Spinal Cord Decussation and Contralateral Sensory Pathways

Steps:

• Identify injury location: Severing at X in cervical spinal cord disrupts ascending sensory tracts.
• Recall sensory pathway: Spinothalamic tract for pain/temperature decussates shortly after entering cord, carrying signals contralaterally.
• Determine affected side: If X is on left, it severs right-body sensory fibers crossing from right.
• Predict outcome: Results in contralateral (right-side) sensory loss below injury.

Why B is correct:

• Spinothalamic tract decussation in spinal cord means left-side injury blocks right-body sensation signals, per neuroanatomy principles.

Why the others are wrong:

• A: Sensory loss is contralateral, not ipsilateral to left injury.
• C: Motor (corticospinal) effects are ipsilateral; paralysis occurs on left, not right.
• D: Specifies "all" sensation, but dorsal columns (proprioception) ascend ipsilaterally before decussating in medulla, so not fully affected contralaterally.

Final answer: B