1 Coordinated Purposeful Movements Voluntary Motor Function: * Posture Control (maintaining a...

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1 Coordinated Purposeful Movements Voluntary Motor Function: * Posture Control (maintaining a position) * Goal Directed Movements * Rhythmic Movements Reflexes: Rapidly executed automatic and stereotyped response to a given stimulus

Transcript of 1 Coordinated Purposeful Movements Voluntary Motor Function: * Posture Control (maintaining a...

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Coordinated Purposeful Movements

Voluntary Motor Function:* Posture Control (maintaining a position)* Goal Directed Movements* Rhythmic Movements

Reflexes:Rapidly executed automatic and stereotyped response to a given stimulus

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Functional basis of the voluntary movement control

Decision Making

Decision Processing

Decision Execution

Level 1

Level 2

Level 3

Joint angles and torquesLoad

Sen

sory

info

rmat

ion

1. Decision making: Planning Based on the task (will) and memory

3. Decision execution: Execution - Executing the movement, and - Informing the upper control level

2. Decision processing: Programming Interpreting the descending commands and processing them

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Receptors & Sensory Information

Mechanoreceptors: Cochlear hear cells, Vestibular System

Kinesthesia: Proprioceptors, Exterocepts (Somatosensory System)

Photoreceptors: Visual Information (direct) 1. Sensory Feedback 2. Defining the ambiance

Manipulating the sensory information!

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Table 5.3 (1)Page 144

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain(Mesencephalon)

Pons

Medullaoblongata

Brain components

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

Diencephalon

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Hierarchical organization of the motor system

Cerebral CortexMotor Area

BrainStem

Spinal Cord

Basal Ganglia

Cerebellum

Thalamus

SensoryReceptors

Muscle Contraction and

Movement

Other Sensory Input

Sensory Information

Table 5.3 (1)Page 144

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

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Hierarchical Organization: Decentralized Control

Parallel Processing: Production and Control of Discrete types of Movements, e.g., Reaching while Controlling the Posture

Posture Control: Medial neuronal system of BS

Distal muscles of limbs: Lateral neuronal system of BS

Eye and Head movement Control : BS

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Cerebral Cortex Area: Primary motor cortex (M1) Premotor Cortex (PM) Supplementary motor area (SMA)

Premotor area & SMA: Coordinating and planning sequences of movements & receive information and project it to the primary motor cortex (to BS)

Somatotopic map!

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A Hierarchical Structure for motor control system

Limbic System

Associative Cortex

Motor Cortex Basal Ganglia

Sensory System

Cerebellum

Spinal Cord

Musculo-skeletal System

Plan

Need

Movement

Aff

eren

t pa

thw

ay

Efferent pathw

ay

Pla

nnin

gP

rogr

amm

ing

Exe

cutio

n

?

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Pathways: The centers and tracts that link the brain with the rest of the body

Sensory pathways (Afferent): Distribute information from peripheral receptors to processing centers in brain

Motor pathways (Efferent): Begin at CNS centers concerned with motor control and end at the effectors they control

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Usual sensory and motor pathways(no reflex arc is considered)

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Limbic System: * A functional grouping* Includes nuclei and tracts along the border between the cerebrum, diencephalons and mesencephalon

Functions of the Limbic System:* Establishing emotional states* Linking the conscious, intellectual functions of the cerebral cortex with the unconscious and automatic function of the brain stem* Facilitating memory storage and retrieval

Limbic System

Motor CortexBasal

Ganglia

Sensory System

Cerebellum

Spinal Cord

Musculo-skeletal System

Plan

Need

Movement

?

Associative Cortex

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Decision Making

Decision Processing

Decision Execution

Level 1

Level 2

Level 3

Commands to muscles

Joint angles and torques

Load

Pro

prio

cept

ive

and

oth

er s

ens

ory

info

rmat

ion

A proposed internal structure of the three levels involved in performing a voluntary movement

LoadAntagonist

Agonist

Interneurons

Decision Making

-MN

-MN

Su

pra

-sp

inal

Intr

a-sp

inal

(ref

lex

loo

ps)

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Muscle fibers and Motor Neurons

Two types of muscle fibers:

1. Intrafusal muscle fibers

2. Extrafusal muscle fibers (main body of the muscle)

Two types of motor neuron:

1. α-motor neurons Innervate the extrafusal muscle fibers. When the alpha nerve fires the motor unit generates tension and/or shortens.

2. γ-motor neurons

Innervate the intrafusal muscle fibers. When the gamma nerve fires the intrafusal muscle fiber generates tension and/or shortens.

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Two types:

1. Muscle Spindle Apparatus

2. Golgi Tendon Organ

Proprioceptors

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Function: Sensinga) Changes in muscle length:

Spatial position

b) Rate of change in muscle length: Stretch reflex

Muscle Spindle

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Two kinds of sensory neurons (afferents)

I. Primary afferents (Ia): fast or dynamic endings

– Rate of stretch – Function: react to oppose stretch

II. Secondary afferents (II): slow or static endings

– Final length of muscle – Function: maintain muscle tone,

posture, positional awareness

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Muscle Tone: A Resting tension

Some motor units are always active.

The contraction does not produce movement, but do tense and firm the muscle.

Remark: the identity of the stimulated motor units changes constantly.

The effect of changes in muscle

spindle length on muscle tone

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Golgi Tendon Organs

Monitors tension developed in muscle and prevents damage during excessive force generation

Ib fibers supply the receptors.

Tension

Firing pattern in the Ib fiber

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Alpha-Gamma CoordinationVoluntary Contraction

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Reflexes

Processing Site

A. Spinal Reflex : Many segments interact to produce a coordinated, highly variable motor response

B. Cranial Reflex Directed by nuclei in brain e.g., the reflex movements in response to a sudden loud noise

Reflex motor behavior occurs automatically, without instructions of higher centers

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Complexity of the Circuit

I. Monosynaptic Reflex (stretch reflex ):• One sensory neuron

• One interneuron• One motor neuron

II. Polysynaptic Reflex (scratch reflex)• One sensory neuron• Multiple interneurons• Multiple motor neurons

Different reflexes:Stretch reflex, Withdrawal or Flexion reflex, Tonic reflex, Golgi tendon reflex, Crossed extensor reflex, etc.

Disynaptic reflex

Trisynaptic reflex{

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Quick stretch of muscle distorts nuclear bag (muscle spindle)

Afferent signal via primary sensory nerve (Ia)

Monosynapse in spinal cord with α-motor neuron

Efferent signal via α-motor neuron

Muscle contraction results to oppose stretch

Reciprocal innervation Collateral Ia synapses inhibitory interneurons

Inhibitory interneuron sends efferent signal to antagonist

→ relaxation of antagonist muscle

I. Stretch ReflexPatellar reflex (knee jerk)

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II. Withdrawal or Flexion Reflex (Disynaptic)

Protective reflex

Longer latency than stretch reflex

Complex nature (coordination of several joints)

Reciprocal inhibition

Nonlinear

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III. Tonic Stretch Reflex (monosynaptic)

• Contributes to muscle tone

• Stabilizes muscle length when it is under constant load

Result: Skeletal muscle length regulation,

→ Posture regulation

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IV. Golgi Tendon Reflex

Disynaptic reflex

Afferent fiber: Ib

Synapses are based on reciprocal inhibition

Complements the tonic stretch reflex

Skeletal muscle length regulation

→ Postural Control

Rectus femoris(extensor)

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Mechanism of postural control during standing:

• RF starts to fatigue • Patelar tendon force decreases• Activity in Ib declines• Normal inhibition of the MN supplying RF will be removes• Muscle will be stimulated to contract more

IV. Golgi Tendon ReflexRectus femoris

(extensor)

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V. Crossed Extensor Reflex

Contralateral reflex arc (crossed extensor reflex) occurs on the opposite side of stimulus

The two occur simultaneously With 250 msec delay between Flexion and extension

Function: maintaining posture and balance