Neuron postsynaptic membrane

Synapse The area where two neurons meet. It includes the presynaptic neuronal terminal plasma membrane of one neuron and the postsynaptic membrane of another neuron. More specifically, it refers to the space or gap between them, often called the synaptic cleft. 

In addition to direct enhancement of channel activity, PTKs can indirectly increase GABA-evoked inhibitory current by recruiting intracellular GABAaR to the surface of postsynaptic membrane. Insulin has been shown to increase surface expression GABAaR in transfected human embryonic kidney cells. In central neurons insulin rapidly increases the expression of functional postsynaptic GABAaR in a tyrosine kinase-dependent manner, resulting in an increase in the amplitude of the miniature inhibitory postsynaptic currents. 

Another example of molecular communication is found in a neuronal synapse, which is a communication junction between two neurons as shown in Fig.2. The presynaptic membrane releases the neurotransmitter molecule that is recognized and captured by the receptor located on the surface of the postsynaptic membrane. 

After release by exocytosis, the neurotransmitter diffuses across the cleft and binds to a receptor on the membrane of the postsynaptic neurone. The binding affects an ion channel, which changes the polarisation of the postsynaptic membrane (see below). 

The neurotransmitters diffuse across the synaptic cleft in a fraction of a millisecond where, on reaching the postsynaptic membrane on an adjacent neuron, they bind to specific receptor sites and trigger appropriate physiological responses. 

Each neuron usually releases only one type of neurotransmitter. Neurons that release dopamine are referred to as dopaminergic, for example, while those that release acetylcholine are cholinergic, etc. The transmitters that are released diffuse through the synaptic cleft and bind on the other side to receptors on the postsynaptic membrane. These receptors are integral membrane proteins that have binding sites for neurotransmitters on their exterior (see p. 224). 

Acetylcholine is synthesized from acetyl-CoA and choline in the cytoplasm of the presynap-tic axon [1] and is stored in synaptic vesicles, each of which contains around 1000-10 000 ACh molecules. After it is released by exocy-tosis (see p. 228), the transmitter travels by diffusion to the receptors on the postsynaptic membrane. Catalyzed by acetylcholinesterase, hydrolysis of ACh to acetate and choline immediately starts in the synaptic cleft [2], and within a few milliseconds, the ACh released has been eliminated again. The cleavage products choline and acetate are taken up again by the presynaptic neuron and reused for acetylcholine synthesis [3j. 

There are more than 10 billion neurons that make up the human nervous system, and they interact with one another through neurotransmitters. Acetylcholine, a number of biogenic amines (norepinephrine, dopamine, serotonin, and in all likelihood, histamine and norepinephrine), certain amino acids and peptides, and adenosine are neurotransmitters in the central nervous system. Amino acid neurotransmitters are glutamic and aspartic acids that excite postsynaptic membrane receptors of several neurons as well as y-aminobutyric acid (GABA) and glycine, which are inhibitory neurotransmitters. Endorphins, enkephalins, and substance P are considered peptidergic transmitters. There are many compounds that imitate the action of these neurotransmitters. 

In the adrenal medulla and the ganglia of parasympathetic and sympathetic nerves, the neurotransmission is mediated by acetylcholine. On the postsynaptic membranes the transmitter activates the neuronal-type of the nicotinic acetylcholine receptor. This receptor type is in fact a sodium channel, its activation leads to a sodium influx and a membrane depolarization. A pharmacological interference at the... 

The intracellular signaltransduction of ofi-adrenoceptors is effectuated by a G-protein-dependent activation of the phospholipase C. This enzyme cleaves phosphatidylinositol, a phospholipid present in cell membranes, into inositol-1,4-5-triphosphate (IP3) and diacylglycerol (DAG). IP3 is a strong inductor of intracellular calcium release which leads to an increase of smooth muscle tone or the liberation of hormones stored in vesicles. Noradrenaline which is released by exocytosis, spreads by diffusion only. Only a small fraction of the total amount of the transmitter released will actually reach the postsynaptic membrane and bind to its specific receptors. Another fraction escapes the synapic cleft by diffusion and is finally enzymatically degraded in the interstitial fluid. Another fraction is taken up postsynaptically and metabolized enzymatically by the target cells (uptake 2). By far most of the transmitter (90%) is actively taken up by the releasing neuron itself (uptake 1 or neuronal re-uptake). In the... 

Nitric oxide (NO) and carbon monoxide are atypical neurotransmitters. They are not stored in synaptic vesicles, are not released in by exocytosis, and do not act at postsynaptic membrane receptor proteins. NO is generated in a single step from the amino acid arginine through the action of the NO synthase (NOS). The form of NOS initially purified was designated nNOS (neuronal NOS), the macrophage form is termed inducible NOS (iNOS), and the endothelial from is called eNOS. 

Mechanism of Action A tricyclic antidepressant that blocks reuptake of the neu-retransmitters norepinephrine and serotonin at neuronal presynaptic membranes, increasing their availability at postsynaptic receptor sites. Therapeutic Effect Relieves depression. 

Presynaptic membrane Part of the first neuron facing a synapse Postsynaptic membrane Part of the second neuron... 

Besides the differentiation of cholinergic and adrenergic neurons in these systems, there is also a variation in the protein receptors with which the neurotransmitters complex at the postsynaptic membrane. 

One of the best-understood examples of a ligand-gated receptor channel is the nicotinic acetylcholine receptor (see Fig. 11-51). The receptor channel opens in response to the neurotransmitter acetylcholine (and to nicotine, hence the name). This receptor is found in the postsynaptic membrane of neurons at certain synapses and in muscle fibers (myocytes) at neuromuscular junctions. 

Was this your answer A neurotransmitter is a small organic molecule released by a neuron into a synaptic cleft. It influences neighboring tissue, such as the postsynaptic membrane of a neuron on the opposite side of tbe cleft, by binding to receptor sites. 

In most instances the arrival of a nerve signal at the presynaptic end of a neuron causes the release of a transmitter substance (neurohormone). Tire transmitter passes across the 10-50 nm (typically 20 nm) synaptic cleft between the two cells and induces a change in the electrical potential of the postsynaptic membrane of the next neuron (Fig. 30-10).149 401 Excitatory transmitters usually cause depolarization of the membrane. By this we mean that the membrane potential, which in a resting neuron is -50 to -70 mv (Chapter 8), falls to nearly zero often as a consequence of an increased permeability to Na+ and a resultant inflow of sodium ions. The resulting postsynaptic... 

What does a neurotransmitter do at the postsynap-tic membrane In the case of acetylcholine in neuromuscular junctions the principal action appears to be one of opening sodium channels and thereby depolarizing the postsynaptic membrane. If enough nerve impulses arrive, an action potential will be initiated in the postsynaptic neuron. In other cases, the first response may be activation of a protein kinase either directly or by opening a channel for Ca2+, which indirectly regulates protein kinases and phosphatases.592 Thus, a complex cascade may be activated. See also Fig. 30-19. 

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