Spinal cord anatomy

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!