Synapse-Types

TYPES OF SYNAPSES

Types of synapses

  • Chemical synapse
  • 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 :  It is the synapse between the axon of one neuron and the soma of the next.  Found in spinal cord and autonomic ganglia.
  • Axoaxonic :  It is a synapse between axons present in the (mammalian) spinal cord between axons of interneurons.
  • Axodentritics : It 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.

synapse_types1
Last modified: Thursday, 26 May 2011, 6:14 AM