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TNPSC Free Notes Biology – Human Nervous System

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

Human Nervous System

Types of Nerve Fibres
Nerve fibres are of two types based on the presence or absence of myelin sheath.
Myelinated nerve fibre:
The axon is covered with myelin sheath
Non-myelinated nerve fibre:
• The axon is not covered by myelin sheath.
• Myelinated and non-myelinated nerve fibres form the white matter and grey
matter of the brain.

Human Nervous System

• The complexity of nervous system can be observed during the course of
• We the human beings differ from other animals in our ability to think and take
actions, which is due to the well developed nervous system.
• Human nervous system is differentiated into
1. Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
3. Autonomic Nervous System (ANS)
• The CNS acts as centre for information processing and control.
• It consists of the brain and the spinal cord.
• The PNS is made up of the nerves which connect the brain and spinal cord to all
parts of the body.
• The ANS is formed of sympathetic and parasympathetic nerves.

Central Nervous System
• The brain and the spinal cord being delicate vital structures are well protected in
bony cavities of the skull and the vertebral column respectively.
• CNS is formed of two types of matter such as white matter or grey matter with
respect to the presence or absence of myelin sheath which we have discussed
• The brain is the controlling centre of all the body activities.
• It is covered by three connective tissue membrane or meninges:
▪ Duramater (dura: tough; mater: membrane)
Is the outermost thick fibrous membrane
▪ Arachnoid membrane (arachnoid: spider)
Is the middle, thin vascular membrane providing web like cushion
▪ Piamater (Pia: soft or tender)
• Is the innermost, thin delicate membrane richly supplied with blood.
• Meningeal membranes protect the brain from mechanical injury.

Human Brain

A human brain is formed of three main parts:
• forebrain
• midbrain and
• hindbrain
• The forebrain is formed of cerebrum and diencephalon.
• The latter consists of dorsal thalamus and ventral hypothalamus.
• Cerebrum is the ‘seat of intelligence’ and forms the major part of the brain.
• It is the largest portion forming nearly two-third of the brain.
• The cerebrum is longitudinally divided into two halves as right and left cerebral
hemispheres by a deep cleft called median cleft.
• Two cerebral hemispheres are interconnected by thick band of nerve fibres called
corpus callosum.
• The outer portion of each cerebral hemisphere is formed of grey matter and is
called cerebral cortex. • The inner or deeper part is formed of white matter and is
called cerebral medulla.
• The cortex is extremely folded forming elevations called gyri with depressions
between them termed as sulci that increase its surface area.
• Each cerebral hemisphere is divisible into a frontal lobe, a parietal lobe, a
temporal lobe and an occipital lobe.
• These lobes are also known as cerebral lobes and are associated with specific
• Any damage in specific lobe inturn affects its function.
• The cerebrum is responsible for the thinking, intelligence, consciousness,
memory, imagination, reasoning and willpower.
• Thalamus present in cerebral medulla is a major conducting centre for sensory
and motor signalling.
• It acts as a relay centre.

• Within the thalamus, information is sorted and edited and plays a key role in
learning and memory.
• It lies at the base of the thalamus.
• It controls involuntary functions like hunger, thirst, sleep, sweating, sexual desire,
anger, fear, water balance, blood pressure etc.
• It acts as a thermoregulatory (temperature control) center of the body.
• It controls the secretion of hormones from anterior pituitary gland and is an
important link between nervous system and endocrine system.
• Meningitis is an inflammation of the meninges.
• It can occur when fluid surrounding the meninges becomes infected.
• The most common causes of meningitis are viral and bacterial infections.
• It is located between thalamus and hind brain.
• The dorsal portion of the mid brain consists of four rounded bodies called corpora
quadrigemina. It controls visual and auditory (hearing) reflexes.
• It is formed of three parts cerebellum, pons and medulla oblongata.
• Cerebellum is the second largest part of the brain.
• It consists of two cerebellar hemispheres and central worm shaped part, the
• It is second largest part of the brain formed of two large sized hemispheres and
middle vermis
• It coordinates voluntary movements and also maintains body balance.
• ‘Pons’ a latin word meaning bridge.
• It is a bridge of nerve fibre that connects the lobes of cerebellum.
• It relay signals between the cerebellum, spinal cord, midbrain and cerebrum.

• It controls respiration and sleep cycle.
Medulla Oblongata
• Medulla oblongata is the posterior most part of the brain that connects spinal cord
and various parts of brain.
• It has cardiac centres, respiratory centres, vasomotor centres to control heart beat,
respiration and contractions of blood vessels respectively.
• It also regulates vomiting and salivation.
Spinal Cord
• Spinal cord is a cylindrical structure lying in the neural canal of the vertebral
• It is also covered by meninges.
• It extends from the lower end of medulla oblongata to the first lumbar vertebra.
• The posterior most region of spinal cord tapers into a thin fibrous thread like
structure called filum terminale.
• Internally, the spinal cord contains a cerebrospinal fluid filled cavity known as
the central canal.
• The grey matter of spinal cord is ‘H’ shaped.
• The upper end of letter ‘H” forms posterior horns and lower end forms anterior
• A bundle of fibres pass into the posterior horn forming dorsal or afferent root.
• Fibres pass outward from the anterior horn forming ventral or efferent root.
• These two roots joins to form spinal nerves.
• The white matter is external and have bundle of nerve tracts.
• Spinal cord conducts sensory and motor impulses to and from the brain.
• It controls reflex actions of the body.
Cerebrospinal Fluid
• The brain is suspended in a special fluid environment called cerebrospinal fluid
• It is lymph like, watery fluid that surrounds and protects the brain within the
• It also fills the central canal of the spinal cord.

• It acts as shock absorbing fluid and protects the brain from damage when it is
subjected to sudden jerk.
• It supplies nutrients to the brain.
• It collects and removes wastes from the brain.
• It is also responsible for maintaining a constant pressure inside the cranium.
Reflex Action
• A reflex is any response that occurs automatically without consciouness.
• There are two types of reflexes.
Simple or basic reflexes:
• These reflexes are inbuilt and unlearned responses.
• Many of the actions we perform in our day to day life are simple reflexes. e.g.,
winking of eyes when any dust particles enters
Acquired or conditioned reflexes:
• These reflexes are the result of practice and learning.
• Playing harmonium by striking a particular key on seeing a music note is an
example of conditioned reflexes which required conscious training effort.
• Most of the reflex actions are monitored and controlled by the spinal cord, hence
also known as spinal reflexes. • The pathway taken by nerve impulse to accomplish
reflex action is called reflex arc.
Peripheral Nervous System
• Peripheral nervous system is formed by the nerves arising from the brain and the
spinal cord.
• The nerves arising from the brain are called cranial nerves.
• Nerves arising from spinal cord are called spinal nerves.
Cranial Nerves
• In man, there are 12 pairs of cranial nerves.
• Some of the cranial nerves are sensory e.g. optic nerve which innervates the eye.

Spinal Nerves
• There are 31 pairs of spinal nerves.
• Each spinal nerve has a dorsal sensory root and the ventral motor root.
• The direction of impulses in dorsal spinal root is towards the spinal cord and in
ventral spinal root away from the spinal cord.
Autonomic Nervous System
• Autonomic nervous system (ANS) is also called as visceral nervous system as it
regulates the function of internal visceral organs of our body through its two
antagonistic (opposite) components sympathetic and parasympathetic systems.
• They enable the body to perform rapid and specific visceral activities in order to
maintain steady state.
• It controls the involuntary functions of the visceral organs.


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