Nervous System :Function, Unit & Structure of Nervous System

Nervous System : Function, Unit & Structure of Nervous System

In multicellular animals, there are present many organs and organ systems. Every organ system performs a these organ systems collectively constitute an organism. Have you ever thought that how can many be made one ? How can unification (integration) be achieved ? We are going to discuss about Nervous System, Function of Nervous System, Unit of Nervous System & Structure of Nervous System.
Nervous System Function, Unit & Structure of Nervous System


Communication specific function. But, all and control are the keys to unlock the secret of integration. Communication makes possible control integration possible. In our body and in the body of other higher animals are present two such systems which control and coordinate the diverse activities of millions of smaller cells, body organs, etc.

One system called nervous system functions by the conduction of nerve impulses like the conduction of an electric current. Whereas, the other called endocrine system works by the release of chemical messengers-the hormones. and control makes

NERVOUS SYSTEM 

The system that controls and coordinates all the activities of various body parts in response to external and internal stimuli by the conduction of nerve impulses is called nervous system. An even more remarkable feature of the nervous system is its ability to respond to several stimuli simultaneously and spontaneously. For example, while watching television we can take our meals and also respire simultaneously. Every set of co-ordinated movements, whether skilled performances or routine tasks like cycling or driving a car, all involve the integrating powers of the nervous system. It is the master system of the body. It controls all other systems by sending and receiving messages through special cells called neurons ( unit of nervous system ).

Function of Nervous System

The major function of nervous system performs are below function of nervous system  :

  1. Control : The main function of Nervous system controls all the functions of various body parts.
  2. Co-ordination : Every body activity involves many body parts. The activities of all the body parts are co-ordinated and integrated by this system. 
  3. High faculties, such as, thinking, reasoning, memory emotions, etc. are controlled by this system. 
  4. Reflexes : All the spontaneous, automatic, involuntary activities are controlled by the nervous system. 
  5. It keeps us informed about the outside world by way of various sense organs and it is also the function of nervous system. 
  6. It keeps us informed about the internal environment of the body. 
  7. The function of nervous system is also to control and co-ordinate voluntary muscular activities. 
  8. Regulates involuntary activities such as beating of heart and breathing.
It was all about function of nervous system. All above 8 points are the most important function of nervous system.

NEURON - The unit of Nervous system 

The nervous system perceives various stimuli, convert them into impulses, convey these impulses to the controlling centre - the brain. In the brain these impulses are converted into orders which are then carried to effectors i.e. muscles and glands.

To carry out these highly specialized functions, the nervous system is made-up of highly specialized cells called neurons (  unit of nervous system ). The structural and functional unit of nervous system are the neurons or nerve cells ( unit of nervous system ). The neurons are able to perform these specialized functions because of their two properties : (i) Irritability and (ii) Conductibility 

Structure of neuron ( Unit of Nervous System )

Structurally a neuron consists of three parts :

  1. Cyton 
  2. Dendrites 
  3. Axon 
(1) Cyton : The main part of neuron is cell body called cyton or perikaryon. It is bounded from the outside by a simple cell membrane. Its cytoplasm is called neuroplasm. In addition to all the usual cell organelles present in an animal cell, neuroplasm also neurofibrils (help in transmission of impulses) and Nissl's granules (synthesize proteins for cell).

Nissl's granules are small fragments of endoplasmic reticulum with ribosomes. The only organelle which is absent is centrosome. This is the reason a nerve cell does not have contains ability to divide.

(b) Dendrites : These are one to many, highly branched but small projections arising from the cyton. They conduct nerve impulses from synapses towards cell body.

(c) Axon : From the cyton arises always one very long process called axon. It may be from few millimetres to one metre in length. In white all neurons ( unit of nervous system ) it is surrounded by a insulating sheath (covering cells) callea neurilemma. An additional sheath called myelin is present in some neurons which shows gap throughout the length called nodes of ranvier.

Some axons may have side branches called collaterals. Each axon terminates into a bulb like structure called synaptic knob which have certain chemicals called neurotrans- mitter. As the impulse reaches the terminal end of an axon, the neurotransmitter named as acetylcholine is released which sets new impulse in the dendrites of next (adjacent) neurons ( unit of nervous system ).

An enzyme soon breaks this chemical to make synapse ready for next transmission. The axon terminal of one neuron is very closely placed to the dendrites of another neuron without any physical or protoplasmic contact. This close proximity is known as synapse. The gap present between the dendrites and axon terminal is called synaptic cleft.

Classification of neurons ( Unit of Nervous System )

According to their functions, the neurons ( unit of nervous system ) are categorized into three types :
(a) Sensory (Afferent) neurons
(b) Motor (Efferent) neurons
(c) Association (Connector) neurons.

(a) Sensory (Afferent) neurons : These neurons ( unit of nervous system ) carry sensory impulses from the sense to the central nervous system. organs

(b) Motor (Efferent) neurons : These neurons transmit impulses from the central A nervous system to the effectors i.e. muscles or glands.

(c) Association (Connector) neurons : These neurons ( unit of nervous system ) are present in the central nervous system (brain and spinal cord) and connect sensory neurons to motor neurons.

Nerve fibres  in Nervous System

An axon of a neuron covered by one or two sheaths is called nerve fibre. The nerve fibre small (microscopic) upto one metre be very may in length. Depending upon the sheaths covering the axon of neuron here called neuraxis.
The nerve fibres are of two types:
(a) Myelinated nerve fibre
(b) Non-myelinated nerve fibre

(a) Myelinated nerve fibres : In these nerve fibres the axon of neuron is surrounded by two sheaths. The inner sheath is called myelin sheath and the outer sheath is called neurilemma. The medullary sheath is not continuous showing constrictions called nodes of Ranvier.

Functions of the myelin sheath :

  1. To increase the speed of nerve impulse conduction. 
  2. To insulate the axon, i.e., prevents mixing of impulses in the adjacent fibres. 


(b) Non-myelinated nerve fibres : In these nerve fibres the axon of neuron is covered by only one sheath called neurilemma. Myelin sheath is absent.

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