In fight or flight conditions, the pupil of the eye dilates. The motor impulse that is initiated in the hypothalamus and ultimately causthis pupillary dilation can be best described by which of the following statements:

Correct Answer: D

Rationale: The impulse will pass through the ventral root of a spinal nerve . In the fight or flight response, the sympathetic nervous system, activated by the hypothalamus, causpupil dilation via the dilator pupillae muscle. The pathway involvpreganglionic neurons from the thoracic spinal cord (T1-T2) exiting through the ventral root, synapsing in the superior cervical ganglion, and then postganglionic fibers traveling via the oculomotor nerve (III) pathway. Choice A is incorrect because this is an autonomic response, not involving somatic upper and lower motor neurons. Choice B is wrong as ganglia (superior cervical) are involved. Choice C is incorrect because the synapse occurs in the spinal cord or ganglion, not brainstem autonomic nuclei. Thus, D correctly identifithe ventral root as part of the sympathetic outflow, making it the right answer.

Correct Answer: C

Rationale: A delta fibers . Fast pain, which is sharp and well-localized, is transmitted by A delta fibers, which are small, myelinated axons with rapid conduction (5-30 m/s). They respond to mechanical and thermal stimuli, quickly signaling acute pain. Choice A, A alpha fibers, is incorrect as these large, myelinated fibers transmit proprioception and motor signals, not pain. Choice B, A beta fibers, is wrong because they carry touch and pressure sensations, not pain. Choice D, C fibers, transmits slow, dull, poorly localized pain, not fast pain. Thus, A delta fibers are specifically responsible for fast pain sensation, making C the correct answer.

Correct Answer: A

Rationale: If the disc between L4 / L5 is herniated sensory changwill likely occur at the medial border of leg , which is false. An L4-L5 disc herniation typically affects the L5 nerve root, causing sensory changin the anterolateral leg and dorsum of the foot, not the medial leg (L4 dermatome). Choice B is true (S1 tests tiptoe standing via gastrocnemius). Choice C is correct (L4 compression affects knee jerk). Choice D is accurate (S1 compression weakens gastrocnemius). Thus, A misattributsensory changes, making it the exception and the correct answer.

Correct Answer: B

Rationale: Substantia gelatinosa of spinal cord . The lateral spinothalamic tracts second-order neurons are in the substantia gelatinosa (Rexed lamina II) of the spinal cords dorsal horn, where first-order neurons from dorsal root ganglia synapse after crossing via the anterior white commissure. Choice A (thalamus) is the third-order neuron site (VPL). Choice C (dorsal root ganglia) is first-order. Choice D (medulla) is unrelated to this tracts second-order site. Thus, B correctly identifithe location, making it the right answer.

Correct Answer: D

Rationale: Dorsal root ganglia, brain stem, diencephalon . In the dorsal column-medial lemniscal pathway: first-order neuron cell bodiare in the dorsal root ganglia (DRG), sensing stimuli; second-order are in the medulla (brainstem, nucleus gracilis/cuneatus), where they decussate; third-order are in the thalamus (diencephalon, VPL), relaying to cortex. Choice A misplacfirst-order (dorsal column is axons). Choice B usvague terms (hindbrain/forebrain). Choice C misnamregions. Thus, D accurately locatthe neurons, making it correct.