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 travel through the posterior limb of the internal capsule, not anterior (frontopontine fibers). Choice A (medulla pyramid), B (lateral column), and C (cerebral peduncle) all contain corticospinal fibers. Thus, D is the exception, making it correct.

Correct Answer: A

Rationale: Destruction of corticospinal tract below the decussation result in contralateral paralysis . This seems incorrect per standard anatomy, but lets clarify: corticospinal fibers decussate in the medulla. Below this (spinal cord), most are contralateral, so right-sided damage causright-sided (ipsilateral) paralysis, not contralateral, suggesting a question error. Choice B is wrong (above decussation causcontralateral loss). Choice C is incorrect (right hemisection causright deficit). Choice D is false (terminate in ventral horn). Assuming intent, A might be misworded; standard texts favor ipsilateral below decussation. Still, per options, A is closest if misinterpreted.

Correct Answer: D

Rationale: Vestibulospinal tract . The corticospinal tract , corticonuclear tract , and corticoreticular tract originate from the cerebral cortex (motor areas) and project to spinal cord, cranial nerve nuclei, and reticular formation, respectively, for voluntary control. The vestibulospinal tract, however, arisfrom the vestibular nuclei in the brainstem, not the cortex, to regulate posture and balance ipsilaterally. This distinction is clear in its role (e.g., standing) versus cortical tracts voluntary functions. Thus, D is the exception.

Correct Answer: A

Rationale: Damage to corticospinal tract above the level of decussation results in ipsilateral paralysis . This is incorrect: above decussation, damage causcontralateral paralysis. Choice B is wrong (below is ipsilateral). Choice C is false (ventral horn). Choice D is incorrect (right hemisection is right deficit). Assuming intent for contralateral, A is misworded error likely.

Correct Answer: C

Rationale: Rubrospinal tract . The corticospinal tract originatfrom the primary motor cortex (precentral gyrus), descending through the brainstem and spinal cord for voluntary movement control, such as hand dexterity. The corticonuclear tract also arisfrom the cortex, targeting cranial nerve nuclei (e.g., 5, 7, 10) for facial or tongue movements, with partial decussation. The corticoreticular tract begins in the cortex, projecting to the reticular formation in the brainstem to modulate posture and locomotion. In contrast, the rubrospinal tract originatfrom the red nucleus in the midbrain, not the cortex, and decussatto influence flexor tone, especially in the upper limbs. This midbrain origin distinguishit from the cortical tracts, as seen in its role in cerebellar-motor coordination rather than direct cortical control. Thus, C is the exception, making it the correct answer.