Describe the attachment of muscles and how they produce movement and provide support.

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John Paddison Assignment 3- Anatomy and Physiology- the Muscular system

Assignment 3 – Anatomy and Physiology – The Muscular system

Task 1

Describe the attachment of muscles and how they produce movement and provide support.

The functions of muscle are to contract and therefore produce movement, support of body parts and transport of materials within the body.    

Muscles move the bone and the nerve control them.  Muscles do other things besides moving bones.  There are three types of muscle are skeletal, cardiac, and smooth.  Other specialised, contractile cells include the myoepithelial cells that surround glandular tissue and the myofibroblast that participate in wound repair (contraction).    

  • Skeletal muscle moves the skeleton and organs like the tongue and eye.  It is under voluntary control.  Its highly organised contractile proteins give a striated appearance.
  • Cardiac muscle contracts the heart.
  • Smooth muscle does not have a striated appearance since its contractile apparatus is organised differently from that of the other muscle types.  It lines viscera, the gastrointestinal tract, the uterus, and the bladder.  It is also found in the walls of blood vessels and the respiratory area.

The skeletal muscle

Tissue organisation:

Individual skeletal muscle cells are called muscle fibres.  Muscle fibres are large and the nuclei reside along the cell boundary.  A basal lamina and connective tissue surround each muscle cell.  They are bound to each other and to surrounding tissue by connective tissue to form a gross ‘muscle’.  Cell junctions do not join skeletal muscle fibres.

 The endomysium consists of the basal lamina and thin connective tissue that surround individual muscle cells junctions.

The perimysium consists of sheets of connective tissue which separate the fibres into groups known as fascicles.

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The epimysium surrounds the groups of fascicles that contain the muscle.  Skeleton muscle is innervated and highly vascularised, due to its high energy needs, by penetration into the epimysium with branches into the peri- and endomysium.  Connective tissue transmits the mechanical force of muscle.  Tendons connect muscle to bone.  The myotendinous junction occurs at the end of the muscle cell where the terminal actin filaments connect to the plasma membrane.

Muscle fibres develop from the fusion of many muscle precursor cells called myoblasts.  Differentiation, which has been studied extensively, requires three stages.

  • Withdrawal from the cell cycle

  • Production and assembly of muscle-specific proteins
  • Cell fusion

Skeleton muscle fibres are mulinucleate cells that arise by fusion of mononucleate myoblasts.  The many nuclei are located at the periphery of the cell.  Mononucleate, satellite cells, associate with the muscle fibre and reside within the muscle basal lamina.  They promote limited regeneration of muscle in an adult.

The structure of striated muscle cells.  In the skeletal muscle structure is an example of how function follows from structure.  The muscle fibre structure is highly organised and easy to understand, the language is hard.  

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Muscle fibres contain many myofibrils, which are organised arrays of myofilaments.  Myofilaments are molecular filaments of two types.  Thick filaments that are composed principally of myosin, and thin filaments, which are composed of actin.

 

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Thick filaments are made of many myosin molecules.  Each myosin molecule contains two myosin heavy chains and two pairs of light chains.  Molecular heads make up the light chains.  The myosin molecules associate by means of their tails to form the thick chain.

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Thin filaments are made up from two chains of actin spiral wound around each other.  Thin filaments also contain other proteins including tropomyosin and troponin that directs contraction.

The release of many myofilaments produces the myofibril, which shows the striations.  The sarcomere is the basic contractile unit of a myofibril. Each myofibril contains many sarcomeres.

  • The Z-disk delineates the borders of sarcomeres.
  • Thin filaments attach to a Z-disc at their plus ends
  • Thick filaments are centred between the Z-discs.

Levers

A lever is a mechanical system that creates movement.  It either ...

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