Structure and function of neuron

a seminar on the detailed structure and function of neuron .WHERE YOU GET EVERY THING AND THAT 'S SUFFICIENT FOR YOUR SEMINAR .

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

2. 2 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

3. 3 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

4. 4 DENDRITES NUCLEUS CELL BODY AXON AXON TERMINAL SYNAPSE (STRUCTURE OF NEURON) DENDRONS

5. 5 (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

6. 6 (B) neurites The processes of neurons are called neurites . These are of two types- Dendrites or Dendrons Axon DENDRITES AXON It may be one or many per neuron . It has both neurofibrils and Nissl’s granules . It is short and tapering . Much branched , practically all long . Conducts impulse towards the cyton . Covered by only one sheath of nerve fibre . It is single per neuron . It has neurofibrils but no Nissl’s granules It is long and uniform in diameter . Branched at the distal end only . Conducts impulse away from the cyton . 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 .

7. 7 DENDRONS DENDRITES AXON AXON TERMINAL (STRUCTURE OF NEURITES)(EXCLUDING THE AREA INN THE CIRCLE)

8. 8 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 On the basis of their structure of poles these are of following type- (A) NONPOLAR NEURONS – 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) UNIPOLLAR NEURONS – 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] 10

11. 11 (C) PSEUDOUNIPOLAR NEURONS – A single process arise from the cyton and then divides into axon and dendrite , such neurons are termed as pseudo- unipolar neurons. (D) BIPOLAER NEURONS – 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. . MULTIPOLAR NEURONS – 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]

12. 12 On the basis of their function neurons are of the following types – SENSORY NEURONS – These are the receptor neurons which connect sense organ with the CNS . They bring sensory impulse from the sense organ to the CNS . 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)

13. 13 On the basis of the covering of the axon neurons are of following types – MEDULLATED OR MYELINATED NERVE FIBRE – These are white in appearance . These neurons consists of the following parts – AXIS CYLINDER – 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 . MEDULLARY SHEATH – 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 . 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 .

14. 14 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. NON-MEDULLATED NERVE FIBRE OR NON MYELINATED NERVE FIBRE – 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) 15

16. 16 On the basis of the pathway of impulse conduction the neurons are of following types – AFFERENT - These are the sensory nerve fibres that carry impulses from the sense organs to the CNS . EFFFERENT – These are the motor nerve fibres which carry nerve impulses from the CNS to the effector organ . (EFFERENT AND AFFERENT NEURON)

17. 17 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. .

18. 18 BIBLIOGRAPHY GOOGLE PINTREST WWW.SCIENCEDISCUSSION.COM WWW.BIOLOGYJUNCTION.CON TRUEMAN’S ELEMENTARY BIOLOGY BOOK BY K.N. BHATIA AND M.P. TYAGI HUMAN PHYSIOLOGY BOOK BBY C.C CHATARJEE

19. 19 THANK YOU