Once the threshold potential is reached,

Correct Answer: C

Rationale: Reaching the threshold triggers rapid Na⁺ channel opening, making an action potential unavoidable due to the all-or-none principle.

Correct Answer: C

Rationale: Vertebrate brains are divided embryonically into forebrain, midbrain, and hindbrain, encompassing all regions like the cerebrum and cerebellum.

Correct Answer: A

Rationale: The limbic system, including the amygdala and hippocampus, governs emotions, learning, and memory.

Correct Answer: A

Rationale: The spinal cord is protected by bone (vertebrae), meninges, and cerebrospinal fluid (CSF), which cushions it; white and gray matter are internal structures.

Correct Answer: A

Rationale: An action potential, a rapid depolarization and repolarization, is the mechanism of nerve impulse propagation along axons.