The spinal cord is protected by three layers of meninges - the dura mater, arachnoid mater, and pia mater. It extends from the foramen magnum to the lower back and gives rise to 31 pairs of spinal nerves that innervate various parts of the body. The spinal cord has gray matter containing nerve cell bodies in the center surrounded by white matter made up of nerve fibers. It is segmented into cervical, thoracic, lumbar, sacral and coccygeal regions.

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
Attheendofthelecture,studentsshouldbeableto:
 Describetheexternalanatomy of thespinalcord.
 Describetheinternalanatomy of thespinal cord.
 Describethespinal nerves:formation, branchesanddistribution viaplexuses.
 Describe themeningesofthespinal cord.
 Defineareflexandreflexarc,anddescribethecomponents of thereflexarc.

5. REVIEW

6. FUNCTIONS
The nervous system has 3 functions:
 Collection of Sensory Input
 Identifies changes occurring
inside and outside the body by
using sensory receptors. These
changes are called stimuli
 Integration
 Processes, analyses & interprets
these changes and makes
decisions
 Motor Output
 It then effects a response by
activating muscles or glands
(effectors) via motor output

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

8. ORGANIZATION
FUNCTIONAL
o Sensory Division (Afferent)
o Motor 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
 The main pathway for information connecting the brain and
peripheralnervoussystem.
 It is elongated, cylindrical, suspended in the vertebral canal and
protectedbyvertebrae
 Surroundedbythemeningesandcerebrospinalfluid(CSF).
 The primary function of spinal cord is a transmission of neural
signalsbetweenthebrainandtherestofthebody.
 Sensory
 Motor
 Localreflexes

11. SPINAL CORD
 Extendsfromforamenmagnumtosecondlumbarvertebra.
 Continuousabovewiththemedullaoblongata.
 Thetaperedinferiorendformsconusmedullaris.
 It is connected to the coccyx by a non-neuronal cord called Filum
Terminale.

12. SPINAL CORD
 Givesriseto31pairsofspinalnerves
 The bundle of spinal nerves extending inferiorly from
lumbosacral enlargement and conus medullaris surround the
filumterminaleandformcaudaequina
 Segmented
 8Cervical
 12Thoracic
 5Lumbar
 5Sacral
 1Coccygeal
 Hastwoenlargements:
 CervicalEnlargement:suppliesupperlimbs.
 LumbosacralEnlargement:supplieslowerlimbs.

13. CROSS SECTION OF SPINAL CORD
 The spinal cord is incompletely divided into two
equal parts, anteriorly by a short, shallow median
fissureandposteriorlybyadeepnarrowseptum,the
posteriormediansulcus.
 Composed of grey matter in the center surrounded
bywhitemattersupportedbyneuroglia.
 Commissures: connections between left and right
halves
 Graywithcentral canalin thecenter
 White
 Roots:spinalnervesariseasrootletsthencombineto
formroots
 Dorsal(posterior)root hasaganglion
 Ventral (anterior)
 Tworootsmergelaterallyand formthespinal nerve

14.  The arrangement of grey matter in the spinal cord
resemblestheshapeoftheletterH.
 Having:
 twoposterior
 twoanterior
 twolateralhorns/columns.
 Consistsof:
 nervecellbodiesandtheirprocesses
 neuroglia
 blood vessels
GREY MATTER

15.  The nerve cells are multipolar, and are of THREE
maincategories:
 Sensoryneurons(Tractcells)
 receive impulses from the periphery of the body
and whose axons constitute the ascending fasciculi
ofthewhitematter.
 locatedinthe dorsalhorns.
 Lowermotorneurons
 transmitimpulses to theskeletal muscles.
 locatedinthe ventral horns
o similar neurons in the lateral horn are the
preganglionic neurons of the autonomic
system.
 Interneurons(connectorneurons)
 linking sensory and motor neurons, at the same or
differentlevels,whichformspinal reflexarcs.
GREY MATTER

16. NEURONALARCHITECTURE OF
SPINAL GREY MATTER
 Cells of the same type are clustered into groups, which
occurinlongcolumns
 In transverse section, these columns appear as layers,
especiallywithinthedorsalhorn
 These layers are called the laminae of Rexed that are
numbered by Roman numerals, starting from the tip of
the dorsal horn and moving ventrally into the ventral
horn.
 The Rexed laminae comprise a system of ten layers
of grey matter (I-X), identified in the early 1950s by
Swedishneuroscientist.

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

18. SubstantiaGelatinosa
• RexedLaminaeII
• Locatedattheapexofthehorn
• Composedoflargeneurons
• Extendsthroughoutthelengthof spinalcord
• Afferents: dorsal root fibers concerned with pain,
temperatureandtouch
NucleusProprius
• RexedLaminaIV
• Locatedanteriortosubstantiagelatinosa
• Composedoflargeneurons
• Extendsthroughoutthelengthof spinalcord
• Afferents: dorsal root fibers concerned with senses of
position&movement(proprioception)

19. NucleusDorsalis (Clark’s column,Nucleusthoracis)
• RexedLaminaVII
• Locatedatthebaseofdorsalhorn
• Composedmostlyoflargeneurons
• ExtendsfromC8toL3-4segments
• Associatedwithproprioceptiveendings
• Afferents: dorsal root fibers concerned with information
frommusclespindlesandtendonorgans.
VisceralAfferentNucleus
• RexedLaminaVII
• Locatedlateraltonucleusdorsalis
• Composedmostlyofmediumsizeneurons
• ExtendsfromT1toL3segments
• Afferents:Visceralafferents

20. NERVE CELL GROUPS IN VENTRAL HORN
 Motor neurons, also called lower motor
neurons.

21. MOTOR NEURONS IN VENTRAL HORN
 AreofTwo types
 Largemultipolarcells
 whose axons pass out in the ventral roots
of spinal nerves as alpha efferents which
innervate extrafusal muscle fibers of
skeletalmuscles.
 Lessnumerous smallermultipolar cells
 whose axons pass out in the ventral roots
of spinal nerves as gamma efferents
which innervate intrafusal muscle fibers
ofneuromuscularspindles
Bothalphaand gamma motorneuronsare
undertheinfluenceofdescending
pathwaysfrombrain

22. Motor neurons areorganizedin3groups:
 Medial:
 Present in most segments, innervates
muscles of neck and trunk (including
intercostalandabdominalmuscles)
 Central:
 Smallest, present in some cervical (phrenic
C3-5, spinal accessory C1-6) and
lumbosacral(L2-S1)segments
 Lateral:
 Present in cervical and lumbosacral
segments,innervatesmusclesofthelimbs
Neuronssupplyingflexormusclesare
locateddorsaltoneuronsforextensor
muscles
MOTOR NEURONS IN VENTRAL HORN

23. NERVE CELL GROUPS IN LATERAL HORN
 SmallColumncomposed of smallneurons
 ExtendsfromT1toL2-3segments:
o Giverisetopreganglionicsympatheticfibers
 ExtendsfromS2-4 segments:
o Give rise to preganglionic parasympathetic
fibers

24. WHITE MATTER
 Consists of mixture of nerve fibers, neuroglia and blood
vessels.
 White color is due to high proportion of myelinated
nervefibers
 The white matter of the spinal cord is arranged in
columns/funiculi;anterior,posteriorandlateral.
 The nerve fibers are arranged as bundles, running
verticallythroughthecord.
 A group of nerve fibers (axons) that share a common
origin, termination and function form a tract or
fasciculus
 These tracts are formed by sensory nerve fibers
ascending to the brain, motor nerve fibers descending
fromthebrainandfibersofconnectorneurons.
 Tracts are often named according to their points of
originanddestination,e.g.spinothalamic,corticospinal.
Dependingontheirfunction,thespinal
tractsaredividedintoascendingand
descendingtracts

26. COMMISSURES OF THE SPINAL CORD
 Grey Commissure:
 Transverse bridge of grey matter connecting the
anteriorandposteriorgrayhornsoneachside
 Is pierced by the central canal that divides it into
anteriorandposteriorparts
 White Commissure:
 Liesventraltothegraycommissure
 Mainlycontainsdecussatingnervefibers

27. CENTRAL CANAL
 The cerebrospinal-filled space that runs longitudinally
throughtheentirelengthofthespinalcord.
 Linedbyependyma(ciliatedcolumnarepithelium)
 Continuouswiththeventricularsystemofthebrain
 Superiorlyopensintothe4th ventricle
 Inferiorly in the conus medullaris, it expands into the
fusiformterminalventricleand terminatesbelowatthe
rootoffilumterminale

28. REGIONAL DIFFERENCES
 Although the general pattern of gray matter is the
same throughout spinal cord, regional differences
areapparentintransversesections
 The amount of white matter increases in a caudal-to-
cranial direction because fibers are added to
ascendingtractsandfibersleavedescendingtracts
 The gray matter is in increased volume in cervical &
lumbosacral enlargements for innervation of upper
&lowerlimbs
 The lateral horn is characteristics of thoracic and
upperlumbarsegments
Cervical
Thoracic
Lumbar
Sacral

29. SPINAL NERVES
 Thirty-onepairsofspinalnerves
 First pair exit vertebral column between skull and atlas, last
four pairs exit via the sacral foramina and others exit
throughintervertebralforamina
 Eight pair cervical, twelve pair thoracic, five pair lumbar,
fivepairsacral,onepaircoccygeal
 Each spinal nerve arises as rootlets which then combine to
formdorsal(posterior)&ventral(anterior)roots.
 Tworootsmergelaterallyandformthespinalnerve.
 Dorsal (posterior) root has a ganglion (dorsal root/sensory
ganglion) that contains the cell bodies of the sensory
neurons
 Each spinal nerve then divides into a smaller dorsal and a
largerventralramus

30. BRANCHES OF SPINAL NERVES
 Dorsal Ramus: innervate deep muscles of the trunk responsible for movements of the vertebral column and
skinnearthemidlineoftheback.
 VentralRamus:whattheyinnervatedependsuponwhichpartofthespinalcordisconsidered.
 Thoracic region: form intercostal nerves that innervate the intercostal muscles and the skin over the
thorax
 Remaining spinal nerve ventral rami (roots of the plexus): form five plexuses (intermingling of
nerves).
o VentralramiofC1-C4=cervicalplexus
o VentralramiofC5-T1=brachialplexus
o VentralramiofL1-L5=lumbarplexus
o VentralramiofL4-S4=sacralplexus
o VentralramiofS4&S5=coccygealplexus
o Communicating Rami: communicate with sympathetic chain
ofganglia.

31. SPINAL MENINGES
 Connective tissue membranes surrounding spinal cord
andbrain
 Dura mater: continuous with epineurium of the spinal
nerves
 Arachnoidmater:thinandwispy
 Pia mater: bound tightly to surface of brain and spinal
cord.
o Forms the filum terminale, which anchors spinal cord to
coccyx and the denticulate ligaments that attach the spinal
cordto theduramater
 Spaces
 Epidural:Containsbloodvessels,connectivetissueandfat.
 Subdural:Containsserousfluid
 Subarachnoid: Contains CSFand blood vesselswithin web-
likestrandsofarachnoidtissue

32. REFLEX & REFLEX ARC
Areflexisarapid,involuntary,stereotypedpatternof responsebroughtby a
sensorystimulus
Aneuralpathwaymediatingthereflexactionsiscalledreflexarc.

33. COMPONENTS OF A REFLEX ARC
Actionpotentialsproducedin Sensoryneuron
Sensoryreceptor
Interneuron
Motorneuron
Effector organ which responds
withareflex

34. QUESTIONS!