Nervous system in man , Nerve cells types & Nature of nerve impulse

From Online Sciences - January 11, 2018

Nervous system in man

The nervous system is highly developed in vertebrates , especially in man , The nervous system and the endocrine glands are working together to control all the functions of human body systems , They receive the information in the form of external & internal stimuli through receptor systems , and then give the proper response .

This is for keeping the human body in a continuous direct communication with his external and internal environment and for keeping the internal conditions of body in an ideal , constant and balanced state ( homeostasis ) .

The nervous system is divided into :

Autonomic nervous system is subdivided into Sympathetic nervous system and Parasympathetic nervous system .

Nerve cell

Nerve cell ( Neuron ) is the structural unit of nervous system , Nerve cell is small in size and cant be recognized by the naked eye , Nerve cell consists of cell body and cell processes .

Cell body

Cell body of the nerve cell contains rounded nucleus , Cytoplasm surrounded the nucleus and known as neuroplasm which contains neurofilaments , all cell organelles as mitochondria and Golgi bodies , except the centrioles , so , neurons can not divide nissils granules .

Nissils granules are minute granules unique for the nerve cells and they are considered as the stored food for the nerve cell which consumes during its activity .

Cell processes

Cell processes : There are two types of them in the nerve cell , which are :

It is surrounded by two sheaths :

Function of the axon : The conduction of nerve impulses from the body of nerve cell to the synapse , The conduction of nerve impulses in myelinated axons ( covered by myelin sheath ) is much more rapid than in non-myelinated nerve fibers ( axons ) , because the myelin sheath acts as an insulator .

The nerve impulse is propagated and conducted through the nerve cell in one direction only , as the nerve impulses enter the nerve cell body through the dendrites , then to the axon , while the terminal arborizations transmit these impulses away from the cell body ( to the next neuron ) through the synapse .

Types of nerve cells

According to the function , nerve cells are classified into three types

In addition to the cell body and the processes of nerve cells , there is another type of cells in the nervous system known as neuroglia .

Neuroglia ( Glial cells )

Another type of cells in the nervous system , have the ability to divide and perform the following functions :


Nerve consists of :

Nerve impulse

Nerve impulse is the message that is transmitted through the nerves from the sense organs ( receptors ) to the central nervous system , then to the effector ( responding ) organs .

Nature of the nerve impulse :

The nerve impulse is an electrical phenomenon with a chemical nature ( electrochemical phenomenon ) , To understand the nature of nerve impulse and its transmission , we have to study the nerve cell during four different conditions .

Nerve cell at rest

At rest , there is a difference in distribution and concentration of ions outside and inside the nerve cell , as the following :

The concentration of sodium ions ( Na+ ) outside the cell is 10:15 times higher than inside , The concentration of potassium ( K+ ) inside the cell is 30 times higher than outside .

The concentration of negative ions inside the cell is higher than outside , due to the presence of chloride ( Cl ) and protein ions , The amount of negative ions inside the cell exceeds the positive ions , so , the inner surface of the cell carries negative charges .

The changes in the nerve cell on stimulation

Propagation of the nerve impulse through the nerve fibers
Return of the nerve cell to its original state ( Repolarization )

Properties of the nerve impulse


Types of Synapse

Mechanism of transmitting the nerve impulse across a synapse


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