1. Map of Essential Concepts System Controls 2 Postural Set Somatic and
Aspects of Movement
Somatic
Motor
System
Postural Set
and
Limb Manipulation
Voluntary
Movement
Spinal Motor
Centers
Dorsolateral
System
Ventromedial
System
Somatic Motor System
Lesion Effects
Motor
Hierarchy
Patient
Case
Cortical
Motor
Centers
Motor
Tracts
Brainstem
Motor
Centers
Map of Essential
Concepts
DM McKeough
© 2009

2. Motor System Somatic Motor System Voluntary movement
Motor system controls 2 aspects of movement
Dorsolateral motor system
Ventromedial motor system
Motor tracts
Motor centers of the cerebral cortex
Motor centers of the brainstem
Motor centers of the spinal cord
Motor hierarchy
Posture and limb manipulation
Lesion effects
Patient case
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3. Somatic Motor System Output: 3 classes of movement
Voluntary movement: purposeful, goal directed, complex, learned movements (ADL)
Rhythmic, repetitive motions (walking): initiation and termination of a sequence of relatively stereotyped and almost automatic voluntary movements
Reflex responses: normal, rapid, stereotyped, involuntary movement initiated by a stimulus
Motor Control System
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4. Voluntary Movement Originates in the Brain 1/3
Assoc Ctx
M1 (UMN) S1
Thalamus
Spinal Cord
(LMN)
Proprioceptors
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5. Control of Voluntary Movement 2/3
The motor control system consists of
Upper motor neurons (UMN)
Originate in motor centers in the brain
Cross the midline
Terminate on lower motor neurons in the brainstem and spinal cord
Lower motor neurons (LMN)
Originate in motor centers in the brainstem and spinal cord
Exit the CNS via cranial and spinal nerves
Initiate movement by commanding skeletal muscles to contract
UMN
LMN
Stimulus
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6. UMN Termination /3
Vast majority (~90%) of UMN terminate on interneurons that then connect to LMN (polysynaptic connection)
Allows integration
Minority of UMN (~10%) make monosynaptic connection with LMN
Pincer grip (most precise prehension)
UMN
Reciprocal
Inhibition
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7. Control of Voluntary Movement
In general, the MC system may be seen as having 2 independent systems concerned with controlling 2 primary aspects of movement:
Independent limb manipulation
Controlled via the dorsolateral motor system
Posture and balance
Controlled via the ventromedial motor system
System comparison
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8. Organization of the System
Dorsolateral system: dedicated to the control of skilled (fractionated) movement of contralateral limbs (appendicular skeleton)
Corticobulbar tract
Lateral corticospinal tract
Rubrospinal tract
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9. Serial and Parallel Processing 1/3
MC system uses both serial and parallel processing
Serial processing: 2 neuron system
Upper Motor Neuron (UMN): projects from higher motor control center (cortex or brainstem) to lower motor center (spinal cord)
Lower Motor Neuron (LMN): projects from the ventral horn to the muscle
Alpha LMN: large diameter neuron that innervate skeletal (extrafusal) muscle
Organized into small, medium, and large motor units
Beta LMN: intermediate diameter neuron that innervates both extrafusal and intrafusal muscle fibers (- co-activation)
Gamma LMN: small diameter neurons that innervate intrafusal muscle fibers (static and dynamic) ά
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10. 2/3 Dorsolateral Motor System Proprioceptive Reflex Connections
(+)
(-)
2/3
Dorsolateral
Motor
System
Proprioceptive
Reflex
Connections
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11. Serial and Parallel Processing 3/3
MC system uses both serial and parallel processing
Serial processing: 2 neuron system
Parallel processing: normal movement is the result of the simultaneous output of both systems
Ventromedial system controls involuntary postural and balance reactions.
Postural anticipation of balance disturbance occurs first
Dorsolateral system controls voluntary limb manipulation
Movement of extremities represents a perturbation to balance
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12. Cortical Motor Centers 1/5
Primary motor cortex (Precentral gyrus, MI, Area 4)
Premotor cortex (MII, Area 6)
Frontal eye field (Area 8)
Broca’s area (Areas 44 & 45)
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13. Function of the Various Motor Areas 2/5
Association and Supplementary Motor Areas
Desired outcome of the action (Goal)
Premotor Area
Movement strategy
Primary Motor Area
Motor plan/ execution
Cerebellum
Timing, coordination, motor learning
Goal
Strategy
Plan
Execution
How movement occurs
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14. Somatotopic Organization 3/5
Motor Homunculus
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15. Comparison of Motor and Sensory Homunculi 4/5
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16. Homunculus /5
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17. Brainstem Motor Centers
Tectum
Vestibular nuclei
Reticular nuclei
Basal ganglia
Cerebellum
Tectum
Tectum
Tectospinal
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18. Spinal Motor Centers /2
Ventral horn is comprised of cell bodies of alpha and gamma lower motor neurons with somatotopic organization
Dorsolateral LMN pool: controls voluntary movement of the extremities, particularly the hands (manipulation), receives UMN input form dorsolateral system
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19. Spinal Motor Centers /2
Ventromedial LMN pool: controls the trunk (posture and balance), receives UMN input from ventromedial system
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20. Lateral Corticospinal Tract
Upper motor neuron
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Lateral corticospinal tract
Pyramidal decussation
UMN
LMN
Stimulus
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21. Rubrospinal Tract Click to animate Last Viewed Motor System
Upper motor neuron
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Lateral corticospinal tract
Pyramidal decussation
UMN
LMN
Stimulus
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22. Central Pathways
Tectospinal
Ventromedial system: dedicated to the control of posture and balance
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Ventral corticospinal tract
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23. Lateral Vestibulospinal Tract
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UMN
Stimulus
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24. Reticulospinal Tract Click to animate Last Viewed Motor System
UMN
Stimulus
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25. Tectospinal Tract Click to animate Last Viewed Motor System
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UMN
Stimulus
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26. Ventral Corticospinal Tract
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UMN
Stimulus
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27. Comparison of Dorsolateral and Ventromedial Motor Systems
Dorsolateral System
Ventromedial System
Function
Skilled (fractionated) movement of contralateral limbs
Posture Balance
Tracts
Crossed
Lateral corticospinal
Rubrospinal
Corticobulbar
Crossed and uncrossed Vestibulospinal
Reticulospinal
Tectospinal
Ventral corticospinal
Spinal projection
Lateral column
Ventral column
Spinal termination
Dorsolateral lower motor neuron pool
Ventromedial lower motor neuron pool
Body segments
Distal limb segments
Trunk Proximal limb segments
Muscles
(+) flexors () extensors
(+) extensors () flexors
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28. Posture and Manipulation 1/3
Postural set
Auto-regulation: ventromedial system sets proprioceptors (muscle spindle, GTO, joint receptors) to automatically maintain position.
Independent limb manipulation
Movement command: dorsolateral system over-rides postural system (resets proprioceptors) to produce independent limb manipulation.
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29. Postural Set 2/3 Last Viewed Motor System Concept Map Exit
Tectospinal tract
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30. Limb
Manipulation
3/3
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31. Lesion Effects 1/3 Gray matter lesions
The body regions and functions served by affected cell bodies
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32. Lesion Effects 2/3 White matter lesions
Interruption of the information transmitted along that tract
All effects are generalized below the lesion level
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33. Involuntary Movement 3/3
S&S of Cerebellar lesions:
Tremor on intention: proximal, slow
Ataxia: trunk or limb
Dysmetria
Dysdiadochokinesia
Hypotonia: proximal > distal
Dysarthria (scanning speech pattern)
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34. Motor Hierarchy MC system consists of 3 levels
Highest level: association cortex, sensory, and motor areas
Concern: select movement goal and strategy
Middle level: BG, Cb, and brainstem motor centers
Concern: specifying spatial, temporal, and force parameters of the motor plan
Lowest level: LMNs, motor plant, FB about sensory consequences of the movement
Concern: producing the movement pattern and supplying sensory FB S1
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35. Motor Tracts Dorsolateral motor system Ventromedial motor system
Lateral corticospinal tract
Rubrospinal tract
Ventromedial motor system
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Ventral corticospinal tract
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36. Motor System Patient Case 1/11
An 86-year-old African-American man suddenly develops weakness and numbness of his right arm and his speech becomes slurred.
Over the next 30 minutes the weakness, numbness, and difficulty speaking become worse.
His hand is weak and clumsy, and when he looks at himself in the mirror, the right half of his face appears to sag.
The man has hypertension, diabetes mellitus, hypercholesterolemia, a body mass index of 35 (BMI of 30 equals obesity), and leads a sedentary lifestyle.
When seen in an emergency room 1 hour later, the right side of his face and arm are almost completely paralyzed and have severe sensory deficit.
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37. Case Follow-Up /11
The man described in this case has sudden onset weakness and sensory loss in his right arm, slurred speech, and the right side of his face is drooping.
The most likely cause of these symptoms is stroke (sudden onset weakness, sensory loss, and impaired speech are warning signs of stroke).
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38. Case Follow-Up /11 R L
The most likely location of the lesion is the left cerebral hemisphere.
This is because longitudinal systems are crossed such that the left hemisphere controls movement and sensation of the right side of the body.
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39. Paresis and Spasticity (Stroke) 4/11
Hemiplegia (motor + sensory) impairment of one side of the body (longitudinal systems)
Domains affected: motor, sensory, speech, cognitive, affect
Outcome: functional deficits (activities of daily living, ADL) due to impairment/ loss of learned, willed, skilled movement
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40. Case Follow-Up /11 R L
The most likely location of the lesion is the left cerebral hemisphere.
This is because longitudinal systems are crossed such that the left hemisphere controls movement and sensation of the right side of the body.
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41. Case Follow-Up /11
The areas that control movement and sensation of the face and arm are located beside each other on adjacent banks of the central sulcus.
Also these areas are perfused by the same artery (middle cerebral).
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42. Case Follow-Up
7/11
Weakness of the right face and arm were caused by occlusion of the middle cerebral artery supplying the precentral gyrus.
Weakness = motor sign
UMN
LMN
Stroke
Lost
function
Impairment
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43. Case Follow-Up
8/11
Impaired sensation of the right face and arm were caused by occlusion of the middle cerebral artery supplying the postcentral gyrus.
Impaired sensation = sensory sign
UMN
LMN
Stroke
Lost
function
Impairment
Click to animate
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44. Case Follow-Up
9/11
Broca’s
area
Because his speech was fluent and coherent, his slurred speech was due to weakness of facial muscles (Dysarthria) rather than lesion of the speech production center (Broca’s area, productive aphasia).
UMN
LMN
Stroke
Lost
function
Impairment
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45. Case Follow-Up /11
Clinical evaluation led to the diagnosis of ischemic infarction (stroke) because of cerebrovascular disease resulting from hypertension and diabetes mellitus.
Etiology and location of the lesion were confirmed by imaging studies. CT
MRI
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46. Case Follow-Up /11
Because the patient was seen within 3 hours of the onset of the stroke, he was treated with tissue plasminogen activator (TPA) in an attempt to dissolve the clot in the middle cerebral artery.
The attempt was successful, and the patient’s strength and sensation gradually returned to normal by the time of discharge the next day.
He was prescribed medications to control his hypertension, lower serum cholesterol and blood glucose. He was also instructed to begin a diet and regular exercise to help control his diabetes and obesity.
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47. The End
© DM McKeough 2009
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48. Dualisms in the Motor System
What are the two subsystems that comprise the somatic motor system?
Dorsolateral and ventromedial motor systems
What are the two prominent types of lower motor neurons?
Alpha and gamma
What are the two sites where the cell bodies of lower motor neurons are located in the spinal cord?
Dorsolateral- and ventromedial LMN pools in the ventral horn