The spinal cord, its tracts and contents

1. THE SPINAL CORD

2. 12-2
Spinal Cord
• Extends from foramen magnum to second
lumbar vertebra
• Segmented
– Cervical
– Thoracic
– Lumbar
– Sacral
• Connected to 31 pairs of spinal nerves
– All are mixed nerves; I.e., contain both
sensory and motor fibers
• Not uniform in diameter throughout length
– Cervical enlargement: supplies upper
limbs
– Lumbar enlargement: supplies lower
limbs
• Conus medullaris: tapered inferior end.
• Cauda equina: origins of spinal nerves
extending inferiorly from lumbosacral
enlargement and conus medullaris.

3. 12-3
Spinal Meninges
– Dura mater: outermost layer; continuous
with epineurium of the spinal nerves
• No firm connections to vertebrae
• Epidural space: external to the dura;
anesthesia injected here in sc. Contains
blood vessels, areolar connective tissue
and fat.
– Arachnoid mater: delicate net-work of
collagen and elastic fibers
• Subarachnoid space: between pia and
arachnoid
• CSF and blood vessels within web-like
strands of arachnoid tissue
• Fluid functions as a shock absorber
– Pia mater: thin layer of elastic and
collagen fibers bound tightly to surface of
brain and spinal cord
• Denticulate ligaments extend from pia
through arachnoid to dura; prevent
lateral movement
• Forms the filum terminale, which
anchors spinal cord to coccyx and the
denticulate ligaments that attach the
spinal cord to the dura mater

4. Location of Ascending and
Descending Tracts of the Spinal Cord

6. 12-6
Spinal Nerves

7. 12-7
Ascending Tracts
• Carry sensory signals up to the
spinal cord
• Typically uses 3 neurons
– 1st order neuron - detects
stimulus and carries it to spinal
cord
– 2nd order neuron - within s.c.;
continues to the thalamus (the
sensory relay station)
– 3rd order neuron - carries
signal from thalamus to
sensory region of cerebral
cortex
• Most have names with prefix
spino-

8. Major Sensory or Ascending Tracts
Name Location Function
Fasciculus
Posterior
gracilis
Column
Discriminative touch,
proprioception
Weight discrimination
Fasciculus
Cuneatus
Posterior
Column
Same as FG
Lateral
Spinothalamic
Lateral
Column
Pain and Thermal
sensations
Anterior
Spinothalamic
Anterior
Column
Itch, Tickle, Pressure,
Crude touch sensations
Posterior and
Anterior
Spinocerebellar
Lateral
Column
Proprioceptors

9. Medial Lemniscus
System
• Also called
posterior column
system.
• Carries
sensations for
two-point
sensation (fine
touch), pressure,
and vibration.

10. Medial Lemniscus
System
• Primary fibers
ascend entire
length of spinal
cord and synapse
with secondary
neurons in
medulla:
Fasciculus gracilis
Fasciculus
cuneatus

11. • Fibers of fasciculus
gracilis synapse in
nucleus gracilis:
Convey sensations from
below midthoracic level.
• Fibers of fasciculus
cuneatus synapse
in nucleus
cuneatus:
Convey sensations from
above midthoracic level.
Also conveys
proprioceptive sensation
from arms to
cerebellum.

12. Medial Lemniscus
System
• Secondary
fibers
decussate.
• Secondary
fibers ascend to
synapse in VPL
of thalamus.
• Tertiary fibers
ascend through
internal capsule
to primary
sensory cortex.

14. Spinothalamic
System
• Lateral
spinothalamic
tract
• Anterior
spinothalamic
tract

15. Lateral
Spinothalamic
Tract
• Carries pain and
temperature
• Primary fibers
ascend or
descend 1-2
spinal cord
segments
before
synapsing with
secondary
fibers.

16. Lateral
Spinothalamic
Tract
• Secondary axons
decussate through
anterior gray and
white
commissures.
• Secondary axons
make up the
lateral
spinothalamic
tract traveling in
the lateral column
of the spinal cord.

17. Lateral
Spinothalamic
Tract
• Secondary fibers
are joined in
brainstem by
fibers of the
trigeminothalam
ic tract:
(Pain and
temperature from
face and teeth.)

18. Lateral Spinothalamic Tract
• Secondary fiber collaterals project to reticular
formation:
Stimulate wakefulness and consciousness.
• Secondary fibers project to ventral
posterolateral (VPL) nucleus of thalamus.

19. Lateral Spinothalamic Tract
• Secondary fibers synapse with tertiary fibers
in VPL.
• Tertiary fibers (corticopetal fibers) synapse in
postcentral gyrus:
Somatic sensory areas 3, 1, 2
• Tertiary fibers form part of internal capsule.

20. Anterior
Spinothalamic
Tract
• Carries light touch
(crude touch),
pressure, tickle, itch
• Primary neurons may
ascend 8-10 spinal cord
segments before
synapsing with
secondary neurons.
• Secondary fibers
decussate in anterior
gray or white
commissures.

21. Anterior
Spinothalamic
Tract
• Secondary fibers
ascend to synapse
with tertiary fibers in
VPL nucleus of
thalamus.
• Tertiary fibers ascend
through internal
capsule to primary
sensory cortex.

22. Posterior Spinocerebellar Tract
• Originates in thoracic and upper lumbar
regions.
• Consists of uncrossed fibers that enter
cerebellum through inferior cerebellar
peduncles.
• Transmits ipsilateral proprioceptive
information to cerebellum.

23. Anterior Spinocerebellar Tract
• Originates in lower trunk and lower limbs.
• Consists of crossed fibers that recross in pons
and enter cerebellum through superior
cerebellar peduncles.
• Transmits ipsilateral proprioceptive
information to cerebellum.

24. Spino-Olivary Tracts
• Project to accessory olivary nuclei and
cerebellum.
• Contribute to movement coordination
associated primarily with balance.

25. Spinotectal Tracts
• Project to superior colliculi of midbrain.
• Involved in reflexive turning of the head and
eyes toward a point of cutaneous stimulation.

26. Spinoreticular Tracts
• Involved in arousing consciousness in the
reticular activating system through cutaneous
stimulation.

27. 12-27
Spinoreticular Tract
• Pain signals from tissue injury
• Decussate in spinal cord and ascend with
spinothalamic fibers
• End in reticular formation (medulla and pons)
• 3rd and 4th order neurons continue to thalamus
and cerebral cortex

28. 12-28
Descending (Motor) Pathways
• Descending tracts deliver efferent impulses from
the brain to the spinal cord, and are divided into
two groups
– Direct pathways equivalent to the pyramidal tracts
– Indirect pathways, essentially all others
• Motor pathways involve two neurons
– Upper motor neuron (UMN)
• Begins with soma in cerebral cortex or brainstem
• Its axon terminates ON the LMN in anterior horn
– Lower motor neuron (LMN)
• Soma in anterior horn; axon leads to muscle
• aka ‘anterior horn motor neuron” (also, final common
pathway)

29. Motor or Descending Tracts of the Spinal Cord
Name Location Function
Lateral
Corticospinal
Lateral
Column
Muscles of the limbs,
hands, and feet
Anterior
Corticospinal
Anterior
Column
Muscles of the axial
skeleton
Corticobulbar Cerebral
Peduncle
Skeletal muscles of the
head and neck via cranial
nerves
Rubrospinal Lateral
Column
Skeletal muscles of the
limbs, hands, and feet
Tectospinal Anterior
Column
Skeletal muscles of the
head and eyes in response
to visual stimuli

30. Motor or Descending Tracts of the Spinal Cord
Name Location Function
Vestibulospinal Anterior
column
Muscle for maintaining
balance in response to head
movements
Lateral
reticulospinal
Anterior
column
Facilitates flexor reflexes
Inhibits extensor reflexes
Medial
reticulospinal
Anterior
column
Facilitates extensor reflexes
Inhibits Flexor reflexes

31. 12-31
The Direct
(Pyramidal) System
• Direct pathways originate with
the pyramidal neurons in the
precentral gyri (aka, primary
motor area).
• Pyramidal neuron is the UMN; it
forms the corticospinal tract
(cortico =cortex; spinal - s.c.)
• UMN synapses in the anterior
horn with LMN
• LMN (anterior horn motor
neurons) activates skeletal
muscles
• The direct pathway regulates
fast and fine (skilled)
movements
• Lateral corticospinal tracts: UMN
decussates in pyramids of
medulla
• Anterior corticospinal tracts:
UMN decussates at the spinal
cord level

32. Indirect (Extrapyramidal) System
12-32
• Upper motor neuron (UMN) originates in nuclei deep in
cerebrum (not in cerebral cortex); .e., in brain stem,
• UMN does not pass through the pyramids
• LMN is an anterior horn motor neuron
• This system includes the rubrospinal, vestibulospinal,
reticulospinal, and tectospinal tracts
• These motor pathways are complex and multisynaptic

33. C1-C4 May need breathing assistance
C5- No wrist or hand control, some
shoulder and bicep control
C6- Includes some wrist control, no
hand control
C7 and T1- Can straighten arms, lacking
in hand and finger control
T1-T8- Most often include hand
control, lack of trunk control
T9-T12- Have most trunk control, can
balance sitting up
Lumbar and Sacral- Loss includes hip
flexor and leg control

34. Diseases of the Spinal Cord

36. Basic Features of Spinal Cord Disease
• UMN findings below the lesion
– Hyperreflexia and Babinski’s
• Sensory and motor involvement that localizes
to a spinal cord level
• Bowel and Bladder dysfunction common
• Remember that the spinal cord ends at about
T12-L1

38. History
• Onset
– Acute, subacute, chronic
• Symptoms
– Pain
– Weakness
– Sensory
– Autonomic
• Past history
• Family history

39. Tempo of Spinal Cord Disease
Acute Subacute Chronic
Trauma
Mass lesion
X
X
X
Infectious
Inherited
X X X
X
Vascular
Autoimmune
X
X
X
X
X
Nutritional X

40. Motor Exam
• Strength - helps to localize the lesion
– Upper cervical
• Quadriplegia with impaired respiration
– Lower cervical
• Proximal arm strength preserved
• Hand weakness and leg weakness
– Thoracic
• Paraplegia
– Can also see paraplegia with a midline lesion in the brain
• Tone
– Increased distal to the lesion

41. Sensory Exam
• Establish a sensory level
– Dermatomes
• Nipples: T4-5
• Umbilicus: T8-9
• Posterior columns
– Vibration
– Joint position sense (proprioception)
• Spinothalamic tracts
– Pain
– Temperature

42. Autonomic disturbances
• Neurogenic bladder
– Urgency, incontinence, retention
• Bowel dysfunction
– Constipation more frequent than incontinence
• With a high cord lesion, loss of blood pressure
control
• Alteration in sweating

43. Investigation of Spinal Cord Disease
• Radiographic exams
– Plain films
– Myelography
– CT scan with myelography
– MRI
• Spinal tap
– If you suspect: inflammation, MS, rupture of a
vascular malformation

44. Etiology of Spinal Cord Disease

45. Traumatic Spinal Cord Disease
• 10,000 new spinal cord injuries per year
• MVA, sports injuries the most common
• Victims under 30 yrs old, male>>females
• Fx/dislocation of vertabrae most likely to
occur at:
– C5,6
– T12, L1
– C1,2

46. Tumors
• Metastatic or primary
• Extramedullary
– Extradural - most common
• Bony - breast, prostate
– Intradural - very rare
• Meninges - meningioma
• Nerve root - schwannoma
– Intramedullary - very rare
• Metastatic
• Primary - astrocytoma or ependymoma

47. B12 Deficiency
• Subacute combined degeneration of the cord
• B12 deficiency
– malabsorption of B12 secondary to pernicious
anemia or surgery
– insufficient dietary intake - vegan
• Posterior columns and CST involvement with a
superimposed peripheral neuropathy

48. Transverse myelitis
• Inflammation of the spinal cord
– Post-infectious
– Post-vaccinial
– Multiple sclerosis
• Pain at level of lesion may preceed onset of
weakness/sensory change/b&b disturbance
• Spinal tap may help with diagnosis

49. Infections Involving the Spinal Cord
• Polio
– only the anterior horn cells are infected
• Tabes dorsalis
– dorsal root ganglia and dorsal columns are involved
– tertiary syphillis
– sensory ataxia, “lightening pains”
• HIV myelopathy
– mimics B12 deficiency
• HTLV-1 myelopathy -
– tropical spastic paraparesis

50. Multiple Sclerosis
• Demyelination is the underlying pathology
• Cord disease can be presenting feature of MS
or occur at any time during the course of the
disease
• Lesion can be at any level of the cord
– Patchy
– Transverse
• Devic’s syndrome or myelitis optica
– Transverse myelitis with optic neuritis

51. Vascular Diseases of the Spinal
Cord • Infarcts
– Anterior spinal artery infarct
• from atherosclerosis, during surgery in which the
aorta is clamped, dissecting aortic aneurysm
– less often, chronic meningitis or following trauma
• posterior columns preserved (JPS, vib)
• weakness (CST) and pain/temperature loss
(spinothalamic tracts)
– Artery of Adamkiewicz at T10-11
– Watershed area
• upper thoracic

52. Vascular Diseases of the Spinal Cord,
cont
• Arteriovenous malformation (AVM) and venous
angiomas
– Both occur in primarily the thoracic cord
– May present either acutely, subacutely or chronically
(act as a compressive lesion)
– Can cause recurrent symptoms
– If they bleed
• Associated with pain and bloody CSF
– Notoriously difficult to diagnose
• Hematoma - trauma, occasionally tumor

53. Other Disease of the Spinal Cord
• Hereditary spastic paraparesis
– Usually autosomal dominant
• Infectious process of the vertabrae
– TB, bacterial
• Herniated disc with cord compression
– Most herniated discs are lateral and only compress a
nerve root
• Degenerative disease of the vertabrae
– Cervical spondylosis with a myelopathy
– Spinal stenosis

54. Classical spinal cord syndromes
• Anterior spinal artery infarct
• Brown Sequard syndrome
• Syringomyelia
• Conus medullaris/caude equina lesions

55. Brown Sequard Syndrome
• Cord hemisection
• Trauma or tumor
• Dissociated sensory loss
– loss of pain and temperature contralateral to lesion, one
or 2 levels below
• crossing of spinothalamic tracts 1-2 segments above where they
enter
– loss of vibration/proprioception ipsilateral to the lesion
• these pathways cross at the level of the brainstem
• Weakness and UMN findings ipsilateral to lesion

56. Syringomyelia
• Fluid filled cavitation in the center of the cord
• Cervical cord most common site
– Loss of pain and temperature related to the
crossing fibers occurs early
• cape like sensory loss
– Weakness of muscles in arms with atrophy and
hyporeflexia (AHC)
– Later - CST involvement with brisk reflexes in the
legs, spasticity, and weakness
• May occur as a late sequelae to trauma
• Can see in association with Arnold Chiari
malformation

57. Conus Medullaris vs. Cauda Equina
Lesion
Finding Conus CE
Motor Symmetric Asymmetric
Sensory loss Saddle Saddle
Pain Uncommon Common
Reflexes Increased Decreased
Bowel/bladder Common Uncommon