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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
2
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
3
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
?
9
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
10
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
12
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)
13
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
15
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)
23
II. Withdrawal or Flexion Reflex (Disynaptic)
Protective reflex
Longer latency than stretch reflex
Complex nature (coordination of several joints)
Reciprocal inhibition
Nonlinear
24
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)
26
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)
27
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