2. Objectives
By the end of this session you should be able
to:
● Describe the spinal cord, its location and
its function.
● Describe the surface features of the spinal
cord and its meningeal coverings.
● Discuss theinternal structure of the spinal
cord.
3. ● List the major ascending tracts in the
spinal cord and theirfunctions.
● Describe the pathways of each major
ascending tract.
● Discuss other minor ascending tracts and
their functions.
4. General features
● The spinal cord extends from the
foramen magnum (medullary
spinal junction) to the first or
second lumbarvertebra.
● It occupies the upper two thirds
of the vertebral column.
● The rest of the vertebral column
is occupied by cauda equina.
5. • Part of the central nervous system
(CNS)
• Protected by the bony structures of
the vertebral column.
• Covered by the three membranes
of the CNS, i.e., the dura mater,
arachnoid and the innermost pia
mater.
General features
6. By age 2 months, it reaches the adult L1-L2 level.
The average length- 45 cm(adult male) and 42 to 43
cm(adult female).
The corresponding average length of the spinal column
is 70 cm.
If the level of the tip of the conus is below the mid-L2
vertebral body, the conus is considered low-lying.
7.
8. ● The spinal cord is dividedto:
○ Cervical spinal cord (8 pairs of nerves).
○ Thoracic spinal cord (12 pairs of nerves).
○ Lumbar spinal cord (5 pairs of nerves).
○ Sacral spinal cord (5 pairs of nerves).
○ Coccygeal spinal cord (1 pair of nerves)
9.
10. SPINAL CORD LEVEL CORRESPONDING
VERTEBRALBODY
Upper cervical Same as cordlevel
Lower cervical +1
Upper thoracic +2
Lower thoracic + 2 to 3levels
Lumbar T 10– T12
Sacral T 12 –L1
11. ● The anterior median
fissure is a deep
longitudinal fissure in
theanterior surface.
● The posterior median
sulcus is a shallow
sulcus in the posterior
surface. It contains the
posterior median
septum (piamater).
12. ● The posterolateral
sulcus is the entry
site for the posterior
root (sensory)fibers.
● The anterolateral
sulcus is the exit site
for the anterior root
(motor)fibers.
13. Coverings of the spinal cord
● The spinal cord is coveredby:
○ Dura mater
○ Arachnoid mater
○ Pia mater
● Filum terminale is a prolongation of
the pia mater from the apex of the
conus medullaris to the posterior
surface of thecoccyx.
14. Coverings of the spinal cord...
● The subarachnoid space at the level of the
cauda equina enlarges to form the lumbar
cistern (site for lumbar puncture and
spinal anesthesia).
● The pia mater attaches to the vertebral
column laterally by the denticulate
ligament.
15. Internal structure
• The inner core of the spinal cord is formed
by grey matter and it is surrounded by
whitematter
16. Gray matter
● Composed of neuronal cell bodies,
dendrites, initial parts of axons, and glial
cells.
● Divided into dorsal (posterior) and ventral
(anterior) horns (H shape in crosssections).
● The grey commissure connects the
anterior and posterior horns. It contains
the central canal.
17. ● The dorsal horn receives sensory
information while the ventral horn
projects motor commands.
● The small lateral grey horn lie in the
thoracic and upper lumbar segments. It
functions as sympathetic synapsearea.
18.
19. LAMINA
I Nucleus posteromarginalis
II Substantia gelatinosa
III and IV Nucleus proprius dorsalis
V Zone anterior to lamina IV
VI Zone at the base of dorsal horn
VII Intermediate zone
VIII Zone in the ventral horn (restricted to medial aspect
in cervical and lumbar enlargements)
IX Medial and lateral anterior horn cell columns.
X cells surrounding the central canal
20. ● The posterior grey horn has four nerve
groups:
○ Substantia gelatinosa group (laminaII)
○ Nucleus proprius group (laminae III &
IV)
○ Nucleus dorsalis group (Clarke’s
column- lamina VII)
○ Visceral afferent nucleus
21. ● The substantia gelatinosa is located in the
apex of the posterior grey horn throughout
the spinal cord.
● It receives afferents conveying pain, touch,
and temperature.
● The nucleus proprius is located anterior to
the substantia gelatinosa throughout the
spinal cord.
● It receives afferents conveying
proprioception, two-point discrimination,
and vibration from the posteriorcolumn.
22. ● Clarke’s column is situated at the base of
the posterior grey horn from the lower
cervical to the middle lumbarsegment.
● It receives proprioceptive input (mainly
muscle and tendon spindles).
● The visceral afferent nucleus lies lateral to
the Clarke’s column from the first thoracic
to the third lumbar segment.
● It receives visceral afferentinformation.
25. ● The nomenclature of the tracts start with the
origin and ends with the destination.
● Ascending tracts named spino____tract. For
example: spinothalamic tracts.
● Descending tracts are usually named
_____spinal tract. For example:corticospinal
tract.
Tracts of the spinal cord
26. PATHWAYS IN THE SPINAL CORD
Ascending (afferent) pathways Descending (efferent)
pathways
28. Basic Concepts
28
● Information conveyed by ascending
tracts may be dividedinto:
○ Exteroceptive information (pain,
temperature, and touch)
○ Proprioceptive information
(e.g.,muscle stretch)
29. ● Each tract usually consists of three
neurons:
○ First-order neuron
○ Second-order neuron
○ Third-order neuron
● Afferent axons of the first-order neurons
have their cell bodies in the dorsal root
ganglia.
30. ● Second-order neurons decussate at
different levels.
● Third-order neurons are usually found
in the thalamus.
● These neurons branch to give input to
motor neurons and the reticular
formation.
31. Spinothalamic Tracts
31
● Also called anterolateral system.
● Consists of two tracts:
○ Anterior spinothalamic tract (crude
touch)
○ Lateral spinothalamic tract (pain
and temperature)
32.
33. Spinothalamic Tracts
33
● They enter the spinal cord and travel
for a segment or two in the
posterolateral tract of Lissauer then
synapse in lamina I, II and IV.
● After synapse, fibers from the second-
order neurons cross to the opposite
side in the white and grey
commissures and travel rostrally.
34. 34
● The anterolateral system shows
somatotopic organization.
● Sensation from lower parts of the body
travel laterally while sensation from
upper parts travel medially.
● second-order neurons synapse in the
ventral posterolateral and
intralaminar thalamic nuclei.
● Third-order neurons send axons that
pass through internal capsule to the
somatosensory cortex
38. Dorsal Column Tracts
38
● Carry fine and discriminative
touch, vibration, and proprioception.
● Divided into:
○ Fasciculus gracilis (lower part of the
body)
○ Fasciculus cuneatus (upper part of
the body)
39. Dorsal Column Tracts
39
● Fasciculus gracilis and cuneatus pass
directly to the ipsilateral posterior
white column and ascend without
synapse till the they reach the nuclei
cuneatus and gracilis in the medulla
oblongata.
40. 40
● Second-order neurons decussate and
ascend forming the medial lemniscus
to synapse in the ventral posterolateral
nucleus of the thalamus.
● third-order neurons pass through the
internal capsule to reach the
somatosensory cortex.
43. Dorsal Spinocerebellar tract
43
● Convey proprioception and deep
pressure from the muscles to the
cerebellum.
● First-order neurons synapse on the
Clarke’s column.
● Fibers from the second-order neurons
enter the ipsilateral lateral white
funiculus.
44. Dorsal Spinocerebellar tract
44
● Fibers from the second-order neurons
ascend join the inferior cerebellar
peduncle and terminate in the
cerebellarcortex.
● Sensory fibers from sacral and lower
lumbar travel rostrally until they meet
and synapse on the Clarke’scolumn.
45. Anterior Spinocerebellar Tract
45
● Has the same function of the posterior
spinocerebellar tract in addition to
sensation from the skin.
● Axons synapse on Clarke’s column and
most of the second-order neurons
decussate and ascend to enter the
cerebellum in the superior cerebellar
peduncle.
50. Objectives
50
By the end of this session you should be able
to:
● Describe the corticospinal tractpathway.
● List other descending tracts and describe
their pathways.
● Define the concept of upper and lower
motor neurons.
51. 51
● Differentiate between upper and lower
motor neuron lesions.
● List the important disorders affecting the
spinal cord and their clinical presentation.
52. Basic Concepts
52
● Asfor the ascending tracts, descending
tracts usually have threeneurons:
○ First-order neuron (its cell body lie
in the cerebral cortex)
○ Second-order neuron (anteriorgrey
horn-very short interneuron)
○ Third-order neuron
53. ● Neuronal cell bodies in the anterior grey
horn and their axons (usually third-order
neuron) are regarded as the lower motor
neurons.
● Every nerve in the descending tracts other
than lower motor neurons is referred to as
an upper motor neuron.
54. • Five descending systems exert tonic effects on
the motor neurons.
• The vestibulospinal tract and the medial
reticulospinal tract tend to facilitate the
motor neurons of antigravity muscles.
• The corticospinal tract, The
corticorubrospinal tract, and the lateral
reticulospinal tract inhibit the antigravity
muscles and facilitate the antagonists.
55. Corticospinal Tracts..
● Also called “pyramidaltracts”
● The corticospinal tracts are fibers concerned
with voluntary skilled movements especially
in the distal parts of the limbs.
● They are the most important descending
tracts in the humanCNS.
56. Corticospinal Tracts..
56
● Corticospinal tracts arise from
the following cortical structures:
○ Primary motor cortex (area4)
○ Secondary motor cortex (area6)
○ Primary somatosensory cortex (areas
3,1 & 2)
57. Corticospinal Tracts..
● Fibers descend through the corona
radiata and pass through the posterior
limb of the internal capsule.
● Then they pass through the crus
cerebri of the midbrain.
58. Corticospinal Tracts..
● Fibers innervating the cervical portion
of the spinal cord lie medially and
those innervating the sacral portion lie
laterally.
● In the pons the tracts are broken into
bundles by the transverse
pontocerebellarfibers.
59. Corticospinal Tracts
● Most fibers cross the midline at the
medulla in the pyramidal decussation to
enter the lateral white funiculus as the
lateral corticospinal tracts.
● Uncrossed fibers descend in the anterior
white funiculus as the anterior
corticospinal tract.
60.
61. Corticospinal Tracts...
● Uncrossed fibers of the anterior
corticospinal tract cross the midline
and innervate the anterior horn cells
of the contralateral side.
● Most of the corticospinal fibers
synapse on interneurons which in turn
synapse with the motor neurons.
62.
63. Reticulospinal Tracts
63
● Reticulospinal tracts influence voluntary
movements, reflexes and sensation (pain).
They may have some autonomicfibers.
● They are dividedinto:
○ Pontine reticulospinal tract
○ Medullary reticulospinal tract
64. Reticulospinal Tracts..
● Pontine fibers are usually uncrossed
and they descend in the anterior
white funiculus.
● Medullary fibers can be crossed or
uncrossed and they descend in the
lateral white funiculus.
65. Rubrospinal Tract..
● The rubrospinal tract affects motor
activity.
● Fibers originate from the red nucleus of
the midbrain, cross the midline and
descend to enter the lateral white
funiculus.
● They synapse on interneurons in the
anterior grey horn.
66. Vestibulospinal Tracts..
66
● The vestibulospinal tracts are important
in maintaining balance andequilibrium.
● They are dividedinto:
○ Lateral vestibulospinal tract
○ Medial vestibulospinal tract
67. Vestibulospinal Tracts...
67
• The vestibular nuclei receive input from
the vestibular nerve and thecerebellum.
• Lateral vestibulospinal tract is involved in
the body posture and balance by
increasing extensor muscle tone.
68. ● Fibers arise from the lateral vestibular
nucleus, descend uncrossed in the anterior
white funiculus and synapse on
interneurons in the anterior greyhorn.
● The medial vestibulospinal tract is
involved in the adjustment of the head
position.
Vestibulospinal Tracts...
68
69. Vestibulospinal Tracts...
69
● Fibers originate from the medial
vestibular nucleus to terminate in the
cervical spinal cord.
● This tract has crossed and uncrossed
fibers and it descends in the anterior
white funiculus.
70. • The medial longitudinal fasciculus (MLF) is
organized as a pair of white matter fiber tracts
that extend through the brainstem and lie near
the midline just ventral to the fourth ventricle
(in the medulla and pons) and cerebral
aqueduct (in the midbrain).
Medial Longitudinal Fasciculus
71. 71
● It has a collection of fibers of some tracts
like:
○ Reticulospinal tracts
○ Tectospinal tract
○ Medial vestibulospinal tract
○ Connect III, IV and VI cranial nerve
nuclei
72. • The MLF contains fibers that ascend and some
that descend within the brainstem tegmentum
and interact with ocular motor control circuitries
involved in the coordination of horizontal,
vertical, and torsional eye movements in
coordination with head and neck movements
74. Basic Concepts
74
● Lesion of a single posterior root will cause
pain in the skin and muscles innervated by
that root.
● Lesion of a single anterior root will cause
paralysis to any muscle supplied exclusively
by that root.
75. 75
● Damage to the anterolateral system will
cause contralateral loss of pain,
temperature and crude touch below the
level of the lesion.
● Damage to the dorsal column causes
ipsilateral disruption of proprioception,
pressure and vibration below the level of
the lesion.
Basic
76. 76
● Damage to the dorsal column can be
assessed by:
○ Tuning fork (vibration)
○ Toe dorsiflexion and
plantarflexion
(proprioception)
○ Two needles (two-pointdiscrimination)
77.
78. ○ Hypertonia in the innervated
muscles
○ Exaggerated deep tendon
reflexes
○ Diminished superficial reflexes
○ Clasp-knife reaction
○ Positive Babinski'ssign
78
79. 79
● LMNLs occur in neurons in the ventral
gray column of the spinal cord and
brainstem (affecting cranial nerves).
● Signs and symptoms include:
○ Flaccid paralysis or
paraparesis of the muscles
innervated by the affected neurons
Lower motor neuron palsy
80. ○ Muscle atrophy
○ Areflexia or diminished reflexes in the
muscles innervated by the affected
neurons
○ Fasciculations
80
Basic Concepts
81. Herpes Zoster
81
● Herpes zoster is a viral infection that
affects sensory neurons.
● It is characterized by pain and
inflammation with vesicles in the area of
distribution of the affected nerve.
● This infection usually occur in the elderly.
82. Tabes Dorsalis
82
● Tabes dorsalis (neurosyphilis) results from
the selective destruction to the dorsal roots.
● This disease affects many sensationsand
reflexes.
● It also causes ataxia and hypotonia.
83. Spinal Shock
83
● Spinal shock results from severe injury to
the spinal cord.
● All sensations, reflexes, and motor
functions of the spinal cord below the
level of the injury will be suppressed as a
result.
● It may last to 24 hours or may extend to 6
weeks.
84. Anterior Cord Syndrome
84
● Results from any trauma or
ischemia of the anterior part of the
spinal cord.
● Signs and symptoms appear after the
period of spinal shock including:
○ Bilateral lower motor neuron paralysis
in the segment of thelesion
85. Anterior Cord Syndrome
85
○ Bilateral spastic paralysis below the
level of the lesion
○ Bilateral loss of pain, emperature,and
light touch sensations below the level
of the lesion
○ Normal dorsal columnsensations
87. Central Cord Syndrome
87
● Usually caused by hyperextension of
the neck.
● Signs and symptoms after
spinal shock include:
○ Bilateral lower motor neuron
paralysis in the segment of the
lesion
88. Central Cord Syndrome
88
• Bilateral spastic paralysis below the
level of the lesion with characteristic
sacral “sparing”
• Bilateral loss of pain, temperature, light
touch, and pressure sensations below
the level of the lesion with
characteristic sacral “sparing”
90. Brown-Séquard Syndrome
90
● Also called spinal cordhemisection.
● Causes include tumours, penetrating
trauma or vertebral column fractures.
● Signs and symptoms afterspinal shock
include:
○ Ipsilateral flaccid paralysis in the
segment of the lesion
91. ○ Ipsilateral spastic paralysis below the
level of the lesion
○ Ipsilateral cutaneous anesthesia in the
segment of the lesion (fibers haven’t
crossed yet)
Brown-Séquard Syndrome
91
92. ○ Ipsilateral loss of vibration, two-point
discrimination, and proprioception
below the level of thelesion
○ Contralateral loss of pain and
temperature sensations below the level
of the lesion
Brown-Séquard Syndrome
92
95. Syringomyelia
95
● Syringomyelia is a developmental or
acquired abnormality in the central
canal usually in the brainstem and
cervical spinalcord.
● It is characterized by cavitation and
gliosis of the central part of the affected
segment.
96. ● Signs and symptoms include:
○ Bilateral loss of pain and temperature
sensations in dermatomes innervated by
the affected segments (cape
distribution)
○ Lower motor neuron weakness is
present in the small muscles of the
hand
Syringomyelia
97. ○ Bilateral spastic paralysis of both
legs may occur along with some
UMNL signs
○ Horner syndrome may bepresent
● Some symptoms are only foundin a
large syrinx.
97
Syringomyelia
100. Amyotrophic Lateral Sclerosis
10
0
● Also called Lou Gehrig disease.
Etiology is unknown
● It affects the corticospinal tract and the
motor neurons of the anterior grey horn.
● Combines signs of both UMN and LMN
lesions
101. Spinal Cord Transection
10
1
● results in loss of all sensory and
voluntarily motor functions below the
level of the injury (spinal shock).
● Signs after spinal shockinclude:
○ All signs and symptoms of
lower motor lesions at the level
of the injury.
102. Spinal cord transection
• Spastic paralysis below the lesion and positive
Babinski’s signbilaterally
○ Loss of superficial reflexes (depends on the
level of thelesion)
○ Loss of all sensations and autonomic
innervation below the level of the lesion
