Muscle and Muscle Receptors Movement Produced Feedback Somatic Motor Innervation Somatic Motor Innervation Body Position Body Position in Space in Space.
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Three Types of Muscle Structure of Skeletal Muscle Force and Length Changes Occur Within A Sarcomere Somatic Motor Innervation of Skeletal Muscle Functional unit of muscle Force of Muscle Contraction is Graded in Two Ways Muscle fatigue Movement Produced Feedback Proprioceptors Body Position in Space Detecting Movement Error Learning Objectives
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Three Types of MuscleThree Types of Muscle
Smooth Smooth Effector organ controlling Effector organ controlling
movement of visceral organsmovement of visceral organs Cardiac Cardiac
Effector organ controlling Effector organ controlling movement of the heartmovement of the heart
Skeletal Skeletal Effector organ controlling Effector organ controlling
movement of bonesmovement of bones
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Structure of Skeletal MuscleStructure of Skeletal Muscle
Contractile tissue: Contractile tissue: Chains of sarcomeres Chains of sarcomeres
((actinactin and and myosinmyosin) ) separated by Z bands.separated by Z bands.
surrounding myofibrils surrounding myofibrils ((endomysiumendomysium), bundles ), bundles of muscle fibers of muscle fibers ((perimysiumperimysium), and ), and muscles (muscles (epimysiumepimysium).).
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Force and Length Changes Force and Length Changes Occur Within A SarcomereOccur Within A Sarcomere
Sliding filament Sliding filament theorytheory: myosin heads : myosin heads successively form successively form and break and break connections (cross connections (cross bridges) pulling actin bridges) pulling actin centrally during a centrally during a concentric concentric contraction.contraction.
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Somatic Motor Somatic Motor Innervation of Skeletal MuscleInnervation of Skeletal Muscle
Skeletal muscle is innervated by alpha motor Skeletal muscle is innervated by alpha motor neuronsneurons
Cell body located in ventral horn of spinal cordCell body located in ventral horn of spinal cord LMN innervating muscles of appendicular LMN innervating muscles of appendicular
skeleton have cell bodies in dorsolateral LMN poolskeleton have cell bodies in dorsolateral LMN pool LMN innervating muscles of axial skeleton have LMN innervating muscles of axial skeleton have
cell bodies in ventromedial LMN poolcell bodies in ventromedial LMN pool Ventral horn is Ventral horn is topographically and and
somatotopically organized organized LMN exit the spinal cord via ventral roots and LMN exit the spinal cord via ventral roots and
travel to skeletal muscles via the PNStravel to skeletal muscles via the PNS
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Topographic OrganizationTopographic Organization
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Somatotopic OrganizationSomatotopic Organization
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Functional Unit 1/2Functional Unit 1/2 The The functional unit functional unit
within a skeletal within a skeletal muscle is a muscle is a motor unit motor unit (single (single LMN and all LMN and all the muscle fibers it the muscle fibers it innervates).innervates).
All-or-none principleAll-or-none principle: : iff threshold is iff threshold is reached, in the reached, in the LMN LMN allall muscle fibers of a muscle fibers of a motor unit motor unit contract contract maximally. maximally. (obligatory excitation-(obligatory excitation-contraction coupling)contraction coupling)
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Functional Unit 2/2Functional Unit 2/2
Innervation ratioInnervation ratio:: Muscle fibers per motor unit Muscle fibers per motor unit The higher the ratio (1:6), the lower the force The higher the ratio (1:6), the lower the force
production and the more precise the control production and the more precise the control The lower the ratio (1:2,000) the higher the force The lower the ratio (1:2,000) the higher the force
and the less precise the controland the less precise the control
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Motor Units 1/2Motor Units 1/2
Small motor unit Small motor unit Small diameter Small diameter LMN LMN few SO (Type I) few SO (Type I)
muscle fibersmuscle fibers Medium motor unit Medium motor unit
Medium diameter Medium diameter LMN LMN medium number medium number FOG (Type IIa) muscle fibersFOG (Type IIa) muscle fibers
Large motor unit Large motor unit Large diameter Large diameter LMN LMN many FG (Type II) many FG (Type II)
muscle fibersmuscle fibers
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Smallest motor unit in the body 1:6 (eye and tongue)
Largest motor unit in the body 1:2,000 (gluteus maximus)
Motor Units 2/2Motor Units 2/2
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Force of Muscle Contraction Force of Muscle Contraction is Graded in Two Ways 1/2 is Graded in Two Ways 1/2
1.1. RecruitmentRecruitment: motor : motor units are recruited units are recruited from small, to from small, to medium, to large medium, to large ((size principlesize principle))
Size Principle Conceptual
Model
Supraspinal input
Ventralhorn
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Force of Muscle Contraction Force of Muscle Contraction is Graded in Two Ways 2/2is Graded in Two Ways 2/2
2.2. Rate modulationRate modulation Increasing discharge frequency produces Increasing discharge frequency produces
increases in contractile force because increases in contractile force because successive muscular twitches summate successive muscular twitches summate ((tetanustetanus))
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Muscle FatigueMuscle Fatigue
Because of the metabolic properties of Because of the metabolic properties of motor units, muscle motor units, muscle fatiguefatigue is governed by is governed by the the reverse size principle reverse size principle (FG fibers fatigue (FG fibers fatigue first followed by FOG followed by SO; first first followed by FOG followed by SO; first large, then medium, then small motor large, then medium, then small motor units).units).
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Movement Produced FeedbackMovement Produced Feedback
The receptors of muscle (The receptors of muscle (proprioceptorsproprioceptors) ) and joints provide feedback about the and joints provide feedback about the state of the state of the motor plant motor plant (the length and (the length and tension of muscles and therefore the tension of muscles and therefore the position of joints).position of joints).
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Body Position in SpaceBody Position in Space
Perception of the Perception of the body’sbody’s position in space is position in space is extrapolated from proprioceptive feedbackextrapolated from proprioceptive feedback Muscle spindles: muscle length & rate of change of muscle Muscle spindles: muscle length & rate of change of muscle
Perception of the Perception of the head’shead’s position in space is position in space is extrapolated from visual + vestibular feedbackextrapolated from visual + vestibular feedback
Body position + head position = spatial orientationBody position + head position = spatial orientation Neck proprioceptors are criticalNeck proprioceptors are critical
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The cerebellum (Cb) is the primary comparator for the motor system
• Cb receives FF from pons that got it from Ctx via corticobulbar tract
• Cb receives FB from proprioceptors via spino-Cb tracts
ProprioceptorsProprioceptors Learning objectives Overview of proprioceptors in motor control Muscle spindles
Intrafusal fibers Sensory and motor regions Afferent fibers Efferent fibers Response of proprioceptors Myotatic Reflex Alpha-Gamma co-activation
Golgi tendon organs Joint receptors Dualisms with muscle spindles
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Learning Objectives Learning Objectives
At the completion of this unit learners will be able to describe At the completion of this unit learners will be able to describe and discuss:and discuss:
proprioception and receptors included in this class of proprioception and receptors included in this class of receptorsreceptors
muscle spindle structure, function, and role in motor controlmuscle spindle structure, function, and role in motor control alpha-gamma co-activationalpha-gamma co-activation auto regulation of resting muscle lengthauto regulation of resting muscle length Golgi tendon organ structure, function, and role in motor Golgi tendon organ structure, function, and role in motor
controlcontrol joint receptors structure, function, and role in motor controljoint receptors structure, function, and role in motor control
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OverviewOverview
Role of proprioceptors in motor controlRole of proprioceptors in motor control Only receptors of movementOnly receptors of movement Collectively proprioceptors provide CNS with Collectively proprioceptors provide CNS with
feedback necessary to perceive current state feedback necessary to perceive current state of the motor plantof the motor plant
Body awarenessBody awareness
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Muscle SpindleMuscle Spindle
Encapsulated Arranged in parallel
with skeletal muscle Sense changes in
muscle length
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Intrafusal FibersIntrafusal Fibers
Nuclear bag: Nuclear bag: One bag per spindleOne bag per spindle
The alpha system: The alpha system: LMN and skeletal muscle LMN and skeletal muscle Produces the force for a movementProduces the force for a movement
Gamma system (Gamma system (δδ): dynamic and static ): dynamic and static δδ MN, MN, intrafusal fibers, Ia and IIintrafusal fibers, Ia and II Provide feedback about muscle length (Provide feedback about muscle length ( system) system)
Negative feedback (error signal):Negative feedback (error signal): Because Because -- δ δ co-activation changes length in both co-activation changes length in both
systems simultaneouslysystems simultaneously The discharge frequency in the The discharge frequency in the δδ system is system is
proportional to the proportional to the errorerror in the length in the in the length in the system. system.
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Dualisms With Muscle SpindlesDualisms With Muscle Spindles
What types of muscle fibers are inside and outside muscle What types of muscle fibers are inside and outside muscle spindles?spindles? Intrafusal and extrafusal fibersIntrafusal and extrafusal fibers
What are the 2 types of intrafusal fibers?What are the 2 types of intrafusal fibers? Nuclear bag and nuclear chainNuclear bag and nuclear chain
What are the 2 types of MS afferents?What are the 2 types of MS afferents? Primary afferents (Ia) and secondary afferents (II)Primary afferents (Ia) and secondary afferents (II)
What are the 2 types of MS efferents?What are the 2 types of MS efferents? Gamma dynamic and gamma staticGamma dynamic and gamma static
What are the 2 characteristics of length change to which What are the 2 characteristics of length change to which muscle spindles are sensitive? muscle spindles are sensitive? Rate of change of muscle length and absolute muscle lengthRate of change of muscle length and absolute muscle length
What mechanism couples extrafusal and intrafusal What mechanism couples extrafusal and intrafusal systems?systems? Alpha-gamma co-activationAlpha-gamma co-activation What are the 2 regions of an intrafusal fiber?What are the 2 regions of an intrafusal fiber? Equatorial (sensory) region and polar (motor) regionsEquatorial (sensory) region and polar (motor) regions
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Golgi Tendon Organ (GTO) 1/3Golgi Tendon Organ (GTO) 1/3
Sense Sense changeschanges in in muscle tensionmuscle tension, , provides CNS with feedback regarding provides CNS with feedback regarding which which motor units motor units are firing.are firing.
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GTO ResponsivenessGTO Responsiveness
Weak response Weak response to passive to passive stretchstretch
Strong response Strong response to active to active contractioncontraction
3/3
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Joint ReceptorsJoint Receptors
Sense change in joint Sense change in joint positionposition
Individual receptors have a Individual receptors have a preferred portion of the ROMpreferred portion of the ROM(( discharge frequency when discharge frequency when in preferred range)in preferred range)
Motor control system knows Motor control system knows where joint is positioned by where joint is positioned by which receptors have which receptors have discharge)discharge)
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