Human brains consist of a huge number of neurons, approximately 10", with numerous interconnections. A schematic diagram of a biological neuron is shown in the figure.
- Soma or cell body:- where the cell nucleus is located.
- Dendrites:- where the nerve is connected to the cell body.
- Axon:- which carries the impulse of the neuron.
Dendrites are tree-like networks made of nerve fibre connected to the cell body. An axon is a single, long interconnection extending from the cell body and carrying signals from the neuron. The end of the axon splits into fine strands. It is found that each strand terminates into a small bulb-like organ called synapse. It is through synapse that neuron introduces its signal to other nearby neurons. The receiving end of these synapses on the nearby neurons can be found both on the dendrites and on the cell body. There are approximately $10 ^ 4$ synapses per neuron in the human brain.
Electric impulses are passed between the synapse and the dendrites. This type of signal transmission involves a chemical process in which specific transmitter substances are released from the sending side of the junction. This results in an increase or decrease in the electric potential inside the body of the receiving cell.
If the electric potential reaches a threshold then the receiving cell fires a and a pulse or action potential of fixed strength and duration is sent out through the axon to the synaptic junction of the other cells. After firing, a cell has to wait for a period of time called refractory period before it can fire again. The synapses are said to be inhibitory if they let passing impulses hinder the firing of the receiving cell or excitatory if they let passing impulse cause the firing of the receiving cell.
Fig: Mathematical Model of Artificial Neuron
Terminology Relationship between Biological and Artificial Neuron
|Weights or Interconnections