The chemical messenger between neurons or a neuron and its target muscle is:

Correct Answer: C

Rationale: Neurotransmitters are chemicals released into the synapse to transmit signals from one neuron to another or to a target muscle.

Correct Answer: A

Rationale: Parkinson’s disease results from dopamine loss in the substantia nigra, impairing motor control and causing tremors and rigidity.

Correct Answer: A

Rationale: The sympathetic system triggers 'fight or flight,' releasing glucose from the liver for energy, unlike parasympathetic relaxation effects.

Correct Answer: C

Rationale: fMRI detects brain activity via blood oxygen level-dependent (BOLD) signals, reflecting neural activation.

Correct Answer: C

Rationale: Three layers of meninges (dura mater, arachnoid mater, pia mater) surround and protect the brain and spinal cord.