The Parasympathetic Nervous System utilizes which neurotransmitter?
A.
Dopamine
B.
Acetylcholine
C.
Norepinephrine
D.
Epinephrine
The Correct Answer and Explanation is:
The correct answer is B. Acetylcholine.
Explanation:
The parasympathetic nervous system (PNS) is a branch of the autonomic nervous system responsible for promoting the “rest and digest” functions of the body. It helps conserve energy, reduce heart rate, and facilitate digestion, among other physiological activities. To accomplish this, the PNS primarily utilizes the neurotransmitter acetylcholine (ACh) at both its preganglionic and postganglionic synapses.
Acetylcholine in the Parasympathetic Nervous System:
- Preganglionic Neurons: The parasympathetic nervous system originates in the brainstem and sacral spinal cord. The first neuron in the pathway, known as the preganglionic neuron, releases acetylcholine to stimulate the postganglionic neuron. The receptors on these postganglionic neurons are nicotinic acetylcholine receptors, which are ionotropic and respond to acetylcholine.
- Postganglionic Neurons: Once the signal is relayed to the postganglionic neuron, it also releases acetylcholine to target tissues such as the heart, smooth muscles, and glands. These target tissues have muscarinic acetylcholine receptors, which are metabotropic (G-protein-coupled) and mediate the various effects of parasympathetic stimulation, such as lowering heart rate, increasing digestive secretions, and constricting pupils.
Contrast with Other Neurotransmitters:
- Dopamine (A): Dopamine is primarily involved in the central nervous system and the sympathetic nervous system for certain functions, but it is not the primary neurotransmitter of the parasympathetic system.
- Norepinephrine (C) and Epinephrine (D): These neurotransmitters are more closely associated with the sympathetic nervous system, which is responsible for the “fight or flight” response. Norepinephrine is the main neurotransmitter released by sympathetic postganglionic neurons, and epinephrine is secreted by the adrenal medulla in response to sympathetic activation.
Thus, acetylcholine is the key neurotransmitter responsible for carrying out parasympathetic functions, helping to maintain homeostasis and restore the body to a state of calm after stress.