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73 Cards in this Set
- Front
- Back
Feedback control of
motor behaviors |
1. Utilize afferent information on moment to
moment basis 2. sensory signal compared with desired state (i.e., internal representation) –reference signal 3.Difference between actual and intended behavior –error signal 4. Negative/proportional feedback in closed loop chain (e.g., thermostat) 5.Gain of feedback (ratio of input to output) |
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Feedforward control of
motor behaviors |
Motor commands in advance to
“expected” perturbations Open loop control Feedback signals do not contribute to second to second variations in behavior Generation of an internal model of desired state Still dependent on sensory information, but a “representation” of this information raising a weight while standing catching a ball |
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General Concepts Regarding Control of
Volitional Tasks |
Motor actions have similar features regardless of conditions
(Donald Hebb 1950s) trajectory of reaching handwriting examples |
|
General Concepts Regarding Control of
Volitional Tasks |
Motor actions have similar features regardless of conditions
(Donald Hebb 1950s) trajectory of reaching handwriting examples Motor plan movement is planned by higher centers abstract form; not series of contractions/consequences Motor program - signal to specify the intended movement given the biomechanical constraints |
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Neural Basis of
Voluntary Movement |
Sensorimotor cortex – skilled
movements Basal Ganglia – initiation and selection of motor programs Cerebellum – coordination, timing, learning |
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Sensorimotor cortex – skilled
movements |
Frontal lobe
– Primary motor cortex (M1,Area 4) – Premotor cortex (PM, Area 6) – Supplementary motor area (SMA, Area 6) Parietal lobe – Primary sensory cortex (S1, Area 1,2,3) – Posterior partial cortex (Areas 5, 7) |
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Primary motor cortex
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participates in specific
trajectory planning delivers commands to lower levels for initiation/ modulation of movement Motor programs located here or at lower levels (CPGs, interneuron networks) |
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Primary somatosensory
cortex |
provides sensory information
required for movement planning and initiation modulation of ongoing movement |
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Primary cells
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Layer 5 – pyramidal
cells (include large Betz cells), distributed in specific cortical areas |
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Cortical maps
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(Penfield 1930-50s)
stimulated the primary somatosensory cortex - asked the patient about the sensation |
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Obtained movements with
stimulation in primary motor cortex |
The results led to a debate
about whether muscles or movements were represented in the cortex. individual muscles are represented in many locations. |
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Cortical control of movement
|
Specific cortical areas participate of specific movements/body parts -
homunculus (“little man”) The area of cortex dedicated to processing information from a particular body part reflects the degree of innervation of that body part. PM and SMA demonstrate similar topography |
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corticospinal tract (CST)
|
comprises
~ 1 million descending axons. At the junction of the medulla and spinal cord, the CST divides into ventral and lateral tracts. Ventral CST projects bilaterally to motor neurons that innervate axial muscles and to the intermediate zone. Lateral CST (shown here) projects to motor neurons of distal muscles and interneurons in intermediate zone. Some axons make monosynaptic connections onto motor neurons, particularly those that control finger movements. Other fibers synapse on interneurons within the spinal cord. |
|
activate cortical
neurons indirectly/non-invasively |
Transcranial magnetic stimulation
(TMS) – also Transcranial Electrical Stimulation (TES) Magnetic coil generates field along cortical surface Faraday’s law – electrical current generated in “wires” (axons) Activate smaller cortical cells which activate pyramidal cells (TES may bypass this, though mechanisms controversial) |
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Multiple pathways
|
Multiple pathways to spinal
cord/brainstem encode similar information Cortical tracts 40% from M1 region S1 and PM areas contribute significantly Typically to interneuron pools – except to distal motor pools |
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executing movements
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Corticospinal neurons make
direct excitatory connections with only some motor neurons Direct connections for fine control of the digits. After a bilateral resection of the corticospinal tracts, monkeys unable to grasp small objects with thumb/index finger |
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Walking after bilateral resection
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Walking after bilateral resection,
– unable to negotiate in feedforward manner (obstacles, balance beam/ladder) – Toe/ankle dorsiflexion problems, can’t walk balance beam |
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discharge of action potentials
|
The discharge of action potentials by neurons in the primary motor
cortex (CM = corticomotoneuronal cell) depends on the motor task. Precision vs Power grip involve separate cortical/subcortical circuits acting on similar IN/MN pools |
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Direction-specific encoding of cortical
cells |
Population vectors encode both direction
and magnitude |
|
Motor cortical cells also encode for force
|
Motor cortical cells alter firing
patterns according to extent of muscle activity required to complete a task Tonic and Phasic cortical cells may participate |
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Premotor area
|
involved in goal-directed movements
Activity prior to visually-guided movements |
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Supplementary motor area
|
ensures correct sequencing of movement (order of
movement) – biomechanical constraints – task performed – external conditions Activity prior to internally-guided movements |
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Posterior parietal cortex
|
encodes complex sensory information
internal sensory representation |
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Four “premotor” areas
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Lateral premotor areas
– Dorsal premotor – Ventral premotor Medial premotor areas – Supplementary motor area – Cingulate area |
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Differences in neural substrates of
movement dependent on task |
Alteration in Premotor (dorsal or ventral) and
Supplementary motor area during visually guided vs. internally guided movements Similar in humans and non-human primates |
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Supplementary Motor Areas
|
-activated during sequential versus simple movements
-active during mental rehearsal |
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Ventral and Dorsal Premotor Areas
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Different tasks utilize different pathways with external ques
- reaching-visual parietal dosal and PM areas - grasping- visual parietal ventral and PM areas |
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Generic pathway for initiation of
volitional movements |
Visual/Auditory association cortices and
Internal representation of body and space (Posterior Parietal Cortex) Dorsolateral Prefrontal Cortex (DLPFC) Premotor or Supplementary Motor Areas Primary Motor Cortex |
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three
levels of control |
spinal cord, brain stem, cerebral cortex
|
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basal ganglia & cerebellum
|
1. Two systems of brain stem
neurons (medial and lateral descending systems) receive input from the cortex & subcortical nuclei and project to the spinal cord 2. The cerebellum and basal ganglia provide feedback through the thalamus (not shown) that regulate cortical and brain stem motor areas. |
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basal ganglia
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involved in
motivation and initiation and selection of motor programs. |
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cerebellum
|
is involved with
the timing and coordination of movements (error detection) and with the learning of motor skills. |
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Equilibrium
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Vestibular apparatus
(inner ear, CN VIII) -Semicircular canals – directional rotational accel/deceleration -Utricle and saccule |
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Utricle and saccule
|
Changes in rate of
linear movement Determining head position in relation to gravity |
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kinocilium and stereocilia
|
Neural signals generated in response to
mechanical deformation of hair cells – Semicircular canals – cupula – Utricle/saccule Movement triggered by fluid movement or particle movement – Endolymph – Otolith (Ca crystals embedded) |
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vestibular nuclei in brain
stem |
Superior/medial from
semicircular and otolilths – output to Medial Longitudinal Fasciculs (MLF) Lateral (Dieter’s nucleus) projects to lateral vestibulospinal tract Descending nucleus inputs from otolisths – projects to cerebellum/RF and SC |
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Extraocular muscles
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Four are rectus muscles (straight)
Two are oblique: superior and inferior |
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Cranial nerve innervations:
|
Lateral rectus: VI (Abducens n.) – abducts eye outward
Medial, superior, inferior rectus & inf oblique: III (Oculomotor n.) – able to look up and in if all work Superior oblique: IV (Trochlear n.) – moves eye down and out |
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MLF
|
medial longitudinal
fasciculus |
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PPRF
|
paramedian pontine
reticular formation Rostral interstitial nucleus – anterior midbrain RF (MLF) |
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Vestibulo-ocular reflex
|
– keep the eyes still in space when the head
moves |
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Vestibulo-colic reflex
|
keeps the head still in space – or on a level
plane when you walk. |
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Vestibular-spinal reflex
|
adjusts posture for rapid changes in
position. |
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Lateral vestibular nucleus/spinal tract
|
•Descends the ipsilateral spinal
chord •Terminates at all levels of the spine. •Excitatory pathway activates postural muscles (proximal to spine) to correct for leftward listing |
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Medial vestibular nucleus/spinal tract
|
•Descends ipsilateral and
contralateral spinal cord but asymmetrically •Terminates in the cervical and thoracic spine. •Excitatory pathway activates postural muscles (proximal to spine) mainly in the neck. |
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Ascending projections to oculomotor nuclei
|
•Both direct contralateral and indirect ipsilateral control of extra ocular muscles
•Counters head movements to keep image stable on retina. •Damage of vestibular nerve/nuclei causes nystagmus a oscillation of horizontal eye movement. |
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Gaze stabilization
|
Vestibuloocular reflex (VOR) – stabilize eyes relative to external world
by compensating head movements Optokinetic nystagmus – elicted by moving object that produce illulsion or head movement (visual ocular response) |
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Gaze shifting
|
Vergence – aligns fovea of each eys with targets and different distances
Smooth pursuit – keep moving stimuli on fovea Saccades – ballistic movements that abruptly change point of fixation |
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Saccades
|
MLF – allows
coordination of conjugate eye movements PPRF –initiates fast horizontal saccadic movment Rostral interstitial nucleus – fast vertical saccadic eye movements |
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Double vision
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diplopia (divergent eye movement)
|
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Misalignment:
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strabismus (what is observed when shine a
light: not reflected in the same place on both eyes) – can be a cause of diplopia Cross eyed Gaze & movements not conjugate (together) Medial or lateral, fixed or not Many causes – Weakness or paralysis of extrinsic muscle of eye – Oculomotor nerve problem, other problems |
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Lazy eye
|
amblyopia
Cover/uncover test at 5 yo If don’t patch good eye by 6, brain ignores lazy eye and visual pathway degenerates: eye functionally blind |
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cerebellum
|
Receives information about goals,
commands, and feedback signals associated with the execution of movement 40X more axons project into it than exit it (Greater number of neurons than rest of CNS) Assists with spatial accuracy and coordination of movement Largely motor function, some cognitive Lateralization, topography of organization Input and output: descending, spinal, brainstem pathways |
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Vestibulocerebellum
|
Flocculonodular lobe (most primitive)
Receives vestibular, postural, ocular information; controls balance and eye movements |
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Spinocerebellum (Vermis)
|
Intermed hemisphere and Vermis –
interposed and fastigial nuclei proprioceptive/exteroceptive inputs Governs “performance of movement” |
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Cerebro- (ponto-) cerebellum
(anterior/posterior lateral areas) |
Lateral hemisphere –Dentate nuclei
Projections from pontine nuclei Information of planned movement |
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Cerebellum cortical layers
|
Molecular layer
Stellate and basket cells Axons of Granule cells (parallel fibers) Terminals of climbing fibers Dendrites of Purkinje cells Purkinje cell layer (projection neurons to nuclei) Granular layer Granule cells Inputs from mossy fibers |
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Mossy fibers
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Originate from SC/BS nuclei
Carry sensory and some cortical information Mossy to granule (parallel fibers) to Purkinje (generates simple spikes) |
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Climbing fibers
|
from inferior olivary nucleus
Receives SC/cortical information Climbing to Purkinje (generate complex spikes – may depress parallel input) |
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Cerebellar outputs
|
cortical and brainstem
|
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Role of Cerebellum
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Role in Memory
Place Cells Motor Learning? Role in Error correction |
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Transitions
|
immediate change in behavior
driven by prior experience and the ability to predict that new demands will exceed “current state” (feed-forward strategies) |
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Adaptations
|
Gradual change in behavior that results from experience
(“feedback strategies”) Driven by demands that exceed “current state” |
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Learning
|
Relatively permanent changes
Resulting from repeated exposure (adaptation may be a precursor) |
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Prism adaptation
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Prisms inserted into eyeglasses
Displace visual field Leads to initial errors in movement accuracy\ With extensive training, throwing with wedge prisms can become a skill. Adaptations results in Learning – which allow faster Transitions |
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Locomotor Adaptations
|
“Podokinetic system” - circuits
that allow directional control of locomotor trajectory through foot contact with the floor (Weber et al. 1998.) |
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Walking on a circular treadmill
|
Angular velocities (11-60º/s);
duration (7.5-60 minutes) Stepping performed over rotational axis or on perimeter instructed to step in-place or walk in a straight line on a circular rotating treadmill |
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“Podokinetic” Adaptation (PKA)
|
Subjects generate curved
walking trajectories with blindfolds Walking forward “in a straight line” Rotation while walking in place Subjects unaware of trajectories |
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Termed...
|
podokinetic afterrotation (PKAR)
Recalibration of trunk and limb position with vestibular information Transfers to overground backward walking |
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How does PKAR occur?
|
Podokinetic stimulation
Overground transfer General adaptation of locomotor trajectory control during stepping vs. specific remodeling to adaptive stimulus |
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Podokinetic stimulation
|
Clockwise rotation, foot
turning relative to trunk trunk must stabilize by turning counterclockwise |
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Overground transfer
|
No PK stimulation
Negative aftereffects of continued CCW rotation of trunk on stable foot |
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Disruption of cerebellar circuits
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Ataxia in humans
Surgical cooling of dentate and interpositus nucleui Disruption of the error correction process? |