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Nervous System consists of brain,
spinal cord, sense receptors and a
whole lot of nerves
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Neuron: The Unit of nervous System
Our nervous system consists of brain,
spinal cord, sense receptors and a whole
lot of nerves
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Structure of the neuron: The three main
parts of a neuron are the cell body,
dendrites and axon
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• It has all the cell organelles like other cells, only centrosome is absent
because nerve cells have lost the ability to divide
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They
conduct nerve impulses to the cyton
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• It is surrounded by white insulating sheath called myelin sheath which
is covered by outermost thin sheath called neurolemma
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Axon terminals are
closely placed near dendrites of another neuron through a gap called
synaptic cleft
Synapse- is the point of contact between terminal branches of the axon
of a neuron with dendrites of another neuron separated by a fine gap
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The nervous system can transmit signals at speeds of 100 meters per
second
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Types of Neurons :
Sensory Neuron – brings impulse from receptor to brain
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Association Neuron- interconnects the sensory and motor neuron
Nerve is bundle of nerve fibres (axons) of separate neurons
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They are of 3 types: sensory, motor and mixed nerve
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Two major divisions of the Nervous System:
1
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2
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The PNS consists of two subdivisions:
A
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B
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The Brain: The brain is a very delicate organ
well protected inside the brain box or
cranium of the skull
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(i) Dura mater - the outermost tough fibrous membrane
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(iii) Pia mater- the innermost highly vascular membrane, richly supplied
with blood
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Parts of the Brain:
The brain has three main parts visible externally,
(1) cerebrum
(2) cerebellum
(3) medulla oblongata
1) Cerebrum (cerebrum: brain)
The cerebrum is the largest portion of the brain
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Their outer surface
is highly convoluted with ridges and grooves
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The outer portion (cortex) of the cerebrum contains cell bodies of the
neurons and, being grayish in colour, is called the gray matter
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Functions - It is seat of intelligence, consciousness, and will power And
Subconscious mind and all voluntary actions
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CEREBELLUM ("little brain")
The cerebellum is a much smaller area of the brain located just at the
base and under the large cerebrum
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This also has an outer cortex made of gray matter
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The main function of the cerebellum is to maintain 'balance' of the body
and coordinate muscular activity
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It is roughly triangular and is continued behind as the
spinal cord
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Three Primary Regions of the Brain:
All parts taken together, the brain may be said to consist of three
primary regions forebrain, midbrain and hindbrain
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Forebrain:
a) Cerebrum (cerebral hemispheres) (seat of intelligence, memory,
consciousness, will power, voluntary actions)
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(ii) Hypothalamus (controls the
body temperature and pituitary)
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Midbrain: A small tubular part
(reflexes involving eyes and
ears)
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Hindbrain:
a) Cerebellum (coordinates muscular act balance of the body)
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c) Medulla oblongata (controls activities of internal organs, heart beat,
breathing, etc
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Spinal Cord has the
arrangement of white and the gray matter is reversed from that in the
brain
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There is a small central canal in the center which runs the
entire length and is continuous with the cavities of the brain
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Functions of the Spinal Cord
The spinal cord is concerned with the following three functions:
(i) Reflexes below the neck
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(iii) Conducts motor responses from the brain to muscles of the trunk
and limbs
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(1) Cranial Nerves – They emerge from brain and are 12 pairs
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Autonomic Nervous System (ANS)
Consist of nerves and ganglia which controls involuntary actions
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Reflexes (Involuntary Actions)
The term “reflex” comes from the Latin word “reflexus” meaning
reflected or directed back
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Reflex arc is the shortest route that can be taken by an impulse from
receptor to an effector
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Voluntary Actions
2
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These are inborn ex:
blinking, coughing, knee jerk, closing of eyelids, sneezing etc
Conditioned reflex: Acquired during lifetime or experience

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