Proprioceptors Three Types of Muscle Functional unit of Muscle Structure of Skeletal Muscle Force of Muscle Contraction Force and Length Changes Muscle and Muscle Receptors Body Position in Space Muscle Fatigue Somatic Motor Innervation Learning.
Download ReportTranscript Proprioceptors Three Types of Muscle Functional unit of Muscle Structure of Skeletal Muscle Force of Muscle Contraction Force and Length Changes Muscle and Muscle Receptors Body Position in Space Muscle Fatigue Somatic Motor Innervation Learning.
Muscle and Muscle Receptors
Map of Essential Concepts
DM McKeough © 2009
Muscle and Muscle Receptors
Force and Length Changes Occur Within A Sarcomere
Somatic Motor Innervation of Skeletal Muscle
Force of Muscle Contraction is Graded in Two Ways
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Three Types of Muscle
Smooth Effector organ controlling movement of visceral organs Cardiac Effector organ controlling movement of the heart Skeletal Effector organ controlling movement of bones Last Viewed
Structure of Skeletal Muscle
Contractile tissue: Chains of sarcomeres ( actin and myosin ) separated by Z bands.
Connective tissue: non-contractile collagen surrounding myofibrils ( endomysium ), bundles of muscle fibers ( perimysium ), and muscles ( epimysium ).
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Force and Length Changes Occur Within A Sarcomere
Sliding filament theory : myosin heads successively form and break connections (cross bridges) pulling actin centrally during a concentric contraction.
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Somatic Motor Innervation of Skeletal Muscle
Skeletal muscle is innervated by alpha motor neurons Cell body located in ventral horn of spinal cord LMN innervating muscles of appendicular skeleton have cell bodies in dorsolateral LMN pool LMN innervating muscles of axial skeleton have cell bodies in ventromedial LMN pool Ventral horn is organized
LMN exit the spinal cord via ventral roots and travel to skeletal muscles via the PNS Last Viewed
Topographic Organization
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Somatotopic Organization
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Functional Unit 1/2
The functional unit within a skeletal muscle is a motor unit (single LMN and all the muscle fibers it innervates).
All-or-none principle : iff threshold is reached, in the all motor unit coupling) LMN muscle fibers of a contract maximally. (obligatory excitation-contraction Last Viewed
Functional Unit 2/2
Innervation ratio : Muscle fibers per motor unit The higher the ratio (1:6), the lower the force production and the more precise the control The lower the ratio (1:2,000) the higher the force and the less precise the control Last Viewed
Motor Units 1/2
Small motor unit Small diameter fibers LMN few SO (Type I) muscle Medium motor unit Medium diameter LMN (Type IIa) muscle fibers medium number FOG Large motor unit Large diameter fibers LMN many FG (Type II) muscle Last Viewed
Motor Units 2/2
Smallest motor unit in the body 1:6 (eye and tongue) Largest motor unit in the body 1:2,000 (gluteus maximus) Last Viewed
Force of Muscle Contraction is Graded in Two Ways 1/2
1.
Recruitment to large ( : motor units are recruited from small, to medium, size principle ) Ventral horn Supraspinal input Size Principle Conceptual Model Last Viewed
Force of Muscle Contraction is Graded in Two Ways 2/2
2.
Rate modulation Increasing discharge frequency produces increases in contractile force because successive muscular twitches summate ( tetanus ) Last Viewed
Muscle Fatigue
Because of the metabolic properties of motor units, muscle fatigue is governed by the reverse size principle (FG fibers fatigue first followed by FOG followed by SO; first large, then medium, then small motor units).
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Movement Produced Feedback
The receptors of muscle ( motor plant proprioceptors ) and joints provide feedback about the state of the (the length and tension of muscles and therefore the position of joints).
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Body Position in Space
Perception of the body’s position in space is extrapolated from proprioceptive feedback Muscle spindles: muscle length & rate of change of muscle length GTO: muscle tension Joint receptors: joint angle Perception of the head’s position in space is extrapolated from visual + vestibular feedback Body position + head position = spatial orientation Neck proprioceptors are critical Last Viewed
Detecting Movement Error
1/2
Error detection requires the comparison of movement intent (efferent, FF) with movement result (afferent FB) No error: FF = FB Error: FF ≠ FB
Detecting Movement Error
2/2
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
Proprioceptors
Overview of proprioceptors in motor control
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Learning Objectives
At the completion of this unit learners will be able to describe and discuss: proprioception and receptors included in this class of receptors muscle spindle structure, function, and role in motor control alpha-gamma co-activation auto regulation of resting muscle length Golgi tendon organ structure, function, and role in motor control joint receptors structure, function, and role in motor control Last Viewed
Overview
Role of proprioceptors in motor control Only receptors of movement Collectively proprioceptors provide CNS with feedback necessary to perceive current state of the motor plant Body awareness Last Viewed
Muscle Spindle
Encapsulated Arranged in parallel with skeletal muscle Sense changes in muscle length Last Viewed
Intrafusal Fibers
Nuclear bag: One bag per spindle Nuclear chain: Multiple chain fibers per spindle Nuclear bag fiber Nuclear chain fiber Last Viewed
Regions
Sensory: Equatorial region Motor: Contractile polar regions
Motor region (Polar) Sensory region (Equatorial) Motor region (Polar)
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Afferent Fibers
Primary Ia , reports rate of change in muscle length (dynamic component of response) Secondary II , reports absolute muscle length (static component of response) Last Viewed
Efferent Fibers
Gamma dynamic To bags, increases sensitivity to rate of length change Gamma static To chains, increases sensitivity to absolute length change Beta lower motor neuron: Innervates both extrafusal and intrafusal fibers (alpha-gamma co-activation, - δ ) Last Viewed
Response of Proprioceptors Last Viewed
Myotatic Knee Jerk Reflex
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Alpha – Gamma Co-activation
The alpha system: LMN and skeletal muscle Produces the force for a movement Gamma system (δ): dynamic and static δ MN, intrafusal fibers, Ia and II Provide feedback about muscle length ( system) Negative feedback (error signal): Because - δ co-activation changes length in both systems simultaneously The discharge frequency in the δ system is proportional to the error in the length in the system.
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Dualisms With Muscle Spindles
What types of muscle fibers are inside and outside muscle spindles?
Intrafusal and extrafusal fibers What are the 2 types of intrafusal fibers?
Nuclear bag and nuclear chain What are the 2 types of MS afferents?
Primary afferents (Ia) and secondary afferents (II) What are the 2 types of MS efferents?
Gamma dynamic and gamma static What are the 2 characteristics of length change to which muscle spindles are sensitive? Rate of change of muscle length and absolute muscle length What mechanism couples extrafusal and intrafusal systems?
Alpha-gamma co-activation What are the 2 regions of an intrafusal fiber?
Equatorial (sensory) region and polar (motor) regions Last Viewed
Golgi Tendon Organ (GTO) 1/3
Sense changes in muscle tension , provides CNS with feedback regarding which motor units are firing.
Afferent fiber Primary afferent: Ib Reflex connections Ib inhibits homonymous LMN (weak) Last Viewed
Golgi Tendon Organ (GTO) 2/3
GTO has no innervation motor Rare passive receptor sensory Last Viewed
3/3 GTO Responsiveness Weak response to passive stretch Strong response to active contraction Last Viewed
Joint Receptors
Sense change in joint position Individual receptors have a preferred portion of the ROM ( discharge frequency when in preferred range) Motor control system knows where joint is positioned by which receptors have discharge) Last Viewed
The End
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