Which one of the following is the correct sequence of events that follows a threshold potential: 1. the membrane becomes depolarized, 2. sodium channels open and sodium ions diffuse inward, 3. the membrane becomes repolarized, 4. potassium channels open and potassium ions diffuse outward while sodium is actively transported out of the cell

Correct Answer: B

Rationale: The sequence is: Na⁺ channels open (2), depolarization occurs (1), K⁺ channels open and Na⁺ is pumped out (4), repolarization follows (3).

Correct Answer: A

Rationale: Accommodation adjusts the lens shape via ciliary muscles to focus light on the retina for near or far objects.

Correct Answer: C

Rationale: The optic disk, where the optic nerve exits, lacks photoreceptors, creating a blind spot.

Correct Answer: B

Rationale: Outer hair cells amplify sound; their loss reduces cochlear sensitivity, impairing hearing but not causing total deafness (inner hair cells remain).

Correct Answer: D

Rationale: Henry Head proposed separate epicritic (touch) and protopathic (pain) pathways, influencing sensory neuroscience.