muscle and muscle receptors movement produced feedback somatic motor innervation somatic motor...

Muscle andMuscle andMuscle ReceptorsMuscle Receptors

MovementMovementProducedProducedFeedbackFeedback

Somatic Motor InnervationSomatic Motor Innervation

Body PositionBody Positionin Spacein Space

Functional unit Functional unit of Muscleof Muscle

Structure of Skeletal MuscleStructure of Skeletal Muscle

DetectingDetectingMovementMovement

ErrorErrorMap of EssentialMap of EssentialConceptsConcepts

DM McKeough© 2009

Three Types Three Types of Muscleof Muscle

Force of Force of Muscle ContractionMuscle Contraction

ProprioceptorsProprioceptors

Force and Length ChangesForce and Length Changes

Muscle FatigueMuscle Fatigue

Learning ObjectivesLearning Objectives

Muscle andMuscle andMuscle ReceptorsMuscle Receptors

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

Last ViewedLast Viewed ExitExitConcept MapConcept Map

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

Last ViewedLast Viewed Muscle ReceptorsMuscle Receptors ExitExitConcept MapConcept Map

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.

Connective tissue: Connective tissue: non-contractile collagen non-contractile collagen

surrounding myofibrils surrounding myofibrils ((endomysiumendomysium), bundles ), bundles of muscle fibers of muscle fibers ((perimysiumperimysium), and ), and muscles (muscles (epimysiumepimysium).).


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.


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


Topographic OrganizationTopographic Organization


Somatotopic OrganizationSomatotopic Organization


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)


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


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


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


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


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))


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).


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).


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

lengthlength GTO: muscle tensionGTO: muscle tension Joint receptors: joint angleJoint receptors: joint angle

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


DetectingDetectingMovementMovementError Error 1/21/2

Error detection requires the comparison of movement intent (efferent, FF) with movement result (afferent FB)

No error: FF = FBError: FF ≠ FB

DetectingDetectingMovementMovementError Error 2/22/2

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

Last Viewed Last Viewed Muscle ReceptorsMuscle Receptors ExitExitConcept MapConcept Map

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

Last Viewed Last Viewed ProprioceptorsProprioceptors ExitExitConcept MapConcept Map

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


Muscle SpindleMuscle Spindle

Encapsulated Arranged in parallel

with skeletal muscle Sense changes in

muscle length


Intrafusal FibersIntrafusal Fibers

Nuclear bag: Nuclear bag: One bag per spindleOne bag per spindle

Nuclear chain: Nuclear chain: Multiple chain fibers Multiple chain fibers

per spindleper spindle

Nuclearbagfiber

Nuclearchainfiber

Last Viewed Last Viewed ExitExitConcept MapConcept MapProprioceptorsProprioceptors

RegionsRegions

Sensory: Sensory: Equatorial regionEquatorial region

Motor: Motor: Contractile polar Contractile polar

regionsregions

Sensory region(Equatorial)

Motor region(Polar)

Motor region(Polar)


Afferent FibersAfferent Fibers

Primary Primary IaIa, reports , reports rate of change rate of change

in muscle length (dynamic in muscle length (dynamic component of response)component of response)

Secondary Secondary IIII, reports , reports absolute muscle absolute muscle

length length (static component (static component of response)of response)


Efferent FibersEfferent Fibers

Gamma dynamic Gamma dynamic To bags, increases To bags, increases

sensitivity to rate of length sensitivity to rate of length changechange

Gamma static Gamma static To chains, increases To chains, increases

sensitivity to absolute sensitivity to absolute length changelength change

Beta lower motor neuron: Beta lower motor neuron: Innervates both extrafusal Innervates both extrafusal

and intrafusal fibers (alpha-and intrafusal fibers (alpha-gamma co-activation, gamma co-activation, - - δδ ) )


ResponseResponseofof

ProprioceptorsProprioceptors


MyotaticMyotaticKnee Jerk ReflexKnee Jerk Reflex


Alpha – Gamma Co-activationAlpha – Gamma Co-activation

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.


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


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.

Afferent fiberAfferent fiber Primary afferent: IbPrimary afferent: Ib

Reflex connectionsReflex connections Ib inhibits homonymousIb inhibits homonymous

LMN (weak) LMN (weak)


Golgi Tendon Organ (GTO) 2/3Golgi Tendon Organ (GTO) 2/3

GTO has GTO has nono motor motor innervationinnervation

Rare Rare passivepassive sensory receptorsensory receptor


GTO ResponsivenessGTO Responsiveness

Weak response Weak response to passive to passive stretchstretch

Strong response Strong response to active to active contractioncontraction

3/3


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)


muscle and muscle receptors movement produced feedback somatic motor innervation somatic motor...

Documents

muscle force of force

length changes force

sarcomere force

space body position

heart effector organ

connective tissue

noncontractile collagen

myofibrils endomysium