The synapse is the neuronal structure in which the signals are transferred from one neuron to another. The synapse consists of a pre-synaptic neuron a synaptic cleft and post-synaptic neuron . It can be as a rule, or excitatory or inhibitory , but the same neuron can receive multiple excitatory synaptic contacts is that inhibitors.
Depending on the location of synapses can be distinguished in broadcasting: ace-dendritic, axo-axonic and associated somatic .
The term pre-synaptic
In the pre-synaptic terminal contains: •
mitochondria for ATP production necessary for the synthesis of NT, enzymatic activity, transport and termination within the NT vesicles, for the Na / K and Ca
• synaptic vesicles containing NT low molecular weight.
• Active zones in which the vesicles pour the contents. •
secretory granules, not all the pre-synapse, NT peptide release high molecular weight.
Neurotransmitters
are produced by pre-synaptic neuron and to date have been identified over 70. Some are popular, others are confined to small sections of the SN.
From chemical point of view are:
- A low molecular weight amino
• Although they are ubiquitous throughout the body are not found outside the cell.
- glutamate (Glu)
Only exciter.
- glycine (Gly)
inhibitor alone.
- GABA (gamma-aminobutyric acid)
An amino acid modified inhibitor alone. Its precursor is the gluttamato.
• Amines
- acetylcholine (Ach) NT
typical of excitatory neuro-muscular junction .
is produced from the synapse and consists acetyl CoA (product of cellular respiration) and choline . The enzyme responsible for the reaction is the creation ChAT
Is inactivated by acetylcholinesterase ( AChE) which breaks down into acetic acid and choline, which is summarized by cholinergic synapses.
- Dopamine (DA)
- noradrenaline (NA)
- Adrenaline
- Serotonin (5-HT)
Dopamine, noradrenaline and adrenaline all derive from the same line metabolic and collectively are called catecholamines . The precursor of catecholamines is tyrosine , thyroid hormone, which is converted to L-dopa (missing in Parkinson's disease), the precursor of DA. The DA is the precursor of NO, which is a precursor of adrenaline.
The serotonin precursor tryptophan is . Catecholamines are inactivated the oxidase (MAO).
- High molecular weight
From 5 to a few tens of amino acids.
are released in very limited areas of the SN. • Peptides
- enkephalin (Enk)
- Somatostatin
- Neuropeptide Y
- Substance P
- etc. • Gas
Uncovered recently as NT.
- nitrogen monoxide (NO). NT
Some are exclusively excitatory (eg glutamate). Only other inhibitors (eg GABA and glycine).
Most inhibitors which can be either excitatory, depending on the type of receptor or ion channel used in the post-synaptic transmission.
Structure and ion channel subtypes
All ion channels are composed of several subunits, of which there are structural variants change the permeability, the duration of opening etc.. Of each ion channel exist in reality families of ion channels that differ in some amino acids. The M2 tract is the one that faces the pore of the channel and determines the selectivity.
In the neuromuscular junction is a cholinergic channel composed of five subunits, two of which dell'α. Each subunit is composed of four stretches of α-helix parallel through the membrane. The unit has the α active site for Ach, in this case two. In fact, the channel Ach is an exception because it requires the binding of two molecules of NT. It is not very selective in permeability cation, it passes both Na + and K +.
The ion channel is called muscle nicotinic receptor , but is found throughout the SN. It takes its name of ' agonist that increases the effectiveness dell'acitelcolina on ion channels, namely nicotine. Naturally occurring toxins in plants and animals of the nicotinic receptor antagonist, that inhibit its effectiveness, including the cobra toxin and curare. There is also a
muscarinic receptor agonist which is muscarine, but it is not an ion channel-dependent transmitter, but a G protein coupled receptor that is indirect or metabotropic . of the muscarinic antagonist atropine is, in high doses in the flowers of belladonna.
glutammaergico channel, activated by the excitatory glutamate and therefore, is divided into three subtypes based channels antagonist on AMPA , NMDA and kainate . The NMDA receptor is permeable to all cations (K +, Na + and Ca + +). It is normally blocked by Mg + + (divalent cation magnesium) that is removed when it reaches-35mV, so the transmitter is at the same time-dependent and voltage-dependent. Are always coupled to AMPA receptors and kainate receptors and provide a late component of the PPS that prolongs the effect. The permeability to Ca + + affects rather than to depolarization, the metabolic change of the neuron. In fact, play a major role in the consolidation of memory traces in neural circuits that govern memory.
Channel GABAergic, and then activated by GABA inhibitory, is divided into two subtypes GABAA and GABAB . GABA is an anion channel permeable to Cl-, but has a smaller effect of Cl-PPSE because it goes against the electrical gradient. GABAB receptor is involved in indirect synapses. GABAA alloy with a multitude of molecules agonists ( barbiturates, benzodiazepines , ethanol etc.) Other than the NT. On the other hand, each molecule is not able to open it in itself, but modifies the operation. It is composed of five subunits, but each has tens of variants, so they can get thousands of different GABAA channels.
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