This document provides an overview of the structure and function of neurons. It discusses the main parts of a neuron including the cyton, neurites (dendrites and axon), and synapse. It describes different types of neurons based on their structure (nonpolar, unipolar, pseudounipolar, bipolar, multipolar), function (sensory, motor, interneurons), myelination (myelinated, unmyelinated), and pathway of impulse conduction (afferent, efferent). The key function of neurons is to receive, transmit, and interpret stimuli to coordinate activities in the body.

1. A SEMINAR ON
“STRUCTURE AND FUNCTION OF NEURON”
By-
Sambit Bhai Patel

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contents PAGE NO.
 What is a neuron ?------------------------------------------------------------ 1
 Cyton ---------------------------------------------------------------------------3
 Neurites------------------------------------------------------------------------4
 Synapse------------------------------------------------------------------------6
 Types of neuron --------------------------------------------------------------8
 On the basis of structure of poles--------------------------------------8
 On the basis of function-----------------------------------------------10
 On the basis of covering on axon--------------------------------------11
 On the basis of pathway of impulse----------------------------------14
 Function----------------------------------------------------------------------15
 Bibliography----------------------------------------------------------------16

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What is a neuron ?
• A neuron is a structural and functional unit of the neural tissue and hence forms the neural system .
These are the longest cell in our body .Fully formed neurons never divide and remain in interphase
through out the life .
• It has the property of excitability and conductivity. Excitability is the ability to initiate nerve impulse in
response to stimuli . Conductivity is the ability to transmit a nerve impulse
• The reaction is called response . The response may be sensation such as pain , muscle contraction , etc. .
• The neurons are the main components of the brain , CNS , etc. .
• Neuron consist of the following parts-
NEURON
CYTON
NEURITES
MULTIPOLAR
BIPOLAR
UNIPOLAR
DENDRITES
AXON

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DENDRITES
NUCLEUS
CELL BODY
AXON
AXON TERMINAL
SYNAPSE
(STRUCTURE OF NEURON)
DENDRONS

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(A) CYTON
• The cyton or the cell body is the head region of the neuron .
• The cyton contains cytoplasm called as neuroplasm , prominent spherical nucleus , mitochondria ,etc. with
nissils granules and neurofibrils .Nissl’s granules are comparatively large and irregular masses of
ribosomes and RER . They probably synthesizes proteins in the cell .
(STRUCTURE OF CYTON)
Cell body

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(B) neurites
• The processes of neurons are called neurites .
• These are of two types-
I. Dendrites or Dendrons
II. Axon
DENDRITES AXON
i. It may be one or many per neuron .
ii. It has both neurofibrils and Nissl’s granules .
iii. It is short and tapering .
iv. Much branched , practically all long .
v. Conducts impulse towards the cyton .
vi. Covered by only one sheath of nerve fibre .
i. It is single per neuron.
ii. It has neurofibrils but no Nissl’s granules
iii. It is long and uniform in diameter .
iv. Branched at the distal end only .
v. Conducts impulse away from the cyton .
vi. Covered by two or three sheath .
• Axon is the cylindrical axis like structure that arise from the cyton . The part of cyton from where the axon
arise is called axon hillock ,which is the most sensitive part of a neuron .

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DENDRONS
DENDRITES
AXON
AXON
TERMINAL
(STRUCTURE OF NEURITES)(EXCLUDING THE AREA INN THE CIRCLE)

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• The axon ends in a group of branches called axon endings or pre synaptic knob .
• Certain axon give rise to lateral side branches called as collateral fibres .
• The plasma membrane and neuroplasm of axon are called axolemma and axoplasm respectively .
• The axon is also called as efferent process because it conducts the nerve impulses away from the cyton .
synapse
• A synapse is the site of junction between an axon ending of a neuron and the dendrite of an another .
• However they do not touch each other and remain separate by a microscopic gap about 200 A° .
• Each neuron receives an impulse through its dendrites and passes it to the next neuron through synapse .
• The impulse transmit through chemicals called neurotransmitters like acetylcholine . (Acetylcholine is the
first neurotransmitter to be discovered )

9. 9(STRUCTURE OF SYNAPSE)
TERMINATING
NEURON
SYNAPTIC
CLEFT
RECIEVING
NEURON

10. TYPES
1) On the basis of their structure of poles these are of following type-
(A) NONPOLARNEURONS–
• These type of neuron bears several branched processes . There no functional differences between the
axon and Dendron . Each processes can bring impulse to the cyton or can take away from the cyton .
These neurons are rare in vertebrates but common in cnidarians such as Hydra
(B) UNIPOLLARNEURONS–
• Such neurons has a single process , which arises from the cyton . True unipolar neurons with an axon
and no dendrite are found in early embryos of invertebrates and vertebrates .
(A) (B)
[(A)-structure of nonpolar neuron(B)-structure of unipolar neuron]
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(C) PSEUDOUNIPOLARNEURONS–
• A single process arise from the cyton and then divides into axon and dendrite , such neurons are
termed as pseudo- unipolar neurons.
(D) BIPOLAERNEURONS–
• These neurons have only two processes ,an axon at one end and a dendrite at another end . Bipolar
neurons are found in the retina of eye , etc. .
(E) MULTIPOLARNEURONS–
• These neurons have several dendrites and an axon . Motor neurons and inter neurons are multipolar .
These are the most common type of neurons . These are present in the gray matter of brain and spinal
cord .
(C) (D) (E)
[ (C) BIPOLAR NEURON (D) MULTIPOLAR NEURON (E)PSEUDOUNIPOLAR NEURON]

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2) On the basis of their function neurons are of the following types –
(A) SENSORYNEURONS–
• These are the receptor neurons which connect sense organ with the CNS . They bring sensory impulse
from the sense organ to the CNS .
(B) MOTOR NEURONS–
• These are the effector neurons which connect the CNS to the effectors . They carry impulses from the
CNS to the effectors .
(C) INTERNEURONS–
• These are the connector neurons that are present in the CNS and occur between the sensory and
motor neurons for distance transmission of impulse . They are neither sensory nor motor but are
meant for the carrying the impulses .
(A) (B) (C)
(MOTORNEURON)
(B)

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3) On the basis of the covering of the axon neurons are of following types –
A. MEDULLATEDOR MYELINATEDNERVEFIBRE –
• These are white in appearance . These neurons consists of the following parts –
a) AXISCYLINDER– It is simply the axon or dendrite of a nerve cell . Its neuroplasm is called as
axoplasm and the membrane surrounding the axis cylinder is called as axolemma . Axolemma
conducts the nerve impulses .
b) MEDULLARYSHEATH– It is also called as myelin sheath . It is composed of the substance myelin
. The myelin sheath act as insulating layer , which prevents the loss of energy of the nerve
impulse . It works like the coating on the electric wire . The myelin sheath is continuous in the
CNS but in PNS it is absent at certain points called nodes of Ranvier . The part of a nerve fibre
between two successive nodes of Ranvier is called as internode . Each segment of myelin sheath
is made up of schwann cell .
c) NEURILEMMA– Outside the myelin sheath there is a layer of schwann cell cytoplasm which is
called as neurilemma . A single large and flat nucleus is present in the cytoplasm . The
neurilemma is continuous over the nodes of Ranvier . As stated above schwann’s cells produce
myelin sheath .

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• A thin layer of connective tissue called endoneurium covers the neurilemma .
• The medullated nerve fibre of brain and spinal cord lack neurilemma .due to lack of neurilemma the
nerve fibre of brain and spinal cord do not regenerate after injury .
• These cells have an incomplete covering of neuroglial cell which produce myelin sheath .
• Neurelemma present in the cells of PNS which enables them to regenerate after injury .
• The colletral fibres arise from the nodes of Ranvier at right angles .
• These modulated nerve fibres are found in the white matter of brain and spinal cord and in the
cranial and spinal nerves .
• Conduction of impulse is more faster in myelinated nerve fibre than the nonmyelinated one
(T.S. OF MYLINATED AXON OF MYELINATED NEURON)

15. B. NON-MEDULLATEDNERVEFIBREOR NON MYELINATEDNERVEFIBRE–
• These neurons are grey in appearance .
• A non-myelinated nerve fibre consist of an axis cylinder surrounded by neurilemma and connective
tissue .they form the grey matter .
• These fibres do not have the node of Ranvier and internodes . They also lack collateral fibres .
• These are found in the autonomic nerves .
• They conduct nerve impulse much slower than the medullated nerve fibres .
(NON-MYELINATED NERVE FIBRE)
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4) On the basis of the pathway of impulse conduction the neurons are of following types –
A. AFFERENT- These are the sensory nerve fibres that carry impulses from the sense organs to the CNS .
B. EFFFERENT– These are the motor nerve fibres which carry nerve impulses from the CNS to the effector
organ .
(EFFERENT AND AFFERENT NEURON)

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FUNCTION
• Neurons are the structural and functional unit of nervous tissue .
• The neural tissue is meant for reception , interpretation and transmission , where the neurons receives
the stimuli
• The sensory neurons carry sensory nerve impulses to the interneurons which send impulse through
motor neurons to the effectors .
• Neurons help in the coordination and interagetation of activities of various body parts .
• The neurons in nervous tissue also act as seat of experiences and memories , etc. .

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BIBLIOGRAPHY
GOOGLE
PINTREST
WWW.SCIENCEDISCUSSION.COM
WWW.BIOLOGYJUNCTION.CON
TRUEMAN’SELEMENTARYBIOLOGYBOOK BY K.N. BHATIAANDM.P. TYAGI
HUMANPHYSIOLOGYBOOKBBY C.C CHATARJEE

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