Muscles

• Types of muscles


  • Skeletal - voluntary
  • Smooth - involuntary
  • Cardiac - involuntary
• Muscles


  • Able to contract
  • Able to possess extensibility
  • Able to possess elasticity
• Extensibility


  The ability to be stretched
• Elasticity


  The ability to return back to its original length after being stretched
• Contractibility


  The ability to become shorter
• Excitability


  The ability to react to a nerve impulse
• These 3 properties (extensibility, elasticity, contractibility) all work together to allow muscles to create movement
• Voluntary muscles


  Muscles that are able to be controlled to carry out a wide range of physical activities
• Involuntary muscles


  Muscles that are not under conscious control
• Smooth muscles


  • Found in many internal organs such as the stomach and intestines
  • Also known as involuntary muscles
  • When they contract, the diameter of the alimentary canal narrows, pushing the contents along
• Cardiac muscle


  • Also known as the heart muscle
  • When this muscle contracts, it reduces the space between the chambers of the heart, pumping the blood around the heart and into the blood vessels
• Muscles


  • Held together in bundles
  • Surrounded by a sheath of connective tissue called the perimysium
  • Allows adjacent bundles to slide easily over one another as they contract
  • Sheaths of connective tissue called epimysium hold the bundles together and taper to form the tendon
• With age


  • The amount of connective tissues increase
  • The increased amounts of connective tissue are also thought to contribute to the decrease in muscular strength
• Muscle cell (muscle fibre)

  An elongated cylinder containing cytoplasm, called the sarcoplasm
• Muscles


  • Excitability
  • Contractability
  • Extensibility
  • Elasticity
• Muscle contraction


  1. Stimulated by a nerve impulse

  2. Shorten in length

  3. Be stretched

  4. Return to original length
• Sliding filament theory


  Explains how muscle contraction occurs
• Muscles are the only tissues that have the ability to contract
• Muscle contraction


  1. Sarcomeres shorten

  2. Actin and myosin filaments slide over one another
• Z lines


  Protein discs in the middle of the thin filaments
• Sarcomere


  Distance between successive Z lines
• A band


  Length of the thick (myosin) filament
• H zone


  Middle of the A band, contains only thick filaments
• I band


  Distance between successive thick filaments, contains only thin filaments
• Muscle contraction


  1. Thin actin filaments slide over thick myosin filaments

  2. Z lines are drawn closer together

  3. Sarcomere is shortened
• Skeletal muscles


  Muscles attached to the bones of the skeleton by the fibrous, inelastic connective tissue called tendons
• Muscle contraction


  1. Muscles can only contract, they cannot push bones apart

  2. Muscles are grouped in pairs, one contracts to pull a bone in one direction, the other contracts to pull the bone in the opposite direction
• Agonist


  The muscle that causes the desired action
• Antagonist


  The muscle that produces movement in the opposite direction to the agonist
• Origin


  The end of the muscle fixed to the stationary bone
• Insertion


  The attachment to the moveable bone of the other end of the muscle
• Belly


  The fleshy portion between the tendons of the origin and the insertion
• Synergist


  Muscles that help the agonist, they may produce the same amount of movement or steady the joint to prevent unwanted movement
• Fixator


  A synergist muscle that acts as a stabiliser of one part of the body during the movement of another part
• Muscle tone


  Maintaining partial contractions of skeletal muscles, with many different fibres taking turns to contract
• Muscle tone holds many of our body parts in position