Cortical Control of Motor Activity – The Corticospinal Tract Flashcards

1
Q

Cortical structures:

A
  • primary motor cortex
  • prefrontal cortex
  • somatosensory and parietal association cortex
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2
Q

Subcortical structures:

A
  • basal ganglia
  • cerebellum
  • thalamus
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3
Q

Types of Movement:

A
  1. Reflexes
    • Stereotyped responses to stimuli
  2. Voluntary
    • Goal-directed
    • Internally generated
    • Improve with practice
  3. Automatic Postural Adjustments
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4
Q

Motor Pathways: Two Main Systems

A
  1. Lateral:
    • Lateral Corticospinal Tract
    • Rubrospinal Tract
  2. Medial:
    • Anterior Corticospinal Tract
    • Lateral Vestibulospinal Tract
    • Medial Vestibulospinal Tract
    • Corticotectal and Tectospinal Tract
    • Reticulospinal Tract
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5
Q

What is the most important system for voluntary movement?

A

Coritcospinal tract

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6
Q

Coritcospinal Tract:

A
  • One neuron
    • Upper Motor Neuron
  • Projects to:
    • Lower motor neurons (LMN) in ventral horn of ALL levels of spinal cord
  • Function
    • Voluntary movement of distal extremities
    • Skilled movements
    • Excites flexor m.’s, inhibits extensor m.’s
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7
Q

Corticospinal Tract:

Route

A
  • CST axons arise from:
    1. Primary motor cortex (area 4) (33% of fibers)
    2. Betz cells (large pyramidal neurons in lamina V of the precentral gyrus) (3% of fibers).
    3. Premotor cortex (area 6) and Supplementary motor area (area 6) (33% of fibers)
    4. Parietal lobe (areas 3, 1 and 2) (33% of fibers)
  • CST axons pass through:
    1. corona radiata
    2. posterior limb of internal capsule
    3. the middle of the cerebral peduncle (crus cerebri)
    4. medullary pyramids
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8
Q

Upper Motor Neuron (UMN) Route:

A
  1. Cerebral cortex
  2. Corona radiata
  3. Internal capsule
    • Posterior limb
  4. Crus cerebri
  5. Ventral pons
  6. Medullary pyramid
    • Pyramidal decussation
  7. Lateral funiculus
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9
Q

Primary Motor Cortex (M-I):

A
  • Somatotopically Organized
  • Tasks that require great precision:
    • Structures have disproportionately larger representations
    • motor homunculus
  • Motor map exhibits overlap & plasticity
    • can change with increased use or disuse​
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10
Q

Lateral Corticospinal Tract:

A
  • 90% of fibers decussate in pyramidal decussation
  • descend in lateral funiculus to all sp cd levels
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11
Q

Anterior / Ventral corticospinal tract:

A
  • 10% of fibers do NOT decussate in pyramids
  • descend in the anterior funiculus
  • decussate in ventral white commissure to thoracic sp cd.
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12
Q
  1. Lesions ABOVE the pyramidal decussation result in _____________ weakness
  2. Lesions BELOW the pyramidal decussation result in ___________ weakness
A
  1. Abovecontralateral
  2. **Below ⇒ **ipislateral
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13
Q

What signs would you expect to find with an UMN lesion?

A
  • Paresis (weakness) or paralysis
  • Spasticity
  • Hyperreflexia
  • Loss of abdominal reflexes
  • Babinski sign:
    • stroking the plantar surface of the foot along the lateral border ⇒ dorsiflexion of the great toe (normal response is plantar flexion)
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14
Q

What signs would you expect to find with an LMN lesion?

A
  • Muscle atrophy
  • Fasciculations
  • Hypotonia
  • Hyporeflexia
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15
Q

Lesion in the Cortex:

A

Contralateral paresis of a particular body part corresponding to area of cortical damage.

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16
Q

Lesion in the Posterior Limb of Internal Capsule:

A

Contralateral hemiplegia

17
Q

Where would a lesion that causes Weber’s Syndrome be located? What is a possible cause?

A
  • Midbrain
    • Cerebral peduncle (Crus cerebri)
  • Possible Cause: Occlusion of PCA
18
Q

Lesion in the Cerebral Peduncle (Crus cerebri):

A
  • Weber Syndrome
    • Possible Cause: Occlusion of PCA
  • Corticospinal Tract lesion
    • Contralateral paralysis of lower face, tongue, arm and leg
  • CN III injury
    • Ipsilateral oculomotor palsy
    • eye deviates laterally, ptosis, pupil is dilated and fixed
19
Q

Where is the lesion that causes medial medullary syndrome located?

A
  • Rostral Medulla
    • Medullary Pyramid
  • Possible Cause: occlusion of vertebral a. or anterior spinal a.
20
Q

Lesion in the Medullary Pyramid:

A
  1. Medial Medullary Syndrome
    • Possible Cause: occlusion of vertebral a. or anterior spinal a.
  2. Corticospinal Tract lesion
    • Contralateral hemiparesis of arm and leg, face is spared
  3. CN XII injury
    • Ipsilateral paralysis and atrophy of tongue
  4. Medial Lemniscus injury
    • Contralateral loss of touch, vibration and joint position sensation from half of the body
21
Q

Lesion in the Spinal Cord:

A
  • Corticospinal Tract lesion
    • Ipsilateral spastic paralysis
    • Ipsilateral Babinski sign