Chemical substance secreted from an activated nerve ending/boutong to the synapse cleft where receivers, receptors, on the postsynaptic membrane in turn are activated, leading to changes in the electrical voltage of the postsynaptic membrane.
There are two main types of neurotransmitters:
1/ Small molecule neurotransmitters
2/ Peptide neurotransmitters, neuropeptides.
1/ Small molecule neurotransmitters comprising:
b) the group of catecholamine transmitters i.e. adrenaline, noradrenaline, dopamine, serotonin and histamine
c) the group of amino acid transmitters i.e. glutamate, aspartate, GABA and glycine.
Glutamate is always proactive/excitatory.
GABA and glycine are always inhibitory/inhibitory/inhibitory. An exception is GABA, which in the retina of the immature nervous system is excitatory and then, in the mature retina, is only inhibitory. Other small molecule neurotransmitters are excitatory in some synapses and inhibitory in others, depending on the properties of the postsynaptic membrane.
2/ peptide neurotransmitters, neuropeptides.
The neuropeptides include substance P, which is important in connection with pain experiences, and the so-called endorphins, "the body's own morphine". The endorphins, when released from the botons, have a pain-reducing effect and provide a feeling of well-being.
A neuron has, according to the general rule, one and the same neurotransmitter in all its botons (exceptions occur).
But the vast majority of botongs, along with swarms of tiny synapse vesicles filled with some kind of small molecule neurotransmitter, contain a few large synapse vesicles loaded with neuropeptide.
Neurons are often named, in functional contexts and when it comes to drug effects, based on the small molecule neurotransmitter they produce.
One takes the name of the transmitter and adds -erg and can then speak of:
It is not uncommon for a neuron, such as a serotoninergic neuron, when active (when it emits action potentials) to produce excitation in some of the neurons contacted and, oddly enough as it may seem, inhibition in others. But, as we said, the effect of a neurotransmitter depends in the vast majority of cases on the characteristics of the postsynaptic membrane.
The neurotransmitters have important effects in addition to bringing about the lightning-fast postsynaptic potential changes:
* the metabolism of the postsynaptic neuron changes locally in the synapse region,
* the way the postsynaptic membrane reacts to the transmitter changes,
* New neurotransmitters, so-called secondary messenger substances, are formed in the postsynaptic region under the influence of the postsynaptic membrane, and spread inside the postsynaptic neuron where metabolism both large and small can be affected.
* Some secondary messengers in turn trigger the emergence of so-called tertiary messengers, which can travel all the way into the cell nucleus and influence the DNA molecules so that different genes are switched off or "turned on".