Top Banner

of 33

Physiology of Skeletal Muscle by Dr. Roomi

Apr 04, 2018

Download

Documents

Mudassar Roomi
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    1/33

    Mechanism of contraction of

    Skeletal musclein the light of its structure

    By

    Dr. Mudassar Ali Roomi (MBBS, M. Phil)

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    2/33

    Muscle Tissue

    Skeletal Muscle

    Cardiac Muscle

    Smooth Muscle

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    3/33

    Skeletal Muscle

    Long cylindrical cells

    Many nuclei per cell

    Striated

    Voluntary

    Rapid contractions

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    4/33

    Cardiac Muscle

    Branching cells

    One or two nuclei per cell

    Striated

    Involuntary

    Medium speed contractions

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    5/33

    Smooth Muscle

    Fusiform cells

    One nucleus per cell

    Nonstriated

    Involuntary

    Slow, wave-like contractions

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    6/33

    Skeletal muscle

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    7/33

    SKELETAL MUSCLE

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    8/33

    Z line Z line

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    9/33

    THICK AND THIN FILAMENTS

    From surface of thickfilaments projectionsarisecross-bridges.

    In centre of sarcomere,

    thick filaments have noprojections (H zone).

    The thin & thick filamentscontain contractile proteins:

    The thick filaments contain

    myosin protein. The thin filaments contain

    actin, tropomyosin &troponin proteins.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    10/33

    Myosin protein: in thick filaments

    In 1 thick filament 200myosin molecules.

    Molecular wt. of eachmyosin molecule = 480,000.

    Each myosin molecule has 6polypeptide chains: 2 heavychains & 4 light chains.

    2 heavy chains are coiledtogether double helix.

    At 1 end two heavy chainsare folded head portion.In head portion 4 lightchains.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    11/33

    Myosin protein: in thick filaments (cont)

    3 parts of myosin molecule:

    Head

    Arm / Neck

    Body / Tail

    There are 2 points in myosinmolecule at which molecule ishighly flexibleHINGES:

    i) Between head & arm / neck

    ii) Between arm & body / tail

    Tail/body is present in thickfilaments.

    Arm & head protrude out fromsurface of filament as cross bridges.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    12/33

    Myosin protein: in thick filaments (cont)

    Cross bridges are absent in

    centre.

    In the centre of filament is tail

    only, while cross bridges areformed by arm & head at

    periphery as cross bridges.

    In myosin head there are 2important sites:

    Actin binding site.

    Catalytic site.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    13/33

    Thin filaments

    3 contractile proteins are present

    here:

    1) ACTIN: Consist of 2 F-actin

    strands. Each strand consist of

    polymerized G actin molecules. Attached to each G actin

    molecule is a molecule of ATP, &

    point of attachment is active

    site on actin strand.

    Active sites are present at every2.7 nm.

    Each G actin has molecular wt.

    42,000.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    14/33

    Thin filaments (cont)

    2) TROPOMYOSIN:

    Consist of 2 strands, with 70,000

    molecular wt.

    Tropomyosin strands at rest

    physically cover active sites onactin filaments.

    3) TROPONIN:

    Attached to tropomyosin at

    intervals.

    It has 3 components: Troponin C, Troponin T, Troponin

    I.

    Molecular wt. 18,000 35,000.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    15/33

    Thin filaments (cont)

    Troponin C Affinity for calcium ions.

    Troponin T Affinity for tropomyosin.(through which troponin complex isattached to tropomyosin)

    Troponin I Affinity for actin strands.

    It is the bond between troponin I &Actin, which keeps tropomyosin strandsin such a position that these physicallycover active sites of actin filaments.

    During muscle contraction this bondis broken.

    Tropomyosin-troponin complex =relaxing protein (keeps muscle relaxedby covering physically the active sites).

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    16/33

    Components of Troponin

    (C,T,I)

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    17/33

    Molecular Mechanism of skeletal muscle

    contraction:

    Muscle is first excited ordepolarized and then contratcs(EXCITATION-CONTRACTIONCOUPLING).

    Action potential enters deep into

    muscle fiber from T-Tubulesaround which are terminalcisternae.

    So depolarization spreads from TTubules terminal cisternae.

    Membrane of terminal cisternaeis depolarized opening ofvoltage gated calcium channels calcium ions move out of theterminal cisternae.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    18/33

    SKELETAL MUSCLE

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    19/33

    When it is in sarcoplasm, calcium is utilized by

    troponin C to initiate muscle contraction

    (excitation-contraction coupling).

    4 calcium ions can bind with 1 molecule of

    troponin C it breaks the bond between

    troponin I & Actin tropomyosin strands

    become loose they reach a deeper position active sites on actin are uncovered.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    20/33

    Muscle contraction involves power strokes.

    Before contraction, a molecule of ATP becomesattached to myosin head.

    It is hydrolyzed to ADP to liberate energy stored inmyosin head.

    When active site is uncoveredmyosin head bindswith active site on actin.

    With stored energy, there is power stroke. At hinges, myosin molecule moves & carries along

    actin / thin filaments.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    21/33

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    22/33

    With energy of 2nd molecule of ATP,it detaches & move back to originalposition 2nd power stroke aseries of power strokes slidingof actin over myosin so that power

    stroke is towards centre ofsarcomere shortening ofsarcomere or contraction ofmuscle.

    Each cross bridge operates

    independently.

    Greater the number of crossbridges coming in contact withmyosin head greater is force ofcontraction.

    When muscle is stretchedmorenumber of cross bridges attachedwith actin filaments increasedcontraction force.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    23/33

    Binding Site Tropomyosin

    Troponin

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    24/33

    Myosin

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    25/33

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    26/33

    FRANK-STARLING LAW:

    Greater the initial length ofmuscle, greater is force ofcontraction up to certainlimits.

    Cardiac muscle also obeysthis law ( increased venousreturn increased lengthof cardiac muscle

    increased fillingincreasedemptying by contraction ofventricle.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    27/33

    Contraction is initiated bycalcium ions.

    As long as calcium ion issufficient in sarcoplasm

    muscle contraction continues. Normally in the wall of

    longitudinal tubule, there iscalcium pump.

    Calcium is released fromterminal cisternae but ispumped back by calciumpump & when calcium is lowin sarcoplasmmusclerelaxes.

    So, even to produce musclerelaxation, we need ATPbecause calcium pump needsATP.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    28/33

    Sarcomere Relaxed

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    29/33

    Sarcomere Partially Contracted

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    30/33

    Sarcomere Completely Contracted

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    31/33

    SLIDING FILAMENT MODEL OF MUSCLE CONTRACTION

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    32/33

    Histological changes during muscle

    contraction:

    RELAXED MUSCLE:

    2-2.5 m length of sarcomere.

    AFTER CONTRACTION:

    1-1.5 m length of sarcomere.

    Length of A band constant.

    Length of I band constant. Z Membranes become closer.

    H zone decreases / disappear

    Sliding of thin over thickfilaments.

    Length of individual filamentsremain the same.

  • 7/29/2019 Physiology of Skeletal Muscle by Dr. Roomi

    33/33