Somatic Motor System Motor Tracts Brainstem Motor Centers System Controls 2 Aspects of Movement Spinal Motor Centers Ventromedial System Somatic Motor.
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Somatic Motor SystemSomatic Motor System
MotorTracts
BrainstemMotor
Centers
System Controls 2Aspects of Movement
Spinal MotorCenters
VentromedialSystem
SomaticMotor
System
VoluntaryMovement
PatientCase Cortical
MotorCenters
Map of EssentialMap of EssentialConceptsConcepts DM McKeough
Motor SystemMotor 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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Control of Voluntary Movement Control of Voluntary Movement 2/32/3
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
UMNLMN
Stimulus
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UMN Termination 3/3UMN Termination 3/3 Vast majority (~90%) of Vast majority (~90%) of
UMN terminate on UMN terminate on interneuronsinterneurons that then that then connect to LMN connect to LMN (polysynaptic connection)(polysynaptic connection) Allows integrationAllows integration
Minority of UMN (~10%) Minority of UMN (~10%) make monosynaptic make monosynaptic connection with LMNconnection with LMN Pincer grip (most Pincer grip (most
precise prehension)precise prehension)
UMN
ReciprocalInhibition
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Control of Voluntary Control of Voluntary MovementMovement
Independent limb manipulationIndependent limb manipulation Controlled via the Controlled via the dorsolateral motor system motor system
Posture and balancePosture and balance Controlled via the Controlled via the ventromedial motor systemmotor system
System comparison
In general, the MC system may be seen as having 2 independent systems concerned with controlling 2 primary aspects of movement:
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Organization of the SystemOrganization of the System
Dorsolateral systemDorsolateral system: : dedicated to the control dedicated to the control of skilled (fractionated) of skilled (fractionated) movement of movement of contralateral limbs contralateral limbs (appendicular skeleton)(appendicular skeleton) Corticobulbar tractCorticobulbar tract Lateral corticospinal tract Rubrospinal tract
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Serial and Parallel Processing Serial and Parallel Processing 1/31/3
MC system uses both serial and parallel processingMC system uses both serial and parallel processing Serial processing: 2 neuron system Serial processing: 2 neuron system
Upper Motor Neuron (Upper Motor Neuron (UMN): UMN): projects from higher motor projects from higher motor control center (cortex or brainstem) to lower motor center control center (cortex or brainstem) to lower motor center (spinal cord) (spinal cord)
Lower Motor Neuron (Lower Motor Neuron (LMNLMN): projects from the ventral horn ): projects from the ventral horn to the muscle to the muscle
Alpha LMNAlpha LMN: large diameter neuron that innervate skeletal : large diameter neuron that innervate skeletal (extrafusal) muscle (extrafusal) muscle
Organized into small, medium, and large motor units Organized into small, medium, and large motor units Beta LMN: intermediate diameter neuron that innervates both Beta LMN: intermediate diameter neuron that innervates both
extrafusal and intrafusal muscle fibers (extrafusal and intrafusal muscle fibers (- co-activation)- co-activation) Gamma LMNGamma LMN: small diameter neurons that innervate : small diameter neurons that innervate
intrafusal muscle fibers (static and dynamic) intrafusal muscle fibers (static and dynamic) ά
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(+)(+)
(-)
DorsolateralMotorSystem
ProprioceptiveReflexConnections
2/32/3
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Serial and Parallel Processing Serial and Parallel Processing 3/33/3
MC system uses both serial and parallel MC system uses both serial and parallel processingprocessing Serial processing: 2 neuron systemSerial processing: 2 neuron system Parallel processing: normal movement is the Parallel processing: normal movement is the
result of the result of the simultaneoussimultaneous output of output of bothboth systems systems Ventromedial system controls involuntary Ventromedial system controls involuntary
postural and balance reactions. postural and balance reactions. Postural anticipation of balance disturbance occurs Postural anticipation of balance disturbance occurs
firstfirst Dorsolateral system controls voluntary limb Dorsolateral system controls voluntary limb
manipulation manipulation Movement of extremities represents a perturbation to Movement of extremities represents a perturbation to
balancebalance
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Cortical Motor Centers Cortical Motor Centers 1/51/5
Cortical Cortical Primary motor cortex Primary motor cortex
(Precentral gyrus, MI, Area 4)(Precentral gyrus, MI, Area 4) Premotor cortex (MII, Area 6)Premotor cortex (MII, Area 6) Frontal eye field (Area 8)Frontal eye field (Area 8) Broca’s area (Areas 44 & 45)Broca’s area (Areas 44 & 45)
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Association and Supplementary Motor AreasDesired outcome of the action (Goal)
Premotor AreaMovement strategy
Primary Motor AreaMotor plan/ execution
CerebellumTiming, coordination, motor learning
Function of the Various Motor Areas 2/5
Goal Strategy Plan Execution
How movement occurs
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Somatotopic Organization 3/5
Motor Homunculus
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Comparison of Motor and Sensory Homunculi 4/5
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Homunculus 5/5
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Spinal Motor Centers Spinal Motor Centers 1/21/2
Ventral horn is comprised Ventral horn is comprised of cell bodies of alpha of cell bodies of alpha and gamma lower motor and gamma lower motor neurons with somatotopic neurons with somatotopic organizationorganization
Dorsolateral LMN poolDorsolateral LMN pool: : controls voluntary controls voluntary movement of the movement of the extremities, particularly extremities, particularly the hands (manipulation), the hands (manipulation), receives UMN input form receives UMN input form dorsolateral systemdorsolateral system
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Spinal Motor Centers Spinal Motor Centers 2/22/2
Ventromedial LMN Ventromedial LMN pool: controls the pool: controls the trunk (posture and trunk (posture and balance), receives balance), receives UMN input from UMN input from ventromedial ventromedial system system
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Click to animateClick to animate
Rubrospinal Rubrospinal TractTract
Upper motor neuron
Pyramidal decussation
Lateral corticospinal tract
UMNLMN
Stimulus
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Central PathwaysCentral Pathways
Tectospinal
Ventromedial system: Ventromedial system: dedicated to the control dedicated to the control of posture and balanceof posture and balance Vestibulospinal tract Reticulospinal tract Tectospinal tract Ventral corticospinal tract
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Posture and Manipulation Posture and Manipulation 1/31/3
Postural setPostural set Auto-regulation: ventromedial system sets Auto-regulation: ventromedial system sets
proprioceptors (muscle spindle, GTO, joint proprioceptors (muscle spindle, GTO, joint receptors) to automatically maintain position.receptors) to automatically maintain position.
Independent limb manipulationIndependent limb manipulation Movement command: dorsolateral system over-Movement command: dorsolateral system over-
rides postural system (resets proprioceptors) to rides postural system (resets proprioceptors) to produce independent limb manipulation.produce independent limb manipulation.
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Postural SetPostural Set
Tectospinal tract
2/32/3
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LimbLimbManipulationManipulation
3/33/3
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Lesion Effects 1/3Lesion Effects 1/3
Gray matter lesionsGray matter lesions The body regions and functions served by The body regions and functions served by
affected cell bodiesaffected cell bodies
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Lesion Effects Lesion Effects 2/32/3
White matter lesionsWhite matter lesions Interruption of the information transmitted Interruption of the information transmitted
along that tractalong that tract All effects are generalized below the lesion All effects are generalized below the lesion
levellevel
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Involuntary Movement Involuntary Movement 3/33/3
S&S of Cerebellar lesions:S&S of Cerebellar lesions: Tremor on intention: proximal, Tremor on intention: proximal,
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Motor HierarchyMotor Hierarchy
MC system consists of 3 levelsMC system consists of 3 levels Highest levelHighest level: association cortex, : association cortex,
sensory, and motor areassensory, and motor areas Concern: select movement goal Concern: select movement goal
and strategyand strategy Middle levelMiddle level: BG, Cb, and : BG, Cb, and
brainstem motor centersbrainstem motor centers Concern: specifying spatial, Concern: specifying spatial,
temporal, and force parameters temporal, and force parameters of the motor planof the motor plan
Lowest levelLowest level: LMNs, motor plant, : LMNs, motor plant, FB about sensory consequences FB about sensory consequences of the movementof the movement
Concern: producing the Concern: producing the movement pattern and supplying movement pattern and supplying sensory FBsensory FB
S1
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Motor TractsMotor Tracts
Dorsolateral motor systemDorsolateral motor system Lateral corticospinal tract Rubrospinal tract
Ventromedial motor systemVentromedial motor system Vestibulospinal tract Reticulospinal tract Tectospinal tract Ventral corticospinal tract
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Motor System Patient Case Motor System Patient Case 1/111/11
An An 86-year-old African-American man suddenly develops 86-year-old African-American man suddenly develops weakness and numbness of his right arm and his speech weakness and numbness of his right arm and his speech becomes slurred. becomes slurred.
Over the next 30 minutes the weakness, numbness, and Over the next 30 minutes the weakness, numbness, and difficulty speaking become worse. difficulty speaking become worse.
His hand is weak and clumsy, and when he looks at himself in 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 mirror, the right half of his face appears to sag.
The man has hypertension, diabetes mellitus, The man has hypertension, diabetes mellitus,
hypercholesterolemia, a body mass index of 35 (BMI of 30 hypercholesterolemia, a body mass index of 35 (BMI of 30 equals obesity), and leads a sedentary lifestyle. equals obesity), and leads a sedentary lifestyle.
When seen in an emergency room 1 hour later, the right side of When seen in an emergency room 1 hour later, the right side of his face and arm are almost completely paralyzed and have his face and arm are almost completely paralyzed and have severe sensory deficit. severe sensory deficit.
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Case Follow-Up Case Follow-Up 2/112/11
The man described in this case has sudden The man described in this case has sudden onset weakness and sensory loss in his right onset weakness and sensory loss in his right arm, slurred speech, and the right side of his arm, slurred speech, and the right side of his face is drooping.face is drooping.
The most likely cause of these symptoms is The most likely cause of these symptoms is
stroke (stroke (sudden onset sudden onset weakness, sensory loss, weakness, sensory loss, and impaired speech are warning signs of and impaired speech are warning signs of stroke).stroke).
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Case Follow-Up Case Follow-Up 3/113/11
The most likely location of the The most likely location of the lesion is the left cerebral lesion is the left cerebral hemisphere.hemisphere.
This is because longitudinal This is because longitudinal systems are crossed such that systems are crossed such that the left hemisphere controls the left hemisphere controls movement and sensation of movement and sensation of the right side of the body.the right side of the body.
R L
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Paresis and Spasticity (Stroke) Paresis and Spasticity (Stroke) 4/114/11
Hemiplegia (motor + sensory) impairment Hemiplegia (motor + sensory) impairment of one side of the body (longitudinal of one side of the body (longitudinal systems)systems)
Outcome: functional deficits (activities of Outcome: functional deficits (activities of daily living, ADL) due to impairment/ loss of daily living, ADL) due to impairment/ loss of learned, willed, skilled movementlearned, willed, skilled movement
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Case Follow-Up Case Follow-Up 5/115/11
The most likely location The most likely location of the lesion is the left of the lesion is the left cerebral hemisphere.cerebral hemisphere.
This is because This is because longitudinal systems are longitudinal systems are crossed such that the left crossed such that the left hemisphere controls hemisphere controls movement and sensation movement and sensation of the right side of the of the right side of the body.body.
R L
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Case Follow-Up Case Follow-Up 6/116/11
• 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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Case Follow-UpCase Follow-Up
Weakness of the right face and arm were caused by occlusion of the middle cerebral artery supplying the precentral gyrus.
Weakness = motor signClick to animate
UMNLMN
Stroke
Lost function
Impairment
7/117/11
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Case Follow-UpCase Follow-Up
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
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UMNLMN
Stroke
Lost function
Impairment
8/118/11
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Case Follow-UpCase Follow-Up
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).
Broca’s area
UMNLMN
Stroke
Lost function
Impairment
9/119/11
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Case Follow-Up Case Follow-Up 10/1110/11
Clinical evaluation led to the diagnosis of ischemic infarction Clinical evaluation led to the diagnosis of ischemic infarction (stroke) because of cerebrovascular disease resulting from (stroke) because of cerebrovascular disease resulting from hypertension and diabetes mellitus.hypertension and diabetes mellitus. Etiology and location of the lesion were confirmed by imaging Etiology and location of the lesion were confirmed by imaging studies.studies.
CT MRI
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Case Follow-Up Case Follow-Up 11/1111/11
Because the patient was seen within 3 hours of the onset Because the patient was seen within 3 hours of the onset of the stroke, he was treated with tissue plasminogen of the stroke, he was treated with tissue plasminogen activator (TPA) in an attempt to dissolve the clot in the activator (TPA) in an attempt to dissolve the clot in the middle cerebral artery. middle cerebral artery.
The attempt was successful, and the patient’s strength The attempt was successful, and the patient’s strength and sensation gradually returned to normal by the time of and sensation gradually returned to normal by the time of discharge the next day. discharge the next day.
He was prescribed medications to control his He was prescribed medications to control his hypertension, lower serum cholesterol and blood glucose. hypertension, lower serum cholesterol and blood glucose. He was also instructed to begin a diet and regular He was also instructed to begin a diet and regular exercise to help control his diabetes and obesity.exercise to help control his diabetes and obesity.
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Dualisms in the Motor SystemDualisms in the Motor System What are the two subsystems that What are the two subsystems that
comprise the somatic motor system?comprise the somatic motor system? Dorsolateral and ventromedial motor systemsDorsolateral and ventromedial motor systems
What are the two prominent types of lower What are the two prominent types of lower motor neurons?motor neurons? Alpha and gammaAlpha and gamma
What are the two sites where the cell What are the two sites where the cell bodies of lower motor neurons are located bodies of lower motor neurons are located in the spinal cord?in the spinal cord? Dorsolateral- and ventromedial LMN pools in Dorsolateral- and ventromedial LMN pools in