NEURON - PowerPoint Presentation

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NEURON

بسم الله الرحمن الرحيمSlide2

OBJECTIVES By the end of this lecture you should be able toDescribe the functional structure of neuron – Cell body, Dendrites, Axon. List the types of Nerve Conduction

List the factors that

affecting nerve

conductionIllustrate the functional importance of is myelin sheath & Node of RanvierDiscreminate between Contiguous Conduction and Saltatory Conduction

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Neuron (nerve cell) consists of Three Basic Parts : 1– Cell Body 2– Dendrites 3– Axon 3NEURONSlide4

NeuronCell bodyHouses the nucleus and organellesDendrites Project from cell body and increase surface area available for receiving signals from other nerve cellsSignal toward the cell bodyDendrite and cell body serve as the neurons input zone. Slide5

NeuronAxonNerve fiberSingle, elongated tubular extension that conducts action potentials away from the cell bodyConducting zone of the neuronSlide6

AxonAxon hillockFirst portion of the axon plus the region of the cell body from which the axon leavesNeuron’s trigger zone(where Action Potential are generated). Axon terminals

Release chemical messengers that simultaneously influence other cells with which they come into close association

Output zone of the neuron

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NeuronSlide8

REMEMBER Dendrites & cell body – Input zone ( Receive) Axon -- Conducting zone Axon Terminals – Output zone Action Potential are initiated at Axon Hillock (trigger zone)8NEURON (cont)Slide9

Action Potentials are propagated from the Axon Hillock to the Axon terminalIn cell body Graded Potentials (Local potentials) are produced in response to incoming signals. Action potentials are Initiated at the Axon Hillock, and conducted throughout a nerve fiberSlide10

Conduction of Action PotentialsTwo types of propagationContiguous conductionConduction in unmyelinated fibersAction potential spreads along every portion of the membraneSaltatory conduction Rapid conduction in myelinated fibersImpulse jumps over sections of the fiber covered with insulating myelin

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Contiguous ConductionSlide12

Myelinated FibersSlide13

Saltatory ConductionSlide14

Saltatory Conduction: Action Potential Propagation in a Myelinated Axon14Slide15

Saltatory ConductionPropagates action potential faster than contiguous conduction because action potential does not have to be regenerated at myelinated sectionMyelinated fibers conduct impulses about 50 times faster than unmyelinated fibers of comparable sizeMyelin Primarily composed of lipidsFormed by oligodendrocytes in CNSFormed by Schwann cells in PNSSlide16

Conduction depends on Two factors: 1) Diameter of the nerve fiber 2) Axon (Nerve fiber) is Myelinated or Unmyelinated 16CONDUCTION IN NERVE FIBERSSlide17

Diameter of Nerve fiber Nerve fiber with small diameter – conducts slowly Nerve fiber with large diameter – conducts fast 17CODUCTION IN NERVE FIBERS (cont)Slide18

Myelinated Nerve Fibers Myelinated nerve fibers conduct FAST then Unmyelinated nerve fibers. Why? Myelinated nerve fibers have saltatory conduction.18CONDUCTION IN NERVE FIBER (cont)Slide19

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SUMMARY Small diameter fiber conduct SLOW Large diameter fiber conduct FAST Myelinated nerve fiber conduct VERY FAST.20CONDUCTION IN NERVE FIBER (cont)Slide21

Regeneration of Nerve FibersRegeneration of nerve fibers depends on its locationSchwann cells in PNS guide the regeneration of cut axonsFibers in CNS myelinated by oligodendrocytes do not have regenerative abilityOligodendrocytes inhibit regeneration of cut central axonsSlide22

ReferencesHuman physiology by Lauralee Sherwood, seventh editionText book physiology by Guyton &Hall,11th editionText book of physiology by Linda .s contanzo,third edition