#Synapse 3 vs 2 plus#
When presynaptic neuron is kept in normal resting, during development of action potential, membrane potential will reach plus 35 mV from resting state of minus 70 mV. The amplitude of spike potential will be less than normal. Now when action potential reaches this presynaptic region, depolarization of presynaptic terminal will not be to the extent it normally occurs. So the presynaptic terminal fails to remain in resting state. Because of this, presynaptic terminal becomes less negative (because of influx of potassium ions) The neuron ending on presynaptic terminal liberates neurotransmitter. In presynaptic inhibition, the events occurring are as follows: 9.8), will be like what has been explained for postsynaptic inhibition but orientation of neuron involved in inhibition will be different. The mechanism of inhibition in all other types namely Renshaw cell (Fig. For example, when biceps muscle is contracting there will be associated relaxation of triceps muscle because of postsynaptic inhibition. Glycine substance is a classical example of inhibitory neurotransmitter at postsynaptic region. No action potential production in postsynaptic region. Postsynaptic membrane becoming more negative (development of inhibitory postsynaptic potential or also known as IPSP) Influx of chloride ions into postsynaptic region Binding of neurotransmitter to receptors on postsynaptic region Release of neurotransmitter from internuncial neuron Action potential production in internuncial neuron Renshaw cell inhibition (feedback or recurrent) This is possible because of the property of convergence. In spatial summation, presynaptic neurons stimulated will be different but stimuli will be applied simultaneously (time of stimulation shall be same, but places of stimulation will be different). In temporal summation, presynaptic neuron stimulated will be same, but many stimuli are applied in rapid succession (timing of stimuli will be different, but place of stimulation will be same). There are two types of summation namely spatial and temporal. But if many subthreshold stimuli are applied at presynaptic region, effects of these stimuli can get added up and lead to action potential development in postsynaptic region. When a stimulus of subthreshold strength is applied, there will not be development of action potential in postsynaptic region.
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In CNS, on an average about 10000 synapses are found on any one neuron. When nerve fibers of different presynaptic neurons end on a common postsynaptic neuron, this is known as convergence. Impulses from one presynaptic nerve fiber may end on postsynaptic region of large number neurons and this is called as divergence.