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Nervous System Nervous system 1 CELLS IN CNS Ectodermal origin • Astrocytes Oligodendrocytes • Astrocytes: • blood brain barrier • 2 types • Fibrous astrocytes in white matter • Protoplasmic astrocytes in gray matter • Oligodendrocytes • Form myelin in CNS 2 Mesodermal origin Microglia • do not develop from cells of neural tube • They come from bone marrow. • These are called microglia • They resemble tissue macrophages. 3 NEURON 4 • Nerve has axon and dendrites and a cell body • Axon starts from axon hillock and ends in terminal buttons which contains vesicles with neurotransmitters. • Nodes of Ranvier: 1 micro metre constrictions, 1mm apart. • Nerve surrounded by myelin sheath . • Myelin formed by schwann cells in PNS but in CNS it is formed by Oligodendrogliocytes. • Transmisssion of transmitters by axoplasmic flow. 5 • Electric Potentials • Non Propagative Propagative. • ALL OR NONE LAW: If the threshold is attained, no change in action potential even if intensity of stimulus is increased. • Refractory Period • Absolute Relative • From firing level to 1/3 from this pt. to start of • Repolarisation after depolarisation. 6 • Myelinated fibres conduct faster • SALTATORY CONDUCTION: Jumping from one node to the other • Depolarisation due to entry of Na ions • Repolarisation due to efflux of K ions • Action potentials starts in axon hillock due to increased Na channels • Energy source is Na K ATP ase. 7 • In CNS neurons are surrounded by glial cells. • 3 types of neuroglia • 1) Microglia - Scavenger cells • 2)Oligodendrocytes :- Forms myelin • 3)Astrocytes: 2 types, Forms blood brain barrier • A) Fibrous • B) Protoplasmic 8 AP reaches pre synaptic terminal Ca Channels open Ca influx Fusion of vesicles with plasma memb Exocytosis 9 Release of neurotransmitter Endocytosis Endosome formation Budding of vesicles from endosome 10 PRESYNAPTIC INHIBITION: Axo axonal synapse Activation of Opening of Direct Presynaptic K channels inhibition Receptors Inc.Cl entry Inc. K efflux Dec. Ca entry Dec. Ca. entry Dec. AP Dec . AP 11 PRE SYNAPTIC FACILITATION:- Axo- axonal synapse Release of serotonin Inc. C AMP Closes K channels Prolongs AP 12 VENTRICLES 13 14 REFLEXES • Reflex arc: • Sense organ • Afferent neuron • Central integrating station • Efferent neuron • Effector. • Bell Magendie law: • Dorsal roots - sensory • Ventral roots - motor. 15 REFLEXES 9 Monosynaptic 9 Polysynaptic 9 Stretch Reflex 9 Stimulus : stretch of muscle 9 Sense organ : muscle spindle. 9 Reflex :contraction of muscle 9 Eg: Knee jerk 9 Triceps jerk 16 REFLEX ARC 17 MUSCLE SPINDLE • Intrafusal fibres • Extrafusal fibres • Intrafusal fibres-1) Nuclear chain fibre. • 2)Nuclear bag fibre. • Afferents - Ia • II • Efferent - Beta (both intrafusal & extrafusal) • - Gamma (only intrafusal) • Gamma efferent discharge-Jendrassik’s maneuver. 18 MUSCLE SPINDLE 19 RECIPROCAL INNERVATION Impulses in Ia fibre of agonist muscle Send collateral to inhibitory interneuron (Golgi tendon organ) this synapses on motor neuron of antagonist muscle inhibits antagonist muscles 20 INVERSE STRETCH REFLEX Also called as autogenic inhibition Ib afferent Inhibitory interneuron (Golgi tendon organ) Relaxation of muscle. This is due to overstretch of muscle. 21 WITHDRAWAL REFLEX Polysynaptic reflex painful stimulus Flexor muscle contraction Inhibition of extensor muscles So the part is withdrawn from stimulus. 22 VISION: ANATOMY. • Sclera • Cornea • choroid • lens • ciliary body • Aqueous humour- produced by ciliary body • Vitreous humor. • Canal of schlemm. PATHOLOGY: • Open Angle Glaucoma • Closed Angle Glaucoma. 23 EYE 24 RETINA • Retina has rods & cones and 4 types of neurons • 1) bipolar cells • 2)ganglion cells • 3)horizontal cells • 4)Amacrine cells • Horizontal cells -connect rods & cones • Amacrine cells - connect ganglion cells. 25 LAYERS: • Layer of pigment epithelium • Layer of Rods & cones • Outer nuclear layer • Outer plexiform layer • Inner nuclear layer • Inner plexiform layer • Ganglion cell layer • Optic nerve fibres 26 PHOTO RECEPTOR MECHANISM • Action potentials are generated only on ganglion cells • Local potentials in the rest of the cells • Normally in darkness: • Na K ATPase in inner segment • Pumps 3Na+ ions into outer segment • Through open Na+ channels in outer segment • Release of neurotransmitter. 27 When light falls on rods. Na+ channel in outer segment closes Hyperpolarisation No release of neurotransmitter Generates action potentials in ganglion cells. Activates cGMP phosphodiesterase CGMP - 5’ GMP Closure of Na+ channels. 28 Rhodopsin Light 11cis retinene All transretinene Alters configuration of opsin Activates transducin 29 Transducin binds with GTP Activates cGMP phosphodiesterase cGMP 5’ GMP Closure of Na channels 30 VISUAL PATHWAYS • Geniculate body has six layers. • 1,2 - magnocellular • 3,4,5,6 - parvocellular. • 1,4,6 - inputs from contralateral eye • 2,3,5 - inputs from ipsilateral eye • 2 types of ganglion cells in retina : • Magno (or) M cells • Parvo (or) P cells . 31 M Magnocellular laminas Superficial Layer 4c Function:- Movement, Location, Spatial Organisation. 32 P Parvocellular laminas Deep layer 4 c Shape, color, texture, finer detail. Young Helmholtz theory: 3 kinds of cones each containing a different photopigment and maximum sensitivity to one of the prime colours. 33 Upper retinal quadrant subserving vision from lower visual field Medial half of lateral geniculate body Superior lip of calcarine fissure. 34 Lower retinal quadrant subserving vision from upper visual field Lateral half of lateral geniculate body Inferior lip of calcarine fissure. Fibres from lateral geniculate body that subserve macular vision Posterior part of calcarine fissure. 35 OPTIC PATHWAY 36 SPEECH & VISUAL AREAS 37 HEARING AND EQUILIBRIUM • Semicircular canals - Rotational acceleration. • Utricule – linear acceleration in • horizontal direction • Saccule – linear acceleration in vertical direction. • ANATOMY: • EXTERNAL & MIDDLE EAR. • External auditory meatus • Tympanic membrane • Eustachian tube • malleus, incus, stapes • foot plate of stapes-oval window. 38 INNER EAR (LABYRINTH) • Outer bony labyrinth • Inner Membranous labyrinth. • Bony labyrinth- perilymph • Membranous labyrinth-endolymph. • Cochlea • Basilar & Reissner’s membrane divide it into 3 chambers • Upper scala vestibuli- perilymph • lower scala tympani – perilymph • communicate through helicotrema • Scala vestibuli- ends in oval window • Scala tympani- ends in round window. 39 ORGAN OF CORTI • extends from apex to base of cochlea. • Tunnel of corti formed by rods of corti. • Outer hair cells- pierce tectorial membrane • inner hair cells do not. • afferent neurons from inner hair cells mainly • efferent neurons reach outer hair cells mainly. 40 INNER EAR 41 Internal structure ORGAN OF CORTI 43 AUDITORY PATHWAYS From cochlea Spiral ganglion Dorsal and ventral cochlear nuclei. Inferior colliculus. Medial geniculate body. Auditory cortex(41) 44 SEMICIRCULAR CANALS,UTRICLE & SACCULE • Semicircular canals contain crista ampullaris located in ampulla. • Crista cmpullaris has sustentacular cells & hair cells closed by cupula. • Utricle & saccule contain macula which has hair cells & sustentacular cells surrounded by otolithic membrane embedded with calcium carbonate crystals(otolith). 45 HAIR CELLS • Contain stereocilia • Also contain kinocilium > clubbed end • GENESIS OF ACTION POTENTIALS • RMP of hair cell is - 60 mV. • Perilymph formed from plasma • Endolymph from stria vascularis(scala media). • Enololymph has high K & low Na • Scala media is relatively 85mV positive than vestibuli & tympani. • Tip links are processes that tie tip of stereo cilium to its neighbour. 46 Shorter stereocilia pushed to higher Cation channel in tip links open K & Ca entry Depolarization AP in neurons K+ enters into sustentacular cells through tight junction. Reaches strio vascularis Secreted into endolymph. 47 TYMPANIC REFLEX Loud Sounds Contraction of tensor tympani & stapedius Decreased sound transmission. 9 lasts 40 – 120 ms, hence can’t protect against gunshot wounds. 48 SMELL AND TASTE • SMELL. • Olfactony receptors are located in olfactory mucous membrane. • Axons of the receptors contact the dendrites of mitral cells and tufted cells to form synapses called olfactory glomeruli. • Granule cells have no axons and make synapses with dendrites of mitral and tufted cells. 49 TASTE • 4 types buds ; made up of 4 types of cells • Type 1 & 2 cells : sustentacular cells • Type 3 cells : gustatory receptor cells • Type 3 cells have a microvillus which project into the taste pore. • Fungiform papillae : tip of tongue • Filiform papillae : dorsum of tongue • Vallate papillae :‘V’ shaped on back of tongue. • Fungiform papillae : 5 taste buds • Vallate papillae : 100 taste buds. 50 TASTE PATHWAYS Taste buds Fibres via facial, glossopharyngeal, and vagus nerves. Nucleus tractus solitarius Ventral posteromedial nucleus of thalamus Post – central gyrus. 51 TASTE RECEPTORS. • Satty > ENaC • Sour > ENaC, HCN • Bitter > T2R family • Sweet > TIR 3 , gustducin. 52 CEREBELLUM • DIVISIONS OF CEREBELLUM • Vestibulocerebellum • Spinocerebellum • Neocerebelum. • Vestibulocerebellum : Oldest part flocculonodular lobe fn> equilibrium • Spinocerebellum : vermis & adjaicent medial hemispheres. Fn: smoothens & coordinates movements. • Neocerebellum : newest part lateral hemisphere • Fn > planning & programming of movements. 53 NUCLEI OF CEREBELLUM • Dentate nucleus • Emboliform nucleus • Fastigial nucleus • Globose nucleus • Neocerebellum output to dentate nucleus • Vestibulocerebellum
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