L16 Neurone, Nerve Fibres And Periph Nerves Flashcards
NS composit
-NS=brain, SC, nerves.
Cranial nerves=brain and its nerves. 12 pairs. Gen bilat symm. Segmental/spinal nerves= SC and its nerves. 31 pairs.
1m cells= sophist func and redund for recov.
Cells= 90% glia, 10% neurones sophist func.
-neuroglia- bind NS=shape. Micro glia emb der from BM, subtypes prob same through bod. Macro from neural tiss, subt var dep on which dig NS. Lot procs from bod. Stain by Golgi-silver impreg- silver ion upt then precip.
-CNS neuroglia 4 maj subt:
Astrocyte- largest count. Vital assis transf nutr and waste prod btw neuron and blood. Allow use gluc, O etc. Constit BBB=imm privelidged, imm cells not X. Phagoc funcs arnd neural tiss. Phys supp for neurons.
Oligodendroc- bring neurons togeth=decr vol req. myelinat=faster conduc. Myelinate up to 250 diff axons simult so dam=big eff.
Ependyma- line ventricles and cent canal of SC for circul CSF. Like ciliated=pump CSF in cavs CNS.
Microglia- imm and inflamm. Imm surv health of NS. Reac v fast if wrong. Scav and rem infec mater AV inflamm. Brains only imm func so bad if BBB breakd, infec can overcome.
-neuroglia and periph NS-
Schwann cell- equiv oligodendroc. Main func insulat periph nerve axons=speed up conduc. 1 Schwann cell myelinated lim segm of 1 axon.
Satellite- phys supp neurons.
Micro glia- imm and inflamm.
-neurone- bod and axon. Somet dendrites.
Nervous system
NS:
CNS(neurones and neuroglia). Grey matter=neurones and proxim processes embedd in glia. White matter= nerve fibres embedd in glia.
Periph NS (cranial and spinal nerves). Periph consis of nerve fibres with epi/peri/endoneurium. Div into ANS (ganglia and assoc nerve fibres). ANS clust neurons=ganglia surr CT caps, 2 types-
Spinal/sensory- fusif swells of coral root of spinal nerves.
Autonomic- in 2 paral chains on ant surf verteb. Or as poorly encapsulate parasympathetic gang near/in organs.
-loss myel sheath eg MS and axon destr and overg glial tiss=leg paral.
-non inflamm dis of periph nerves (periph neuropathy) and inflamm neuritis comm degen changes in periph nerves=sens decr, motor weakn.
-mat nerve cells NO mitosis, not repl. May be regen of dam periph nerves if proxim axons still att bods. Distal segm wallerian degen. Neurolemmal sheaths of degen axons rem intact and imp in regen.
LO1: desc struc of periph nerve.
-neuron= spec func unit of NS. All have 1 cell bod and 1 axon. Somet dendrites= incr SA cel bod for contact other cell types.
-cell bod and histol- vary dep on func and loc.
demonstr diff things eg eg stain for nissl subst. Or nuc. All cell bods one cent nuc. Cell bod engine 4-120um diam, vary shape. Conts-nuc, nucleolus, nissl subst for prot synth, Golgi for pack nt.
Unstained bods app grey as high abs incid light. White relfec light axons. Nerve nuc= hyp grey matter-clusters cell bods in CNS. If in periph NS would= ganglion. Term ganglion also used for eg cyst/raised inguinal LN.
-axon- axonal mem. Myel sheath Schwann cells. Node ranvier. Axonal termin. Internodal mem under sheath. Nodal mem. Init segm after bod. Axonal hillock somet.
-init segm- AP starts here moves away bod. Anoth travs tow bod to inform cell metab demands. Pathol us if init elsewhere. Eg tingling. High dens VG Na channs. Mem btw cell bod and first myel NOT myelinated=init segm.
-ion chann vary nodal to internodal mem. Diff densities. Na at nodes. K at Schwann.
-hillock- axon not trav straight in init segm- kink.undulation apps as elev mem=hillock. Esp sensory neurons.
LO2: relate de myel to slow conduc in nerve.
LO3: recog diffs btw myel and unmyel nerve fibres and ascribe partic roles to each.
-actual axon var thickn and length- unmyel us thin. Heavy myel thick. Lev myel var btw types. Conduc velocity= 6xfibre diam for myelinated.
-myelinated- us VG Na in nodal mem. K internodal. If de myel reverts to mixed exp.
-unmyel- mix VG Na and K through length. Myel of thin axon eg 0.5um. Thick 2.5um. Schwann cell and its nuc on outs. Lot reps ensheath. On AV Schwann wraps 100x rnd axon. Push Plip cytop out and nuc to periph.
Cert dis= demyel-MS in CNS only. Guillain Barre and DM in periph NS only. Polyneuropathies.
LO4: Id nerve fibres in TS and LS.
-axon in LS- saltatory conduc imp jumps btw nodes. Likely NS began unmyel. Still fems as axons of TS diam under 1um conduct faster if unmyel. Eg C pain fibres.
Unmyel req depol along ent axon length. Myel only depol at nodes.
-myel axon TS- sheath of 1 Schwann cell covs AV 100um. 2 success Schwann Sep by unmyel node 1um long.
TS nerve fascicle lab Sudan black targ myel sheath-collec axon comm ori or destin.
-collects of cells in NS- white matter in CNS= fibre tracks. Periph NS nerve fibre.
Nerves rel shiny white app if myel sheath. Axons=white matter-periph nerve is typ eg.
LO1 contin
-periph nerve 3 cellul envs- epineurium binds periph nerves togeth. Perineurium arnd fascicle covs axons sim ori/destin. Endoneurium env of cell mem of axon.
-mem envs of cranial and spinal nerves- periph NS outside to in:
Epineurium- ensheaths nerve, interf as circular bands att adj to nerve fascicle.
Perineurium- ensheaths fascicle collec of axons.
Endoneurium- ensheaths 1 cell axon.
-mem envs of fibre tracts in CNS- are contin with coverings of brain and SC called meninges. Outs to in:
Dura mater, arachnoid mater, pit mater.
Eg optic nerve. Also plane where CSF cont.
Reac nerve cell to traumat inj eg axon cut
-init cell bod incr vol as exp nissl subst and prot incr= nuc to periph-chromatolytic reac.
Proxim segm of axon soon seals up dam=neuroma prevs leak cell cont. =nerve stump. Distal segm cut off from nutr supp of bod, soon dies-wallerian degen of myel=debris and remn. Infilt of Mac and microglia. Anterograde transneuronal degen of next cell. Proxim part axon us reg rows=wallerian regen. New segm axon us re innerv less acc so not orig targ.
CNS
- dendrites=elong procs receive stim from env (sensory organs) or other neurons and conduc tow bod.
- nissl subst/bods- aggregs RER- basophillic as high conc rRNA.
- termin axon may div (termin arborizat) to br end in small swells (boutons). In close proxim to neuron of effector cell=synapse. Stim= rel snap vesics with nt.
- multipolar- cells with over 2 procs (1 dend and 1 axon). Most of CNS is.
- pseudo- unipolar 1 stem from bod formed by fus 1st part dend and axon.
- neuroglia v br. Btw neurons. Struc and metab supp. 4 types- astrocyte, oligodendroc, microglia, ependymal.
- grey and white matter CNS. Grey cell bods and assoc fibres. White nerve fibres as lot myel. Collects fibres= tracts=func grps. Grey cent in SC, White surr. Secondary mig in brain=cerebrum and cerebellum grey convoluted outer lay=cortex. Grey matter deep nuc.
Periph NS
-aff sensory inp tow CNS. Efferent/motor away from CNS.
Nerve fibres=axons surr by Schwann sleeve-neurolemma.
Schwann= supp. If fib just surr Schwann cytop as invag=unmyel. 1 schwann may enclose sev unmyel fibres. Lip so poor preserved in histol proc eg alc, xylene. Need spec fixative eg osmium tetroxide retains.
-ganglia- accum cell bods out CNS. Aff bods in spinal or cerebrum gang in dorsal root spinal nerves. Auton gang assoc with nerves of ANS.
-cerebrospinal gang- gang of sensory nerves rnd with large ovoid nuc. Each cell surr by 1 lay satellite cells-neuroglia.
Pseudo unipolar =1 myel prev and an axon to CNS.
Cell bods groped mostly at periph of gang-fibres grouped in mid (mostly myel)=disting from ANS.
-autonomic gang- no periph arr bods. Gang cells small, us multipolar, sev dend procs. Us unmyel. Caps/sat ill defined lay arnd bods. Bod nuc often eccentric.
LO: Outline great var of synap connects in NS
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