Properties and Functions of Synapses

There is an interval between depolarisation of the presynaptic terminal and the earliest appearance of a postsynaptic response. This interval is called synaptic delay. The synapse is the prime locus in the integration of neuronal signals. The synapse is also a site where functional properties are changed as a result of previous activity. For example, prolonged activity transmitted across a synaptic junction may result in a reduction of the threshold of firing of the neurons to further afferent inputs. This indicates that synapses are the site of changes in the storage of information (learning and memory).

The synapse is thus modifiable i.e., it shows plasticity. A variety of chemical agents (drugs etc.) act at synapses to alter nervous system's behaviour. A postsynaptic neuron is an integrator of information that is received from presynaptic neurons. Synaptic transmission is a one way process except in electric synapses. Synapses are the site of several pathological disorders viz., Parkinsonism, myasthenia gravis, and psychiatric disorders like schizophrenia. So far we have discussed the action potential and its effect at the synapse i.e. release of neurotransmitter. Acetylcholine is just one of the examples of a neurotransmitter. There are many more physiologically active chemicals that are produced by nerve cells.