Which structure is NOT involved in conveyance of the stimulus from the posterior tibial nerve to the cerebral cortex during somatosensory evoked potential monitoring?

Which structure is NOT involved in conveyance of the stimulus from the posterior tibial nerve to the cerebral cortex during somatosensory evoked potential monitoring?

• A. Corticospinal tract
• B. Medial lemniscus
• C. Brain stem
• D. Internal capsule

Answer: (A)

The somatosensory evoked potential pathway carries sensory information from the posterior tibial nerve along the dorsal column–medial lemniscus route up to the cortex. After entering the spinal cord via the dorsal roots, the signal climbs in the dorsal columns to the medulla, decussates as it becomes the medial lemniscus, then travels to the thalamus (VPL) and finally to the primary somatosensory cortex through the internal capsule. The corticospinal tract is a motor pathway from cortex to spinal cord and does not convey sensory information to the cortex, so it is not part of the afferent conduction for SSEP. Thus the structure not involved is the corticospinal tract. The brainstem, internal capsule, and medial lemniscus are all integral components of the ascending sensory pathway.

The somatosensory evoked potential pathway carries sensory information from the posterior tibial nerve along the dorsal column–medial lemniscus route up to the cortex. After entering the spinal cord via the dorsal roots, the signal climbs in the dorsal columns to the medulla, decussates as it becomes the medial lemniscus, then travels to the thalamus (VPL) and finally to the primary somatosensory cortex through the internal capsule. The corticospinal tract is a motor pathway from cortex to spinal cord and does not convey sensory information to the cortex, so it is not part of the afferent conduction for SSEP. Thus the structure not involved is the corticospinal tract. The brainstem, internal capsule, and medial lemniscus are all integral components of the ascending sensory pathway.