Transcript Lateral Corticospinal Tract In the Spinal Cord

SPINAL CORD III
Major Pathways of the
Spinal Cord - Motor
C.R. Houser
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MAJOR PATHWAYS
Motor
Corticospinal Pathway
Somatosensory
• Dorsal Column
(Medial Lemniscal) System
• Anterolateral
(Spinothalamic) System
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Motor and Sensory Pathways
Blumenfeld, Fig. 7.4.
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Motor Pathways
Lateral Pathways
Medial Pathways
•Corticospinal (Lateral)
•Rubrospinal
•Vestibulospinal
•Reticulospinal – Medullary
- Pontine
•Tectospinal
Blumenfeld,
Fig. 6.7.
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Corticospinal Tract
• Many cell bodies are
located in the primary
motor area (Area 4) of
the precentral gyrus frontal lobe.
• Specific representation
of body parts – Motor
homunculus.
• Face and upper limb on
lateral surface.
• Lower limb on medial
surface.
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LATERAL
CORTICOSPINAL
TRACT
Cortex
Spinal Cord 6
LATERAL
CORTICOSPINAL
TRACT
Voluntary Motor
Control
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LATERAL CORTICOSPINAL TRACT
Cortex
Forebrain
Areas 4, 6,
3,1,2 & 5
Internal
Capsule
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Midbrain
Cerebral
Peduncle
(Basis Pedunculi)
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Pons
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Upper and Lower Medulla
Medullary
Pyramid
Decussation
of Pyramids
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Spinal Cord (Cervical Level)
Lateral Corticospinal tract
Alpha motor neuron
to skeletal muscle
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Corticospinal Tract
• The majority of the corticospinal
fibers cross in the decussation
of the pyramids.
• A small portion of the fibers
remain ipsilateral and descend
in the lateral and anterior
columns.
• Many fibers in the anterior
column (anterior corticospinal
tract) eventually cross in the
spinal cord and innervate motor
neurons in the contralateral
ventral horn.
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Corticospinal Tract
Internal capsule  Cerebral peduncle
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Corticospinal Tract
in the Midbrain
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Corticospinal Tract in Pons
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Corticospinal Tract in Medulla
Medullary Pyramid 
Decussation of the
Pyramids
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Lateral Corticospinal Tract
In the Spinal Cord
(Lateral columns)
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Lesions of Spinal
Cord Pathways
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For each of the illustrated lesions 1) Identify the region of the brainstem
and the specific location of the lesion.
2) Will the clinical problem be on the Left
or Right side of the body?
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L
#1
R
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LATERAL
CORTICOSPINAL
TRACT
L
R
Voluntary Motor
Control
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L
#2
R
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LATERAL
CORTICOSPINAL
TRACT
L
R
Voluntary Motor
Control
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R
L
#3
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LATERAL
CORTICOSPINAL
TRACT
L
R
Voluntary Motor
Control
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L
#4
R
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LATERAL
CORTICOSPINAL
TRACT
L
R
Voluntary Motor
Control
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This patient had a selective lesion of one
pyramid. Which pyramid was damaged?
What functional consequences would
you expect?
L
Left
R
Right
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What are the functions of the
Corticospinal Tract?
• Has facilitatory effects primarily on
motor neurons that innervate flexor
and distal muscles.
• Is necessary for isolated and skilled
movements of the digits.
• Is primarily concerned with voluntary,
goal-directed or skilled movements.
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Broad Classification of
Motor Syndromes
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Classification of Motor Disorders – Considers:
1. Ability to produce desired movements –
weakness or paralysis;
2. Muscle tone
Definition of muscle tone:
• Normal resistance of a muscle to active or passive
stretch.
Can be influenced by:
• Alterations in local reflexes and descending
pathways.
Clinical Terms for altered muscle tone:
• Atonia, hypotonia, flaccidity – Absent or decreased
tone.
• Hypertonia – increased muscle tone (spasticity or
rigidity).
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Lower Motor Neuron Signs
• Result from damage of Motor Neurons –
Cell Bodies or Axons
Upper Motor Neuron Signs
• Result from damage of multiple descending
motor pathways – some with excitatory effects
and others with inhibitory effects on the
spinal cord circuitry.
• Reflect loss of the normal balance of
excitatory and inhibitory inputs to the motor
neurons – in favor of increased excitability of
spinal level reflexes.
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Lower Motor Neuron Signs
Muscle
Spindle
Damage of Motor Neuron –
Cell Body or Axon
Dorsal
Root
Gang.
↓ Strength
↓ Reflexes
↓ Tone
Atrophy
γ motor
X
α motor
Extensor
Muscle
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Upper Motor Neuron Signs
Cx & Brainstem
Damage of multiple
descending motor pathways,
some with excitatory effects
X
X
and others with inhibitory
+ + _Periphery
effects on spinal cord
+
circuitry.
↓ Strength
↑ Reflexes
↑ Tone
Babinski response
(Extensor plantar response)
Muscle
Spindle
Dorsal
Root
Gang.
γ motor
α motor
Extensor
Muscle
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Lower Motor Neuron
Syndrome
Upper Motor Neuron
Syndrome
Strength
Weakness /
Paralysis / Paresis
Weakness /
Paralysis / Paresis
Reflexes
Hyporeflexia
Hyperreflexia
Muscle
Tone
Hypotonia
(Flaccidity)
Hypertonia
(Spasticity)
Atrophy
Atrophy of
Muscles
Minimal (disuse)
atrophy
Other Signs
Fibrillations &
Fasciculations
Extensor Plantar
Response (Babinski)
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Spasticity – characterized by:
1. Increased sensitivity of the stretch reflex
(hyperreflexia).
2. Increased muscle tone (hypertonia) with increased
resistance to passive movement.
• May be greater on one side of the joint than the
other (flexors of upper limb and extensors of
lower limb).
• Velocity dependent.
3. Clasp-knife or lengthening reaction (may see).
4. Clonus (variable)
5. Stereotyped patterns of movement (unable to
“fractionate” movements at individual joints).
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Conclusions:
• Upper motor neuron signs result from
damage of multiple descending motor
pathways.
• Damage of the corticospinal tract
contributes primarily to weakness of
distal / flexor muscles and loss of
isolated and skilled movements.
• Alterations in other descending motor
pathways contribute to the typical
increases in reflexes and muscle tone.
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