Chemical Synapses

CHEMICAL SYNAPSES :
SYNAPSE:
DEFINITION:
The word synapse is of greek origin . Two scientists C.scott sherrington and his collegues coined this . it is derived from two words .
1. Syn : means together.
2. haptein : to clasp . means to keep holding something together .(4)
CHEMICAL SYNAPSE:
DEFINITION:
Chemical synapses are defined as : Biological junctions through which neurons signals can be exchanged To each other and to non neuronal cells such as in the muscles and The glands and they allow the neurons to form circuit in central nervous System.
They are thus very important biological computations that underlie perceptions and thoughts. They are the source of connecting and controlling

Excitatory and inhibitory synapses are indicated on the soma and proximal dendrites and currents initiated at each, flowing through the possynaptic membrane and the region of the axon hillock, where the spike is thought to be initiated.

TERMINATION:The signal is usually terminated by either
1.Breakdown of the neurotransmitter or
2.by re uptake of neurotransmitter . the later is mainly in the presynaptic neuron to avail the recycling of neurotransmitters . Reuptake:
Follwing the fusion of the synaptic vesicles and the release of the neurotransmitters in the synaptic cleft , small neurotransmitters such as , glycine arecleared rapidly from the space for their recycling by the specialized membrane protein in post or the presynaptic membrane .
Breakdown:
Some neurotransmitters are brokendown without any direct reuptake for example the acetylecholine and the large ones , the choline part of the acetylecholine is to large degree taken up by the presynaptic membrane for recycling . however the peptides must be resynthesized by the soma of the neuron

2.Homotropic modulation .
3.Heterotropic modulation.
DESENSITIZATION:
Desensitization of the postsynaptic neuron is ; the decrease in response to same neurotransmitter stimulus.
Means the strength of synaps may be diminished in response as the action potential arrives in repid succession –ie refered as a phenomenon that give rise to so called frequency dependence of synaps .
Our nervous system exploy this property for the computational purpose , and can turn this synaps to such means as phosphorylation of proteins involved .
HOMOTROPIC MODULATION :
It is the Modulation of presynaptic neuron by its own neurotransmitters .
It is a form of autocrine signaling . this signaling includes usually the size ,numbers and the replenishment rate of the vesicles . it is often inhibitory with the effect of presynaptic inhibition ,making neurotransmitters self regulating .
EXAMPLE:
One example of the neurons of SNS that release the noradrinaline which beside forms the affecting postsynaptic receptors alsoaffect alpha 2 adrenergic receptors inhibiting the further release of noradrenaline this effect is utilized by chlonidine to perform inhibitory effect on