CBSE Class 10 Answered

(Explaining in detail -

Following sequence of events take place in synaptic transmission from a presynaptic neuron to a postsynaptic cell.

i) The process begins with a wave of electrochemical excitation called an action potential traveling along the membrane of the presynaptic cell, until it reaches the synapse.

ii) The electrical depolarization of the membrane at the synapse causes channels to open that are permeable to calcium ions.

iii) Calcium ions flow through the presynaptic membrane, rapidly increasing the calcium concentration in the interior.

iv) The high calcium concentration activates a set of calcium-sensitive proteins attached to vesicles that contain a neurotransmitter chemical.

v) These proteins change shape, causing the membranes of some vesicles to fuse with the membrane of the presynaptic cell. This causes the opening of the vesicles and dumping their neurotransmitter contents into the synaptic cleft.

vi) The neurotransmitter diffuses within the cleft. Some of it escapes, but some of it binds to chemical receptor molecules located on the membrane of the postsynaptic cell.

vii) The binding of neurotransmitter causes the receptor molecule to be activated in some way. This is the key step by which the synaptic process affects the behavior of the postsynaptic cell.

viii) Due to thermal shaking, neurotransmitter molecules eventually break loose from the receptors and drift away.

ix) The neurotransmitter is either reabsorbed by the presynaptic cell, and then repackaged for future release, or else it is broken down metabolically. )