Coordination and Control:

Components of nervous system

1. Neurons (nerve cells)

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The structural and functional unit of the nervous
system in all animals including man is the neuron. This is a highly specialized cell which contains the typical organelles found in most eukaryotic cells. This cell is highly adapted for communication because of its wire like projection; the dendrites which are often further branched and carry impulses towards the central cell body. The cell body is a thicker region of the neuron containing the nucleus and most of the cytoplasm. The axon is the projection, generally very long, that carries impulses away from the cell body. Usually a neuron has a single axon. Fatty substances covering the axon is the myelin sheath along with short regions of exposed axon are called nodes of Ranvier. Many axons and even dendrites combine to form a single nerve.

Neurons are of three types.

a)Sensory neurons: they carry nerve impulses (message from receptors to central nervous system.

b)Motor neurons: they carry nerve impulse (orders) from central nervous system to effectors.

c)Associated neurons: they form central nervous system and are responsible for analyzing the message and issuing orders.

Composition of Neuron:

Aneuron is ade up of three components.

1-Axon

2-Dendrites

3-Soma

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There are several differences between axons and dendrites:

Axons	Dendrites
Take information away from the cell body Smooth Surface Generally only 1 axon per cell No ribosomes Can have myelin	Bring information to the cell body Rough Surface (dendritic spines) Usually many dendrites per cell Have ribosomes No myelin insulation Branch near the cell body