If the knee jerk is lost, which of the following roots is most likely affected:

Correct Answer: B

Rationale: L4 . The knee jerk reflex (patellar reflex) tests the integrity of the L3-L4 nerve roots, primarily L4, via the femoral nerve, which innervatthe quadriceps femoris. Loss of this reflex indicatL4 root dysfunction, often due to disc herniation (e.g., L3-L4). Choice A, L3, contributbut is less dominant than L4. Choice C, S1, affects ankle jerk and plantar flexion, not knee jerk. Choice D, S2, is unrelated (e.g., affects plantar muscles). Thus, L4 is the most likely affected root, making B the correct answer.

Correct Answer: B

Rationale: Fasciculus cuneatus transmits information coming from areas inferior to T6 . The fasciculus cuneatus carriproprioception, vibration, and fine touch from the upper body (above T6), while the fasciculus gracilis handlbelow T6. Choice A is true (faster myelinated fibers). Choice C is correct (ipsilateral loss below lesion). Choice D is accurate (excludfree nerve endings, used by spinothalamic). Thus, B misattributcuneatus function, making it the wrong statement and the correct answer.

Correct Answer: C

Rationale: It is concerned with proprioception (muscle-joint sense) . The medial lemniscus, formed by decussating fibers from the nucleus gracilis and cuneatus in the medulla, carriproprioception, vibration, and fine touch to the thalamus (VPL), then cortex. Choice A is wrong (begins in medulla, not spinal cord). Choice B is false (spinothalamic tracts are separate). Choice D is incorrect (ends in thalamus, not cortex directly). Thus, C accurately describits role, making it correct.

Correct Answer: D

Rationale: Spinotectal. The spinotectal tract carriafferent sensory information (e.g., pain, touch) from the spinal cord to the tectum (superior colliculus) in the midbrain, contributing to spinovisual reflexlike head/eye turning toward stimuli. Choice A (anterior spinothalamic) is for crude touch to thalamus. Choice B (lateral spinothalamic) is for pain/temperature. Choice C (posterior spinocerebellar) is for unconscious proprioception to cerebellum. Thus, D correctly identifithe spinotectal tracts role, making it the right answer.

Correct Answer: B

Rationale: Massage applied to the skin over a painful joint may reduce pain sensitivity . The gate control theory posits that non-painful input (e.g., touch via large A-beta fibers) can inhibit pain signals (A-delta, C fibers) at the spinal cords dorsal horn via interneurons, reducing pain perception. Massage activatA-beta fibers, supporting this. Choice A is wrong (small fibers transmit pain). Choice C is incorrect (A-delta/C fibers increase pain). Choice D is false (large fiber loss increaspain). Thus, B aligns with the theory, making it correct.