Transcript The Motor System

System Controls 2
Aspects of Movement
Somatic
Motor
System
Voluntary
Movement
Postural Set
and
Limb Manipulation
Spinal Motor
Centers
Dorsolateral
System
Somatic Motor System
Ventromedial
System
Lesion Effects
Patient
Case
Map of Essential
Concepts
Motor
Hierarchy
Cortical
Motor
Centers
Motor
Tracts
Brainstem
Motor
Centers
DM McKeough
© 2009
Motor System
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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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Somatic Motor System
Output: 3 classes of movement
 Voluntary movement: purposeful,
goal directed, complex, learned
movements (ADL)
Motor Control System
 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
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Voluntary Movement
Originates in the Brain
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Assoc Ctx
M1 (UMN)
S1
Thalamus
Spinal Cord
(LMN)
Proprioceptors
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Control of Voluntary Movement
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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
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Motor System
Stimulus
UMN
LMN
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UMN Termination
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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)
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UMN
Reciprocal
Inhibition
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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
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Controlled via the dorsolateral motor system
 Posture
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and balance
Controlled via the ventromedial motor system
 System
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Organization of the System
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Dorsolateral system:
dedicated to the control of
skilled (fractionated)
movement of contralateral
limbs (appendicular
skeleton)
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Corticobulbar tract
Lateral corticospinal tract
Rubrospinal tract
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Serial and Parallel Processing
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MC system uses both serial and parallel processing
 Serial processing: 2 neuron system
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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
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(extrafusal) muscle
 Organized into small, medium, and large
motor units
Beta LMN: intermediate diameter neuron that innervates
ά
both extrafusal and intrafusal muscle fibers (- coactivation)
Gamma LMN: small diameter neurons that innervate
intrafusal muscle fibers (static and dynamic)
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Dorsolateral
Motor
System
Proprioceptive
Reflex
Connections
(-)
(+)
(+)
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Serial and Parallel Processing
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MC system uses both serial and parallel
processing
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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.
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Postural anticipation of balance disturbance occurs first
Dorsolateral system controls voluntary limb
manipulation
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Movement of extremities represents a perturbation to
balance
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Cortical Motor Centers
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Cortical
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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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Function of the Various Motor Areas
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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
How movement occurs
Goal
Strategy
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Plan
Execution
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Somatotopic Organization
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Motor Homunculus
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Comparison of Motor and Sensory Homunculi
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Homunculus
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Brainstem Motor Centers
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Brainstem
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Tectum
Vestibular nuclei
Reticular nuclei
Basal ganglia
Cerebellum
Tectum
Tectum
Tectospinal
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Spinal Motor Centers
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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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Spinal Motor Centers
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Ventromedial LMN
pool: controls the
trunk (posture and
balance), receives
UMN input from
ventromedial system
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Lateral Corticospinal
Tract
Upper motor neuron
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Lateral corticospinal tract
Pyramidal decussation
Stimulus
UMN
LMN
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Rubrospinal Tract
Upper motor neuron
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Lateral corticospinal tract
Pyramidal decussation
Stimulus
UMN
LMN
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Central Pathways
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Ventromedial system:
dedicated to the control
of posture and balance
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Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Ventral corticospinal tract
Tectospinal
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Lateral Vestibulospinal
Tract
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Motor System
Stimulus
UMNMap
Concept
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Reticulospinal
Tract
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Stimulus
Concept
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Tectospinal Tract
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Stimulus
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UMN
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Ventral Corticospinal
Tract
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Stimulus
UMN
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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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Posture and Manipulation
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Postural set
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Auto-regulation: ventromedial system sets
proprioceptors (muscle spindle, GTO, joint
receptors) to automatically maintain position.
Independent limb manipulation
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Movement command: dorsolateral system overrides postural system (resets proprioceptors) to
produce independent limb manipulation.
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Postural Set
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Tectospinal tract
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Limb
Manipulation
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Lesion Effects
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Gray matter lesions
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The body regions and functions served by affected
cell bodies
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Lesion Effects
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White matter lesions
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Interruption of the information transmitted along that
tract
All effects are generalized below the lesion level
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Involuntary Movement
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S&S of Cerebellar lesions:
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Tremor on intention: proximal, slow
Ataxia: trunk or limb
Dysmetria
Dysdiadochokinesia
Hypotonia: proximal > distal
Dysarthria (scanning speech pattern)
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Motor Hierarchy
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MC system consists of 3 levels
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Highest level: association cortex,
sensory, and motor areas
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Concern: select movement goal
and strategy
Middle level: BG, Cb, and
brainstem motor centers
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S1
Concern: specifying spatial,
temporal, and force parameters of
the motor plan
Lowest level: LMNs, motor plant,
FB about sensory consequences of
the movement
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Concern: producing the movement
pattern and supplying sensory FB
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Motor Tracts
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Dorsolateral motor system
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Lateral corticospinal tract
Rubrospinal tract
Ventromedial motor system
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Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Ventral corticospinal tract
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Motor System Patient Case
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An 86-year-old African-American man suddenly develops
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Over the next 30 minutes the weakness, numbness, and
difficulty speaking become worse.
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His hand is weak and clumsy, and when he looks at himself in
the mirror, the right half of his face appears to sag.
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weakness and numbness of his right arm and his speech
becomes slurred.
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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Case Follow-Up
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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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Case Follow-Up
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The most likely location of the
lesion is the left cerebral
hemisphere.
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R
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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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Paresis and Spasticity (Stroke)
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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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Case Follow-Up
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The most likely location of
the lesion is the left cerebral
hemisphere.
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L
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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Case Follow-Up
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• 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-Up
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Weakness of the right face and arm were
caused by occlusion of the middle cerebral
artery supplying the precentral gyrus.
Weakness = motor sign
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Stroke
UMN
LMN
Lost
function
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Motor System
Impairment
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Case Follow-Up
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Impaired sensation of the right face and arm
were caused by occlusion of the middle
cerebral artery supplying the postcentral
gyrus.
Stroke
UMN
LMN
Impaired sensation = sensory sign
Lost
function
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Impairment
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Case Follow-Up
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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).
Stroke
UMN
LMN
Lost
function
Impairment
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Case Follow-Up
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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.
MRI
CT
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Case Follow-Up
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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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The End
© DM McKeough 2009
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Dualisms in the Motor System
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What are the two subsystems that comprise the
somatic motor system?
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What are the two prominent types of lower
motor neurons?
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Dorsolateral and ventromedial motor systems
Alpha and gamma
What are the two sites where the cell bodies of
lower motor neurons are located in the spinal
cord?
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Dorsolateral- and ventromedial LMN pools in the
ventral horn