The internal arcuate fibers arise from the:

Correct Answer: A

Rationale: gracile and cuneate nuclei . Internal arcuate fibers are axons of second-order neurons in the gracile and cuneate nuclei (medulla) that curve medially, decussate, and form the medial lemniscus in the dorsal column pathway (proprioception, touch). Choice B (solitary nucleus) processtaste/visceral sensation, not touch. Choice C (accessory cuneate) is for unconscious proprioception to cerebellum. Choice D (nucleus dorsalis) is for spinocerebellar tracts. Thus, A correctly identifithe source, making it the right answer.

Correct Answer: D

Rationale: Contralateral loss of sensation occurs as a result of a hemisection above the level of the medulla . Both pathways anterolateral (pain/temperature, crossin spinal cord) and dorsal column-medial lemniscal (touch/proprioception, crossin medulla) ascend contralaterally above the medulla. A hemisection there disrupts crossed fibers, causing contralateral loss. Choice A is wrong (dorsal column decussatin medulla). Choice B is false (first synapse is spinal cord or medulla, not DRG). Choice C is incorrect (free nerve endings are spinothalamic, not dorsal column). Thus, D is true for both, making it correct.

Correct Answer: B

Rationale: Gracile . The posterior (dorsal) horn contains sensory nuclei: nucleus dorsalis (Clarkes, A) for spinocerebellar tracts, nucleus proprius for touch, and substantia gelatinosa for pain/temperature. The gracile nucleus is in the medulla, not the spinal cords posterior horn, processing dorsal column input. Thus, B is the exception, making it correct.

Correct Answer: D

Rationale: Medullary reticulospinal tracts is tonically active . The medullary reticulospinal tract inhibits extensors and is not tonically active (pontine reticulospinal is). Choice A is true (vestibulospinal supports antigravity). Choice B is correct (pontine is uncrossed). Choice C is accurate (rubrospinal is lateral). Thus, D misattributtonic activity, making it the wrong statement and the correct answer.

Correct Answer: A

Rationale: Lesions of this area alone produce more severe paralysis than destruction of primary motor area , which is false. The premotor area plans movements (C, D), receiving inputs , but its lesion causapraxia, not severe paralysis (primary motor areas role). Choice A overstatits impact, making it the exception and the correct answer.