An electrical signal that propagates along the membrane of a neuron or muscle fiber; a rapid change in membrane potential that involves a depolarization followed by a repolarization.

Correct Answer: A

Rationale: An action potential (AP) is the electrical signal (depolarization-repolarization) in neurons or muscles. Nerve and muscle action potentials are specific types, and synaptic potential is graded.

Correct Answer: D

Rationale: Wallerian degeneration is the breakdown of the axon and myelin distal to an injury in the PNS. Astrocytes are glia, motor neurons are cells, and action potentials are signals.

Correct Answer: C

Rationale: A reverberating circuit involves postsynaptic neurons feeding back to earlier neurons, creating sustained activity. Convergent and divergent describe synapse patterns, and parallel is not standard.

Correct Answer: B

Rationale: The somatic nervous system innervates voluntary skeletal muscles. Autonomic controls involuntary muscles/glands, CNS is brain/spinal cord, and enteric governs digestion.

Correct Answer: B

Rationale: Sensory receptors (e.g., olfactory receptors in the nose) detect chemical changes (odors). Enteric plexuses control digestion, cranial nerves transmit signals, and neuroglia support.