Spinal cord
Dr.Jagadeesh
Topic outcomes
Topic outcomes:
 3.1Describe the extent, size and coverings of spinal cord.
 3.2 Define and distinguish the spinal segments.
 3.3 Describe the internal structure : grey
horns, group of neurons and white matter
location of ascending and descending tracts.
matter -columns,
 3.4 Discuss the grey matter and white matter of spinal cord.
 3.5 Describe the arteries and veins of spinal cord.
 3.6 Explain the congenital anomalies of spinal cord.
Introduction
 Spinal cord is the caudal part of
central nervous system.
 Cylindrical in shape.
 45 cm in length in adults.
 Average diameter 1cm
 Occupies upper two thirds of
vertebral column.
 Extent:
Beginning – foramen magnum/upper
border of C1 vertebra.
Termination – lower border of L1.
External structure
Coverings(Meninges) & spaces
Covered by 3 meninges:
• Dura mater
• Archnoid mater
• Pia mater
Spaces:
 Outer to dura mater- extra
dural space.
 Deep to dura mater- subdural
space.
 Between the arachnoid & pia
mater - subarachnoid space.
Dura mater
 The dura mater is a dense, strong, fibrous
membrane that encloses the spinal cord
and the cauda equina.
 It is continuous above through the foramen
magnum with the meningeal layer of dura
covering the brain. Inferiorly, it terminates at
the level of the lower border of the second
sacral (S2) vertebra.
 The dural sheath lies loosely in the vertebral
canal and is separated from the wall of the
canal by the extradural space,which
contains loose areolar tissue and the
internal vertebral venous plexus.
 The dura mater extends along each nerve
root and becomes continuous with the
connective tissue surrounding each spinal
nerve (epineurium).
Arachnoid mater
 The arachnoid mater is a delicate
impermeable membrane that covers the
spinal cord and lies between the pia
mater internally and dura mater
externally.
 It is separated from the pia mater by a
wide space, the subarachnoid space,
which is filled with cerebrospinal fluid.
 The arachnoid mater is continuous
above through the foramen magnum
with the arachnoid covering the brain.
Inferiorly, it ends at the level of the lower
border of the second sacral vertebra.
 The arachnoid mater continues along the
spinal nerve roots, forming small lateral
extensions of the subarachnoid space.
Pia mater & pial modifications
 The pia mater, a vascular membrane
that closely covers the spinal cord and
continues below the spinal cord as
filum terminale which ends at the level
of 1st coccygeal vertebra.
 Pia is thickened on either side between
the nerve roots to form ligamentum
denticulatum(21 pairs) which passes
laterally to adhere to the arachnoid and
dura so that the spinal cord is
suspended in the middle of the dural
sheath.
 Pia mater is thickened in the anterior
median fissure to form median
longitudanal band called linea
splendens.
 Pial modifications: are filum terminale,
ligamentum denticulatum, linea
splendens
Spinal cord enlargements
Two enlargements:
1. Cervical enlargement - C3 to T2
spinal segments - Nerve supply to
upper limb.
2. Lumbar enlargement - L1 to S3
spinal segments-Nerve supply to
lower limb.
Conus medullaris
• Conical lower ending of
the spinal cord is conus
medullaris
• Central canal is dilated to
form terminal ventricle.
Cauda equina
• The bundle of nerve fibres
arising from the conus
medullaris is called cauda
equina (tail of horse).
Fissure and sulci
• Anterior median fissure.
• Posterior median sulcus.
• Anterior lateral sulcus.
• Posterior lateral sulcus.
Spinal nerve roots
• Dorsal root (DR)
• Ventral root (VR)
• Spinal ganglion (SG) or
dorsal root ganglion
• Spinal nerve ( SN) 31 pairs
(8+12+5+5+1).
Spinal nerve roots & Spinal nerve
• Dorsal root has a ganglion made up of pseudounipolar cells.
• With two processes - peripheral process is a dendrite. Central
process is an axon.
• Dorsal root Joins with the ventral root to form spinal nerve.
• Spinal nerve divides into 2 rami - dorsal ramus & ventral ramus
Spinal segments
31 spinal segments:
• 8 Cervical (C)
• 12 Thoracic (T)
• 5 Lumbar (L)
• 5 Sacral (S)
• 1 Coccygeal (Co)
Spinal segments
Relation of the spinal segments
to vertebral spines:
•
•
•
•
•
Cervical segments: - 1(C4 at C3)
Upper thoracic: - 2
Lower thoracic: - 3 (T12 at T9).
L 1 & L 2: at 10th thoracic spine.
L 3 & L 4: at 11th thoracic spine.
• L 5: at 12 th thoracic spine.
• Sacral and coccygeal: L 1 lumbar
spine.
Spinal segments
Internal structure
Internal structure of Spinal cord
 Inner grey matter &
outer white matter.
 Distribution of cell
bodies in the grey
matter.
 White matter has
tracts & fibres.
Internal structure of Spinal cord
Grey matter
 On cross section, the grey matter is seen
as an H-shaped pillar with anterior and
posterior grey columns, or horns, united
by a thin grey commissure containing the
small central canal.
 A small lateral grey column or horn is
present in the thoracic and upper lumbar
segments of the cord.
 The amount of grey matter present at any
given level of the spinal cord is related to
the amount of muscle innervated at that
level.
 Thus, grey matter is greatest in the
cervical and lumbosacral enlargements of
the cord, which innervate the muscles of
the upper and lower limbs.
Grey matter
 As in other regions of the central nervous system, the grey matter of the
spinal cord consists of a mixture of nerve cell bodies and their processes,
neuroglia, and blood vessels.
 The nerve cells are multipolar, and the neuroglia forms an intricate
network around the nerve cell bodies and their neurites.
Nerve cell groups in the Anterior grey column:

Most nerve cells are large and multipolar, and their axons pass out in the anterior roots of the
spinal nerves as alpha efferents, which innervate skeletal muscles.

The smaller nerve cells are also multipolar, and the axons of many of these pass out in the
anterior roots of the spinal nerves as gamma efferents, which innervate the intrafusal muscle
fibers of neuromuscular spindles.

The nerve cells of the anterior grey column may be divided into three groups : medial, central,
lateral.
1.
Medial group innervates the skeletal muscles of the neck and trunk, including the intercostal and
abdominal musculature.
2.
Central group innervate the diaphragm (phrenic nucleus), sternocleidomastoid and trapezius
muscles (accessory nucleus).
3.
Lateral group is present in the cervical and lumbosacral segments, innervates the skeletal
muscles of the limbs.
Grey matter
Nerve cell groups in the Posterior grey column:
 Four nerve cell groups : two group that extend throughout the length of the
cord & two group that are restricted to the thoracic and lumbar segments.
1. Substantia gelatinosa group - situated at the apex of the posterior grey
column. Receives afferent fibers concerned with pain, temperature, and
touch from the posterior root.
2. Nucleus proprius- situated anterior to the substantia gelatinosa. Receives
fibers associated with the senses of position and movement
(proprioception), two-point discrimination, and vibration.
3. Nucleus dorsalis (Clarke's column) - situated at the base of the posterior
grey column and associated with proprioceptive endings (neuromuscular
spindles and tendon spindles).
4. Visceral afferent nucleus - situated lateral to the nucleus dorsalis; it is
associated with receiving visceral afferent information.
Nucleus dorsalis and visceral afferent nucleus is absent in cervical and sacral
region
Grey matter
Nerve cell groups in the Lateral grey column:
 The intermediolateral group of cells form the small lateral grey column,
extends from the first thoracic to the second or third lumbar segment of the
spinal cord.
 The cells are relatively small & give rise to preganglionic sympathetic fibers.
Grey matter: REXED’S classification
 Lamina I – IV corresponds
to dorsal horn head.
 Lamina V corresponds to
neck.
 Lamina VI corresponds to
base of dorsal horn.

Lamina VII- corresponds to
intermediate area.
 Lamina VIII & IX occupies
the ventral horn
 Lamina X is the grey matter
surrounding the central
canal.
White matter
Funiculus or white
columns:
 Anterior column
 Posterior column
 Lateral column.
The columns contains
ascending &
descending tracts.
Sources of nerve fibres of white matter
 Afferent fibres from dorsal root ganglion cells.
 Long ascending fibres from cells of spinal cord to supraspinal levels.
 Long descending fibres from supra spinal sources to the
spinal cord cells.
 Efferent fibres from anterior and lateral grey column cells
which pass into ventral roots of spinal nerves.
 Fibres making intra-segmental and inter-segmental
connections within the cord.
Sources of nerve fibres of white matter
Tract
 Tract is a collection of nerve fibres within central
nervous system connecting two masse of grey matter.
 Tract is a collection of nerve fibres having the same
origin, course and termination.
 Tracts may be ascending or descending.
 Tracts are named after the masses of grey matter
connected by them. E.g. – corticospinal tract,
spinothalamic tract.
 Tracts are sometimes referred to as fasciculi or
leminisci .
Anterior funiculus
Ascending tract:
 Anterior/ventral
spinothalamic tract.
Descending tracts:
 Anterior/ventral corticospinal
 Vestibulospinal
 Tectospinal
 Reticulospinal
Lateral funiculus
Ascending tracts:
Descending tracts:
 Posterior spinocerebellar





 Anterior spinocerebellar
 Lateral spinothalamic
 Spinotectal
 Dorsolateral (tract of Lissauer)
Lateral corticospinal
Rubrospinal
Lateral reticulospinal
Olivospinal
Descending autonomic fibres
Posterior funiculus
Ascending tracts:
 Medial part - Fasciculus gracilis.
 Lateral part - Fasciculus cuneatus.
Descending tract:
 Septomarginal.
Spinal cord tracts - Overall
Descending tracts
Descending tracts
 Begins in the cortical or
subcortical areas and
descends down to spinal
cord.
 Controls motor activities,
achieved by the
interconnections between
the major motor
components of the
nervous system.
 Divided into:
- Pyramidal tract(corticospinal tract).
- Extrapyramidal tracts.
Major Descending tracts origin & function
Tracts
Origin
Functions
Corticospinal
Lateral & anterior
Motor cortex of
cerebrum
Controls voluntary
movements
Rubrospinal
Red nucleus of
midbrain
Facilitatory influence of
flexor tone
Reticulospinal
Medial & Lateral
Reticular formation
voluntary movements and
muscle tone
Tectospinal
Superior colliculus
Spinovisual reflexes
Vestibulospinal
Medial & Lateral
Lateral vestibular
nucleus
Controls body equilibrium
Olivospinal
Inferior olivary nucleus
Controls motor tone
Pyramidal tract - Corticospinal tract
 Originates in the motor cortex.
 Pass through genu of the internal
capsule, crus cerebri, pons,
pyramids of medulla.
 Decussates and descends in the
lateral column of the spinal cordlateral cortricospinal tract.
 10% does not cross and
descends in the anterior column
of the spinal cord and form
anterior corticospinal tract.
 They relay in the anterior horn
cells of the spinal cord.
 These anterior horn cells project
directly to muscle and control
muscular contraction.
Pyramidal tract - Corticospinal tract
Pyramidal tract - Corticospinal tract
Upper motor lesion- hemiplegia:
• Loss of motor power – paralysis.
• Increased muscle tone – spasticity.
• Increased reflexes» Exaggerated knee jerk
» Babinski’s positive
• No wasting of muscles.
Lower motor lesion – Poliomyelitis:
• Loss of motor power- paralysis.
• Loss of muscle tone.
• Loss of reflexes.
• Wasting of muscles.
Corticobulbar tract
 Fibres originate in the region
of sensorimotor cortex.
 Pass through posterior limb
of internal capsule & middle
portion of crus cerebri to the
cranial nerve nuclei in the
brain stem.
 Projects through cranial
nerves to areas of supply for
motor functions.
Extrapyramidal tracts- Vestibulospinal tract
 Two components:
 Lateral vestibulospinal – arise from lateral
vestibular nucleus in the brain stem and course
downward, uncrossed, in the anterior funiculus of
the spinal cord.
 Medial vestibulospinal – arise from medial
vestibular nucleus in the brain stem and descend
within the cervical spinal cord,with both crossed &
uncrossed, in the anterior funiculus of the spinal
cord to terminate at cervical levels.
 Function - provide excitatory input to extensor
muscles.
Extrapyramidal tracts- Rubrospinal tract
 Arises from the red nucleus of midbrain.
 Cross in the midbrain and descends in the pons, medulla
and in the lateral column of the spinal cord.
 Synapses in the ventral horn interneurons of the spinal
cord.
 Controls motor tone.
Extrapyramidal tracts- Reticulospinal tract
 Arises in the reticular formation of the brain stem.
 Descends in both the ventral and lateral white
columns.
 Both crossed and uncrossed descending fibres
are present.
 Terminate on dorsal grey column neurons may
modify transmission of sensation of body, egpain.
Extrapyramidal tracts- Tectospinal tract
 Arises from superior colliculus of the midbrain.
 Decussates & passes through contralateral anterior
white column.
 Relay in ventral grey interneurons.
 Function causes sudden movement of head in response
to visual or auditory stimuli.
Descending autonomic tracts
 Arising from the hypothalamus and brain stem.
 Project to preganglionic sympathetic neurons in the
thoracolumbar segments spinal cord.
 To preganglionic parasympathetic neurons in sacral
segments.
 Modulate autonomic functions.
Medial longitudinal fasciculus
 Arises from vestibular nuclei in the brain stem.
 Descends run close to and intermingles tectospinal tract.
 Terminates in the ventral grey interneurons of the
cervical segments of the spinal cord.
 Function coordinates head and eye movements.
Ascending tracts
Ascending tracts
 Ascending tracts are seen in spinal cord & brain stem.
 They are multineuronal pathways by which afferent
impulses arising from various parts of the body are
conveyed to different parts of the brain.
 Usually three set of neuron:
- First order neuron
- Second order neuron
- Third order neuron.
First order neurons- dorsal root ganglia
 Each neuron in dorsal root ganglion gives off a
peripheral process & a central process.
 The peripheral processes of the neurons form the
afferent fibres of peripheral nerves. They end in relation
to sensory end organs situated in various tissues.
 The central processes of these neurons enter the spinal
cord through the dorsal nerve roots.
Second order neurons
 Having entered the spinal cord the central processes as
a rule, terminate by synapsing with cells in spinal grey
matter.
 Some of them may run upwards in the white matter of
the cord to form ascending tracts.
 The majority of ascending tracts are however formed by
axons of cells in spinal grey matter.
 These are second order neurons.
Third order sensory neurons
 In the case of pathways that convey sensory information
to the cerebral cortex the second order neurons end by
synapsing with neurons in the thalamus.
 Third order sensory neurons located in the thalamus
carry the sensations to the cerebral cortex.
Major Ascending tracts & their functions
 Anterior spinothalamic –Simple touch and pressure.
 Lateral spinothalamic – Pain & temperature
 Fasciculus gracilis & Fasciculus cuneatus - Proprioceptiive
impulses, vibration sense, fine touch, tactile localization &
discrimination
 Anterior spinocerebellar -Proprioceptive impulses.
 Posterior spinocerebellar -Proprioceptive impulses.
 Spinotectal & spino olivary - Spinovisual reflexes.
 Dorsolateral tract -pain & temperature
Spinothalamic tracts
 Anterior spinothalamic
tract- ascend in the
anterior funiculus and
ascend to the medulla.
 Fibres of lateral
spinothalamic tract enter
the lateral funiculus.
 Merges with the medial
lemniscus.
 Ascend through medulla,
pons and midbrain (spinal
lemniscus)
 End ultimately in the
thalamus.
 End in the thalamus (VPL
nucleus).
Anterior spinothalamic tract
Lateral spinothalamic tract
Spinoreticular tract
 Begin from the spinal neurons mainly in lamina VII.
 Fibres are partly crossed & partly uncrossed.
 Fibres ascend in the ventrolateral part of the spinal cord,
intermingling with spinothalamic tracts.
 They end in the reticular formation of the medulla &
pons.
 Probably carries the pain.
Spino-olivary tract
 Is also a crossed tract.
 It lies at the junction of the anterior & lateral funiculi of
the spinal cord.
 The fibres of the tract end in accessory olivary nuclei.
 May carry exteroceptive impulses.
Spino mesencephalic tract
 A number of tracts travel from spinal cord to different
areas in the midbrain.They are collectively referred to as
spinomesencephalic tracts.
 Spinotectal tract – connect spinal cord to the superior
colliculus.
 It is a crossed tract.
 It carries impulses like pain & temperature, that regulate
reflex movements of the head & eyes in response to
stimulation of some parts of the body.
 Some reach pretectal nuclei or some reticular formation
of midbrain.
Spinocerebellar tracts
 Carry proprioceptive
impulses arising in muscle
spindles, Golgi tendon
organs and other receptors
in cerebellum.
 First order neurons of this
pathway are located in
dorsal nerve root ganglia.
 Central process of these
neurons end in the spinal
grey matter.
 Second order neurons
are arranged in a number
of groups.
 Dorsal spinocerebellar
uncrossed– remains
ipsilateral lying in the
lateral funiculus.
 Ascends to the medulla
become incorporated into
the inferior cerbellar
peduncle and reach
cerbellum.
Spinocerebellar tracts
Blood supply of spinal cord
Arterial supply
 The spinal cord receives its arterial
supply from three small arteries.
 Two posterior spinal arteries and
one anterior spinal artery.
 These longitudinally running
arteries are reinforced by small
segmental arteries that arise from
arteries outside the vertebral
column and enter the vertebral
canal through the intervertebral
foramina.
 Anterior and posterior spinal
arteries anastomose on the surface
of the cord and send branches into
the substance of the white and grey
matter.
Arterial supply
Anterior spinal artery:
The anterior spinal artery is
formed by the union of two
arteries, each of which arises
from the vertebral artery inside
the skull.
The anterior spinal artery
then descends on the anterior
surface of the spinal cord
within the anterior median
fissure.
Branches from the anterior
spinal artery supply the
anterior two-thirds of the spinal
cord.
Arterial supply
Posterior spinal arteries:
The posterior spinal arteries
arise either directly from the
vertebral arteries inside the skull
or indirectly from the posterior
inferior cerebellar arteries.
They descend on the posterior
surface of the spinal cord close to
the posterior nerve roots and
gives off branches that enter the
substance of the cord.
The posterior spinal arteries
supply the posterior one-third of
the spinal cord.
Arterial supply
Segmental spinal arteries:
At each intervertebral foramen, posterior and
anterior spinal arteries are reinforced by small
segmental arteries on both sides.
The arteries are branches of deep cervical,
intercostal, and lumbar arteries.
Segmental artery enters the vertebral canal,
gives rise to anterior and posterior radicular
arteries that accompany the anterior and
posterior nerve roots to the spinal cord.
Additional feeder arteries enter the vertebral
canal.One large feeder artery, the great anterior
medullary artery of Adamkiewicz, arises from the
aorta a major source of blood to the lower twothirds of the spinal cord.
Arterial supply
Venous drainage
 Through internal vertebral
venous plexus.
 6 longitudinal spinal veins.
 They communicate superiorly
within the skull with the veins
of the brain and the venous
sinuses and drain through
intervertebral foramina into:
- Vertebral veins in the neck.
- Azygos vein in the thorax.
- Lumbar veins in the lumbar
region.
- Lateral sacral veins in the
sacral region.
Clinical importance
Lumbar puncture
Lumbar puncture:
 Obtaining the CSF from the lumbar
cistern for diagnostic purposes.
 Done between L3 and L4 vertebrae.
Layers that the spinal needle traverse are:
1. Skin
2. Superficial fascia
3. Supraspinous ligament
4. Interspinous ligament
5. Ligamentum flavum
6. Epidural space containing the internal
vertebral venous plexus
7. Dura mater
8. Arachnoid mater.
Spinal cord anomalies - Spina bifida occulta
• Congenital absence of
spinous process and
lamina of vertebra.
• No visible meninges or
neural tissue.
• Often incidental finding.
Spinal cord anomalies - Spina bifida cystica
Meningocele :
• Congenital defect in
vertebral arches with
cystic distension of
meninges.
• No abnormality of neural
tissue.
Spinal cord anomalies - Spina bifida cystica
Meningomyelocele:
• Congenital defect in
vertebral arches with
cystic distension of
meninges.
• With structural or
functional abnormality of
spinal cord or cauda
equina.
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