CHEMICAL TRANSMISSION AT SYNAPTIC CLEFT LEVEL
--------------------------------------------------------------------------------------------------------------------------------
We have seen that the nerve impulse as it travels rapidly over nerve fibre is electrical when the impulse reaches the terminal end of the axon and is to be transmitted to another neuron or muscle through the space called synaptic cleft where the transmission becomes chemical At the terminal ends of the axon there are knobs which contain synaptic vesicles when stimulated by the nerve impulse these vesicles release a substance called neurotransmitter into the gap between the neuron and the receiving structure
Neurotransmitter is defined as a substance released by a neuron acting rapidly briefly and at short range on the membrane of an adjacent neuron or membrane of effector organ producing a change in conductance which either increases or decreases the excitability of the post synaptic cell following are the criteria which a substance must fulfill to be called as neurotransmitters
(a) It should be present at the nerve ending
(b) It should be released on stimulation of the nerve
(c) The effects of the alleged substance when applied experimentally to the target cells must be indentical to the effects of stimulating pre synaptic pathway
(d) The enzymes required for synthesis and metabolism of the substance should be present in the neurons
with the advent of resarch sophisticated techniques of indentifying location and functions of neurotransmitters as many as 40 or more substances have been suggested to be the candidates as neurotransmitters However the role of noradrenaline dopamine accetylcholine 5-hydroxytryptamine GABA glycine and glutamate have well been understood Details of some of these neurotransmitter are given
0 Comments