Spinal cord

Central Nervous System

2. The spinal cord
•Thespinalcord,enclosedinthe
vertebralcolumn,extendsfromthe
foramenmagnumoftheskulltothefirst
orsecondlumbarvertebra,justinferior
totheribs.
•About42cm(17inches)longand1.8cm
(3/4ofaninch)thickandthespinal
cordprovidesatwo-wayconduction
pathwaytoandfromthebrain.

3. •Thespinalcordisprotectedbybone,
meninges,andcerebrospinalfluid.
•Cerebrospinalfluidfillsthe
subarachnoidspacebetweenthe
arachnoidandpiamatermeninges.

4. Gross Appearance
•Cylindrical in shape
•Foramen magnum L1/L2 (adult)
•L3 (newborn)
•Occupies upper ⅔ of vertebral canal
•Surrounded by 3 layers of meniges:
–duramater
–arachnoidmater
–piamater
•CSF in subarachnoid space

5. Longitudinal depressions
a. Posterior Median Sulcus-PMS
b. Anterior Median Fissure -AMF
Enlargements of the spinal cord
a. Cervical enlargement (biggest)
-pectoral girdle –C4-C8
b. Lumbar enlargement -
supplies and innervates lower limbs

6. •Conusmedullaris:-thespinalcord
terminatesinataperingcone-shaped
structurecalledtheconusmedullaris.
•Filumtermniale
•Anterior median fissure
•Posterior median sulcus
•31 pairs of spinal nerves attached to it
by the anterior roots & posterior roots

7. •Thefilumterminale:-
afibrousextensionof
theconuscoveredby
piamater,extends
inferiorlyfromthe
conusmedullaristo
thecoccyx,whereit
anchorsthespinal
cordsoitisnotjostled
bybodymovements

8. •Denticulateligaments:-
Thepiamaterofthe
spinalcordhasapairof
denticulateligaments
with21attachmentsper
sidewhichattachittothe
arachnoidanddura
mater.

9. Gray Matter
•H-shapedpillarwithanterior&
posteriorgrayhorns
•Unitedbygraycommissure
containingthecentralcanal
•Lateralgraycolumn(horn)presentin
thoracic&upperlumbarsegments
•Amountofgraymatterrelatedtothe
amountofmuscleinnervated
•Consistsofnervecells,neuroglia,
bloodvessels

10. Nerve cells in the anterior gray columns
•Large and multipolar
–Axons pass out in the anterior nerve roots
as α-efferents
•Smaller nerve cells are multipolar
–Axons pass out in anterior roots as ɣ-
efferents

11. Nerve cells in the
posterior gray columns
•4 nerve cell groups
1.Substantiagelatinosa
2.Nucleus proprius
3.Nucleus dorsalis
(Clark’s column)
4.Visceral afferent
nucleus

12. 1.Substantiagelatinosa
–situated at the apex
–throughout the length of spinal cord
–composed mainly of Golgi Type II
neurons
–receives afferent fibresconcerning with
pain, temperature & touch from
posterior root

13. •Nucleus proprius
–anterior to substantiagelatinosa
–present throughout the whole length
of spinal cord
–main bulk of cells in posterior gray
column
–receives fibers from posterior white
column that are assoc with
proprioception, 2-point discrimination
& vibration

14. •Nucleus dorsalis(Clark’s column)
–base of posterior column
–C8 –L3 / L4
–associated with proprioceptiveendings
(neuromuscular spindles & tendon
spindles)
•Visceral afferent nucleus
–lateral to nucleus dorsalis
–T1 –L3
–receives visceral afferent informations

15. The gray matter
•Thegraymatterofthecordlookslikethe
letterHorlikeabutterfly.Itconsistsof
mirrorimagelateralgraymassesconnected
byacrossbarofgraymatter,thegray
commissure,thatenclosesthecentral
canal.Thetwodorsalprojectionsofthegray
matterarethedorsal(posterior)horns,
andtheventralpairaretheventral
(anterior)horns.Thethoracicand
superiorlumbarsegmentsofthecordhave
anadditionalpairofgraymattercolumns,
thesmalllateralhorns.

16. Lateral horns
•Formed by the intermediolateral
group of cells
•T1 –L2 / L3
•Cells give rise to preganglionic
sympathetic fibres
•In S2, S3, S4; they give rise to
preganglionicparasympathetic
fibres

17. •The gray commissureand central canal
–connects the gray on each side
–central canal in the centre
–posterior gray commissure
–anterior gray commissure
–central canal present throughout
–superiorly continuous with the central canal
of medulla oblongata
–inferiorly, expands as terminal ventricle
–terminates within the root of filumterminale

18. a.DorsalRoot-posterior-sensorynerves
b.DorsalRootGanglion(containssensory
nervecellbodies).
c.VentralRoot-anterior-motorneurons
"AMPS"anterior/motorandposterior/sensory.
Spinalnervesstartwherethedorsalroot
gangliaandventralrootfuseorcometogether
andjointobecomeamixednerve/exitthe
spineattheintervertebralforamen.

20. •Thespinalgraymattercanbedividedfurther
accordingtoitsneurons’relativeinvolvementin
innervatingthesomaticandvisceralregionsofthe
body.
•Spinalgraymatterhasthefollowingfourzones.
–Somatic sensory (SS)
–Visceral sensory (VS)
–Visceral (autonomic) motor (VM)
–Somatic motor (SM).

21. White Matter
•The white matter of the spinal cord is composed
of myelinatedand nonmyelinatednerve fibers
that allow communication between different
parts of the spinal cord and between the cord
and brain. These fibers run in three directions:
–Ascending—up to higher centers (sensory
inputs)
–Descending—down to the cord from the
brain or within the cord to lower levels
(motor outputs)
–Transverse—across from one side of the
cord to the other (commissural fibers)
•Consists of nerve fibres, neuroglia, blood vessels

24. •Thewhitematteroneachsideofthe
cordisdividedintothreewhite
columns,orfuniculinamed
accordingtotheirpositionas
–Dorsal (posterior) funiculi
–Lateral funiculi
–Ventral (anterior) funiculi

25. Tracts
•Ascending
•Descending
•Transverse

26. Ascending Tracts
•Fibresthat ascend from spinal cord
to higher centres
•Conduct afferent information which
may or may not reach consciousness
•Information may be
–exteroceptive(pain, temperature, touch)
–proprioceptive(from muscles & joints)

27. •The nonspecific and specific ascending
pathways send impulses to the sensory
cortex
–These pathways are responsible for
discriminativetouch (2 pt. discrimination) and
conscious proprioception(body position
sense).
•The spinocerebellartracts send impulses
to the cerebellum and do not contribute to
sensory perception

28. Ascending Pathway

30. Lateral spinothalamictract
•Pain & temp pathways
•1
st
-order neurons
•Pain conducted by A-
type fibres& C-type
fibres
•2
nd
-order neurons
–decussate to the opposite
side
–ends in thalamus (ventral
posterolateralnucleus
•3
rd
-order neurons
–ends in sensory area in
postcentralgyrus

31. Anterior (ventral)
spinothalamictracts
•Light (crude) touch
and pressure pathways

32. Posterior (Dorsal)
spinocerebellartract
•Musclejointsensepathways
tocerebellum
•Unconsciousproprioception
•Musclejointinfofrom
musclespindles,GTO,joint
receptorsofthetrunk&
lowerlimbs
•Infoisusedbythe
cerebellum in the
coordinationofmovements
&maintenanceofposture

33. Anterior (Ventral)
spinocerebellartract
•Majority of 2
nd
-order
neurons cross to the
opposite side
•Enter cerebellum
through superior
cerebellarpeduncle
•Info from trunk, upper
& lower limbs
•Also carries info from
skin & subcuttissue

34. Posterior (Dorsal) white
column
•Discriminativetouch,vibratorysense,
consciousmusclejointsense(conscious
proprioception)

35. Descending Tracts
•Descending tracts deliver motor
instructions from the brain to the
spinal cord
•Divided into two groups
–Pyramidal, or corticospinaltracts:-
concerned with voluntary, discrete, skilled
movements
–Indirect pathways, essentially all others
•Motor pathways involve two neurons
–Upper motor neuron (UMN)
–Lower motor neuron (LMN)
•aka ‘anterior horn motor neuron” (final
common pathway)

36. Pyramidal (Corticospinal) Tracts
•Originate in the precentralgyrusof brain (aka, primary
motor area)
–I.e., cell body of the UMN located in precentralgyrus
•Pyramidal neuron is the UMN
–Its axon forms the corticospinaltract
•UMN synapses in the anterior horn with LMN
–Some UMN decussate in pyramids = Lateral corticospinaltracts
–Others decussate at other levels of s.c. = Anterior corticospinal
tracts
•LMN (anterior horn motor neurons)
–Exits spinal cord via anterior root
–Activates skeletal muscles
•Regulates fast and fine (skilled) movements

37. Corticospinal
tracts
1.Location of UMN cell
body in cerebral cortex
2.Decussationof UMN
axon in pyramids are at
exit level of LMN
3.Synapse of UMN and
LMN occurs in anterior
horn of s.c.
4.LMN axon exits via
anterior root

38. ExtrapyramidalMotor Tracts
•Includes all motor pathways not part of the pyramidal system
•Upper motor neuron (UMN) originates in nuclei deep in
cerebrum (notin cerebral cortex)
•UMN does notpass through the pyramids!
•LMN is an anterior horn motor neuron
•This system includes
–Rubrospinal
–Vestibulospinal
–Reticulospinal
–Tectospinaltracts
•Regulate:
–Axial muscles that maintain balance and posture
–Muscles controlling coarse movements of the proximal portions of limbs
–Head, neck, and eye movement

39. Reticulospinaltract
•Thetworecticulospinal
tractshavediffering
functions:
•Themedialreticulospinal
tractarisesfromthepons.
Itfacilitatesvoluntary
movements,andincreases
muscletone.
•Thelateralreticulospinal
tractarisesfrom
themedulla.Itinhibits
voluntarymovements,and
reducesmuscletone

40. Tectospinaltract
•Thispathwaybeginsat
thesuperiorcolliculusofthe
midbrain.Thesuperior
colliculusisastructurethat
receivesinputfromtheoptic
nerves.Theneuronesthen
quicklydecussate,andenter
thespinalcord.They
terminateatthecervical
levelsofthespinalcord.
•The tectospinaltract
coordinatesmovementsof
theheadinrelationtovision
stimuli.

41. Rubrospinaltract
•The rubrospinaltract
originatesfromthered
nucleus,a midbrain
structure.Asthefibres
emerge,theydecussate
(crossovertotheotherside
oftheCNS),anddescendinto
thespinalcord.Thus,they
have
acontralateralinnervation.
•Itsexactfunctionisunclear,
butitisthoughttoplayarole
inthefinecontrolofhand
movements

42. VestibulospinalTracts
•Therearetwovestibulospinal
pathways;medialandlateral.
Theyarisefromthevestibular
nuclei,whichreceiveinputfrom
theorgansofbalance.Thetracts
conveythisbalanceinformation
tothespinalcord,whereit
remainsipsilateral.
•Fibresinthispathway
controlbalanceandpostureby
innervatingthe‘anti-gravity’
muscles(flexorsofthearm,and
extensorsoftheleg),vialower
motorneurones.

45. Other Tracts
•Spinotectaltract
–Thetectospinaltract(alsoknownascolliculospinaltract)is
anervepathwaythatcoordinatesheadandeyemovements.
Thisneuraltractispartoftheindirectextrapyramidaltract.Tobe
specific,thetectospinaltractconnectsthemidbraintectum
andcervicalregionsofthespinalcord.
•Spinoreticulartract
–Thespinoreticulartractisanascendingpathwayinthewhitematter
ofthespinalcord,positionedcloselytothelateralspinothalamictract.
Thetractisfromspinalcordtoreticularformationtothalamus.
–Itisresponsibleforautomaticresponsestopain,suchasinthecaseof
injury.
•Spino-olivarytract
–Thisisanon-specificindirectascendingpathwayandisconnectedto
olivarynucleiinthebrain.Itislocatedintheventralfuniculusof
thespinalcord.Thistractcarriesproprioceptioninformation
frommusclesandtendonsaswellascutaneousimpulsesto
theolivarynucleus.

46. Spinal Meninges
•Dura mater
•Arachnoidmater
•Piamater

47. Dura mater
•Dense,strongfibrousmembrane
•Enclosesthespinalcord&cauda
equina
•Continuousabovewithmeningeal
layerofduracoveringthebrain
•EndsatthelevelofS2
•Separatedfromwallofvertebral
canalbytheextraduralspace
•Containslooseareolartissueand
internalvertebralvenousspace

48. Arachnoidmater
•Delicateimpermeablemembrane
•Liesbetweenpiaandduramater
•Separatedfrompiamaterby
subarachnoidspace
•Continuousabovewitharachnoid
matercoveringthebrain
•Endsonfilumterminaleatlevelof
S2

49. Piamater
•Vascular membrane
•Closely covers spinal cord
•Thickened on either side between
nerve roots to form the ligamentum
denticulatum

50. Blood supply
Arteries of the spinal cord
•Anterior spinal artery
•Posterior spinal artery
•Segmental spinal arteries

51. Anteriorspinalartery
•Formedbytheunionof2arteries
•Fromvertebralartery
•Supplyanterior⅔ofspinalcord
Posteriorspinalarteries
•Arisefromvertebralarteryor
posteriorinferiorcerebellararteries
(PICA)
•Descendclosetotheposteriorroots
•Supplyposterior⅓ofspinalcord

53. Segmental spinal arteries
•Branches of arteries outside the
vertebral column
•Gives off the anterior & posterior
radiculararteries
•Great anterior medullaryartery of
Adamkiewicz
•Arise from lateral intercostalartery
or lumbar artery at any level from
T8 –L3

55. Venous drainage
•Venousdrainagelargelyfollowsarterial
supply. That is, there
areanteriorandposteriorspinal
veinsandanteriorandposteriorradicular
veins,whichfreelycommunicatewith
theinternalvertebralplexusintheepidural
space.Thisisinturndrainstothe
cerebralduralvenoussinusesandcerberal
veinsaswellastheexternalvertebral
plexus.
•Theveinsofthespinalcordandvertebral
columnarevalveless.

57. Applied anatomy
Spinal shock
•Followsacuteseveredamagetothe
spinalcord
•Allcordfunctionsbelowthelevelof
thelesionbecomedepressedorlost
•Sensoryimpairmentandflaccid
paralysisoccur
•Segmentalspinalreflexesare
depressed
•Persistsforlessthan24hours(may
beaslongas1–4weeks)

58. Poliomyelitis
•Acuteviralinfectionoftheneurones
ofanteriorgraycolumn
•Motornucleiofcranialnerves
•Deathofmotorneuronecells→
paralysis&wastingofmuscles
•Musclesoflowerlimbmoreoften
affected

59. Spinal Nerves
•Aspinalnerveisamixednerve,whichcarries
motor,sensory,andautonomicsignalsbetween
thespinalcordandthebody.Inthehumanbody
thereare31pairsofspinalnerves,oneoneach
sideofthevertebralcolumn.
•Thesearegroupedintothecorresponding
–Cervicalnerves8pairs
–Thoracicnerves12pairs
–Lumbarnerves5pairs
–Sacralnerves5pairs
–Coccygealnervesonepair
•Thespinalnervesarepartoftheperipheral
nervoussystem.

60. Structure of spinal nerve
•3 layers of Connective tissues
–Epineurium
•Outermost layer
•Consists of dense network
of collagen fibers
–Perineurium
•Middle layer
•Divide nerve into series of
compartments which
contain bundles of axons
(fascicles)
–Endoneurium
•Innermost layer
•Surround individual axons

61. •Spinal nervesconsist of two types of
nerves:
–Sensorynerves
–Motornerves

62. •Sensorynervesdeliver
informationtospinal
cordfrommusclesand
jointsaboutbody
positionand also
transmitsensationssuch
astouch,pressure,pain
andtemperature.

63. Motor nerves
Motornervespassinformationreceivedfrom
brainthroughspinaltractstotheskeletal
musclestodirectprecisevoluntarymovements.
Spinalnervesarelinkedtospecificmuscles:
•Cervicalspinalnervessupplythemusclesof
neck,shoulders,armsandhands,and
diaphragm.
•Thoracicspinalnervessupplytruckmuscles
andmusclesinvolvedwithbreathing.
•Lumbarandsacralspinalnervessupplyhip,
legandfootmuscles.
•Sacralnervessupplyanalandurethral
sphincters.

65. Distribution of
Spinal Nerves
Spinal Nerves:
–Consist of dorsal root and ventral root
–Branch to form pathways to
destination
–Includes motor and sensory nerves
Dermatomes:
a.Each pair of spinal nerves controls a region
of body surface sensation -the exception
to this is C1, which does not.
b.From dorsal and ventral ramifibers
c.Damage to the spinal nerve results in loss
of sensation to a region of skin
d.This is a helpful diagnostic tool, sometimes
pain is referred from one nerve to a
corresponding region of skin.

66. Spinal Nerves: Rami
•The short spinal nerves branch into
three or four mixed, distal rami
–Small dorsal ramus–to back
–Larger ventral ramus–to
plexuses/intercostals
–Tiny meningealbranch –to meninges
–Ramicommunicantesat the base of the
ventral ramiin the thoracic region –
to/from ANS

67. Nerve Plexuses
•AllventralramiexceptT
2-T
12forminterlacing
nervenetworkscalledplexuses
•Plexusesarefoundinthecervical,brachial,
lumbar,andsacralregions
•Eachresultingbranchofaplexuscontains
fibersfromseveralspinalnerves
•Fiberstraveltotheperipheryviaseveral
differentroutes
•Eachmusclereceivesanervesupplyfrom
morethanonespinalnerve
•Damagetoonespinalsegmentcannot
completelyparalyzeamuscle

68. Spinal Nerve Innervation:
Back, AnterolateralThorax, and
Abdominal Wall
•Thebackisinnervatedby
dorsalramiviaseveral
branches
•Thethoraxisinnervated
byventralramiT
1-T
12as
intercostalnerves
•Intercostalnervessupply
musclesoftheribs,
anterolateralthorax,and
abdominalwall

69. The 4 Major Plexuses of
Ventral Rami
1.Cervical plexus
2.Brachial plexus
3.Lumbar plexus
4.Sacral plexus

70. Cervical Plexus
•Thecervicalplexusis
formedbyventralramiof
C
1-C
4(C5)
•Most branchesare
cutaneousnervesofthe
neck,ear,backofhead,
andshoulders
•Themostimportantnerve
ofthisplexusisthe
phrenicnerve
•Thephrenicnerveisthe
majormotorandsensory
nerveofthediaphragm

71. Brachial Plexus
•FormedbyC
5-C
8andT
1
(C
4andT
2mayalso
contributetothis
plexus)
•Itgivesrisetothe
nervesthatinnervate
theupperlimb

72. Trunks and Cords of
Brachial Plexus
•Nerves that form brachial plexus originate from:
–superior, middle, and inferior trunks
–large bundles of axons from several spinal nerves
–lateral, medial, and posterior cords
–smaller branches that originate at trunks

73. Brachial Plexus: Nerves
•Axillary–innervates the
deltoid and teresminor
•Musculocutaneous–sends
fibers to the biceps brachii
and brachialis
•Median–branches to most
of the flexor muscles of
forearm
•Ulnar–supplies the flexor
carpiulnarisand part of the
flexor digitorumprofundus
•Radial –innervates
essentially all extensor
muscles

74. Lumbar Plexus
•Arises from (T12) L
1-L
4and
innervates the thigh,
abdominal wall, and psoas
muscle
•The major nerves are the
femoraland the obturator

75. Sacral Plexus
•ArisesfromL
4-S
4and
servesthebuttock,
lowerlimb,pelvic
structures,andthe
perineum
•Themajornerveisthe
sciatic,thelongestand
thickestnerveofthe
body
•Thesciaticisactually
composed oftwo
nerves:thetibialand
thecommonfibular
(perineal)nerves

76. Nerve plexuses -Summary
•Cervical–C1-C4
–Phrenicnerve
•Brachial–C5 –T1
(roots/trunks/divisions/cords)
–Axillary, MC, median, ulnar, radial
•Lumbar–L1-L4
–Femoral, obturator
•Sacral–L4-S4
–Sciatic (common peroneal/tibial), pudendal

77. Figure 13–13a
5 Patterns of Neural Circuits in
Neuronal Pools
1.Divergence:
–spreads
stimulation to
many neurons
or neuronal
pools in CNS
2.Convergence:
–brings input
from many
sources to
single neuron

78. Figure 13–13c
3.Serial processing:
–moves
information in
single line
4.Parallel
processing:
–moves same
information along
several paths
simultaneously
5 Patterns of Neural Circuits in Neuronal Pools

79. Figure 13–13e
5.Reverberation:
–positive feedback
mechanism
–functions until inhibited

80. Reflex activity
•5 components of
a reflex arc
–Receptor
–Sensory neuron
–Integration
center (CNS)
–Motor neuron
–Effector

81. 4 Classifications of Reflexes
1.By early development
–Innate or Acquired
2.By type of motor response
–Somatic or Visceral
3.By complexity of neural circuit
–Monosynaptic or Polysynaptic
4.By site of information processing
–Spinal or Cranial

82. Spinal Reflexes
•Range in increasing order of
complexity:
–monosynaptic reflexes
–polysynaptic reflexes
–intersegmentalreflex arcs:
•many segments interact
•produce highly variable motor response

83. Monosynaptic Reflexes
•Have least delay
between sensory
input and motor
output:
–e.g.,stretch reflex
(such as patellar
reflex)
•Completed in 20–
40 msec

84. Muscle Spindles
•The receptors in stretch
reflexes
•Bundles of small,
specialized intrafusal
muscle fibers:
–innervated by sensory
and motor neurons
•Surrounded by
extrafusalmuscle
fibers:
–which maintain tone and
contract muscle

85. Postural Reflexes
•Postural reflexes:
–stretch reflexes
–maintain normal upright posture
•Stretched muscle responds by
contracting:
–automatically maintain balance

86. Polysynaptic Reflexes
•More complicated than
monosynaptic reflexes
•Interneuronscontrol more than 1
muscle group
•Produce either EPSPs or IPSPs

87. The Tendon Reflex
•Prevents skeletal muscles from:
–developing too much tension
–tearing or breaking tendons
•Sensory receptors unlike muscle
spindles or proprioceptors

88. Withdrawal Reflexes
•Move body part away
from stimulus (pain or
pressure):
–e.g.,flexor reflex:
•pulls hand away from
hot stove
•Strength and extent of
response:
–depends on intensity
and location of
stimulus

89. Reciprocal Inhibition
•For flexor reflex to work:
–Thestretchreflexofantagonistic
(extensor)musclemustbeinhibited
(reciprocalinhibition)byinterneurons
inspinalcord

90. Crossed Extensor Reflexes
•Occur simultaneously,
coordinated with
flexor reflex
•e.g.,flexor reflex
causes leg to pull up:
–crossed extensor reflex
straightens other leg
–to receive body weight
–maintained by
reverberating circuits

91. Integration and Control
of Spinal Reflexes
•Though reflex behaviors are automatic:
–processing centers in brain can facilitate or
inhibit reflex motor patterns based in spinal
cord
•Higher centers of brain incorporate lower,
reflexive motor patterns
•Automatic reflexes:
–can be activated by brain as needed
–use few nerve impulses to control complex
motor functions
–walking, running, jumping

92. Superficial reflexes
•Stroking of the skin elicits muscle contraction
–Involves functional upper motor pathways as well
as cord level reflex arcs
•Plantar reflex (L4-S2) Babinskiis normal in
infants
–Usually indicative of CNS damage in adults
•Abdominal reflex (T8-T12)
–Absent with corticospinallesion

93. Spinal Cord Trauma:
Transection
•Cross sectioning of the spinal cord
at any level results in total motor
and sensory loss in regions inferior
to the cut
•Paraplegia–transectionbetween
T
1and L
1
•Quadriplegia–transectionin the
cervical region

94. Applied anatomy/physiology
Peripheral Neuropathies
•Regional loss of sensory or motor function
•Due to trauma or compression
•Example: if your foot “falls asleep”
Shingles
•Caused by varicella-zoster virus (chickenpox)
•After chickenpox, virus hides in neurons of spinal cord
•Later in life, attacks neurons in dorsal roots of nerves =
painful rash/blisters
•Distribution of rash corresponds to dermatome nerves
affected

95. THANK YOU