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PTP 512 Neuroscience in Physical Therapy Motor Control: Action System. Min H. Huang, PT, PhD, NCS Reading Assignments S & W: 478-480, 493-494, 69-74, 75-76, 76-77, 78-81 L-E: 187-189, 201-204, 221-222. Objectives. Describe and demonstrate spinal modulated reflexes

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ptp 512 neuroscience in physical therapy motor control action system

PTP 512Neuroscience in Physical TherapyMotor Control: Action System

Min H. Huang, PT, PhD, NCS

Reading Assignments

S & W: 478-480, 493-494, 69-74, 75-76, 76-77, 78-81

L-E: 187-189, 201-204, 221-222

objectives
Objectives
  • Describe and demonstrate spinal modulated reflexes
  • Differentiate reflexes vs. voluntary movement
  • Differentiate feedback vs. feedforward control
  • Explain recruitment patterns of motor units to generate force in muscles
  • Indicate the role of each neural structure involved in motor control
  • Describe the clinical implications following lesions to each neural structure
movement control
Movement Control

Reflexic

Voluntary

With conscious intention to move

  • Stereotyped motor response to a specific sensory stimulus
  • Neurons involved
    • Sensory neurons
    • Interneurons
    • Motor neurons
  • Reflex responses are often complex and can change depending on the task
rapid flexion movements at the elbow
Rapid flexion movements at the elbow

Parkinson’s Disease

The three traces in each panel are, from top to bottom, rectified biceps, and triceps EMG, angular position.

Cerebellar deficits

Berardelli, 1996

motor neurons
Motor Neurons
  • Alpha motor neuron (lower motor neuron)
  • Motor neuron pool
  • Motor unit
  • Motor unit innervation ratio (MUIR)
  • Compare MUIR between finger extensor vs. deltoid muscle
  • A motor neuron controls the amount of force that is exerted by muscle fibers

Click to view animationFigure 1.4. Byrne, 1997.

http://nba.uth.tmc.edu/neuroscience/s3/chapter01.html

control of muscle force rate cod
Control of Muscle Force: Rate Cod
  • ↑in the rate of action potentials fired by the motor neuron causes ↑in the amount of force that the motor unit generates.

Click to view animation. Figure 1.5. Byrne, 1997.

http://nba.uth.tmc.edu/neuroscience/s3/chapter01.html

control of muscle force size principle
Control of Muscle Force: Size Principle
  • When the input to motor neurons increases, smaller motor neurons are recruited and fired action potentials first.
  • Small motor neurons innervate slow-twitch fibers; Intermediate-sized motor neurons innervate fast-twitch, fatigue-resistant fibers; Large motor neurons innervate fast-twitch, fatigable muscle fibers.

Click to view animation. Figure 1.6. Byrne, 1997.

http://nba.uth.tmc.edu/neuroscience/s3/chapter01.html

stretch reflex dtr
Stretch Reflex (DTR)

Stimulus excites muscle spindle which sends signals via Ia afferents to α motor neuron

  • Excitation of agonist
  • Excitation of synergist
  • Inhibition of antagonist (i.e. reciprocal inhibition or reciprocal innervation)
  • Click to view animation

Shunway-Cook, 2007

stretch reflex dtr1
Stretch Reflex (DTR)

Muscle spindle information also goes to supraspinal regions via a long-loop reflex pathway, i.e. transcortical reflex, or functional stretch reflex.

Click to view abnormal DTR

Shunway-Cook, 2007

task dependent modulation of stretch reflexes
Task-Dependent Modulation of Stretch Reflexes

Pearson, 2008

For example, perturbation of one arm causes different responses in the contralateral arm, depending on the task.

slide14

Task instructions and environmental stiffness modify stretch reflex

PTB: rapid stretches to biceps

SLR: short-latency stretch reflex (monosynaptic)

LLR: long-latency stretch reflex (polysynaptic and transcortical)

Shemmell, 2009

flexor withdrawal
Flexor Withdrawal

Noxious stimulus to skin causes protective withdrawal of limb through

  • Excitation of ipsilateral flexor muscles
  • Inhibition of ipsilateral antagonistic extensor muscles

Pearson, 2008

  • Click to view animation
crossed extension
Crossed Extension

Typically occurs in conjunction with flexor withdrawal. Noxious stimulus causes contralateral

  • Excitation of extensor muscles
  • Inhibition of flexor muscles

Pearson, 2008

  • Click to view animation
autogenic inhibition
Autogenic Inhibition

Contraction or stretch of muscle pulls on the Golgi tendon organ (GTO). GTO sends signal to α motor neuron via Ib afferents and causes

  • Inhibition of agonist muscle
  • Excitation of antagonist muscle

Shunway-Cook, 2007

  • Click to view animation
autogenic inhibition gto function
Autogenic Inhibition: GTO Function
  • Protect muscle if contracting too hard, or fatigue
  • Clasp-knife reflex thought to be mediated in part through autogenic inhibition
    • Related to GTO

Young, 2008

plantar and finger flexors reflexes
Plantar and Finger Flexors Reflexes

Plantar (Babinski)

Finger flexor (Hoffman)

Tap or flick the terminal phalanx of the 3rd or 4th digit

Positive Response

flexion of terminal phalanx of thumb

UE equivalent of Babinski

  • Stroke foot firmly
  • Normal response
    • toes plantarflex
  • Positive response
    • great toe flexes toward the top of the foot and some spraying of other toes
babinski sign
Babinski Sign
  • Positive Babinski or Hoffman reflexes are signs of upper motor neuron lesions

Normal response

Positive response

View Hoffman Reflex http://neuroexam.com/neuroexam/content.php?p=33

View Babinski Reflex http://neuroexam.com/neuroexam/content.php?p=32

slide24

DESIRED OUTPUT

EFFECTOR

OUTPUT

COMPARATOR

– +

EFFECTOR

SENSOR

feedback control
Feedback Control

Shunway-Cook, 2007

slide26

ADVANCED INFORMAITON

SENSOR

DESIRED OUTPUT

EFFECTOR

OUTPUT

feedforward control
Feedforward Control

Shunway-Cook, 2007

feedback vs feedforward control
Feedback vs. Feedforward Control
  • Feedforward control uses initial inputs from vision
  • Feedback control uses somatosensory inputs from arm

Shunway-Cook, 2007

prefrontal cortex
Prefrontal Cortex
  • Strategic planning, decision to move
  • Motivation
  • Changing strategy to move, adaptive
  • Selection of appropriate actions for a particular behavioral context
posterior parietal cortex
Posterior Parietal Cortex
  • Ensuring that movements are targeted accurately to objects in external space
  • Processing spatial relationships of objects in the world
  • Building a representation of external space
primary motor cortex area 4 execution of voluntary movement
Primary Motor Cortex (Area 4): Execution of Voluntary Movement

Evarts’ study (1968)

monkeys made wrist flexion/extension

  • Fire 5-100 msec before movement onset
  • Encodes force of movement: the rate of neuronal firing ↑ with increased resistance to movement

View animationFigure 3.7

http://neuroscience.uth.tmc.edu/s3/chapter03.html

primary motor cortex area 4 execution of voluntary movement1
Primary Motor Cortex (Area 4): Execution of Voluntary Movement
  • Encodes direction anddistanceof movement

Vectors show firing of neurons to movements in different directions ( indicates max response)

Monkeys moved lever toward light

primary motor cortex area 4 execution of voluntary movement2
Primary Motor Cortex (Area 4): Execution of Voluntary Movement
  • Encode the speedof movement
    • Movement velocity profile is typically “bell-shaped”
    • Firing rates of neurons correlate with acceleration and deceleration of the velocity profile

Hand velocity during a reaching task.

Rosenbaum, 1995

true or false all of the neurons that control the biceps muscle may be located together
True or false: “All of the neurons that control the biceps muscle may be located together”

Incorrect! Because

  • Primary Motor Cortex (M1) does not generally control individual muscles directly, but appears to control movements of individual body parts or sequences of movements
  • Stimulation of small regions of MI causes movements that require activity of many muscle. Conversely, movements of individual muscles are correlated with activity of widespread areas of the MI.
pre motor cortex
Pre-motor Cortex
  • Involved in more complex, task-oriented process of movement control than primary motor cortex, and the selection of appropriate motor plans for voluntary movements.

View animation Figure 3.2

http://neuroscience.uth.tmc.edu/s3/chapter03.html

Lundy-Ekman, 2007

premotor cortex
Premotor Cortex
  • Signal the preparation for movement: “motor set neurons” fire when preparing to make a movement, and then turn silent during movement execution
  • Signal various sensory aspects associated with particular motor acts: “mirror neurons” fire selectively during a particular action, e.g. drinking coffee, and also when seeing or hearing others drinking coffee.

View animation Figure 3.10 http://neuroscience.uth.tmc.edu/s3/chapter03.htm

videos on mirror neurons
Videos on mirror neurons

Mirror Neuron. NOVA Science Now. http://www.pbs.org/wgbh/nova/body/mirror-neurons.html

Mirror Neuron. Human Spark. http://www.pbs.org/wnet/humanspark/video/web-exclusive-video-mirror-neurons/404/

premotor cortex1
Premotor Cortex
  • Sensitive to the behavioral context of a particular movement: neurons fire selectively to the inferred intentions of a movement, not just the movement itself
  • Signals correct and incorrect actions
  • Involved in voluntary movements activated by external stimuli, e.g. sensory stimuli, and visually guided sequences of movement

View animation Figure 3.12

http://neuroscience.uth.tmc.edu/s3/chapter03.html

supplemental motor area sma
Supplemental Motor Area (SMA)
  • Involved in the selection of complex sequential movements and the coordination of bilateral movements
    • Bilateral SMA are activated during the execution of complex sequential movements, and also during mental rehearsal of complex sequential movements
    • Mental rehearsal is a treatment technique involving the SMA
slide41

Shumway-Cook, 2007

View animation Figure 3.13.

http://neuroscience.uth.tmc.edu/s3/chapter03.html

supplemental motor area sma1
Supplemental Motor Area (SMA)
  • Involved in learning sequential movements
  • Involved in selecting movements that are initiated internally
  • Transform kinematic information (position, velocity) of a movement plan to dynamic (force) information of a movement plan
cerebellum
Cerebellum
  • Review Lundy’s Fig 10.16
slide45

Fine tuning of movement in feedback control: cerebellum compare “efferent copy” of motor program with incoming sensory feedback to correct for deviations from the intended movement outcome.

slide46

Motor learning and feedforward control: cerebellum evaluates sensory information and movement errors to modify the strength of synaptic connections in cerebellar cortex. As a result, future movements in a similar context will be modified.

cerebellum1
Cerebellum
  • Non-motor function
    • Timing in perceptual tasks: may serve as a centralized clock for body functions
    • Recall of habits/skills learned through repetition
    • Language process related to movement, e.g. verbs
cerebellum clinical dysfunction
Cerebellum: Clinical Dysfunction

http://library.med.utah.edu/neurologicexam/html/coordination_abnormal.html#12

  • Speech Rapid Alternating Movements
  • Dysarthria
  • Tremor
  • Hand Rapid Alternating Movements
  • Finger-to-nose
  • Foot rapid alternating movements
  • Tandem Gait

The University of Utah 2001

cerebellum clinical dysfunction1
Cerebellum: Clinical Dysfunction
  • Muscle tone ↓
  • Ataxic gait: unable to walk heel-to-toe
  • Truncal ataxia: involving trunk
  • Appendicular ataxia: involving limbs
  • Dysarthria: slurred, uncoordinated speech
  • Nystagmus: visual guidance of movement deteriorates
cerebellum clinical dysfunction2
Cerebellum: Clinical Dysfunction
  • Dysmetria
    • Hypermetria is most common: past-pointing, overshooting of target
    • Hypometria
  • Intention tremor
  • Dysdiadochokinesis
    • Impaired sequential movements
    • Test: rapid alternating movements (RAM)
basal ganglia
Basal Ganglia

Blumefeld, 2010

slide52

Dopaminergic Modulation

  • TURNS UP
  • motor activity

Cholinergic Modulation

TURNS DOWN motor activity

Facilitate or select appropriate movement

Inhibit unwanted or inappropriate movement

four parallel channels of information processing through basal ganglia
Four Parallel Channels of Information Processing through Basal Ganglia
  • Motor channel: movement
  • Oculomotor channel: eye movements
  • Prefrontal channel: cognitive process
  • Limbic channel: emotion, motivation drive
basal ganglia clinical dysfunctions
Basal Ganglia: Clinical Dysfunctions

Huntington’s disease Macrographia

  • Problems in scaling of movements

Parkinson’s disease

Micrographia

basal ganglia clinical dysfunctions1
Basal Ganglia: Clinical Dysfunctions
  • Parkinson’s Disease View the video
    • What are the movement problems of this patient?
    • Why the patient was able to ride the bike but has difficulties initiating walking and lost his balance during walking?
neuronal networks involved in externally guided movements
Neuronal Networks Involved in Externally Guided Movements
  • Cerebellum-Premotor areas
    • Preferentially involved in generation and/or guidance of movement initiated by external sensory cues, e.g. visual cues
    • Patients with cerebellar deficits showed improved motor performance with eyes closed
neuronal networks involved in internally initiated movements
Neuronal Networks Involved in Internally Initiated Movements
  • Basal ganglia-SMA
    • Preferentially involved in internally generated sequential movements
    • Patients with Parkinson’s disease can overcome freezing in movement initiation when external sensory cues are present, e.g. visual or auditory. ) (to by pass this BG-SMA loop)
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