Muscles

Muscles

Synovial joints
1. muscles produce force by contraction
  1. therefore you'll require 2 muscles to make a joint move 2 ways
    1. when one muscle contracts, the other must relax
      1. coordination of oppositely pulling muscles
        ANTAGONISTIC
2. joints may be controlled by groups of muscles working together
  1. SYNERGISTS
3. i.e. elbow
Muscle Types
1. Cardiac muscle
  1. made of atrial and ventricular muscle
    1. striated
  2. powerful
    1. no fatigue
  3. excitory (conductive), contract feebly but conduct
  4. made of cells in rows, called intercalated disks
    1. form gap junctions, allows free flow of ions
      1. action potential --> v. quick
2. Involuntary (smooth) muscle
  1. controlled by autonomic nervous system
  2. not striated
  3. single nucleus
  4. contraction is slow
    1. no fatigue
  5. e.g. arterial walls, intestine (peristalsis), iris of eye (circular and radial)
3. Voluntary (skeletal) muscle
  1. made of myosin and actin
  2. multi-nucleated
  3. made of fibres which are covered by a cell surface membrane
  4. muscle cell cytoplasm = sarcoplasm
    1. many mitocondria and sarcoplasmic reticulum
  5. striated
  6. powerful
    1. but fatigues
myosin is a polypeptide with 2 attachment/binding sites complementary to ATP and actin
Actin is made of 2 types of polypeptide
1. 2 strands of actin (which has myosin binding sites)
2. Tropomyosin (blocks actin binding site for myosin)
3. Troponin (binds to Ca2+, actin and tropomyosin)
Sliding Filament Theory
1. 1. Action Potential travels down a motor neurone and triggers release of Ca2+ ions into muscles from sarcoplasmic reticulum
2. 2, Ca2+ combines with troponin
3. 3. Troponin changes shape
4. 4.Troponin pulls tropomyosin off actin, exposing actin binding site for myosin
5. 5. Myosin binds to actin and forms myosin actin crossbridges
6. 6. Myosin pulls the actin over it -- the POWER STROKE
7. 7. Myosin releases the actin and actin returns
  1. ATP is needed to form and break cross bridges
Neuromuscular junctions
1. 1. Action Potential arrives at neuromuscular junction
  1. 2.Vesicles containing ACh move and fuse with presynaptic membrane
    1. 3. Releases ACh by exocytosis
      1. 4. ACh diffuses across neuro muscular junction
        5. ACh binds to complementary receptors on postsynaptic membrane
        6. t-tubules carry depolarisation deep into the muscle. This causes sarcoplasmic reticulum to release Ca2+

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