Neurotransmitter

Neurotransmitters ( from ancient Greek. Νεῦρον neuron, sinew ',' nerve ' and Latin neurotransmitters, send over ', ' transfer ') are biochemical messengers that transmit at chemical synapses, the excitement from one nerve cell to other cells (synaptic transmission).

The neurotransmitters are synthesized in the cell body or nerve endings of the axon of the sending neuron.

Mode of action

In the presynaptic membrane region of the neuron Propagated electrical pulses, action potentials, induce calcium influx via short-term, the distribution of neurotransmitters from storage memories, the synaptic vesicles. This process is an exocytosis: Fusion of the vesicle with the presynaptic membrane, the Quantum is released at each contained transmitter molecules in the ( extracellular ) and enters the synaptic cleft by diffusion to the receptors on the postsynaptic membrane of the postsynaptic cell.

This membrane proteins of the subsynaptic region recognize the particular transmitter specifically to its molecular spatial structure and charge distribution by complementary structures. The binding of a transmitter molecule leads to the transformation of the receptor protein, which directly ( ionotropic ) or indirectly ( metabotropic ) certain ion channels in this region are temporarily opened.

Depending on the number of receptors with bound transmitter arise as ion currents of different strengths with corresponding postsynaptic potential differences ( PSP). Either these, determined by the encountered in the membrane association of receptors to ion channels of certain ion species, now depolarizing so that they as excitatory postsynaptic potential ( EPSP) promote excitation of the postsynaptic cell or lead to the formation of an action potential, or so, that they inhibit or prevent the energization this as inhibitory postsynaptic potential ( IPSP ).

Apart from the actual neurotransmitters are not rare nor Kotransmitter distributed ( Kotransmission ), which may affect the transmission of excitation in different ways as neuromodulators. The binding of transmitters to Rezeptormolküle is usually reversible after detachment thus again possible. The boundaries of their effect not only by diffusion but by enzymatic cleavage (eg, cholinesterases ), inclusion in glial cells, presynaptic reuptake into the neuron or postsynaptic receptor internalization, including (as endocytosis ). In addition, the prompt Inaktivation of ion channels ( desensitization ) is postsynaptic possible. Furthermore, presynaptic autoreceptors located on the transmitter whose release can limit negatively fed. In addition, numerous other presynaptic receptors are known mainly metabotropic G- protein - coupled receptors, bringing various modifications of synaptic transmission result.

For the effect of a synaptic transmission is not the presynaptic distributed as a transmitter chemical substance matters, but the postsynaptic trained susceptibility of the downstream cell. For example, calls to the same transmitter acetylcholine in skeletal muscle - mediated by ionotropic nicotinic - muscarinic NM - depolarization produced and in the heart muscle - mediated via metabotropic muscarinic M2 - muscarinic - hyperpolarization. In one case, this leads to a stimulation of skeletal muscle fibers, in the other case, a decrease of excitability of cardiac muscle cells.

Examples

The most important transmitter in the peripheral nervous system, acetylcholine is so distributed not only at the motor endplate of muscle fibers, but also in the parasympathetic part of the autonomic nervous system as well as preganglionic in the sympathetic part, postganglionic is mostly here noradrenaline ( but are, for example, the sweat glands are cholinergic innervation ).

The most important neurotransmitter in the central nervous system (CNS ) is glutamate, with excitatory effect; the main transmitter of inhibitory synapses are gamma -aminobutyric acid ( GABA) and glycine. Other common neurotransmitters are dopamine and serotonin in addition to acetylcholine and norepinephrine, also at synapses in the CNS.

Chemical mapping

Biochemically seen the most known neurotransmitters are next to acetylcholine ( choline eg possible from methionine or serine, cholinergic transmission ) either

  • Derivatives of amino acids ( by or after decarboxylation) - such as dopamine or norepinephrine, and epinephrine ( from tyrosine, catechol - aminergic ) or histamine ( from histidine, histaminergic ) or GABA ( from glutamate, GABAergic ) or serotonin ( from tryptophan, serotonergic ) - or is it
  • ( α - ) amino acids - such as glycine ( glycinergic ) or glutamate ( glutamatergic ) - or is it
  • Oligopeptides, ie, short chains of compound amino acids ( peptidergic ) - such as oxytocin, vasopressin ( ADH), somatostatin ( SIH ), tachykinin, cholecystokinin, neurotensin and opioid- acting neuropeptides, opioid peptides, such as endorphins.

Besides acting Phosphosester of purines such as AMP, ADP, ATP and UTP and UDP also at synapses as (co - ) transmitter.

Classification

The neurotransmitters can be divided into different types according to material classes. The main neurotransmitters are:

Biogenic amines

  • Acetylcholine
  • Catecholamines:
  • Noradrenaline
  • Adrenaline
  • Dopamine
  • Serotonin
  • Dimethyltryptamine
  • Histamine ( biochemical structure, however different from other biogenic amines)

Neuropeptides

  • Endorphins and enkephalins
  • Substance P
  • Somatostatin
  • Insulin
  • Glucagon

Amino acids

  • Inhibitory amino acid transmitters
  • γ -aminobutyric acid = GABA = 4- aminobutyric acid
  • Glycine
  • β -alanine
  • Taurine
  • Excitatory amino acid transmitters
  • Glutamic acid
  • Aspartic acid
  • Cysteine
  • Homocysteine

Soluble gases

  • Nitric oxide
  • Carbon monoxide
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