For substances within the blood to reach the neurons within the brain, they must first pass through a cellular membrane derived in part from:

Correct Answer: C

Rationale: Astrocytes form part of the blood-brain barrier, with their end-feet surrounding capillaries, regulating substance passage. Schwann cells are in the PNS, microglia are immune cells, and neurolemma is PNS-specific.

Correct Answer: D

Rationale: A neuron consists of three main parts: the axon (A), which transmits signals away from the cell body; the cell body (B), which contains the nucleus and maintains the neuron; and dendrites (C), which receive signals. Since all listed options are parts of a neuron, 'all of the above' (D) is correct.

Correct Answer: A

Rationale: Medullary postural reflexes are controlled by the medulla oblongata and include the positive supporting reaction (A), which maintains stance against gravity. The placing reaction (B) is a midbrain reflex, the tonic neck reflex (C) involves medullary and spinal integration but is not exclusively medullary, and the stretch reflex (D) is a spinal reflex, not primarily medullary.

Correct Answer: C

Rationale: Optic nerve lesions cause unilateral blindness (not homonymous hemianopia, ruling out A), optic chiasm lesions cause bitemporal hemianopia (not unilateral blindness, ruling out B). Visual evoked potentials (C) test the visual pathway’s integrity, while D is vague and incomplete. C is correct.

Correct Answer: B

Rationale: Pain uses both myelinated (A-delta) and unmyelinated (C) fibers (not only myelinated, ruling out A). Perception occurs in the cortex (B, correct), referral is visceral to somatic (C is correct but less central), and cordotomy relief is temporary (not long-lasting, D). B is the most definitive.