Muscle and Muscle Receptors Movement Produced Feedback Somatic Motor Innervation Somatic Motor Innervation Body Position Body Position in Space in Space Functional unit Functional unit of Muscle of Muscle Structure of Skeletal Muscle Structure of Skeletal Muscle Detecting Movement Error Map of Essential Concepts DM McKeough © 2009 Three Types Three Types of Muscle of Muscle Force of Force of Muscle Contraction Muscle Contraction Proprioceptors Force and Length Changes Force and Length Changes Muscle Fatigue Muscle Fatigue Learning Objectives Learning Objectives

Muscle and Muscle Receptors Three Types of Muscle Three Types of Muscle Three Types of Muscle Three Types of Muscle Structure of Skeletal Muscle Structure of Skeletal Muscle Structure of Skeletal Muscle Structure of Skeletal Muscle Force and Length Changes Occur Within A Sarcomere Force and Length Changes Occur Within A Sarcomere Force and Length Changes Occur Within A Sarcomere Force and Length Changes Occur Within A Sarcomere Somatic Motor Innervation of Skeletal Muscle Somatic Motor Innervation of Skeletal Muscle Somatic Motor Innervation of Skeletal Muscle Somatic Motor Innervation of Skeletal Muscle Functional unit of muscle Functional unit of muscle Functional unit of muscle Functional unit of muscle Force of Muscle Contraction is Graded in Two Ways Force of Muscle Contraction is Graded in Two Ways Force of Muscle Contraction is Graded in Two Ways Force of Muscle Contraction is Graded in Two Ways Muscle fatigue Muscle fatigue Muscle fatigue Muscle fatigue Movement Produced Feedback Movement Produced Feedback Movement Produced Feedback Movement Produced Feedback Proprioceptors Proprioceptors Proprioceptors Body Position in Space Body Position in Space Body Position in Space Body Position in Space Detecting Movement Error Detecting Movement Error Detecting Movement Error Detecting Movement Error Learning Objectives Learning Objectives Learning Objectives Learning Objectives Last Viewed Last Viewed Exit Concept Map Concept Map

Three Types of Muscle Smooth Smooth Effector organ controlling movement of visceral organs Effector organ controlling movement of visceral organs Cardiac Cardiac Effector organ controlling movement of the heart Effector organ controlling movement of the heart Skeletal Skeletal Effector organ controlling movement of bones Effector organ controlling movement of bones Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Structure of Skeletal Muscle Contractile tissue: Contractile tissue: Chains of sarcomeres (actin and myosin) separated by Z bands. Chains of sarcomeres (actin and myosin) separated by Z bands. Connective tissue: Connective tissue: non-contractile collagen surrounding myofibrils (endomysium), bundles of muscle fibers (perimysium), and muscles (epimysium). non-contractile collagen surrounding myofibrils (endomysium), bundles of muscle fibers (perimysium), and muscles (epimysium). Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

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. Sliding filament theory: myosin heads successively form and break connections (cross bridges) pulling actin centrally during a concentric contraction. Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Somatic Motor Innervation of Skeletal Muscle Skeletal muscle is innervated by alpha motor neurons Skeletal muscle is innervated by alpha motor neurons Cell body located in ventral horn of spinal cord 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 appendicular skeleton have cell bodies in dorsolateral LMN pool  LMN innervating muscles of axial skeleton have cell bodies in ventromedial LMN pool  LMN innervating muscles of axial skeleton have cell bodies in ventromedial LMN pool Ventral horn is topographically and somatotopically organized Ventral horn is topographically and somatotopically organizedtopographicallysomatotopicallytopographicallysomatotopically LMN exit the spinal cord via ventral roots and travel to skeletal muscles via the PNS LMN exit the spinal cord via ventral roots and travel to skeletal muscles via the PNS Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Topographic Organization Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Somatotopic Organization Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Functional Unit 1/2 The functional unit within a skeletal muscle is a motor unit (single  LMN and all the muscle fibers it innervates). 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  LMN all muscle fibers of a motor unit contract maximally. (obligatory excitation-contraction coupling) All-or-none principle: iff threshold is reached, in the  LMN all muscle fibers of a motor unit contract maximally. (obligatory excitation-contraction coupling) Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Functional Unit 2/2 Innervation ratio: Innervation ratio: Muscle fibers per motor unit Muscle fibers per motor unit The higher the ratio (1:6), the lower the force production and the more precise the control 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 The lower the ratio (1:2,000) the higher the force and the less precise the control Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Motor Units 1/2 Small motor unit Small motor unit Small diameter  LMN  few SO (Type I) muscle fibers Small diameter  LMN  few SO (Type I) muscle fibers Medium motor unit Medium motor unit Medium diameter  LMN  medium number FOG (Type IIa) muscle fibers Medium diameter  LMN  medium number FOG (Type IIa) muscle fibers Large motor unit Large motor unit Large diameter  LMN  many FG (Type II) muscle fibers Large diameter  LMN  many FG (Type II) muscle fibers Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Smallest motor unit in the body 1:6 (eye and tongue) Largest motor unit in the body 1:2,000 (gluteus maximus) Motor Units 2/2 Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Force of Muscle Contraction is Graded in Two Ways 1/2 1.Recruitment: motor units are recruited from small, to medium, to large (size principle) Size Principle Conceptual Model Supraspinal input Ventral horn Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

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) Increasing discharge frequency produces increases in contractile force because successive muscular twitches summate (tetanus) Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

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). 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). Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Movement Produced Feedback The receptors of muscle (proprioceptors) and joints provide feedback about the state of the motor plant (the length and tension of muscles and therefore the position of joints). The receptors of muscle (proprioceptors) and joints provide feedback about the state of the motor plant (the length and tension of muscles and therefore the position of joints). Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

Body Position in Space Perception of the body’s position in space is extrapolated from proprioceptive feedback Perception of the body’s position in space is extrapolated from proprioceptive feedback Muscle spindles: muscle length & rate of change of muscle length Muscle spindles: muscle length & rate of change of muscle length GTO: muscle tension GTO: muscle tension Joint receptors: joint angle Joint receptors: joint angle Perception of the head’s position in space is extrapolated from visual + vestibular feedback Perception of the head’s position in space is extrapolated from visual + vestibular feedback Body position + head position = spatial orientation Body position + head position = spatial orientation Neck proprioceptors are critical Neck proprioceptors are critical Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

DetectingMovement 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

DetectingMovement 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 Learning objectives Overview of proprioceptors in motor control Muscle spindles Intrafusal fibers Sensory and motor regions Afferent fibers Afferent fibers Afferent fibers Afferent fibers Efferent fibers Efferent fibers Efferent fibers Efferent fibers Response of proprioceptors Response of proprioceptors Response of proprioceptors Response of proprioceptors Myotatic Reflex Alpha-Gamma co-activation Golgi tendon organs Joint receptors Dualisms with muscle spindles Dualisms with muscle spindles Dualisms with muscle spindles Dualisms with muscle spindles Last Viewed Last Viewed Muscle Receptors Muscle Receptors Exit Concept Map Concept Map

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 proprioception and receptors included in this class of receptors muscle spindle structure, function, and role in motor control muscle spindle structure, function, and role in motor control alpha-gamma co-activation alpha-gamma co-activation auto regulation of resting muscle length auto regulation of resting muscle length Golgi tendon organ structure, function, and role in motor control Golgi tendon organ structure, function, and role in motor control joint receptors structure, function, and role in motor control joint receptors structure, function, and role in motor control Last Viewed Last Viewed Proprioceptors Exit Concept Map Concept Map

Overview Role of proprioceptors in motor control Role of proprioceptors in motor control Only receptors of movement Only receptors of movement Collectively proprioceptors provide CNS with feedback necessary to perceive current state of the motor plant Collectively proprioceptors provide CNS with feedback necessary to perceive current state of the motor plant Body awareness Body awareness Last Viewed Last Viewed Proprioceptors Exit Concept Map Concept Map

Muscle Spindle Encapsulated Arranged in parallel with skeletal muscle Sense changes in muscle length Last Viewed Last Viewed Proprioceptors Exit Concept Map Concept Map

Intrafusal Fibers Nuclear bag: Nuclear bag: One bag per spindle One bag per spindle Nuclear chain: Nuclear chain: Multiple chain fibers per spindle Multiple chain fibers per spindle Nuclear bag fiber Nuclear chain fiber Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Regions Sensory: Sensory: Equatorial region Equatorial region Motor: Motor: Contractile polar regions Contractile polar regions Sensory region (Equatorial) Motor region (Polar) Motor region (Polar) Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Afferent Fibers Primary Primary Ia, reports rate of change in muscle length (dynamic component of response) Ia, reports rate of change in muscle length (dynamic component of response) Secondary Secondary II, reports absolute muscle length (static component of response) II, reports absolute muscle length (static component of response) Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Efferent Fibers Gamma dynamic Gamma dynamic To bags, increases sensitivity to rate of length change To bags, increases sensitivity to rate of length change Gamma static Gamma static To chains, increases sensitivity to absolute length change To chains, increases sensitivity to absolute length change Beta lower motor neuron: Beta lower motor neuron: Innervates both extrafusal and intrafusal fibers (alpha-gamma co-activation,  - δ ) Innervates both extrafusal and intrafusal fibers (alpha-gamma co-activation,  - δ ) Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

ResponseofProprioceptors Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Myotatic Knee Jerk Reflex Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Alpha – Gamma Co-activation The alpha system:  LMN and skeletal muscle The alpha system:  LMN and skeletal muscle Produces the force for a movement Produces the force for a movement Gamma system (δ): dynamic and static δ MN, intrafusal fibers, Ia and II Gamma system (δ): dynamic and static δ MN, intrafusal fibers, Ia and II Provide feedback about muscle length (  system) Provide feedback about muscle length (  system) Negative feedback (error signal): Negative feedback (error signal): Because  - δ co-activation changes length in both systems simultaneously 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. The discharge frequency in the δ system is proportional to the error in the length in the  system. Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Dualisms With Muscle Spindles What types of muscle fibers are inside and outside muscle spindles? What types of muscle fibers are inside and outside muscle spindles? Intrafusal and extrafusal fibers Intrafusal and extrafusal fibers What are the 2 types of intrafusal fibers? What are the 2 types of intrafusal fibers? Nuclear bag and nuclear chain Nuclear 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 static Gamma dynamic and gamma static What are the 2 characteristics of length change to which muscle spindles are sensitive? What are the 2 characteristics of length change to which muscle spindles are sensitive? Rate of change of muscle length and absolute muscle length Rate of change of muscle length and absolute muscle length What mechanism couples extrafusal and intrafusal systems? What mechanism couples extrafusal and intrafusal systems? Alpha-gamma co-activation Alpha-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) regions Equatorial (sensory) region and polar (motor) regions Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Golgi Tendon Organ (GTO) 1/3 Sense changes in muscle tension, provides CNS with feedback regarding which motor units are firing. Sense changes in muscle tension, provides CNS with feedback regarding which motor units are firing. Afferent fiber Afferent fiber Primary afferent: Ib Primary afferent: Ib Reflex connections Reflex connections Ib inhibits homonymous  LMN (weak) Ib inhibits homonymous  LMN (weak) Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Golgi Tendon Organ (GTO) 2/3 GTO has no motor innervation GTO has no motor innervation Rare passive sensory receptor Rare passive sensory receptor Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

GTO Responsiveness Weak response to passive stretch Weak response to passive stretch Strong response to active contraction Strong response to active contraction 3/3 Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

Joint Receptors Sense change in joint position Sense change in joint position Individual receptors have a preferred portion of the ROM (  discharge frequency when in preferred range) 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) Motor control system knows where joint is positioned by which receptors have  discharge) Last Viewed Last Viewed Exit Concept Map Concept Map Proprioceptors

The End © DM McKeough 2009 Last Viewed Last Viewed Concept Map Concept Map