Nervous system - srmuniv.ac.in · do not develop from cells of neural tube ... • Crista cmpullaris has sustentacular cells & hair cells closed by cupula.

Nervous system

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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

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Mesodermal originMicroglia

• do not develop from cells of neural tube• They come from bone marrow.• These are called microglia• They resemble tissue macrophages.

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NEURON

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• 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.

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• 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.

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• 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.

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• 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

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AP reaches pre synaptic terminal

Ca Channels open

Ca influx

Fusion of vesicles with plasma memb

Exocytosis

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Release of neurotransmitter

Endocytosis

Endosome formation

Budding of vesicles from endosome

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PRESYNAPTIC INHIBITION:Axo axonal synapse

Activation of Opening of DirectPresynaptic K channels inhibitionReceptors

Inc.Cl entry Inc. K efflux

Dec. Ca entry Dec. Ca. entry

Dec. AP Dec . AP

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PRE SYNAPTIC FACILITATION:-Axo- axonal synapse

Release of serotonin

Inc. C AMP

Closes K channels

Prolongs AP

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VENTRICLES

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REFLEXES

• Reflex arc:• Sense organ• Afferent neuron• Central integrating station• Efferent neuron• Effector.• Bell Magendie law:• Dorsal roots - sensory• Ventral roots - motor.

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REFLEXES

MonosynapticPolysynapticStretch ReflexStimulus : stretch of muscleSense organ : muscle spindle.Reflex :contraction of muscleEg: Knee jerk

Triceps jerk

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REFLEX ARC

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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.

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MUSCLE SPINDLE

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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

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INVERSE STRETCH REFLEX

Also called as autogenic inhibitionIb afferent

Inhibitory interneuron (Golgi tendon organ)

Relaxation of muscle.This is due to overstretch of muscle.

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WITHDRAWAL REFLEX

Polysynaptic reflexpainful stimulus

Flexor muscle contraction

Inhibition of extensor muscles

So the part is withdrawn from stimulus.

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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.

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EYE

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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.

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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

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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.

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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’ GMPClosure of Na+ channels.

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RhodopsinLight

11cis retinene

All transretinene

Alters configuration of opsin

Activates transducin

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Transducin binds with GTP

Activates cGMP phosphodiesterase

cGMP 5’ GMP

Closure of Na channels

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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 .

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M

Magnocellular laminas

SuperficialLayer 4c

Function:-Movement,Location,Spatial Organisation.

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P

Parvocellular laminas

Deep layer 4 cShape, 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.

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Upper retinal quadrant subserving vision from lowervisual field

Medial half of lateral geniculate body

Superior lip of calcarine fissure.

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Lower retinal quadrant subserving vision fromupper 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

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SPEECH & VISUAL AREAS

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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.

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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.

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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.

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INNER EAR

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Internal structure

ORGAN OF CORTI

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AUDITORY PATHWAYS

From cochlea

Spiral ganglion

Dorsal and ventral cochlear nuclei.

Inferior colliculus.

Medial geniculate body.

Auditory cortex(41)

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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).

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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.

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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.

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TYMPANIC REFLEX

Loud Sounds

Contraction of tensor tympani & stapedius

Decreased sound transmission.lasts 40 – 120 ms, hence can’t protect against gunshot wounds.

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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.

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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.

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TASTE PATHWAYS

Taste buds

Fibres via facial, glossopharyngeal, and vagus nerves.

Nucleus tractus solitarius

Ventral posteromedial nucleus of thalamus

Post – central gyrus.

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TASTE RECEPTORS.

• Satty > ENaC• Sour > ENaC, HCN• Bitter > T2R family• Sweet > TIR 3 , gustducin.

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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.

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NUCLEI OF CEREBELLUM

• Dentate nucleus• Emboliform nucleus• Fastigial nucleus• Globose nucleus• Neocerebellum output to dentate nucleus• Vestibulocerebellum output directly to brainstem.• Spinocerebellum output through emboliform, fastigial,

globose nuclei.

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LAYERS AND NEURONS• 3 layers• external molecular layer• purkinje cell layer• internal granular layer• 5 types of neurons purtinje, granule, basket, stellate, golgi

cells.• purkinje cells are largest and only output from cerebellar

cortex.• Granule, are excitatory.• Purkinjecells, stellate, basket, golgicells are inhibitory• Climbing and mossy fibres are inputs.

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FUNDAMENTAL CIRCUIT

• Climbing fiber has strong excitatory effect on purkinje cells

• Mossy fibres have weak excitatory effect on purkinje cells.

• Granule cells excite stellate and basket cells which inturn inhibit purkinje cells

• This is called feed forward inhibition• Purkinje cells inhibit deep cerebellar nuclei.• GABA secreted by stellate, basket, golgi, purkinje cells• Glutamate by granule cells

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CEREBELLUM

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CEREBELLUM

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BASAL GANGLIA

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NEURO TRANSMITTERS

• Excitatory Amino acids : Gultamate • Aspartate• Inhibitory Aminoacids • Glycine• GABA• Glutamate is the main excitatory transmitter in brain

and spinal cord.• GABA is the major inhibitory mediator in brain.

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HYPOTHALAMUS

• Anterior hypothalamus controls response to heat.• Posterior hypothalamus controls response to cold.• Lateral hypothalamus feeding centre.• Ventromedial nucleus of hypothalamus satiety centre.• Anterior hypothalamus : Osmoreceptor• Thirst• Sexual behavior• Circadian rhythm• Pituitary hormone regulation• defensive behavior.

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TEMPERATURE REGULATION

HEAT :.Increased heat loss.Cutaneous vasodilatation.Sweating.Increase in respiration.Decreased heat production.Anorexia.Apathy and inertia.

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COLD

• Decreased heat loss• cutaneous vasoconstriction• Pilo erection• curling up• Increased heat production• shivering• Hunger• Increased voluntary activity• Increased secretion of norepinephrine/ epinephrine.

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NON SHIVERING THERMOGENESISMechanism

Sympathetic stimulation

Epinephrine & norepinephrine

Direct Indirect

Action on liver & muscle cells Cells in brownfat with large numberof mitochondria

Glycogenolysis Produces no ATP but all heat

Increase BMR

Heat

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CEREBRO SPINAL FLUID• CSF formation by choroid plexus around blood vessel and venticular

walls• Volume is 150 ml.• Rate of CSF formation is 550ml/day• Rate of CSF turnover is 3 times/day.• pH of CSF IS 7.34• CSF presssure is 50-180 mm Hg.• Ion with maximum CSF/plasma ratio is Magnesium.• Minimum CSF/plasma ratio is cholesterol and protein.• Equal CSF/plasma ratio is with osmolality• All negative ions are more in CSF.

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CSF CONSTITUENTS

• Appearance clear and colourless.• proteins : 20 -40 mg/dl.• Glucose : 40-70 mg/dl.• Chlorides : 720-750 mg/dl.• CSF Sugar is about 2/3 of plasma sugar.

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EMOTION

• Sensory aspect is in limbic system• expressive emotions develop in hypothalamus.• sensory aspect characterised by 3 parts• cognition is awareness of sensation and its cause.• Affect means development of feeling.• Conation is the desire to take action.• Expresion is motor part and consists of Autonomic

system.

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EEG.

• EEG consists of 4 waves.• These are alpha waves, beta waves, theta waves,

olelta waves.• Beta waves:• parietal & frontal region.• Frequency > 14 Hz.• Low amplitude.• seen in awake patients, at rest with eyes open,

children, drowsiness.

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• ALPHA WAVE :• Parieto occipital region.• seen in awake patients at rest with eyes closed.• Frequency .8 – 13 Hz.• High amplitude• THETA WAVE :• seen in hippocampus• In children & drowsiness• high amplitude• frequency 4 7 Hz.

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• DELTA WAVE : • seen in infant and n REM sleep• Large amplitude• Frequency 3 – 5 Hz.

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NORMAL EEG

• Alpha wave reflects synchronized brain activity.• Alpha wave wax & wane & are suppressed completely

with eye opening or mental activity.• Alpha block is when eyes are opened alpha rhythm is

replaced by fast irregular low voltage activity.• Desynchronization is when alpha pattern is replaced by

another wave pattern during sensory stimulation or mental concentration. Also called alerting response.

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SLEEP PATTERN

• 2 types of sleep.• n REM Sleep or slow wave sleep or orthodox sleep.• constitutes 70 – 80% of total sleep.• REM Sleep or paradoxical sleep.• constitutes 20-30% of total sleep.

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STAGES OF nREM SLEEP

• Stage I : consists of theta waves.• Stage II : consists of sleep spindles and • K complexes.• Stage III : consists of delta waves which are• first to appear & then K-complexes.• Stage IV : consists of predominant delta • waves.

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REM SLEEP

• Arousal is difficult.• Mixed frequency, low amplitude waves.• predominant beta activity. • Dreaming is seen.• Tone of neck is lost.• Penile tumescence.• Night mares.• Narcolepsy.

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