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anatomy of spinal chord

1. Khaleel Alyahya, PhD, MEd
King Saud University
School of Medicine
@khaleelya
ANATOMY OF SPINAL CORD

2. Tweet of Today

3. Resources
Human Anatomy & Physiology
Elaine Marieb
Introduction to Human Body
Gerard Tortora
Human Brain
John Nolte
Google

4. OBJECTIVES
At the end of the lecture, students should be able to:
Describe the external anatomy of the spinal cord.
Describe the internal anatomy of the spinal cord.
Describe the spinal nerves: formation, branches and distribution via plexuses.
Describe the meninges of the spinal cord.
Define a reflex and reflex arc, and describe the components of the reflex arc.

5. REVIEW

6. FUNCTIONS
The nervous system has 3 functions:
Collection of Sensory Input
Identifieschangesoccurring
insideandoutsidethebodyby
usingsensoryreceptors.These
changesarecalledstimuli
Integration
Processes,analyses&interprets
thesechangesandmakes
decisions
Motor Output
Ittheneffectsaresponseby
activatingmusclesorglands
(effectors)viamotoroutput

7. ORGANIZATION
STRUCTURAL
oCentral Nervous System (CNS)
Brain & Spinal Cord
oPeripheral Nervous System (PNS)
Nerves & Ganglia
•Cranial nerves
•Spinal nerves

8. ORGANIZATION
FUNCTIONAL
oSensory Division (Afferent)
oMotor Division (Efferent)
Autonomic
Somatic

9. Nucleus
A group of neurons
within the CNS
Ganglion
A group of neurons outside
the CNS
Tract
A group of nerve fibers (axons)
within the CNS
Nerve
A group of nerve fibers
(axons) outside the CNS

10. SPINAL CORD
Themainpathwayforinformationconnectingthebrainand
peripheralnervoussystem.
Itiselongated,cylindrical,suspendedinthevertebralcanaland
protectedbyvertebrae
Surroundedbythemeningesandcerebrospinalfluid(CSF).
Theprimaryfunctionofspinalcordisatransmissionofneural
signalsbetweenthebrainandtherestofthebody.
Sensory
Motor
Localreflexes

11. SPINAL CORD
Extendsfromforamenmagnumtosecondlumbarvertebra.
Continuousabovewiththemedullaoblongata.
Thetaperedinferiorendformsconusmedullaris.
Itisconnectedtothecoccyxbyanon-neuronalcordcalledFilum
Terminale.

12. SPINAL CORD
Givesriseto31pairsofspinalnerves
Thebundleofspinalnervesextendinginferiorlyfrom
lumbosacralenlargementandconusmedullarissurroundthe
filumterminaleandformcaudaequina
Segmented
8Cervical
12Thoracic
5Lumbar
5Sacral
1Coccygeal
Hastwoenlargements:
CervicalEnlargement:suppliesupperlimbs.
LumbosacralEnlargement:supplieslowerlimbs.

13. CROSS SECTION OF SPINAL CORD
Thespinalcordisincompletelydividedintotwo
equalparts,anteriorlybyashort,shallowmedian
fissureandposteriorlybyadeepnarrowseptum,the
posteriormediansulcus.
Composedofgreymatterinthecentersurrounded
bywhitemattersupportedbyneuroglia.
Commissures:connectionsbetweenleftandright
halves
Graywithcentralcanalinthecenter
White
Roots:spinalnervesariseasrootletsthencombineto
formroots
Dorsal(posterior)roothasaganglion
Ventral(anterior)
Tworootsmergelaterallyandformthespinalnerve

14. Thearrangementofgreymatterinthespinalcord
resemblestheshapeoftheletterH.
Having:
twoposterior
twoanterior
twolateralhorns/columns.
Consistsof:
nervecellbodiesandtheirprocesses
neuroglia
bloodvessels
GREY MATTER

15. Thenervecellsaremultipolar,andareofTHREE
maincategories:
Sensoryneurons(Tractcells)
receiveimpulsesfromtheperipheryofthebody
andwhoseaxonsconstitutetheascendingfasciculi
ofthewhitematter.
locatedinthedorsalhorns.
Lowermotorneurons
transmitimpulsestotheskeletalmuscles.
locatedintheventralhorns
osimilarneuronsinthelateralhornarethe
preganglionicneuronsoftheautonomic
system.
Interneurons(connectorneurons)
linkingsensoryandmotorneurons,atthesameor
differentlevels,whichformspinalreflexarcs.
GREY MATTER

16. NEURONAL ARCHITECTURE OF
SPINAL GREY MATTER
Cellsofthesametypeareclusteredintogroups,which
occurinlongcolumns
Intransversesection,thesecolumnsappearaslayers,
especiallywithinthedorsalhorn
TheselayersarecalledthelaminaeofRexedthatare
numberedbyRomannumerals,startingfromthetipof
thedorsalhornandmovingventrallyintotheventral
horn.
TheRexedlaminaecompriseasystemoftenlayers
ofgreymatter(I-X),identifiedintheearly1950sby
Swedishneuroscientist.

17. NERVE CELL GROUPS IN DORSAL HORN
Four main groups
1.SubstantiaGelatinosa
2.NucleusProprius
3.NucleusDorsalis
Clark’scolumn
Nucleusthoracis
4.VisceralAfferentNucleus

18. SubstantiaGelatinosa
•RexedLaminaeII
•Locatedattheapexofthehorn
•Composedoflargeneurons
•Extendsthroughoutthelengthofspinalcord
•Afferents:dorsalrootfibersconcernedwithpain,
temperatureandtouch
Nucleus Proprius
•RexedLaminaIV
•Locatedanteriortosubstantiagelatinosa
•Composedoflargeneurons
•Extendsthroughoutthelengthofspinalcord
•Afferents:dorsalrootfibersconcernedwithsensesof
position&movement(proprioception)

19. Nucleus Dorsalis (Clark’s column, Nucleus thoracis)
•RexedLaminaVII
•Locatedatthebaseofdorsalhorn
•Composedmostlyoflargeneurons
•ExtendsfromC8toL3-4segments
•Associatedwithproprioceptiveendings
•Afferents:dorsalrootfibersconcernedwithinformation
frommusclespindlesandtendonorgans.
Visceral Afferent Nucleus
•RexedLaminaVII
•Locatedlateraltonucleusdorsalis
•Composedmostlyofmediumsizeneurons
•ExtendsfromT1toL3segments
•Afferents:Visceralafferents

20. NERVE CELL GROUPS IN VENTRAL HORN
Motorneurons,alsocalledlowermotor
neurons.

21. MOTOR NEURONS IN VENTRAL HORN
AreofTwotypes
Largemultipolarcells
whoseaxonspassoutintheventralroots
ofspinalnervesasalphaefferentswhich
innervateextrafusalmusclefibersof
skeletalmuscles.
Lessnumeroussmallermultipolarcells
whoseaxonspassoutintheventralroots
ofspinalnervesasgammaefferents
whichinnervateintrafusalmusclefibers
ofneuromuscularspindles
Both alpha and gamma motor neurons are
under the influence of descending
pathways from brain

22. Motorneuronsareorganizedin3groups:
Medial:
Presentinmostsegments,innervates
musclesofneckandtrunk(including
intercostalandabdominalmuscles)
Central:
Smallest,presentinsomecervical(phrenic
C3-5,spinalaccessoryC1-6)and
lumbosacral(L2-S1)segments
Lateral:
Presentincervicalandlumbosacral
segments,innervatesmusclesofthelimbs
Neurons supplying flexor muscles are
located dorsal to neurons for extensor
muscles
MOTOR NEURONS IN VENTRAL HORN

23. NERVE CELL GROUPS IN LATERAL HORN
Small Column composed of small neurons
ExtendsfromT1toL2-3segments:
oGiverisetopreganglionicsympatheticfibers
ExtendsfromS2-4segments:
oGiverisetopreganglionicparasympathetic
fibers

24. WHITE MATTER
Consistsofmixtureofnervefibers,neurogliaandblood
vessels.
Whitecolorisduetohighproportionofmyelinated
nervefibers
Thewhitematterofthespinalcordisarrangedin
columns/funiculi;anterior,posteriorandlateral.
Thenervefibersarearrangedasbundles,running
verticallythroughthecord.
Agroupofnervefibers(axons)thatshareacommon
origin,terminationandfunctionformatractor
fasciculus
Thesetractsareformedbysensorynervefibers
ascendingtothebrain,motornervefibersdescending
fromthebrainandfibersofconnectorneurons.
Tractsareoftennamedaccordingtotheirpointsof
originanddestination,e.g.spinothalamic,corticospinal.
Depending on their function, the spinal
tracts are divided into ascending and
descending tracts

26. COMMISSURES OF THE SPINAL CORD
GreyCommissure:
Transversebridgeofgreymatterconnectingthe
anteriorandposteriorgrayhornsoneachside
Ispiercedbythecentralcanalthatdividesitinto
anteriorandposteriorparts
WhiteCommissure:
Liesventraltothegraycommissure
Mainlycontainsdecussatingnervefibers

27. CENTRAL CANAL
Thecerebrospinal-filledspacethatrunslongitudinally
throughtheentirelengthofthespinalcord.
Linedbyependyma(ciliatedcolumnarepithelium)
Continuouswiththeventricularsystemofthebrain
Superiorlyopensintothe4
th
ventricle
Inferiorlyintheconusmedullaris,itexpandsintothe
fusiformterminalventricleandterminatesbelowatthe
rootoffilumterminale

28. REGIONAL DIFFERENCES
Althoughthegeneralpatternofgraymatteristhe
samethroughoutspinalcord,regionaldifferences
areapparentintransversesections
Theamountofwhitematterincreasesinacaudal-to-
cranialdirectionbecausefibersareaddedto
ascendingtractsandfibersleavedescendingtracts
Thegraymatterisinincreasedvolumeincervical&
lumbosacralenlargementsforinnervationofupper
&lowerlimbs
Thelateralhornischaracteristicsofthoracicand
upperlumbarsegments
Cervical
Thoracic
Lumbar
Sacral

29. SPINAL NERVES
Thirty-onepairsofspinalnerves
Firstpairexitvertebralcolumnbetweenskullandatlas,last
fourpairsexitviathesacralforaminaandothersexit
throughintervertebralforamina
Eightpaircervical,twelvepairthoracic,fivepairlumbar,
fivepairsacral,onepaircoccygeal
Eachspinalnervearisesasrootletswhichthencombineto
formdorsal(posterior)&ventral(anterior)roots.
Tworootsmergelaterallyandformthespinalnerve.
Dorsal(posterior)roothasaganglion(dorsalroot/sensory
ganglion)thatcontainsthecellbodiesofthesensory
neurons
Eachspinalnervethendividesintoasmallerdorsalanda
largerventralramus

30. BRANCHES OF SPINAL NERVES
DorsalRamus:innervatedeepmusclesofthetrunkresponsibleformovementsofthevertebralcolumnand
skinnearthemidlineoftheback.
VentralRamus:whattheyinnervatedependsuponwhichpartofthespinalcordisconsidered.
Thoracicregion:formintercostalnervesthatinnervatetheintercostalmusclesandtheskinoverthe
thorax
Remainingspinalnerveventralrami(rootsoftheplexus):formfiveplexuses(interminglingof
nerves).
oVentral rami of C1-C4= cervical plexus
oVentral rami of C5-T1= brachial plexus
oVentral rami of L1-L5= lumbar plexus
oVentral rami of L4-S4= sacral plexus
oVentral rami of S4 & S5= coccygeal plexus
oCommunicatingRami:communicatewithsympatheticchain
ofganglia.

31. SPINAL MENINGES
Connectivetissuemembranessurroundingspinalcord
andbrain
Duramater:continuouswithepineuriumofthespinal
nerves
Arachnoidmater:thinandwispy
Piamater:boundtightlytosurfaceofbrainandspinal
cord.
oFormsthefilumterminale,whichanchorsspinalcordto
coccyxandthedenticulateligamentsthatattachthespinal
cordtotheduramater
Spaces
Epidural:Containsbloodvessels,connectivetissueandfat.
Subdural:Containsserousfluid
Subarachnoid:ContainsCSFandbloodvesselswithinweb-
likestrandsofarachnoidtissue

32. REFLEX & REFLEX ARC
Areflexisarapid,involuntary,stereotypedpatternofresponsebroughtbya
sensorystimulus
Aneuralpathwaymediatingthereflexactionsiscalledreflexarc.

33. COMPONENTS OF A REFLEX ARC
Action potentials produced in SensoryneuronSensoryreceptor
InterneuronMotorneuron
Effectororganwhichresponds
withareflex

34. QUESTIONS!