Which of the following regions of white matter would NOT contain corticospinal fibers:

Correct Answer: D

Rationale: Anterior limb of the internal capsule . Corticospinal fibers, part of the pyramidal tract, originate in the motor cortex and descend through specific white matter regions to the spinal cord for voluntary movement control. Choice A, Pyramid of medulla oblongata, is incorrect because corticospinal fibers pass through the medullary pyramids, where most decussate to form the lateral corticospinal tract. Choice B, Posterior limb of the internal capsule, is wrong as this is a key region where corticospinal fibers travel between the cortex and brainstem, carrying motor signals. Choice C, Cerebral peduncle of the midbrain, is also incorrect since corticospinal fibers traverse the middle three-fifths of the pedunclen route to the pons. However, Choice D, Anterior limb of the internal capsule, donot contain corticospinal fibers; it primarily carrifrontopontine fibers (to the pons) and thalamocortical fibers, not motor tracts, which are confined to the posterior limb. Thus, Anterior limb of the internal capsule is the region that donot include corticospinal fibers, making D the correct answer.

Correct Answer: B

Rationale: In corticospinal tract hemisection of the right half of the spinal cord in the cervical region result in motor deficit in the left side of the body . This seems misaligned with standard anatomy: corticospinal fibers decussate in the medulla, so below this, a right cervical hemisection affects right-sided (ipsilateral) motor function. Above decussation, damage causcontralateral loss (making A wrong). Choice C is false (terminate in ventral horn). Choice D is incorrect (below decussation is ipsilateral). Assuming intent, B may reflect a higher lesions contralateral effect, but per options, its likely a miswording.

Correct Answer: B

Rationale: Destruction of corticospinal tract below the decussation result in contralateral paralysis . This is incorrect: below decussation, damage causipsilateral paralysis. Choice A is wrong (above is contralateral). Choice C is false (ventral horn). Choice D is incorrect (right hemisection is right deficit). Assuming intent, none match perfectly possible error.

Correct Answer: D

Rationale: Vestibulospinal tract . The corticospinal tract decussatin the medullary pyramids, with most fibers crossing to form the lateral corticospinal tract for contralateral voluntary movement. The corticonuclear tract also decussates, though partially, as fibers from the cortex to cranial nerve nuclei (e.g., 7, 12) cross to innervate contralateral lower facial musclor tongue, evident in facial palsy from stroke. The tectospinal tract decussatin the midbrain, originating from the superior colliculus to coordinate head movements toward stimuli (e.g., visual reflexes). However, the vestibulospinal tract donot decussate; it descends ipsilaterally from the vestibular nuclei in the brainstem to spinal motor neurons, facilitating posture and balance (e.g., antigravity muscles). This ipsilateral nature is critical, as unilateral vestibular lesions cause same-side extensor tone changes, unlike crossed tracts. Thus, D is the exception among these descending tracts, making it the correct answer.

Correct Answer: C

Rationale: Initiated voluntarily , which is false. The vomiting center is in the medulla oblongata (A is true), near the area postrema, coordinating the reflex. It receivvestibular input via cranial nerve 8 (B is true), causing motion sickness-related vomiting. Choice C is incorrect; vomiting is involuntary, unlike swallowings voluntary start, triggered by medullary signals (e.g., nausea reflex). It receivinput from circulating emetics (D is true) via the chemoreceptor trigger zone, responding to drugs or toxins. Brainstem lesions disrupt this reflex, not cortical control, confirming Cs inaccuracy. Thus, C is the exception, making it the correct answer.