12 Motor system I Introduction • Skeletal muscle contraction is initiated by lower motor neuron • Lower motor neuron is a part of local reflex circuits • The information from several sources is integrated in the lower motor neuron – Higher levels of CNS Upper motor neuron, tectum, n. ruber, brain stem – Proprioception http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Introduction • Skeletal muscle contraction is initiated by lower motor neuron • Lower motor neuron is a part of local reflex circuits • The information from several sources is integrated in the lower motor neuron – Higher levels of CNS Upper motor neuron, tectum, n. ruber, brain stem – Proprioception http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Introduction • Skeletal muscle contraction is initiated by lower motor neuron • Lower motor neuron is a part of local reflex circuits • The information from several sources is integrated in the lower motor neuron – Higher levels of CNS Upper motor neuron, tectum, n. ruber, brain stem – Proprioception http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Introduction • Skeletal muscle contraction is initiated by lower motor neuron • Lower motor neuron is a part of local reflex circuits • The information from several sources is integrated in the lower motor neuron – Higher levels of CNS Upper motor neuron, tectum, n. ruber, brain stem – Proprioception http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Introduction • Skeletal muscle contraction is initiated by lower motor neuron • Lower motor neuron is a part of local reflex circuits • The information from several sources is integrated in the lower motor neuron – Higher levels of CNS Upper motor neuron, tectum, n. ruber, brain stem – Proprioception http://www.frontiersin.org/files/Articles/42416/fnhum-07-00085- HTML/image_m/fnhum-07-00085-g001.jpg Lower motor neuron • α motoneuron – Innervation of contractile elements – Extrafusal fibers – Muscle contraction • γ motoneuron – Innervation of muscle spindles – Intrafusal fibers – Alignment of muscle spindles – Gamma loop • β motoneuron http://epomedicine.com/wp-content/uploads/2016/07/gamma-loop.jpg Stretch reflex http://www.slideshare.net/ananthatiger/cns-4 Lower motor neuron Topography http://www.slideshare.net/drpsdeb/presentations Motor unit • A typical muscle is innervated by about 100 motoneurons which are localized in motor nucleus • Each motoneuron innervate from 100 to 1000 muscle fibers and one muscle fiber is innervated by a single motoneuron • The ensemble of muscle fibers innervated by a single neuron and corresponding motoneuron constitutes the motor unit Motor unit • A typical muscle is innervated by about 100 motoneurons which are localized in motor nucleus • Each motoneuron innervate from 100 to 1000 muscle fibers and one muscle fiber is innervated by a single motoneuron • The ensemble of muscle fibers innervated by a single neuron and corresponding motoneuron constitutes the motor unit Motor unit • A typical muscle is innervated by about 100 motoneurons which are localized in motor nucleus • Each motoneuron innervate from 100 to 1000 muscle fibers and one muscle fiber is innervated by a single motoneuron • The ensemble of muscle fibers innervated by a single neuron and corresponding motoneuron constitutes the motor unit Neuromuscular junction http://classes.midlandstech.edu/carterp/Courses/bio210/chap09/210_figure_09_11_labeled.jpg Neuromuscular junction https://s3.amazonaws.com/classconnection/803/flashcards/9818803/png/initiation-151586429D6310D1C56.png Muscle fibers http://www.sivabio.50webs.com/mus019.jpg Types of muscle contraction • Isometric contraction  Muscle does not shorten during contraction http://www.slideshare.net/drpsdeb/presentations • Isotonic contraction  Constant tension  The muscle shortens during contraction Types of muscle fibers Fast fibers  Performance  Fast fatigue-resistant – normal performance  Fast fatigable – high performance Slow fibers  Endurance  Fatigue resistant http://www.slideshare.net/drpsdeb/presentations Types of muscle fibers Fast fibers  Performance  Fast fatigue-resistant – normal performance  Fast fatigable – high performance Slow fibers  Endurance  Fatigue resistant http://www.slideshare.net/drpsdeb/presentations The recruitment of motor neurons m. gastrocnemius in a cat http://www.slideshare.net/drpsdeb/presentations Proprioception • Information about the position of body parts in relation to each other (The sum of information about lengths of particular muscles) • Information about movement (The force and speed of muscle contraction) • Reflex regulation of muscle activity • Muscle spindles – Lie in parallel with extrafusal muscle fibers • Golgi tendon organ – Arranged in series with extrafusal muscles http://www.slideshare.net/CsillaEgri/presentations Proprioception • Information about the position of body parts in relation to each other (The sum of information about lengths of particular muscles) • Information about movement (The force and speed of muscle contraction) • Reflex regulation of muscle activity • Muscle spindles – Lie in parallel with extrafusal muscle fibers • Golgi tendon organ – Arranged in series with extrafusal muscles http://www.slideshare.net/CsillaEgri/presentations Muscle spindles • Nno-force generating contractile structures • The contractility is for spindle length adjustment • Encapsulated structure filled with a fluid • Intrafusal fibers – Lie in parallel with extrafusal muscle fibers (Stretch/shorten along with extrafusal fibers) – Efferent connections (into muscle spindle) • γ motoneuron – Afferent connections (from muscle spindle) • Information about change in muscle length • Reflex regulation of the α motoneuron activity http://www.slideshare.net/CsillaEgri/presentations • Nno-force generating contractile structures • The contractility is for spindle length adjustment • Encapsulated structure filled with a fluid • Intrafusal fibers – Lie in parallel with extrafusal muscle fibers (Stretch/shorten along with extrafusal fibers) – Efferent connections (into muscle spindle) • γ motoneuron – Afferent connections (from muscle spindle) • Information about change in muscle length • Reflex regulation of the α motoneuron activity http://www.slideshare.net/CsillaEgri/presentations Muscle spindles Muscle spindles • Nno-force generating contractile structures • The contractility is for spindle length adjustment • Encapsulated structure filled with a fluid • Intrafusal fibers – Lie in parallel with extrafusal muscle fibers (Stretch/shorten along with extrafusal fibers) – Efferent connections (into muscle spindle) • γ motoneuron – Afferent connections (from muscle spindle) • Information about change in muscle length • Reflex regulation of the α motoneuron activity http://www.slideshare.net/CsillaEgri/presentations Muscle spindle • Static fibers • Dynamic fibers • Afferent connections (from spindle) – II – static fibers • Information about muscle length (position) • Ia – static and dynamic fibers • Information about muscle length and contraction (movement) – Reflex regulation of the α motoneuron activity • Efferent connections (from spindle) – Static γ motoneurons • Dynamic γ motoneurons – Spindle length adjustment http://www.slideshare.net/CsillaEgri/presentations Muscle spindle • Static fibers • Dynamic fibers • Afferent connections (from spindle) – II – static fibers • Information about muscle length (position) • Ia – static and dynamic fibers • Information about muscle length and contraction (movement) – Reflex regulation of the α motoneuron activity • Efferent connections (from spindle) – Static γ motoneurons – Dynamic γ motoneurons – Spindle length adjustment http://www.slideshare.net/CsillaEgri/presentations Muscle spindle • Static fibers • Dynamic fibers • Afferent connections (from spindle) – II – static fibers • Information about muscle length (position) • Ia – static and dynamic fibers • Information about muscle length and contraction (movement) – Reflex regulation of the α motoneuron activity • Efferent connections (into spindle) – Static γ motoneurons – Dynamic γ motoneurons – Spindle length adjustment http://www.slideshare.net/CsillaEgri/presentations Afferent signaling from muscle spindles II – Static fibers • Static response Ia – Static and dynamic fibers • Static and dynamic response http://www.slideshare.net/CsillaEgri/presentations Efferent signaling into the muscle spindle • γ motoneurons adjust the length of intrafusla fibers • Regulation of sensitivity • α and γ coactivation • http://www.slideshare.net/CsillaEgri/presentations Golgi tendon organs • Non-contractile encapsulated structures • Collagen fibers • Ia fibers • Mechanoreception • Arranged in series with extrafusal muscles • Information about changes in tendon tension/force • Reflex regulation of the α motoneuron activity http://www.slideshare.net/CsillaEgri/presentations Reaction of muscle spindles and the Golgi tendon organs to muscle fiber stretch/contraction Stretch (passive) Muscle spindles reaction Contraction (active) Golgi tendon organ reaction http://www.slideshare.net/drpsdeb/presentations Recapitulation http://images.persianblog.ir/559630_iXFiuRo0.jpg