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Muscles and Motor Locomotion

  • Muscle Movement

    • Muscles do work by contracting

      • Skeletal muscles come in antagonistic pairs

        • Flexor vs. extensor

      • Contracting = shortening

        • Move skeletal parts

      • Tendons

        • Connect bone to muscle

      • Ligaments

        • Connect bone to bone

  • Structure of Striated Skeletal Muscle

    • Muscle fiber

      • Muscle cell

        • Divided into sections = sarcomeres

    • Sarcomere

      • Functional unit of muscle contraction

      • Alternating bands of thin (actin) and thick (myosin) protein filaments

  • Actin

    • Complex of fibers

      • Brain of actin molecules and tropomyosin fibers

        • Tropomyosin fibers secured with troponin molecules

  • Myosin

    • Single protein

      • Myosin molecule

        • Long protein with globular head

  • Thick and thin filaments

    • Myosin tails aligned together and heads pointed away from center of sarcomere

  • Interaction of Thick and Thin Filaments

    • Cross bridges

      • Connections formed between myosin heads and actin

      • Cause muscle to shorten

  • Muscle Cell Organelles

    • Sarcoplasm

      • Muscle cell cytoplasm

      • Contains many mitochondria

    • Sarcoplasmic reticulum

      • Organelle similar to ER

        • Network of tubes

    • Stores Ca2+

      • Ca2+ released from sarcoplasmic reticulum through channels

      • Ca2+ restored to sarcoplasmic reticulum by Ca2+ pumps

        • Pump Ca2+ from cytosol

        • Pumps use ATP

  • Muscle at Rest

    • Interacting proteins

      • At rest, troponin molecules hold tropomyosin fibers, so that they cover the myosin-binding sites on actin

        • Troponin has Ca2+ binding sites

  • Motor Neurons

    • Motor neuron triggers muscle contraction

      • Release acetylcholine (Ach) neurotransmitter

  • Nerve Trigger of Muscle Action

    • Nerve signal travels down T-tubule

      • Stimulates sarcoplasmic reticulum of muscle cell to releases stored Ca2+

      • Flooding muscle fibers with Ca2+

  • Ca2+ Triggers Muscle Action

    • At rest, tropomyosin blocks myosin-binding sites on actin

      • Secured by troponin

    • Ca2+ binds to troponin

      • Shape change accuses movement of troponin

      • Releasing tropomyosin

      • Exposes myosin-binding sites on actin

  • How Ca2+ Controls Muscle

    • Sliding filament mode

      • Exposed actin binds to myosin

      • Fibers slide past each other

        • Ratchet system

      • Shorten muscle cell

        • Muscle contraction

      • Muscle doesn’t relax until Ca2+ is pumped back into sarcoplasmic reticulum

        • Requires ATP

  • How It All Works

    • Action potential causes Ca2+ release from sarcoplasmic reticulum

      • Ca2+ binds to troponin

    • Troponin moves tropomyosin, uncovering myosin binding site on actin

    • Myosin bonds actin

      • Uses ATP to ratchet each time

      • Releases and bonds to next actin

    • Myosin pulls actin chain along

    • Sarcomere shortens

      • Z discs move closer together

    • Whole fiber shortens

      • Contraction

    • Ca2+ pumps restore Ca2+ to sarcoplasmic reticulum

  • Fast Twitch and Slow Twitch Muscles

    • Slow twitch muscle fibers

      • Contract slowly, but keep going for a long time

        • More mitochondria for aerobic respiration

        • Less sarcoplasmic reticulum

          • Ca2+ remain in cytosol longer

      • Long distance runner

      • “Dark” meat = more blood vessels

    • Fast twitch muscle fibers

      • Contract quickly, but get tired rapidly

        • Store more glycogen for anaerobic respiration

      • Sprinter

      • “White” meat

  • Muscle Limits

    • Muscle fatigue

      • Lack of sugar

        • Lack of ATP to restore Ca2+ gradient

      • Low O2

        • Lactic acid drops pH which interferes with protein function

      • Synaptic fatigue

        • Loss of acetylcholine

    • Muscle cramps

      • Build up of lactic acid

      • ATP depletion

      • Ion imbalance

        • Massaging or stretching increases circulation

  • Diseases of Muscle Tissue

    • ALS

      • Amyotrophic lateral sclerosis

      • Lou Gehrig’s disease

      • Motor neurons degenerate

    • Myasthenia gravis

      • Autoimmune

      • Antibodies to acetylcholine receptors

  • Botox

    • Bacteria Clostridium botulinum toxin

      • Blocks release of acetylcholine

      • Botulism can be fatal

  • Rigor Mortis

    • No life, no breathing

    • No breathing, no O2

    • No O2, no aerobic respiration

    • No aerobic respiration, no ATP

    • No ATP, no Ca2+ pumps

    • Ca2+ stays in muscle cytoplasm

    • Muscle fibers continually contract

    • Eventually, tissues breakdown and relax

      • Measure of time of death

Muscles and Motor Locomotion

  • Muscle Movement

    • Muscles do work by contracting

      • Skeletal muscles come in antagonistic pairs

        • Flexor vs. extensor

      • Contracting = shortening

        • Move skeletal parts

      • Tendons

        • Connect bone to muscle

      • Ligaments

        • Connect bone to bone

  • Structure of Striated Skeletal Muscle

    • Muscle fiber

      • Muscle cell

        • Divided into sections = sarcomeres

    • Sarcomere

      • Functional unit of muscle contraction

      • Alternating bands of thin (actin) and thick (myosin) protein filaments

  • Actin

    • Complex of fibers

      • Brain of actin molecules and tropomyosin fibers

        • Tropomyosin fibers secured with troponin molecules

  • Myosin

    • Single protein

      • Myosin molecule

        • Long protein with globular head

  • Thick and thin filaments

    • Myosin tails aligned together and heads pointed away from center of sarcomere

  • Interaction of Thick and Thin Filaments

    • Cross bridges

      • Connections formed between myosin heads and actin

      • Cause muscle to shorten

  • Muscle Cell Organelles

    • Sarcoplasm

      • Muscle cell cytoplasm

      • Contains many mitochondria

    • Sarcoplasmic reticulum

      • Organelle similar to ER

        • Network of tubes

    • Stores Ca2+

      • Ca2+ released from sarcoplasmic reticulum through channels

      • Ca2+ restored to sarcoplasmic reticulum by Ca2+ pumps

        • Pump Ca2+ from cytosol

        • Pumps use ATP

  • Muscle at Rest

    • Interacting proteins

      • At rest, troponin molecules hold tropomyosin fibers, so that they cover the myosin-binding sites on actin

        • Troponin has Ca2+ binding sites

  • Motor Neurons

    • Motor neuron triggers muscle contraction

      • Release acetylcholine (Ach) neurotransmitter

  • Nerve Trigger of Muscle Action

    • Nerve signal travels down T-tubule

      • Stimulates sarcoplasmic reticulum of muscle cell to releases stored Ca2+

      • Flooding muscle fibers with Ca2+

  • Ca2+ Triggers Muscle Action

    • At rest, tropomyosin blocks myosin-binding sites on actin

      • Secured by troponin

    • Ca2+ binds to troponin

      • Shape change accuses movement of troponin

      • Releasing tropomyosin

      • Exposes myosin-binding sites on actin

  • How Ca2+ Controls Muscle

    • Sliding filament mode

      • Exposed actin binds to myosin

      • Fibers slide past each other

        • Ratchet system

      • Shorten muscle cell

        • Muscle contraction

      • Muscle doesn’t relax until Ca2+ is pumped back into sarcoplasmic reticulum

        • Requires ATP

  • How It All Works

    • Action potential causes Ca2+ release from sarcoplasmic reticulum

      • Ca2+ binds to troponin

    • Troponin moves tropomyosin, uncovering myosin binding site on actin

    • Myosin bonds actin

      • Uses ATP to ratchet each time

      • Releases and bonds to next actin

    • Myosin pulls actin chain along

    • Sarcomere shortens

      • Z discs move closer together

    • Whole fiber shortens

      • Contraction

    • Ca2+ pumps restore Ca2+ to sarcoplasmic reticulum

  • Fast Twitch and Slow Twitch Muscles

    • Slow twitch muscle fibers

      • Contract slowly, but keep going for a long time

        • More mitochondria for aerobic respiration

        • Less sarcoplasmic reticulum

          • Ca2+ remain in cytosol longer

      • Long distance runner

      • “Dark” meat = more blood vessels

    • Fast twitch muscle fibers

      • Contract quickly, but get tired rapidly

        • Store more glycogen for anaerobic respiration

      • Sprinter

      • “White” meat

  • Muscle Limits

    • Muscle fatigue

      • Lack of sugar

        • Lack of ATP to restore Ca2+ gradient

      • Low O2

        • Lactic acid drops pH which interferes with protein function

      • Synaptic fatigue

        • Loss of acetylcholine

    • Muscle cramps

      • Build up of lactic acid

      • ATP depletion

      • Ion imbalance

        • Massaging or stretching increases circulation

  • Diseases of Muscle Tissue

    • ALS

      • Amyotrophic lateral sclerosis

      • Lou Gehrig’s disease

      • Motor neurons degenerate

    • Myasthenia gravis

      • Autoimmune

      • Antibodies to acetylcholine receptors

  • Botox

    • Bacteria Clostridium botulinum toxin

      • Blocks release of acetylcholine

      • Botulism can be fatal

  • Rigor Mortis

    • No life, no breathing

    • No breathing, no O2

    • No O2, no aerobic respiration

    • No aerobic respiration, no ATP

    • No ATP, no Ca2+ pumps

    • Ca2+ stays in muscle cytoplasm

    • Muscle fibers continually contract

    • Eventually, tissues breakdown and relax

      • Measure of time of death

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