Types of synapse
Types of synapses is Chemical synapse and Electrical synapse.
Chemical synapse
All the synapses present in the central nervous system are chemical synapses. In these, the first neuron secretes a chemical substance called as a neurotransmitter at the synapse.
The transmitter travels and acts on receptor (protein in nature) present in the membrane of the next neuron.
According to the functional nature of the receptor there may be excitation or inhibition or modification of the sensitivity of the neuron.
There are about 30 such different transmitter substances reported. The chemical synapses always transmit the signals in one direction (unidirectional transmission) that is from the presynaptic neuron to the post synaptic neuron.
The unidirectional conduction allows signals to be directed toward specific goals, discrete and highly focused areas of the nervous system to perform its varied functions of sensation, motor control , memory and many others.
Electrical synapse
Have channels directly connecting one neuron to the other and electricity is being conducted from one nerve cell to the other.
The channels are usually small tubular structures made up of protein and referred to as gap junctions.
The gap junctions allow free movement of ions from the interior of one cell to the other. Only few such synapses are found in the central nervous system.
In smooth muscles the action potentials are transmitted from one fiber and in the cardiac muscle from one cell, to the next by way of the gap junctions.
The conduction through electrical synapse is by-way or bi-directional i.e. the signals are transmitted in either direction.
Synaptic junctions of the nervous system
Axosomatic
Axosomatic is the synapse between the axon of one neuron and the soma of the next. Found in spinal cord and autonomic ganglia.
Axoaxonic
Axoaxonic is a synapse between axons present in the (mammalian) spinal cord between axons of interneurons.
Axodentritics
Axodentritics is a synapse between axon of a neuron and dendrite of another neuron. Present in the dorsal horn of the spinal cord.
Dentrodentritic
Synapse between the dentrites of different somas. Present in the cerebellum.