Muscle Contraction

Structure
1. Whole muscle
  1. Bundle of muscle fibre
    1. Single muscle fibre
      1. Muscle cells share nuclei called a sarcoplasm
      2. Myofibril
        Sarcomere
        Actin
        Thin two strands twisted together, globular protein
        Tropomyosin forms long threads that that are wound around the Actin filaments
        Myosin
        Thick long rod- shaped fibres with bulbous heads that project from it
        Made up of two types of protein; globular protein which makes up the two bulbous heads and fibrous protein which are arranged into a fillament
Contraction
1. Nervous control
  1. A action potential activates the contraction
    1. A action potential spreads across the actin filaments causing the tropomyosin molecules to pull away from the actin
      1. This leaves the binding sites on the actin clear the the tropomyosin blocks the binding sites
2. Sliding filament mechanism
  1. Actin
    1. Used as the anchor for the myosin molecule's bulbous head
  2. Myosin
    1. Myosin head attaches forms bonds to actin and then pulls itself along using them
    2. Nervous impulses move tropomyosin out of the way of the binding site
      1. Now the myosin heads can join with the binding sites on the actin filament
        The angle of the myosin head changes thus moving the actin filament as this happens the ADP is released
        ATP attaches to the myosin head causing the it to detach from the actin filament
        Calcium ions activate ATPase, which hydrolyses the ATP into ADP this releases energy used to return the muosin head to its orginal position
        The myosin head, now attached to a ADP molecule, will be reattached to the actin filament and so the cycle will begin again moving the actin filament further along
Neuromuscular Juction
1. Where a junction links a motor neuron and a skeletal muscle fibre
2. There are many of these junctions across the muscle to help create the contraction faster than if there was only one junction
3. When a impulse arrives at the junction the synaptic vesicles fuse with the presynaptic membrane and release their acetylcholine
  1. Acetylcholine diffuses to the postsynaptic membrane, making it more permeable to sodium ions which depolarise the membrane
    1. Acetylcholine is then broken down by acetylcholinesterase to ensure the muscle is not over stimulated
      1. The choline and ethanoic acid (acetyl) then diffuse back into the neuron where they recombine into acetylcholine using the energy produced by the mitochondria within the neurone
Muscle Relaxation
1. Nervous stimulation ceases so calcium ions are actively transported back into the endoplasmic reticulum using energy from the hydrolysis of ATP
  1. The reabsorption of calcium ions allows the tropomyosin to block the actin filament again
    1. Myosin are unable to bind to the actin

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Muscle Contraction

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	Created by xmishcharliex over 11 years ago