1 spinal cord iii major pathways of the spinal cord - motor c.r. houser
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SPINAL CORD IIIMajor Pathways of the
Spinal Cord - Motor
C.R. Houser
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MAJOR PATHWAYSMotorCorticospinal 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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Lateral Pathways
•Corticospinal (Lateral)•Rubrospinal
Medial Pathways
•Vestibulospinal•Reticulospinal – Medullary
- Pontine•Tectospinal
Blumenfeld, Fig. 6.7.
Motor Pathways
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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
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LATERAL CORTICOSPINAL TRACT
Voluntary Motor Control
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ForebrainCortex
Areas 4, 6, 3,1,2 & 5
Internal Capsule
LATERAL CORTICOSPINAL TRACT
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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 R
#1
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LATERAL CORTICOSPINAL TRACT
Voluntary Motor Control
L R
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L R
#2
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LATERAL CORTICOSPINAL TRACT
Voluntary Motor Control
L R
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L R
#3
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LATERAL CORTICOSPINAL TRACT
Voluntary Motor Control
L R
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L R
#4
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LATERAL CORTICOSPINAL TRACT
Voluntary Motor Control
L R
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This patient had a selective lesion of one pyramid. Which pyramid was damaged? What functional consequences would you expect?
Left Right
L R
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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 toneDefinition 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 SignsMuscle Spindle
Dorsal Root Gang.
Extensor Muscle
α motor
γ motor
Damage of Motor Neuron – Cell Body or Axon
↓ Strength
↓ Reflexes
↓ Tone
Atrophy X
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Upper Motor Neuron SignsMuscle Spindle
Dorsal Root Gang.
Extensor Muscle
α motor
γ motor
Damage of multiple descending motor pathways, some with excitatory effects and others with inhibitory effects on spinal cord circuitry.
↓ Strength
↑ Reflexes
↑ Tone
Babinski response(Extensor plantar response)
_
Cx & Brainstem
+ +
+Periphery
X X
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Lower Motor Neuron Syndrome
Upper Motor Neuron Syndrome
Reflexes
Muscle Tone
Atrophy
Other Signs
Strength Weakness / Paralysis / Paresis
Weakness / Paralysis / Paresis
Hyporeflexia Hyperreflexia
Hypotonia (Flaccidity)
Hypertonia (Spasticity)
Atrophy of Muscles
Minimal (disuse) atrophy
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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