Title: The Spinal Cord
1 The Spinal Cord
- Basic Neuroscience
- James H. BaƱos, Ph.D.
2Grey and White Matter
3Grey and White Matter
Grey Matter Cell Body
White Matter Myelinated axon
4Grey and White Matter
- Grey matter
- Cortex
- Nucleus (CNS)
- Ganglion (PNS) Exception Basal Ganglia
5Grey 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
6Grey 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
7The Spinal Cord
8General 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!!!
9General Organization
White matter (tracts of axons)
Grey Matter (cell bodies)
10General 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
11General Organization
- Each set of rootlets forms a spinal nerve that
innervates a corresponding segment of the body,
called a dermatome
12General Organization
13General 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
14General Organization
- The spinal cord is housed within the vertebral
column
15General Organization
- Each cord segment has a corresponding vertebra of
the same name (e.g., C3) - Spinal nerves enter/exit underneath their
corresponding vertebral segment
16General 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
17General Organization
18General Organization
- Cord is not of uniform thickness throughout its
length. Why not?
19General 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.
20General Organization
Cervical enlargement C5 - T1
Lumbar enlargement L2 - S3
21The Spinal Cord in Cross Section
22Cord 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)
23Cord Sections -- Cervical
- Cervical cord is wide, flat, almost oval in
appearance. Why?
24Cord Sections -- Cervical Enlargement
- Whats different about the cervical enlargement .
Why?
Cervical
Cervical Enlargement
25Cord Section -- Thoracic
- Less White matter than cervical
- Rounder appearance
- Less prominent ventral horns than cervical
enlargement
26Cord Section -- Lumbar
- Less White matter than thoracic
- Rounder appearance
- Larger ventral horns, especially in lumbar
enlargement
Lumbar
Lumbar Enlargement
27Cord Section -- Sacral
- Not much white matter
- Mostly grey, although not much of that either
28(No Transcript)
29Cross Sectional Organization
Posterior intermediate sulcus
Posterior median sulcus
Tract of Lissauer
Anterior white commissure
Anterior median fissure
30Grey Matter
31Grey Matter
- Posterior (dorsal) Horn
- Intermediate Grey
- Anterior (ventral) Horn
32Grey Matter Posterior Horn
- Mostly Interneurons
- Substantia gelatinosa
- Pain/temp proc
- Body of the posterior horn
- Sensory proc
33Grey Matter Intermediate Grey
- Clarkes Column
- T1-L3
- Balance/proprio.
- Intermediolateral Column
- T1-L3
- Sympathetic neurons
34Grey Matter Anterior Horn
35White Matter The Big Four Pathways
Corticospinal tract
Dorsal Columns
Spinothalamic tract
Spinocerebellar tracts
36The 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
37Corticospinal Tract
38Corticospinal 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
39Motor Homunculus
40Motor Homonculus
HAL
Arms
Legs
Head
41Corticospinal Tract
Spinal Cord
Medulla
Pons
Midbrain
42Corticospinal Tract
43Upper 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
44Upper 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
45Upper 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
46Upper 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
47Upper 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
48Babinskis 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.
49Related Terms
- Spasticity -- Increased muscle tone and increased
reflex contraction (UMN) - Clonus -- Rythmic contractions and relaxations
seen when a spastic muscle is stretched (UMN)
50Basics 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
51Dorsal Column/ Medial Lemniscus
- Discriminative Touch
- Conscious Proprioception
52Dorsal 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
53Dorsal Columns/Medial Lemniscus
54Spinocerebellar Tracts
- Unconscious Proprioception
55Dorsal (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
56Dorsal (Posterior) Spinocerebellar Tract
L3
T1
Spinal Cord
Medulla
Pons
Midbrain
To Cerebellum
57Ventral (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
58Ventral (Anterior) Spinocerebellar Tract
59Spinothalamic Tract
60Spinothalamic 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
61Spinothalamic Tract
62Spinothalamic Tract
63L1
L1
L2
L2
L3
L3
L4
L4
L5
L5
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