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Muscle Contraction 10/19/2009 CONTROL OF MOVEMENT: STRIATED MUSCLES SKELETAL (STRIATED) MUSCLE: - each muscle = ____________________________________lots of muscle cells (muscle fibers) - each muscle cell =packed _______________________________________ with myosin and actin filament proteins -Myosin: Filamentous___________________________________________ protein with cross bridges -Actin: _________________________________________________Filamentous protein where cross bridges of myosin bind ANATOMY OF SKELETAL MUSCLE Axon______________ of alpha motor_____________ neuron Endplate________ Extrafusal muscle fiber ________Muscle Tendon_________ Myofibril Actin_____________ filament __________________Myosin filament ___________Z discs (bands) MUSCLE CONTRACTION Watch muscle contraction movie Myosin Myosin cross bridges filament Actin filaments Actin MtfMovement of filament actin filament Myosin cross bridge Movement of myosin filament Heads of cross bridges: 1. Attach to active sites on actin filaments 2. “Ratchet” forward 3. Release 4. Repeat -Onlyoccurs in the presence of calcium How is calcium released? From___________________________ activity at neuromuscular ________junction 1 10/19/2009 NEUROMUSCULAR JUNCTION Synapse between terminal of alpha_________________ motor neuron and a muscle___________ fiber is called a neuromuscular junction; Terminals of alpha motor neurons synapse on motor_____________ enplates - grooves along the surface of muscle fibers; When motor neuron fires, _____________acetylcholine is liberated from terminals at the endplate and depolarizes muscle fibers - endplate________________; potentials Depolarization of muscle fiber opens ________voltage- dependent_________________________ calcium channels , producing a large _______calcium influx into the fiber; Calcium triggers the actin-myosin “rowing” action leading to the contraction__________ of muscle fibers; Calcium is extruded from fiber by “pump”; Endplate potential ______always cause muscle fiber to fire = contraction or “twitch” of fiber. MOTOR UNITS Motor unit: _______________________________________One alpha motor neuron + its axon + all the ___________________________________muscle fibers it innervates (contacts) Motor pool: All______________________________________ motor neurons that innervate fibers of __________________a single muscle Muscle fibers Alpha motor neurons Axons - weak muscular contraction = ______________________few motor units activated _ - strong contraction = lots_______________________ of motor units activated - discrete/fine movements = __________________________small motor units – few fibers ____________activated - crude/gross movements = big__________________________ motor units – lots of units ____________activated 2 10/19/2009 Localization and distribution of motor neurons in the spinal cord Somatosensory (mechano) and nociceptive (pain) receptors Glabrous skin: skin_________________________________ that does not have hair follicles (hairless) Hairy skin: skin__________________________________ that covers the rest of the body There are 3 groups of somatosensory receptors: 1. ______________Nociception 2. ______________Hapsis 3. ______________ Proprioception Epidermis Dermis 3 10/19/2009 Somatosensory pathway from receptors to somatosensory (primary) cortex: How pain reaches the somatosensory cortex 4 10/19/2009 How is the phenomenon of “referred pain” produced? Arm and shoulder pain “referred” from heart pain receptors during heart attack. MONOSYNAPTIC STRETCH REFLEX Involves: - _________________intrafusal muscle - _________________________________muscle spindle receptor (signals stretch) - ________________________________________spindle afferent neuron (pseudounipolar __________________________sensory neuron) - ______________________________intrafusal (gamma) motor neuron - ____________________________________extrafusal muscle and motor neuron Watch stretch reflex movie 5 10/19/2009 How muscle spindles work! - Gamma motor neurons provide the ________overall ________________________________sensitivity of the muscle spindles - without gamma motor neurons, the spindles would become __________________________“slack” and unresponsive to_______________ stretch. - gamma motor neurons function __________to adjust the length_______________________ of intrafusal muscles titto an appropriate degree of tension Gamma motor neurons Muscle spindles Extrafusal muscle Spindle “slack” - insensitive to strech Spindle “tight” - ready to respond to strech POLYSYNAPTIC REFLEXES: EXAMPLE OF WITHDRAWAL FROM PAIN - reflexes requiring interneurons_________________________ in the spinal cord - concept of _______________________________antagonistic muscles (flexor vs. ____________________________extensor muscles) - ex., biceps vs. triceps of arms - reciprocal innervation (excitatory vs. inhibitory) -excitatory ________________________________________ and inhibitory interneurons work ____________________________________together to withdraw limb from pain. 6 10/19/2009 CROSSED EXTENSOR REFLEX Think of this reflex as being ____________“connected” with previous polysynaptic withdrawal reflex For example, if flexion reflex triggered in one leg, extensor___________________________________ reflex is triggered in other leg All thi s h appens _________________________;attht the leve l o fthf the sp ina l cor d the brain has nothing to do with it. This serves to: - _______________________________________help remove or push entire body away from _______________________painful stimulus; - _______________________________________help restore balance when flexed leg is _____________________withdrawn. An example of a complex sensorimotor reflex is ________.walking - spinal cat when placed on a treadmill can ______________________________________initiate normal walking when provided with ______________________________________somatosensory feedback of treadmill. GOLGI TENDON REFLEX or how not to shred your muscles and bones! Golgi Tendon Organ: ______________________receptor organ sensitive ________________________________________to stretch and located at the junction of the _____________________________tendon and muscle. - only contacts ________________________inhibitory interneurons. - if maximally activated, completely___________________ inhibits ________________________________alppyha motor neuron activity. - helps prevent tearing of muscles and tendons from bone Golgi____________ tendon organ_______ ____________________Pseudounipolar _________neuron alpha______________________ motor neuron inhibitory_________________________ interneuron 7.
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