acetylcholine It is an essential neurotransmitter for the functioning of the nervous system. It is the first identified neurotransmitter and is found in both vertebrates and invertebrates. In humans, it plays different roles, being known mainly for acting on cognitive functions, such as learning and memory.
The synthesis of acetylcholine occurs at the axonal terminals and is made by the enzyme Choline-O-Acetyl-Transferase (ChAT), from choline and acetyl-coenzyme A. After being synthesized, acetylcholine is stored in vesicles and later released by exocytosis. Acetylcholine only interacts with specific receptors. Dysfunctions of the cholinergic neurotransmission system are related to the development of neurological and psychiatric syndromes.
Read too: Antidepressants—What is the relationship between these drugs and neurotransmitters?
Acetylcholine summary
Acetylcholine is a neurotransmitter that stands out as the first identified.
It is essential for the functioning of the nervous system.
It is synthesized by the enzyme Choline-O-Acetyl-Transferase (ChAT).
Interacts with specific receptors.
Its action is interrupted when it is hydrolyzed into choline and acetate.
Dysfunctions of the cholinergic neurotransmission system are related to the development of neurological and psychiatric syndromes, such as Alzheimer's, schizophrenia, Parkinson's and epilepsy.
What is acetylcholine?
Acetylcholine was the first neurotransmitter to be discovered and can be found in both vertebrates and invertebrates. Occurs in the central nervous system, peripheral nervous system, and neuromuscular junction. With regard to its chemical structure, acetylcholine is an ester of acetic acid and choline and has a molar mass of 146.2 g/mol. Acetylcholine presents a key role in the nervous system, both centrally and peripherally.
Synthesis and release of acetylcholine
Acetylcholine is produced in axon terminals from choline and acetyl coenzyme A. Choline supply comes mainly from the diet, while acetyl-CoA levels are guaranteed through glucose metabolism, under the action of the enzyme ATP-citrate lyase. The enzyme responsible for the synthesis of acetylcholine is called Choline-O-Acetyl-Transferase (ChAT).
After acetylcholine synthesis takes place, this important neurotransmitter is transported and stored in synaptic vesicles so that it can be released. Release occurs through the process of exocytosis., and, after being released, acetylcholine will act only on specific receptors, which are present on pre- and post-synaptic membranes.
See too: Noradrenaline—a hormone or a neurotransmitter?
Classes of acetylcholine receptors and their functions
There is dyour classes of acetylcholine receptors present in vertebrates:
Ligand-dependent ion channel: acts at the neuromuscular junction. Acetylcholine, when released by the motor neuron, is bound to this receptor, which causes the opening of the ion channel, generating an excitatory activity. This type of receptor is also found elsewhere in the peripheral nervous system and in the central nervous system.
metabotropic receptor: it is found in the central nervous system and heart of vertebrates. In the heart, acetylcholine activates a signal transduction pathway, which includes G proteins. These proteins inhibit adenylate cyclase and open potassium channels present in the muscle cell membrane. these actions reducein the heart rate, that is, they are responsible for an inhibitory effect.
The action of acetylcholine in the body is only interrupted when the neurotransmitter is hydrolyzed into acetate and choline. This process is dependent on the enzyme acetylcholinesterase, present in the synaptic clefts.
Functions of acetylcholine in the nervous system
Acetylcholine it is vital for the functioning of our nervous system, because the acute blockade of cholinergic neurotransmission is a lethal action in the body, while its gradual loss is related to the progressive loss of neural functions.
Between the functions that we can attribute to this neurotransmitter, we can highlight:
stimulation of muscles;
functioning of the autonomic nervous system;
sleep regulation;
important role in cognitive functions such as memory and learning.
Acetylcholine and Cholinergic System Problems
Disorders of the cholinergic neurotransmission system are related to the development ofneurological and psychiatric syndromes. Among the diseases related to the cholinergic system are:
Alzheimer's: is the most studied. Primary neurochemical changes are observed in the brain of people with this disease. The patient has problems such as changes in memory and learning capacity, among other changes. To learn more about this disease, click here.
Parkinson's disease: a degenerative, chronic and progressive disease, such as Alzheimer's disease. The person with Parkinson's, however, presents tremors at rest, stiffness between the joints, motor slowness and imbalance as the main symptoms. To learn more about this disease, click here.
Epilepsy: a relatively common neurological condition which is characterized by the occurrence of epileptic seizures. To learn more about this disease, click here.
Schizophrenia: a psychiatric disorder that can cause changes such as delusions, hallucinations and disorganized thinking.
In addition to the aforementioned diseases, smoking, the habit of smoking, is also a problem that is related to disturbances in the cholinergic system.
By Vanessa Sardinha dos Santos
Biology teacher