Which primary vesicle of the embryonic nervous system does not differentiate into more vesicles at the secondary stage?

Correct Answer: B

Rationale: The embryonic brain forms three primary vesicles: prosencephalon, mesencephalon, and rhombencephalon. The prosencephalon divides into telencephalon and diencephalon, and the rhombencephalon into metencephalon and myelencephalon. The mesencephalon (B) remains undivided as the midbrain. B is correct.

Correct Answer: D

Rationale: The trigeminal ganglion (D) (cranial nerve V) relays cutaneous sensations from the face. Otic (A) is autonomic (salivary), vestibular (B) is balance, and geniculate (C) is taste/facial. D is correct.

Correct Answer: B

Rationale: The autonomic nervous system regulates involuntary functions like heart rate and sweating, which increase during exercise. The somatic system controls voluntary movements, the enteric system governs digestion, and the central nervous system (CNS) includes the brain and spinal cord but isn’t a functional division in this context.

Correct Answer: D

Rationale: The cerebral cortex is responsible for the highest level of sensory integration, processing, and decision-making, such as interpreting shower temperature and deciding to adjust it. The thalamus relays signals, the spinal cord handles reflexes, and skeletal muscle executes commands.

Correct Answer: C

Rationale: During the relative refractory period, the membrane is hyperpolarized (more negative than resting potential, -70 mV) due to potassium efflux, but recovering. -45 mV is plausible, as it’s below threshold (-55 mV) but above full hyperpolarization.