TNPSC Free Notes Biology – 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.

Nervous System

• The nervous system is made up of nervous tissues.
• It is formed of three distinct components namely the neurons, neuroglia and nerve
fibres.
Neuron or nerve cell:
• A neuron or nerve cell is the structural and functional unit of the nervous system.
• It is the longest cell of the human body with a length of over 100µm.
• Information is conducted through neurons in the form of electrical impulses from
one part of the body to another.
Neuroglia:
• Neuroglia are also called as glial cells.
• They are non-exciting, supporting cell of the nervous system.
• They do not initiate or conduct nerve impulses.
Nerve fibres:
• The nerve fibres are the long slender processes of neurons.
• A number of nerve fibres are bundled up together to form nerves.
Structure of Neuron:
A neuron typically consists of three basic parts:
1. Cyton, 2. Dendrites and 3. Axon.
Cyton:
• Cyton is also called cell body or perikaryon.
• It has a central nucleus with abundant cytoplasm called neuroplasm.
• Neurons do not have the ability to divide.
• Several neurofibrils are present in the cytoplasm that helps in transmission of
nerve impulses to and from the cell body.
Dendrites:

• These are the numerous branched cytoplasmic processes that project from the
surface of the cell body.
• They conduct nerve impulses towards the cyton.
• The branched projections increase the surface area for receiving the signals from
other nerve cells.
Axon:
• The axon is a single, elongated, slender projection.
• The end of axon terminates as fine branches which terminate into knob like
swellings called synaptic knob.
• The plasma membrane of axon is called axolemma, while the cytoplasm is called
axoplasm.
• It carries impulses away from the cyton.
• The axons may be covered by a protective sheath called myelin sheath which is
further covered by a layer of Schwann cells called neurilemma.
Synapse:
• A junction between synaptic knob of axon of one neuron and dendron of next
neuron is called synaptic junction.
• Information from one neuron can pass to another neuron through these junctions
with the release of chemicals known as neurotransmitters from the synaptic knob.
Types of Neurons:
The neurons may be of different types based on their structure and functions.
Structurally the neurons may be of the following types:
Unipolar neurons:
• Only one nerve process arises from the cyton which acts as both axon and
dendron.
• Unipolar neurons are located in the ganglia of cranial and spinal nerves.

Bipolar neurons:

• The cyton gives rise to two nerve processes of which one acts as an axon while
another as a dendron.
• These are found in the retina of the eye, inner ear and the olfactory area of the
brain.
Multipolar neurons:
• The cyton gives rise to many dendrons and an axon.
• They are mostly interneurons.
On the basis of functions neurons are categorized as:
• Sensory or afferent neurons
This carry impulses from the sense organ to the central nervous system.
• Motor or efferent neurons
This carry impulses from the central nervous system to effector organ such as the
muscle fibre or the gland.
• Association neurons
This conduct impulses between sensory and motor neuron.

On the basis of functions neurons are categorized as:
• Sensory or afferent neurons
This carry impulses from the sense organ to the central nervous system.
• Motor or efferent neurons
This carry impulses from the central nervous system to effector organ such as the
muscle fibre or the gland.
• Association neurons
This conduct impulses between sensory and motor neuron.

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