Which neurotransmitter is primarily responsible for the 'fight or flight' response, mediating increased heart rate, bronchodilation, and vasoconstriction in certain vascular beds?

✓ Correct Answer: Option C

Norepinephrine is the primary neurotransmitter of the sympathetic nervous system, mediating the 'fight or flight' response. It acts on adrenergic receptors to increase heart rate, dilate bronchi, and modify blood flow.