Question

Define temporal and special summation

Answer 1

Answer) Excitatory postsynaptic potentials occur due to activity in one synaptic knob is small, but excitatory postsynaptic potentials produced by each of the active knobs summate.

Summation of potentials occurs at the axon hillock.

This summation may be temporal or spatial (special).

Spatial (special) summation -

Summation of inputs from many presynaptic membranes is called spatial summation.

Simultaneous stimulation by several presynaptic neurons occur.

Excitatory postsynaptic potentials spread from several synapses to axon hillock.

If we stimulate two afferent nerve fibers simultaneously, both of which make synaptic connections with the motor neuron, their excitatory postsynaptic potentials get summated to the critical level and thus may produce a spike discharge from the motor neuron. This is called spatial summation.

Temporal summation -

Summation of successive inputs from a single presynaptic membrane is called temporal summation.

High frequency stimulation by one presynaptic neuron occurs.

Excitatory postsynaptic potentials spread from one synapse to axon hillock.

If we stimulate one afferent nerve fiber for the second time before the decay of first stimulation, neither of which alone can generate spike from the motor neuron; however each produces some excitatory postsynaptic potentials which may get summated to the critical level necessary for the initiation of a spike potential. This is called temporal summation.