Neurons are the basic structural and functional units of the nervous system. Neurons are also called nerve cells. It carries nerves impulse at a speed of 100 m/sec. The nervous systems of humans are composed of millions of neurons of different sizes and shape performing different functions.
Neurons transmit nerve impulses from one part to another part of the body. Structure of neurons:
Neurons are composed of three parts.
I. Cell body
It is the central part of neurons. It consists of a nucleus, cytoplasm, and other cell organelles like Golgi complex, Mitochondria, Ribosome, and Endoplasmic reticulum.
It receives nerve impulse from dendrites and carries it to the axon.
It is also concerned with the biosynthesis of materials necessary for the growth and maintenance of neurons.
It is an elongated, threadlike, unbranched structure that arises from one side of the cell body. Axon of a large neuron is covered by a white protective sheet called myelin sheath and has internal nodes called nodes of Ranvier. The distance between two nodes is covered by Schwan cell
It carries nerve impulses away from the cell body.
These are the small fibers-like structures that arise from the cell body. Function: These carries nerve impulse towards the cell body. Tasspfrigarmasuthgbsfunction:
There are three types of neurons on the basis of their function.
i. Sensory neuron.
ii. Motor neuron.
iii. Associative neuron.
i. Sensory neuron:
Those neurons which carry nerve impulse (message) from the receptor (sense organ) to CNS (brain and spinal cord) are called a sensory neuron. In these neurons cell body is on one side, the axon is short whereas the dendrites are long.
ii. Motor neuron:
Those neurons which carry nerve impulses away from CNS to effectors are called motor neurons. The cell body is in the length of the neuron. They have long axons and short dendrites.
iii. Associative neurons:
They are also called mixed or intermediate neurons. They are present in the brain and spinal cord. They make a connection between sensory and motor neurons. They have short axons and dendrites.