Which receptor paring below is correct?
a) nicotinic: norepinephrine
b) nicotinic; acetylchline
c) muscarinic: norepinephrine
d) alpha 1: acetylcholine
The Correct Answer and Explanation is:
The correct answer is b) nicotinic; acetylcholine.
Explanation:
The autonomic nervous system (ANS) regulates involuntary body functions through the use of neurotransmitters and receptors. Different types of receptors interact with specific neurotransmitters to produce various physiological effects.
1. Nicotinic Receptors:
Nicotinic receptors are a subtype of acetylcholine (ACh) receptors. They are found in both the somatic nervous system and the autonomic nervous system.
- In the somatic nervous system, nicotinic receptors are located on skeletal muscle cells, and when ACh binds to these receptors, it triggers muscle contraction.
- In the autonomic nervous system, nicotinic receptors are present in the ganglia (where pre- and post-ganglionic neurons communicate) and on cells of the adrenal medulla. When ACh binds to nicotinic receptors in these areas, it facilitates the transmission of signals across the synapse between neurons. Thus, nicotinic receptors are directly activated by acetylcholine (ACh), which is why the correct pairing is “nicotinic: acetylcholine.”
2. Muscarinic Receptors:
Muscarinic receptors are another type of ACh receptor, but they are different from nicotinic receptors. These are G protein-coupled receptors found on target organs of the parasympathetic nervous system (e.g., heart, smooth muscle, glands). Muscarinic receptors are activated by acetylcholine, not norepinephrine.
3. Adrenergic Receptors:
Receptors like alpha 1 and beta 1 are types of adrenergic receptors. They are activated by norepinephrine (NE) or epinephrine (E). For example:
- Alpha 1 receptors are located on smooth muscle cells and respond to norepinephrine, leading to vasoconstriction.
- Beta 1 receptors are found primarily in the heart and increase heart rate when stimulated by norepinephrine or epinephrine.
4. Incorrect Pairings:
- a) Nicotinic: norepinephrine is incorrect, as nicotinic receptors are activated by acetylcholine, not norepinephrine.
- c) Muscarinic: norepinephrine is also incorrect, as muscarinic receptors are specifically activated by acetylcholine.
- d) Alpha 1: acetylcholine is incorrect, as alpha 1 receptors are activated by norepinephrine, not acetylcholine.
Thus, nicotinic: acetylcholine is the correct receptor-neurotransmitter pairing.