Neurotransmitters and neuromodulators: how do they work?

It can be said that in all neurons there is a way of communicating with each other called synapses.

At synapses, neurons communicate with each other using neurotransmitters, which are molecules responsible for sending signals from one neuron to the next. Other particles called neuromodulators also intervene in the communication between nerve cells

Thanks to neurotransmitters and neuromodulators, the neurons of our brain are capable of generating the torrents of information that we call "mental processes", but these molecules are also found in the periphery of the nervous system, in the synaptic terminals of motor neurons (central nervous system neurons that project their axons to a muscle or gland), where they stimulate muscle fibers to contract them.

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 the other as a neuromodulator.

Hence their difference: neurotransmitters create or not action potentials (electrical impulses that are produced in the cell membrane), activate receptors postsynaptic (receptors of postsynaptic cells or neurons) and open ion channels (proteins of the neuronal membranes that contain pores that when open, allow the passage of charge particles such as ions) while neuromodulators do not create action potentials but regulate the activity of ion channels.

In addition, neuromodulators modulate the efficacy of postsynaptic cell membrane potentials produced at ion channel-associated receptors. This occurs through the activation of G proteins (particles that carry information from a receptor to the effector proteins). A neurotransmitter opens a channel, whereas a neuromodulator affects one or two dozen G proteins, which produce cAMP molecules, opening many ion channels at once.

There is a possible relationship of rapid changes in the nervous system and neurotransmitters and slow changes with neuromodulators. Similarly, latency (i.e., changes in postsynaptic membrane potential due to the effect of a neurotransmitter) of neurotransmitters is 0.5-1 milliseconds, on the other hand, that of neuromodulators is several seconds. Furthermore, the "life expectancy" of neurotransmitters is 10-100 ms. and that of neuromodulators is from minutes to hours.

Regarding the differences between neurotransmitters and neuromodulators according to their shape, that of neurotransmitters is similar to that of small 50-mm vesicles. in diameter, but that of neuromodulators is that of large 120-mm vesicles. diameter.

Types of receivers

Neuroactive substances can bind to two types of receptors, which are the following:

Ionotropic receptors

They are receptors that open ion channels. In most, neurotransmitters are found.

Metabotropic receptors

G protein-bound receptors. Neuromodulators often bind to metabotropic receptors.

There are also other types of receptors that are the autoreceptors or presynaptic receptors that participate in the synthesis of the substance released at the terminal. If there is excess release of the neuroactive substance, it binds to the autoreceptors and produces an inhibition of the synthesis avoiding the exhaustion of the system.

Classes of neurotransmitters

Neurotransmitters are classified into groups: acetylcholine, biogenic amines, transmitter amino acids, and neuropeptides.

1. Acetylcholine

Acetylcholine (ACh) is the neurotransmitter of the neuromuscular junction, is synthesized in the septal nuclei and nasal nuclei of Meynert (nuclei of the anterior brain), it can be both in the central nervous system (where is found in the brain and spinal cord) as in the peripheral nervous system (the rest) and causes diseases such as myasthenia gravis (disease neuromuscular disease due to skeletal muscle weakness) and muscle dystonia (a disorder characterized by involuntary movements of the torsion).

2. Biogenic amines

The biogenic amines are serotonin and catecholamines (adrenaline, norepinephrine and dopamine) and they act mainly by metabotropic receptors.

• The serotonin it is synthesized from raphe nuclei (in the brain stem); norepinephrine in the locus coeruleus (in the brain stem) and dopamine in the substantia nigra and ventral tegmental area (from where projections are sent to various regions of the brain previous).

• The dopamine (DA) is related to pleasure and mood. A deficit of this in the substantia nigra (portion of the midbrain and a fundamental element in the basal ganglia) produces Parkinson's and the excess produces schizophrenia.

• The noradrenaline It is synthesized from dopamine, is related to fight and flight mechanisms, and a deficit causes ADHD and depression.

• The adrenalin is synthesized from norepinephrine in the adrenal capsules or adrenal medulla, activates the sympathetic nervous system (system responsible for the innervation of smooth muscles, heart muscle and glands), participates in fight and flight reactions, increases heart rate and contracts vessels blood; produces emotional activation and is related to stress pathologies and general adaptation syndrome (syndrome that consists of subjecting the body to stress).

• The biogenic amines They play important roles in regulating affective states and mental activity.

3. Transmitting amino acids

The most important excitatory transmitter amino acids are glutamate and aspartate and inhibitors are GABA (gamma immunobutyric acid) and glycine. These neurotransmitters are distributed throughout the brain and participate in almost all synapses in the CNS, where they bind to ionotropic receptors.

4. Neuropeptides

Neuropeptides are formed by amino acids and act primarily as neuromodulators in the CNS. The mechanisms of chemical synaptic transmission can be affected by psychoactive substances whose effect on the brain is modifying the efficiency with which nerve chemical communication occurs, and this is why some of these substances are used as therapeutic tools in the treatment of psychopathological disorders and diseases neurodegenerative.