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Laurie L. Wellman Ph.D. Theodore Tzavaras MD2015
Eastern Virginia Medical School
Dr. Craig Goodmurphy Anatomy Guy
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1. Name the two major descending motor systems Compare and contrast these systems
2. Identify the two lateral motor system tracts
3. Identify the four medial motor system tracts
4. Outline the major motor feedback loops.
5. Discuss abnormal posturing: decorticate and decerebrate
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Descending Motor Systems Lateral & Medial systems
Named for their location The lateral system (2 tracts) decussates The medial system (4 tracts) travels bilaterally
■ ■
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Descending Motor Systems Lateral Systems
Lateral corticospinal tract Origin: primary motor cortex Decussation: cervicomedullary
junction (pyramidal decussation) Extent: entire cord Function: movement of
contralateral limbs
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Descending Motor Systems Lateral Systems
Rubrospinal tract Origin: red nucleus Decussation: midbrain Extent: cervical cord Function: movement of
contralateral limbs (human function uncertain)
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Descending Motor Systems Medial Systems
Anterior corticospinal tract Origin: primary motor cortex Decussation: none Extent: cervical & upper thoracic
cord Function: bilateral axial & girdle
muscles
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Descending Motor Systems Medial Systems
Vestibulospinal tracts (med. & lat.) Origin: Mmed. & inf. vestibular n.
Llat. vestibular nuclei Decussation: none Extent: Mcervical and thoracic Lentire cord Function: Mhead & neck Lbalance
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Descending Motor Systems Medial Systems
Reticulospinal tract Origin: pontine & medullary
reticular formations Decussation: none Extent: entire cord Function: gait & posture related
movements
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Descending Motor Systems Medial Systems
Tectospinal Origin: superior colliculus Decussation: midbrain Extent: cervical cord Function: head & eye movement
coordination
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Descending Motor Systems Lateral & Medial tracts
Lateral motor system [unilateral] Lateral corticospinal tract Rubrospinal tract Medial Motor System [bilateral] Anterior Corticospinal Vestibulospinal tract Reticulospinal tract Tectospinal Tract
1. ■ ■ 2. ■ ■ ■ ■
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Major Feedback Loops Don’t project directly to LMNs
Cortico-basal ganglia loop Cortico-cerebellar loop
■ ■
Basal ganglia
Cere
bellu
m
Cortex Br
ains
tem
Spinal Cord
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Abnormal Posturing
Cortex
RN
MRF
PRF
VN
Flexors Extensors
Brainstem
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Abnormal Posturing Decorticate (flexor)
Damage rostral to the red nucleus ■
Cortex
RN
MRF
PRF
VN
Flexors Extensors image source: wikimedia commons
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Abnormal Posturing Decerebrate (extensor)
Damage caudal to the red nucleus ■
Cortex
RN
MRF
PRF
VN
Flexors Extensors image source: wikimedia commons
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Don’t Do
Don’t Do
Get overwhelmed by the details. Break-down the motor loops into the
two major feedback systems. Approach the tracts as one unit. Locate each tract within the spinal
cord. Then, add it’s extent, origin, decussation, and function while keeping an eye out for patterns.
Recall the “red nucleus flexes the elbows,” & in flexor posturing, “the red nucleus is de-corticated.”