A nerve fiber obeys an all-or-none law insofar as it either fires or does not fire depending on whether the stimulus is above a threshold.

Correct Answer: A

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: A

Rationale: A neuron consists of three basic parts: the cell body, dendrites, and axon. The axon is a long, slender projection that transmits nerve impulses away from the cell body to other neurons or target cells. Myelin is a protective sheath around some axons, the pons is a part of the brainstem, and the dura mater is a meningeal layer. Therefore, axon is the correct answer as it is one of the fundamental components of a neuron.

Correct Answer: C

Rationale: Neurotransmitters are chemical substances released at axonal endings to propagate nervous impulses across synapses. Ions and the sodium-potassium pump are involved in generating action potentials, while nerve glue and action potentials are not substances released at axonal endings. Thus, C is the correct answer.

Correct Answer: A

Rationale: The sympathetic nervous system prepares the body for 'fight-or-flight' responses during threatening situations by increasing heart rate, dilating pupils, and redirecting blood flow. The parasympathetic nervous system has the opposite effect, while the cerebrum, somatic nervous system, and afferent nervous system are not primarily responsible for this response. Thus, A is the correct answer.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.