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What are the two types of Nervous System ? ( 2021 Updated )

We are going to discuss about the two types of Nervous System, as well as the Function of Nervous System, Unit of Nervous System & Structure of Nervous System.

If you have any doubt related to Nervous System, then it is going to be clear in this article because we are going to cover mostly topics related to Nervous System.

types of nervous system
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.

But before knowing about the two types of Nervous System , you should know about Nervous System.

Right...

What is 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.

two types of nervous system

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
(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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What are the two types of Nervous System ?

Division of Nervous System is into two major parts. Those two types of Nervous System are :-

I. Central Nervous System (CNS) : All the parts of the nervous system which are present along the median longitudinal axis of the body constitute the central nervous system. It consists of brain and spinal cord.

II. Peripheral Nervous System ( PNS ) : It is formed by all the whitish thread-like nerves that connect the various body parts with the CNS.

The PNS is again divided into 2 subdivisions :

1. Somatic nervous system (SNS) : It is the voluntary part of PNS. It conducts impulses to and from skeletal (voluntary) muscles, bones, ligaments, joints and skin receptors.

2. Autonomic nervous system (ANS) It is the involuntary part of nervous system that controls the involuntary activities of various body parts.

It includes all those nerves, nerve fibres, ganglia (aggregates of cell bodies of neuron) that carry impulses from viscera to CNS which controls involuntary actions of smooth muscles, cardiac muscles and glands.


So lets get started discussing about CNS...

CENTRAL NERVOUS SYSTEM ( CNS )

Central Nervous System is the first among the two types of Nervous SystemIt consists of two parts :
  1. Brain 
  2. Spinal cord 

The Brain

Position, Protection and Meninges The human brain is highly developed. It is largest amongst all the animals. In an average it approximately weighs about 1350 g.

It is made-up of about 1000 billion neurons. The brain is placed and well protected in the cranial cavity or brain box of skull, It is surrounded by three protective membranous covering called meninges which continue backwards on the spinal cord.

what are the two types of nervous system

These are Piamater (innermost, very thin, tough and highly vascular membrane), Arachnoid (thin delicate middle layer and non-vascular) and Duramater (outermost, thick, non-vascular, tough fibrous membrane), from inner to outerside.

Between the meninges, spaces are present. These are filled with cerebro spinal fluid (CSF). The same fluid is also filled in the central spaces of brain and central canal of spinal cord.

So here is its function...

Functions of CSF : 

  1. It serves as shock absorbing medium. It protects the brain and the rest of CNS against jerk and jolts. 
  2. It maintains constant pressure in and around the brain.

Structure of Brain

Human brain is a whitish, bilaterally symmetrical structure. It is divisible into three regions :
  1. Fore-brain 
  2. Mid-brain 
  3. Hind-brain

1. Fore-Brain 

It is differentiated into three parts :
(a) Olfactory lobes
(b) Cerebrum
(c) Diencephalon

(a) Olfactory lobes : The olfactory lobes of human brain are a pair of poorly developed, club-shaped, widely separated bodies. They are visible from the ventral surface only. The olfactory lobes are concerned with the sense of smell.

(b) Cerebrum : It is the largest part and forms 4/5th weight of the brain. It consists of right and left lobes called cerebral hemispheres.

They cover all the parts of the brain superiorly and lie side by side. Their surface is highly folded or convoluted with ridges and grooves to increase the surface area.

Each cerebral hemisphere is hollow from inside and their walls have 2 regions, outer cortex and inner medulla. The outer portion of cerebrum contains grey coloured cell bodies and hence called grey matter, which is folded to form convolutions.


The folds (gyri) and grooves (sulci) increase the surface area to accommodate more neurons and hence believed to have more intelligence.

The inner portion consists of axons of neurons which is white in colour, hence, called white matter. The two cerebral hemispheres are separated from each other by a very deep groove known as cerebral fissure.

The two hemispheres are held together by a transverse band of nerve fibres called corpus callosum. Each cerebral hemisphere is divided into four lobes called frontal lobe, parietal lobe, occipital lobe and temporal lobe.

Functions of Cerebrum : 
  • It is the seat of memory, will power, emotions, experiences, intelligence, reasoning, learning, invent and plan. 
  • It initiates and controls the movements of striped muscles. 
  • It controls the conscious sensations and all voluntary actions. 
  • (iv) It perceives the sensory impulses, such as, pain, touch, taste, smell, hearing and sight. 
  • What is called subconscious or uncon- scious mind is also located in the cerebrum. Many past experiences are covered up by more recent impressions which dominate conscious activity. Past experiences may be recalled in dreams or when hypnotized or when skilfully questioned. 
(c) Diencephalon : It is a small rhomboidal lobe. It is completely covered superiorly by large cerebrum but visible from the inferior surface as a small area.

It lies between cerebrum and midbrain. It is distinguishable into two parts- the thalamus and hypothalamus.

Functions of Diencephalon : Diencephalon of human brain controls many body functions, such as :
  • Hypothalamus temperature, control of pituitary gland and blood pressure. controls body 
  • Thalamus acts as a relay centre for pain pressure impulses to cerebrum.

2. Mid-brain 

Mid-brain of humans is significantly small, thick stalk, about 2 cm long. It connects the fore-brain with cerebellum and pons of hind brain.

Functions of Mid-brain:
  • It connects the hind brain with fore brain and conveys impulses. 
  • It controls the sight and auditory impulses (hearing).

3. Hind-brain 

It is the posterior, small part of the brain. It is differentiated into three parts :
(a) Pons varolii
(b) Cerebellum
(c) Medulla oblongata.

(a) Pons varolii : It is centrally located below cerebellum.

Functions :
It carries impulses from medulla oblongata to fore-brain. It also carries impulses from one hemisphere of the cerebellum to other and coordinates muscular movements on both sides.

(b) Cerebellum : It is the largest part of hind-brain. It is present below the cerebrum and above the medulla oblongata, behind the pons.

It consists of two large lateral lobes called cerebellar hemispheres. Its surface is marked by a large number of transverse fissures which give it a laminated appearance core of white matter.

It has an inner surrounded by grey matter (cortex) which is greatly folded. It has no convolutions.

Functions : 
It helps to maintain the balance or equilibrium during movements and it controls and coordinates muscular activity (balance of the body).

(c) Medulla oblongata : It is about 2.5 cm long that extends from pons to spinal cord. It is almost triangular in shape. It is also hollow from inside.
Functions : 
It controls the involuntary activities of internal organs like beating of heart, movement of breathing, sneezing, swallowing, vomiting, coughing, hiccupping and peristaltic movement of alimentary canal.

The Spinal Cord

The spinal cord is a long, unsegmented, cord like structure extending from medulla oblongata of brain through the neural canal of the vertebral column to the lumbar region.

It is about 45 cm in length and 35 g in weight. It is also covered by three membranes called meninges. Spaces present between these meninges are full of cerebro-spinal fluid (CSF).

Walls of vertebrae, meninges and CSF protect the spinal cord. Like-brain, spinal cord is also made-up of grey matter and white matter.

But...

In the spinal cord the arrangement of white and grey matter is reverse i.e white matter is external and grey matter is internal in position. The spinal cord is hollow from inside containing a cavity called central canal.

Functions of Spinal Cord: 

The spinal cord performs two important functions:
  • The spinal cord tracts serve as two-way conduction paths between peripheral nerves and the brain. Ascending tracts conduct sensory impulses up the cord to the brain while descending tracts conduct motor impulses down the cord from the brain. 
  • The spinal cord functions as reflex centre which controls all the spinal reflexes. 
  • It controls reflexes below neck.

PERIPHERAL NERVOUS SYSTEM ( PNS ) 

All the whitish, thread-like nerves, which connect the various body parts with the central nervous system, collectively constitute the peripheral nervous system. It is divided into two :
  1. Somatic Nervous System
  2. Autonomic Nervous System

Somatic nervous system

It consists of Cranial and Spinal nerves.

Cranial nerves : Those nerves which arise from the brain are called cranial nerves. There are 12 pairs of cranial nerves.

The cranial nerves olfactory nerves may be sensory, example (nose), optic nerves (eye) and auditory nerves (ear), motor, example - occulomotor nerves (going to eye muscles) and mixed in nature, example - facial nerves (going to and coming from face).

Spinal nerves : Spinal nerves arise from the spinal cord and these are 31 pairs in man. These are classified into the following five groups :

  1. Cervical spinal nerves in the neck - 8 pairs 
  2. Thoracic spinal nerves in thorax - 12 pairs 
  3. Lumbar spinal ne -5 pairs rves in abdomen 
  4. Sacral spinal nerves in hip region 5 pairs 
  5. Coccygeal spinal nerves in tail region -1 pair 
All spinal nerves are mixed nerves.

Autonomic nervous system (ANS) 

That part of the nervous system which controls all the involuntary activities of various body parts is called autonomic nervous system. It is divided in two parts :

(A) Sympathetic
(B) Parasympathetic

Emotions and Autonomic Nervous System: 

Autonomic nervous system is strongly influenced by emotions, such as, sorrow, happiness, anger, fear, sexual stimulation, etc.

Long continuous emotional stresses may cause certain disorders like high blood pressure, stomach ulcers, etc.


Conclusion or Summary of the Nervous System

According to Wikipediathe nervous system is a highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body.

So,

In this article, we have mainly discussed that, "What are the two types of Nervous System ?". The following points are covered briefly in this articles -
  • What is Nervous System ?
  • Function of Nervous System.
  • Unit of Nervous System.
  • Structure of Nervous System.
  • What are the two types of Nervous System ?
  • Their functions etc.
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