We can say that in all neurons there is a way of communicating with each other called synapses.
At synapses, neurons communicate with each other via neurotransmittersWhat molecules are responsible for sending signals from one neuron to another. Other particles called neuromodulators are also involved in communication between nerve cells.
Thanks to neurotransmitters and neuromodulators, the neurons in our brain are able to generate the torrents of information that we call “mental processes”But these molecules are also found at the periphery of the nervous system, at the synaptic endings of motor neurons (neurons of the central nervous system that project their axons towards a muscle or a gland), where they stimulate the contraction of muscle fibers.
Differences between neurotransmitter and neuromodulator
Two or more neuroactive substances can be in the same nerve terminal and one can function as a neurotransmitter and another as a neuromodulator.
Hence their difference: neurotransmitters may or may not create action potentials (electrical impulses that occur in the cell membrane), activate postsynaptic receptors (receptors of postsynaptic cells or neurons) and open ion channels (proteins of neuronal membranes). which contain pores which, once opened, allow the passage of charged particles such as ions) while neuromodulators do not create action potentials but regulate the activity of ion channels.
In addition, neuromodulators modulate the efficiency of postsynaptic cell membrane potentials produced at receptors associated with ion channels. This happens through the activation of G proteins (particles that carry information from a receptor to effector proteins). A neurotransmitter opens a channel, while a neuromodulator affects one or two dozen G proteins, Which produce cAMP molecules, opening many ion channels at once.
There is a possible relationship between rapid changes in the nervous system and neurotransmitters and slow changes with neuromodulators. Likewise, the latency (i.e. changes in postsynaptic membrane potential due to the effect of a neurotransmitter) of neurotransmitters is 0.5 to 1 milliseconds, while that of neuromodulators is several seconds. . In addition, the “life expectancy” of neurotransmitters is 10 to 100 ms. and that of neuromodulators is from a few minutes to a few hours.
In terms of the differences in shape between neurotransmitters and neuromodulators, that of neurotransmitters is similar to that of small 50mm vesicles. in diameter, but that of neuromodulators is that of large vesicles of 120 mm. of diameter.
Types of Receivers
Neuroactive substances can bind to two types of receptors, namely:
These are receptors that open ion channels. Most of them have neurotransmitters.
G protein receptors. In metabotropic receptors, neuromodulators usually bind.
There are also other types of receptors which are the autoreceptors or presynaptic receptors involved in the synthesis of the substance released at the terminal. If there is an excessive release of the neuroactive substance, it binds to autoreceptors and produces inhibition of synthesis preventing exhaustion of the system.
Classes of neurotransmitters
Neurotransmitters are classified into groups: acetylcholine, biogenic amines, transmitter amino acids and neuropeptides.
Acetylcholine (ACh) is the neurotransmitter of the neuromuscular junction, It is synthesized in the septal and nasal nuclei of Meynert (nuclei of the forebrain), can be both in the central nervous system (where the brain and spinal cord are located) and in the peripheral nervous system (the rest) and causes diseases such as myasthenia gravis (neuromuscular disease due to weakness of skeletal muscles) and muscular dystonia (a disorder characterized by involuntary twisting movements).
2. Biogenic amines
The biogenic amines are serotonin and catecholamines (adrenaline, norepinephrine and dopamine). and act primarily through metabotropic receptors.
- Serotonin is synthesized from rafe nuclei (in the brainstem); norepinephrine in the locus coeruleus (in the brainstem) and dopamine in the substantia nigra and ventral tegmental area (from where projections are sent to various regions of the forebrain).
- Dopamine (DA) is linked to pleasure and mood. A deficiency of it in the substantia nigra (part of the midbrain and building block in the basal ganglia) produces Parkinson’s disease and the excess produces schizophrenia.
- Norepinephrine is synthesized from dopamine, is linked to fight-and-flight mechanisms, and deficiency causes ADHD and depression.
- Adrenaline is synthesized from noradrenaline in the adrenal capsules or the adrenal medulla, activates the sympathetic nervous system (the system responsible for the innervation of smooth muscles, heart muscle and glands), participates in fight and flight reactions , increases heart rate and constricts blood vessels; it produces emotional activation and is linked to stress pathologies and general adaptation syndrome (a syndrome that involves subjecting the body to stress).
- the biogenic amines they play an important role in the regulation of affective states and mental activity.
3. Transmission of amino acids
The most important transmitting excitatory amino acids are glutamate and aspartate and the inhibitors are GABA (gamma immunobutyric acid) and glycine. These neurotransmitters are distributed throughout the brain and participate in almost all CNS synapses, where they bind to ionotropic receptors.
Neuropeptides are formed from amino acids and act primarily as neuromodulators in the CNS. The mechanisms of chemical synaptic transmission can be affected by psychoactive substances the effect on the brain is the modification of the efficiency with which nerve chemical communication occurs, which is why some of these substances are used as therapeutic tools in the treatment of psychopathological disorders and neurodegenerative diseases.