Which structure is associated with the embryologic development of the peripheral nervous system?

Correct Answer: A

Rationale: The neural crest (A) gives rise to the peripheral nervous system (PNS), including sensory and autonomic ganglia. The neuraxis (B) is the central nervous system (CNS) axis, rhombencephalon (C) forms brainstem and cerebellum (CNS), and neural tube (D) forms the CNS. A is correct.

Correct Answer: A

Rationale: The peripheral nervous system (PNS) controls peripheral structures. The trigeminal ganglion (A) is a sensory relay, not directly controlled by PNS motor output. Gastric plexus (B), sympathetic chain (C), and cervical plexus (D) are PNS autonomic/somatic effectors. A is the least directly controlled.

Correct Answer: B

Rationale: The soma, or cell body, of a neuron contains the nucleus, which houses the cell’s genetic material. Dendrites receive signals, axons transmit them, and the synaptic end bulb releases neurotransmitters, but only the soma contains the nucleus.

Correct Answer: B

Rationale: Upper motor neurons (UMNs) in the CNS target lower motor neurons (LMNs) in the spinal cord or brainstem, which then innervate skeletal muscles. UMNs don’t directly target muscles or other brain regions like the cortex or thalamus.

Correct Answer: B

Rationale: From a resting potential of -70 mV, the membrane must depolarize to the threshold (around -55 mV), a change of about +15 mV, to trigger an action potential via summation.