pain perception.

Why the others are wrong:

• A: Block at X halts all sensory input, preventing both movement and feeling.
• B: Block at Y disrupts spinal reflex synapse, stopping movement while allowing some sensation.
• D: No block permits both reflex movement and conscious feeling.

Final answer: C