Acetylcholine (neurotransmitter): functions and characteristics
The transmission of the nerve signal is carried out through bioelectric impulses generated by neurons and transported from one to another until the message reaches its destination.
This transport depends largely on the action of neurotransmitters, substances that are transmitted from one neuron to another through the synapse and they cause an excitatory or inhibitory effect on the postsynaptic neuron.
One of said neurotransmitters and in fact the first to be identified is acetylcholine, substance that we will talk about in this article.
Acetylcholine: a neurotransmitter
Acetylcholine is a substance classified as an ester, made by compounds of an oxygenated acid and an organic radical. As I have already mentioned, it is about the first neurotransmitter to be discovered, in 1914, and the different elements that are responsible for its synthesis and elimination make up the so-called cholinergic system.
Acetylcholine is primarily viewed as an excitatory-type neurotransmitter, but it can also exert an inhibitory action depending on the type of synapse in which it acts.
On the other hand, acetylcholine is considered to be one of the main neurotransmitters in the nervous system and one of the most common, being able to be found throughout the entire brain and in the autonomic nervous system.
Synthesis
Acetylcholine synthesis occurs inside neurons, specifically in their cytoplasm, through the union of acetic acid or acetyl-CoA and choline thanks to the enzyme choline acetyltransferase.
After that, the acetylcholine is sent along the axon to the terminal button, where it will be stored until its use and release in the synaptic space.
Acetylcholine receptors
The action of acetylcholine occurs through its interaction with a series of receptors that react to its presence in the different locations where this neurotransmitter acts. Specifically, we can find in the nervous system two main types of cholinergic receptors.
Muscarinic receptor
It is a type of metabotropic receptor, that is, it requires the use of chains of second messengers to that allow the opening of ion channels. This implies that its action is usually slow and has a longer effect over time.
This type of receptor is usually the one with the highest level of presence in the brain, as well as in the el parasympathetic nervous system. They can have a performance both excitatory and inhibitory.
Nicotinic receptor
This type of receptor, which also has an affinity for nicotine, is ionotropic, which generates a rapid response from the receptor that allows the immediate opening of the channel. Its effect is fundamentally excitatory. They are usually found in the connections between neuron and muscle.
Neurotransmitter degradation
Most neurotransmitters are received by the presynaptic neuron after being emitted. In this sense, acetylcholine has the particularity that it is not reuptained but is degraded by the acetylcholinesterase enzyme present in the synapse itself.
Acetylcholine has a very short life time at synapses because it degrades very quickly.
Principal functions
Acetylcholine is a neurotransmitter that can be excitatory or inhibitory depending on the receptors and the location where it is released. It can act in different places and have different functions for the body, some of the main ones being the following.
1. Motor control
Voluntary movement of muscles It requires the action of acetylcholine to be able to perform, by causing the muscle contractions necessary for movement. In this aspect, the functioning of acetylcholine is excitatory, acting through ionotropic receptors.
2. Autonomic nervous system activity
Acetylcholine is one of the main components by which our body can prepare itself for action in the face of different stimuli or deactivate itself once the threat has ceased. This neurotransmitter acts at the preganglionic level, that is, in the transmission of nerve impulses between spinal cord and ganglion, both in the sympathetic and parasympathetic systems.
In the parasympathetic system, this action also occurs at the postganglionic level, between the target organ and the ganglion. In the case of the parasympathetic system, we can observe how the action of acetylcholine produces an inhibitory effect. Among other actions allows the heart rate to decrease, as well as the increase of the action of the intestine and of the visceral functioning.
3. Paradoxical dream
Paradoxical sleep or REM sleep is affected by the action of acetylcholine, which participates in the structure of sleep and gives it different distinctive characteristics.
- Related article: "The 5 phases of sleep: from slow waves to REM"
4. Hormone production and management
Acetylcholine also has neuroendocrine function in the pituitary, since its action causes an increase in vasopressin synthesis or a decrease in prolactin synthesis.
- You may be interested: "Pituitary (pituitary) gland: the nexus between neurons and hormones"
5. Awareness, attention and learning
The ability of human beings to learn through perception is largely mediated by the action of acetylcholine, as well as the fact of maintaining attention and even the level of conscience. Acetylcholine causes that the cerebral cortex remains active and allows learning.
6. Memory formation
Acetylcholine is also a substance of great importance when it comes to form memories and configure our memory, participating in the management of hippocampus from this area.
7. Pain perception
Acetylcholine activity greatly mediates pain perception.
Bibliographic references:
- Gómez, M. (2012). Psychobiology. CEDE PIR Preparation Manual. 12. CEDE: Madrid.
- Hall, J.E. & Guyton, A.C. (2006). Textbook of Medical Physiology. 11th edition. Philadelphia, Pennsylvania: Elsevier.
- Kandel, E.R.; Schwartz, J.H. & Jessell, T.M. (2001). Principles of neuroscience. Fourth edition. McGraw-Hill Interamericana. Madrid.
- Katzung, B. (2007). Basic & Clinical Pharmacology, 10th Edition. Mc Graw Hill Medical.
- Martina. M. & González, F.J.A. (1988). Compendium of psychoneuropharmacology. Editions Díaz de Santos.