Biological Neural Network

Introduction to Biological Neural Network: 

Human Brain consist of a large number, more than a billion of neural cells that processes information. Each cell works like a single processor. The massive interaction between all cells and their parallel processing only makes the brain’s abilities possible.
The features of Biological Neural Network are attributed to its structure and function. The fundamental unit of the network is called a Neuron or a Nerve cell.

 Its schematic structure is shown below:

The structure of neuron consists of a :

1.  Dendrites:  These are branching fibers that extend from cell body or soma. Tree like nerve fibers (dendrites) are associated with cell body and receive signals from other neurons.

2.   Soma or Cell body: Soma or a cell body of a neuron contains the nucleus and other structures. It supports chemical processing and production of neurotransmitters.

3.  Axon:  Extending from the cell body is a single long fibre called Axon, which eventually branches into strands and sub-strands.  It carries information away from the soma to synaptic sites of other neurons, muscles or glands.

4.  Axon Hillock:  It is the site of summation for incoming information. At any moment the collective influence of all neurons that conduct impulses to a given neuron will determine whether or not an action potential will be initiated at the axon hillock and propagated along the axon.

5.  Myelin Sheath: It consists of fat containing cells that insulate the axon from electrical activities. This insulation acts to increase the rate of transmission on signals. A gap exists between each myelin sheath cell along the axon. Since fat inhibits the propagation of electricity, the signals jump from one gap to the next.

6.  Node of Ranvier:  These are the gaps (about 1μm) between myelin sheath cells.  Since fat serves as a good insulator, the myelin sheaths speeds the rate of transmission of an electrical impulse along the axon.

7.  Synapse: It is a point of connection between two neurons or a neuron and a muscle or a gland. Electro-chemical communication between neurons takes place at these junctions.

8.  Terminal Buttons:  These are small knobs at the end of axon that release chemical called Neuro-Transmitters.

Information Flow: 

The transmission of a signal from one cell to another at a synapse is a complex chemical process in which specific transmitter substances are released from sending side of the junction. The effect is to raise or lower the electrical potential inside the body of receiving cells.

 If this potential reaches a threshold, a n electrical activity in the form of short impulses is generated. When this happens the cell is set to have fired. These electrical signals of fixed strength and duration are sent down to the axon. Generally, the electrical activity is confined to the interior of a neuron, whereas the chemical mechanism operates at the synapses.

Dendrites serve as receptor for signals from other neurons, whereas the purpose of axon is transmission of generated neural activity to other nerve cells (inter-neuron). Or muscle fibers(motor-neuron) or receptor neuron(which receive information from muscles or sensory organs)

Features:

1.  Size of cell body of typical neuron  ranges from 10-80 μm

2.  Gap at synaptic junction is about 200 nano-meters (nm) wide

3.  Total length of neuron varies from 0.01mm for internal neurons in brain to 1meter for neurons in the limbs.

4.  If the induced polarization potential is positive at the post- synaptic neuron then the synapse is termed as Exitatory

5.  If the induced polarization potential is negative at the post- synaptic neuron then the synapse is termed as Inhibitory