Descending Pathways

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Good Afternoon!!
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Objectives

• Identify major cortical inputs to the motor
  pathways
• List the descending pathways
• differentiating characteristics
• Trace the lateral corticospinal tract
• Identify sites of decussation

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Descending Pathways

• Lateral Systems
• Corticospinal
• Lateral
• Rubrospinal

• Medial systems
• Corticospinal
• Anterior
• Reticulospinal
• Tectospinal
• Vestibulospinal

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Descending Pathways

• Direct Systems
• Corticospinal
• Lateral
• Anterior

• Indirect Systems
• Rubrospinal
• Reticulospinal
• Tectospinal
• Vestibulospinal
• Interstitiospinal (??)

Motor Cortex Input
? Input
?
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• Lateral systems
• Fine voluntary movement
• Distal muscles
• Medial systems
• Postural and reflex movement
• Proximal and axial muscles

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Motor Cortex

• M1 Primary
• precentral gyrus
• SMA supplementary
• anteromedial
• Premotor Area
• Anterolateral
• Cingulate Motor
• ??

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SMA
Premotor
Primary Motor
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Lateral Corticospinal Tract

• Most direct pathway
• but 50 of axons cerebellum via pons
• Voluntary motor control
• fine movement/distal muscles
• monosynaptic
• gross movement
• synapse on spinal interneurons
• double decussating

gt50 of CS axons
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Lateral Corticospinal Tract

• M1 (and premotor cortex)
• Centrum Semiovale
• Corona Radiata
• Internal Capsule -- posterior limb
• Cerebral Peduncle
• Pontine Tegmentum
• Medullary Pyramid

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Sagittal Imaging
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Central (Rolandic) Sulcus

• Its more posterior than youd expect
• Pearlfollow the superior frontal sulcus back to
  the precentral sulcus
• Remember All anatomy is variable

Roland
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Primary Motor Sensory Cortex

• Precentral Sulcus
• Primary Motor
• Postcentral Sulcus
• Primary Sensory

Motor
Sensory
Roland
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Functional Imaging (fMRI)
Roland
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Transverse (Axial) Imaging
Brain Imaging
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Coronal Imaging
TENT
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Wallerian Degeneration

• Motor Cortex Injury
• Degeneration of first order motor neurons
• Outlines the corticospinal tract

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Precentral Gyrus
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Corona Radiata
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Pontine Tegmentum
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Medullary Pyramid
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Essential Points

• Identify major cortical inputs to the motor
  pathways
• M1primary motor cortex
• Premotor Cortex
• SMAsupplementary motor area
• Cingulate Motor Area

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Essential Points

• List the descending pathways
• Lateral Corticospinal
• Anterior Corticospinal
• Rubrospinal
• Tectospinal
• Vestibulospinal
• Reticulospinal

Direct
Indirect
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Essential Points

• Differences
• Lateral Corticospinal
• Rubrospinal
• Anterior Corticospinal
• Tectospinal
• Vestibulospinal
• Reticulospinal

Distal muscles Fine movement
Proximal and axial muscles Gross and postural
movement
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Essential Points

• Trace the lateral corticospinal tract
• M1 (and premotor cortex)
• Centrum Semiovale
• Corona Radiata
• Internal Capsule -- posterior limb
• Cerebral Peduncle
• Pontine Tegmentum
• Medullary Pyramid

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Essential Points
Double Decussating

• Identify sites of decussation
• Lateral Corticospinal
• Anterior Corticalspinal
• Rubrospinal
• Tectospinal
• Vestibulospinal
• Reticulospinal

Medullary Pyramid
Not Applicable
Midbrain Tegmentum
Midbrain
Not Applicable
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