How much of a change in the membrane potential is necessary for the summation of postsynaptic potentials to result in an action potential being generated?

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.

Correct Answer: D

Rationale: The circle of Willis, an arterial ring at the brain’s base, encircles the pituitary stalk (infundibulum), providing blood to the brain. The cavernous sinus, pineal gland, and aqueduct are not within its structure.

Correct Answer: A

Rationale: C7 supplies the index finger dermatome. The axial line separates C5/C6 (anterior/posterior), T4 is at the nipple, and T10 supplies the umbilicus.

Correct Answer: C

Rationale: The thorax/abdomen is innervated segmentally by anterior rami of T1-L1. Above the 2nd rib is C2-C4 (supraclavicular nerves), deficits require multiple segments due to overlap, and T10 supplies the umbilicus.

Correct Answer: B

Rationale: The great auricular nerve (C2-C3, cervical plexus) supplies the ear, not CN V. Supraorbital (V1), mental (V3), and lacrimal (V1) are trigeminal branches.