Acetylcholine
Acetylcholine is a neurotransmitter, which is a chemical messenger responsible for transmitting signals between nerve cells (neurons) in the peripheral and central nervous systems.
Function
Acetylcholine plays a crucial role in various physiological processes, acting as a neurotransmitter in both the central nervous system (CNS) and the peripheral nervous system (PNS).
Neuromuscular Junction
In the neuromuscular junction, acetylcholine is released from the nerve endings and binds to receptors on muscle cells, triggering muscle contractions.
Autonomic Nervous System
In the autonomic nervous system, acetylcholine is involved in the transmission of signals in the parasympathetic division, which regulates relaxation, digestion, and other restful activities.
Location and Synthesis
Acetylcholine is synthesized in the cytoplasm of nerve terminals by the enzyme choline acetyltransferase.
Receptors
There are two types of acetylcholine receptors:
Nicotinic Receptors
Nicotinic receptors are found in the neuromuscular junction and in the autonomic ganglia of the sympathetic and parasympathetic systems. Activation of these receptors leads to muscle contractions.
Muscarinic Receptors
Muscarinic receptors are located in various target organs of the parasympathetic system, such as the heart, smooth muscles, and glands. Activation of muscarinic receptors can have various effects depending on the organ.
Regulation and Degradation
The regulation and degradation of acetylcholine are mediated by the enzyme acetylcholinesterase, which breaks down acetylcholine into choline and acetate. This process prevents prolonged stimulation and allows for efficient signal transmission.