Which of the following neurotransmitter is most associated with sympathetic nervous system activity
The correct answer and explanation is:
The neurotransmitter most associated with sympathetic nervous system activity is norepinephrine (also called noradrenaline).
Explanation:
The sympathetic nervous system (SNS) is part of the autonomic nervous system, responsible for the “fight or flight” response during stressful or emergency situations. When the SNS is activated, it prepares the body to respond quickly by increasing heart rate, dilating pupils, redirecting blood flow to muscles, and releasing energy stores.
Key neurotransmitters in the SNS:
- Norepinephrine (NE): This is the primary neurotransmitter released by the postganglionic sympathetic neurons at the target organs. When an action potential reaches these neurons, norepinephrine is released into the synaptic cleft, where it binds to adrenergic receptors (alpha and beta receptors) on the target tissues to exert its effects such as increasing heart rate, constricting blood vessels, and relaxing airway muscles.
- Acetylcholine (ACh): While acetylcholine is the main neurotransmitter for parasympathetic postganglionic neurons, in the sympathetic system, it is released only by the preganglionic neurons at the synapse with the postganglionic neurons (in the sympathetic ganglia).
- Epinephrine (adrenaline): This is mainly released by the adrenal medulla into the bloodstream during sympathetic activation, acting as a hormone that complements norepinephrine’s effects systemically.
Why norepinephrine?
- It directly mediates the majority of sympathetic nervous system effects at the target organs.
- It binds to adrenergic receptors to modulate vascular tone, heart function, and other physiological responses typical of sympathetic activation.
- Its action is localized to synapses between postganglionic sympathetic neurons and their effector cells.
In summary, norepinephrine is the principal neurotransmitter associated with sympathetic nervous system activity because it is the main chemical messenger released by sympathetic postganglionic neurons that activates adrenergic receptors, triggering the classic “fight or flight” responses in the body.