The dorsal root of a spinal nerve primarily contains:

Correct Answer: A

Rationale: Dorsal roots carry sensory (afferent) fibers to the CNS.

Correct Answer: B

Rationale: Glutamic acid (glutamate) is the primary excitatory neurotransmitter in the CNS. Leucine, lysine, and valine are not neurotransmitters.

Correct Answer: C

Rationale: Tetrodotoxin (from pufferfish) blocks voltage-gated Na+ channels, halting action potentials. Strychnine blocks glycine, neostigmine inhibits acetylcholinesterase, curare blocks nicotinic receptors.

Correct Answer: B

Rationale: The dorsal root ganglion (DRG) houses the cell bodies of sensory neurons, adjacent to the spinal cord. The dorsal gray horn processes sensory signals, the spinal cord is a broader structure, and the brain is not the site for sensory neuron cell bodies.

Correct Answer: B

Rationale: The pia mater is the innermost meningeal layer, adhering closely to the brain and spinal cord. The arachnoid mater is the middle layer, dura mater the outermost, and tentorium cerebelli is a dura extension.