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
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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
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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
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Somatosensory pathway from receptors to somatosensory (primary) cortex:
How pain reaches the somatosensory cortex
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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
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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.
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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 level of fth the spi nal cord 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
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