~nn19 movement

7/31/2019 ~NN19 Movement

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Control of

Movement

Lecture 19


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Motor Systems

Functions

movement

posture & balance

communication

Guided by sensory systems

internal representation of world & self detect changes in environment

external & internal ~


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3 Classes of Movement

Voluntary

complex actions

reading, writing, playing piano

purposeful, goal-oriented

learned

improve with practice ~


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3 Classes of Movement

Reflexes involuntary, rapid, stereotyped

eye-blink, coughing, knee jerk

graded control by eliciting stimulus

Rhythmic motor patterns

combines voluntary & reflexive acts

chewing, walking, running

initiation & termination voluntary

once initiated, repetitive & reflexive ~


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Movement & Muscles

Movement occurs at joints

Contraction & relaxation of ofopposing muscles

agonists

prime movers

antagonists

counterbalance agonists

decelerate movement ~


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Movement & Muscles

Movement control more than contraction& relaxation

Accurately time control of many

muscles

Make postural adjustment duringmovement

Adjust for mechanical properties ofjoints & muscles

inertia, changing positions ~


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Sensorimotor Integration

Perceptual development

Active interaction required

environmental feedback important

Held & Hein (1950s)

kittens passively moved

depth perception deficits& related responses, blinking,looming ~


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Sensorimotor Integration

Sensory inputs guide movement

visual, auditory, tactile

location of objects in space

Proprioceptive & vestibular

position of our body

Critical for planning & refiningmovements ~


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Error Correction: Feedback

During or after movement

Compare actual position withintended position

if different ----> make correction

muscle contractions

Limited to slow movements ~


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Error Correction: Feed-forward

Sensory events control movements inadvance

ballistic movements

Predictioninternal model of events

e.g. catching ball

representation of ball trajectory properties of musculoskeletal system

Reevaluation after response completed ~


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Sensorimotor Impairments

Impaired proprioception ---> motor deficits

Large-fiber sensory neuropathy

A & A afferents degenerate

proprioceptive & tactile feedback

Cant hold arm steady w/o visual input

starts to drift after few secondspsuedo-athetosis ~


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Sensorimotor Impairments

Feed-forward control

eyes open: ballistic movements OK

eyes closed:

ballistic movements highly inaccurate

hand drifts at end of movement

Eyes open only prior to movement errors greatly reduced

lack of info about starting position ~


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Organization of Motor Control

Hierarchical & Parallel

Parallel

pathways active simultaneously

e.g. moving arm

1. muscles producing movement

2. postural adjustments duringmovement

Recovery of function after lesion

overlapping functions ~


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Hierarchical Control of Movement

3 levels of controlSpinal cord (SC)

Brainstem

Cortex

Division of responsibility

higher levels: general commands

spinal cord: complex & specific

Each receives sensory input

relevant to levels function ~


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Hierarchical Control: Spinal Cord

Automatic & stereotyped responses

reflexes

rhythmic motor patterns

Can function without brain

Spinal interneurons

same circuits as voluntary movement Pathways converge on motor neurons

final common path ~


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Hierarchical Control: Spinal Cord

Motor neurons in ventral horn

Topographical organization of motor nuclei

a.k.a. motor neuron pools

longitudinal columns across 1-4 spinalsegments

according to 2 rules ~


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Topographical organization of motor nuclei

Proximal-distal rule

medial: proximal muscles

lateral: distal muscles

Parallel control systems

proximal: postural

distal : manipulative ~

P D

Flexor-Extensor ruleventral: extensors

dorsal: flexors

F

E


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Modulates neurons in spinal cordinterneuerons & motor neurons

2 main parallel pathways

Medial

to ventromedial spinal cord

postural / proximal muscles

Lateral

to dorsolateral spinal cord

manipulative / distal muscles ~

Hierarchical Control: Brain Stem


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2 tracts

Corticobulbar --->cranial nerves

facial muscles

Corticospinal ---> spinal nerves

Origin of axons

1/3 from primary motor cortex (M1)1/3 from premotor areas

1/3 from somatosensory cortex ~

Hierarchical Control: Cortex


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Corticospinal Tract

Direct control & Indirect controlParallel pathways

Direct ---> spinal neurons

Indirect control via

cortico-reticulospinal tact

cortico-rubrospinal tract ~


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Corticospinal Tract

More parallel pathways

Lateral corticospinal tract

contralateral projections

decussate at medullary pyramid

distal muscles

Ventral corticospinal tract ipsilateral projection

proximal muscles ~


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Effects of Lesions

Motor cortex & projections

locus of damage determines deficit

Cerebral Vascular Accidents (CVA)

most common cause ~


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2 classes of abnormal function

Negative signs

Loss of function

e.g., weakness, loss of strength

Positive signs

stereotyped, abnormal responses

release phenomena

loss of normal inhibitory influences

e.g., lesion of basal ganglia --->

involuntary movements ~


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Positive Signs: Babinski Sign

Lesion of corticospinal tract

Plantar reflex

Stroke firmly stroke sole of foot

heel ---> toe

Normal: flexion

toe curl down

Lesion: Extension

toes curl up and fan ~


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Muscle Weakness

Lesions produce different syndromes

Lower motor neuron syndrome

spinal motor neurons

lesion: soma or axon

symptoms

weakness

fasciculations

atrophy ~


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Muscle Weakness

Upper motor neuron syndromedescending motor pathways

imbalance of excitatory/inhibitory

interneurons

symptoms

spasticity occurs

tonicity & deep tendon reflexes

atrophy is rare

no fasciculations ~


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Parallel Control & Recovery

Fractionation of movement

independent control of single muscles

via direct input from corticospinal tract

Lesion in medullary pyramids

can no longer grasp objects

locomotion, posture unaffected Parallel pathways assume control ~


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Parallel Control & Recovery

Monkeys: If premotor outflow sparedindirect control via brainstem

strength returns

but movement slow

M1 ---> lateral brainstem intact

cortico-rubrospinal & cortico-reticulospinal tracts assume control

humans: fewer fibers ---> less recovery ~

~nn19 movement

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