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The Spinal Cord

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Title: The Spinal Cord


1
The Spinal Cord
  • Basic Neuroscience
  • James H. BaƱos, Ph.D.

2
Grey and White Matter
3
Grey and White Matter
Grey Matter Cell Body
White Matter Myelinated axon
4
Grey and White Matter
  • Grey matter
  • Cortex
  • Nucleus (CNS)
  • Ganglion (PNS) Exception Basal Ganglia

5
Grey and White Matter
  • White Matter
  • Nerve (PNS)
  • Tract (CNS)
  • Fasciculus/Funiculus -- Group of fibers with
    common origin and destination
  • Lemniscus -- Ribbon-like fiber tract
  • Peduncle -- Massive group of fibers -- usually
    several tracts

6
Grey and White Matter
  • Tracts are named with origin first, then
    destination
  • Corticospinal tract -- cortex to spinal cord
  • Mammilothalamic tract -- Mammilary bodies to
    thalamus
  • Spinocerebellar tract -- Spinal cord to
    cerebellum
  • Corticobulbar tract -- Cortex to brain stem

7
The Spinal Cord
8
General Organization
  • Spinal cord is SMALL!
  • 42-45 cm long
  • 1 CM wide at widest point
  • Does not extend all the way to the bottom of the
    spinal column
  • Pattern of grey/white matter is reversed in the
    cord
  • White matter tracts on outside
  • Grey matter on the inside
  • Staining reverses this!!!

9
General Organization
White matter (tracts of axons)
Grey Matter (cell bodies)
10
General Organization
  • Spinal cord is segmented anatomically
  • Input and output occurs in groups of rootlets
    arranged in a series longitudinally along the
    cord
  • Dorsal rootlets -- Input -- carry sensory
    information
  • Ventral rootlets -- Output -- motor neurons

11
General Organization
  • Each set of rootlets forms a spinal nerve that
    innervates a corresponding segment of the body,
    called a dermatome

12
General Organization
13
General Organization
  • There are 31 segments in the spinal cord
  • 8 cervical (C1 - C8)
  • 12 Thoracic (T1 - T12)
  • 5 Lumbar (L1 - L5)
  • 5 Sacral (S1 - S5)
  • 1 Coccygeal

14
General Organization
  • The spinal cord is housed within the vertebral
    column

15
General Organization
  • Each cord segment has a corresponding vertebra of
    the same name (e.g., C3)
  • Spinal nerves enter/exit underneath their
    corresponding vertebral segment

16
General Organization
  • But wait! Something doesnt add up!
  • How can spinal nerves exit below their
    corresponding vertebral segment if the cord is
    only 42cm-45cm long?
  • Answer Spinal nerves extend down to the
    appropriate vertebral segment forming the cauda
    equina
  • This means cord segments and vertebral segments
    dont line up

17
General Organization
18
General Organization
  • Cord is not of uniform thickness throughout its
    length. Why not?

19
General Organization
  • Cord is not of uniform thickness throughout its
    length. Why not?
  • Answer
  • Segments of the cord innervate parts of the body
    that differ in complexity
  • There are fewer white matter tracts lower in the
    cord.

20
General Organization
Cervical enlargement C5 - T1
Lumbar enlargement L2 - S3
21
The Spinal Cord in Cross Section
22
Cord Sections
  • Segments of the spinal cord have a similar
    organization, but vary in appearance.
  • Always know where you are in the cord (i.e.,
    cervical, thoracic, lumbar, sacral)

23
Cord Sections -- Cervical
  • Cervical cord is wide, flat, almost oval in
    appearance. Why?

24
Cord Sections -- Cervical Enlargement
  • Whats different about the cervical enlargement .
    Why?

Cervical
Cervical Enlargement
25
Cord Section -- Thoracic
  • Less White matter than cervical
  • Rounder appearance
  • Less prominent ventral horns than cervical
    enlargement

26
Cord Section -- Lumbar
  • Less White matter than thoracic
  • Rounder appearance
  • Larger ventral horns, especially in lumbar
    enlargement

Lumbar
Lumbar Enlargement
27
Cord Section -- Sacral
  • Not much white matter
  • Mostly grey, although not much of that either

28
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29
Cross Sectional Organization
Posterior intermediate sulcus
Posterior median sulcus
Tract of Lissauer
Anterior white commissure
Anterior median fissure
30
Grey Matter
  • Laminar
  • Laminae of Rexed

31
Grey Matter
  • Posterior (dorsal) Horn
  • Intermediate Grey
  • Anterior (ventral) Horn

32
Grey Matter Posterior Horn
  • Mostly Interneurons
  • Substantia gelatinosa
  • Pain/temp proc
  • Body of the posterior horn
  • Sensory proc

33
Grey Matter Intermediate Grey
  • Clarkes Column
  • T1-L3
  • Balance/proprio.
  • Intermediolateral Column
  • T1-L3
  • Sympathetic neurons

34
Grey Matter Anterior Horn
  • Lower Motor Neurons

35
White Matter The Big Four Pathways
Corticospinal tract
Dorsal Columns
Spinothalamic tract
Spinocerebellar tracts
36
The Big Four
  • Corticospinal tract
  • Voluntary motor
  • Dorsal columns/ medial lemniscus
  • Discriminative touch
  • Conscious proprioception
  • Spinocerebellar tract (dorsal and ventral)
  • Unconscious proprioception
  • Spinothalamic tract
  • Pain/temperature

37
Corticospinal Tract
  • Voluntary Motor

38
Corticospinal Tract
  • First order neuron (upper motor neuron)
    originates in precentral gyrus
  • Passes through internal capsule
  • 90 decussates in caudal medulla
  • Lateral corticospinal tract
  • 10 undecussated
  • Anterior corticospinal tract
  • Synapses on second order neuron (lower motor
    neuron) in ventral gray of the cord
  • Second order neuron innervates muscle

39
Motor Homunculus
40
Motor Homonculus
HAL
Arms
Legs
Head
41
Corticospinal Tract
Spinal Cord
Medulla
Pons
Midbrain
42
Corticospinal Tract
43
Upper Lower Motor Neurons
  • Upper Motor Neuron
  • Motor Cortex to Ventral Grey Horn
  • Modulatory influence on stretch reflex arc
  • Lower Motor Neuron
  • Ventral Grey Horn to Neuromuscular Junction
  • Efferent of stretch reflex arc
  • Helps maintain tone
  • Sensory Neuron
  • Stretch receptors in muscle and tendons
  • Helps maintain tone
  • Afferent of basic stretch reflex arc

Motor Ctx
UMN
Ventral Grey Horn
LMN
44
Upper Lower Motor Neurons
  • Maintenance of Tone
  • Input from stretch receptors causes lower motor
    neuron to supply tonic stimulation to the muscle
  • The upper motor neuron modulates this -- will
    tend to override the tonic signal from the
    sensory neuron

UMN
LMN
45
Upper Lower Motor Neurons
  • Reflex Arc
  • Afferent is sensory neuron detecting a sudden
    stretch
  • Signal is strong and results in a strong response
    by the lower motor neuron
  • Strong signal usually overcomes mild cortical
    input from the UMN

UMN
LMN
46
Upper Lower Motor Neurons
  • Upper Motor Neuron Signs
  • Spastic paresis
  • Hypertonia
  • Hyperreflexia
  • No muscle atrophy (until perhaps late in the
    course)
  • Positive Babinski
  • Why?
  • Loss of voluntary UMN signal
  • Loss of modulation of tone and reflexes by UMN --
    the circuit runs unchecked

Motor Ctx
UMN
Ventral Grey Horn
LMN
47
Upper Lower Motor Neurons
  • Lower Motor Neuron Signs
  • Flaccid paresis/paralysis
  • Muscle fasciculations
  • Hypotonia
  • Hyporeflexia
  • Muscle atrophy
  • Negative Babinski
  • Why?
  • Loss of LMN for voluntary movement
  • Loss of efferent component of reflex arc and tone
    pathway

Motor Ctx
UMN
Ventral Grey Horn
LMN
48
Babinskis Sign
  • In response to stimulation of the sole of the
    foot, the toes will usually curl downward.
  • When UMN inhibition is removed, the toes will
    curl upward (Dorsiflexion). This is referred to
    as a positive Babinski or presence of Babinskis
    sign.

49
Related Terms
  • Spasticity -- Increased muscle tone and increased
    reflex contraction (UMN)
  • Clonus -- Rythmic contractions and relaxations
    seen when a spastic muscle is stretched (UMN)

50
Basics of Localization
  • If all limbs are checked for upper and lower
    motor neuron signs, you can begin to localize
    lesions
  • Left-right differences are also very important

51
Dorsal Column/ Medial Lemniscus
  • Discriminative Touch
  • Conscious Proprioception

52
Dorsal Columns/Medial Lemniscus
  • First order neuron begins in receptor
  • Enters cord at tract of Lissauer
  • Legs run in fasciculus gracilis (medial dorsal)
  • Arms run in fasciculus cuneatus (lateral dorsal)
  • Synapse on nucleus gracilis and nucleus cuneatus
    (caudal medulla)
  • 2nd order neuron decussates and runs from NG NC
    to thalamus (as medial lemniscus)
  • 3rd order neuron runs from thalamus to
    postcentral gyrus

53
Dorsal Columns/Medial Lemniscus
54
Spinocerebellar Tracts
  • Unconscious Proprioception

55
Dorsal (Posterior) Spinocerebellar Tract
  • Involves Clarks Column, a longitudinal gray
    matter body from about T1 to L3
  • Below Clarks Column
  • Runs with f. gracilis, synapses in Clarks
    Column, joins dorsal spinocerebellar tract
  • Level of Clarks Column
  • Synapses in Clarks Column, joins dorsal
    spinocerebellar tract
  • Above Clarks Column
  • Runs with f. cuneatus, synapses in lateral
    cuneate nucleus (caudal medulla), projects to
    ipsilateral cerebellum

56
Dorsal (Posterior) Spinocerebellar Tract
L3
T1
Spinal Cord
Medulla
Pons
Midbrain
To Cerebellum
57
Ventral (Anterior) Spinocerebellar Tract
  • Supplements Dorsal Spinocerebellar Tract
  • Information from more diverse array or receptors
  • Originates from scattered cells in the
    intermediate grey caudal to L1 (which in turn
    have input from proprioceptive axons or their
    collaterals
  • Crosses twice, to end up in ipsilateral
    cerebellum

58
Ventral (Anterior) Spinocerebellar Tract
59
Spinothalamic Tract
  • Pain and Temperature

60
Spinothalamic Tract
  • First order neurons originate in pain receptors,
    enter cord at tract of Lissauer, and synapse in
    substantia gelatinosa or nucleus proprius
  • Second order neurons cross at the anterior white
    commissure, rising 1 or 2 cord levels in the
    process, and form contralateral spinothalamic
    tract
  • A third order neuron (not technically
    spinothalamic tract) projects to the cortex

61
Spinothalamic Tract
62
Spinothalamic Tract
63
L1
L1
L2
L2
L3
L3
L4
L4
L5
L5
64
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