eguruchela

The Muscular tissue

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    • All muscle is made of many long, cylindrical fibres arranged in parallel arrays. These fibres are composed ofnumerous fine fibrils, called myofibrils.

    Muscle fibres contract (shorten) in response to stimulation, then relax (lengthen) and return to their uncontracted state in a coordinated fashion.

    Their action moves the body to adjust to the changes in the environment and to maintain the positions of the various parts of the body.

    The muscles play an active role in all body movements. Muscles are of three types as follows:

  • Skeletal
  • Smooth
  • Cardiac

    • Skeletal muscle

    The skeletal muscle tissue is closely attached to skeletal bones. In a typical muscle such as the biceps, striated (striped) skeletal muscle fibres are bundled together in a parallel fashion.

    A sheath of tough connective tissue encloses several bundles of muscle fibres.

    Skeletal mascular tissue

    Stuctural organization of Skeletal Muscle

    Muscle - It is a collection of fascicles.

    Fascicle - It is a collection of muscle cells.

    Muscle cell or fiber - It is collection of myofibrils plus other cell organelles.

    Myofibril - It is series of sarcomeres.

    Sarcomeres - Basic unit of muscle structure and function.

    Filaments - Thick filaments and thin filaments.

    Smooth muscle

    The smooth muscle fibres taper at both ends (fusiform) and do not show striations. The cell junctions hold them together and they are bundled together in a connective tissue sheath.

    The wall of internal organs such as the blood vessels, stomach and intestine contains this type of muscle tissue.

    Smooth muscles are involuntary as their functioning cannot be directly controlled.

    Skeletal mascular tissue

    The characteristics of smooth muscle

  • Non-striated. Actin and myosin have a diffuse organization.
  • Spindle-shaped cells with single and central nucleus.
  • When the muscle contracts, it may twist as it shortens.
  • Calmodulin is calcium binding protein (insted of troponin).
  • Little internal stores of calcium.
  • Functions over large range of muscle lengths.
  • Motor neuron connections are variable.
  • Sensitive to a number of hormones and neurotransmitters.

    • Cardiac muscle

    The cardiac muscle tissue is a contractile tissue present only in the heart. Cell junctions fuse the plasma membranes of cardiac muscle cells and make them stick together.

    The communication junctions (intercalated discs) at some fusion points allow the cells to contract as a unit (when one cell receives a signal to contract, its neighbours are also stimulated to contract).

    Skeletal mascular tissue

    Properties of muscle tissue

    Excitability ability to respond to stimuli
    Contractibility ability to contract
    Extensibility ability to stretch muscle without tearing of a muscle
    Elasticity ability to return to its normal shape