Skeletal Muscle: contraction, tension, fibre

• Myofilament is composed of actin and myosin.
• What is actin?

  It forms a thin filament, structural scaffold that runs along the myofilament.
• What is myosin?

  It forms a thick filament and acts as a motor molecule attaching to actin and generating a force to pull.

  
• Myosin and Actin bind together when calcium is present forming cross bridges and allowing contraction to occur.

  
• How many stages in Cross Bridge Cycling?

  5
• What is the first stage of cross bridge cycling?

  The molecule on ATP binds to the myosin, which preps for it to be released energy into myosin. the binding causes head myosin to release actin = no more cross bridge.

  
• What happens in second stage cross bridge cycling?

  The myosin burns the head of ATP to make energy. Then stores the energy by changing the shape of myosin, ready to pull on actin again.

  
• What happens in the third stage of cross bridge cycle?

  The energised myosin head can bind to actin, which forms a cross bridge.

  
• What happens in the final stage of cross bridge cycle?

  The P is released. Myosin heads to change conformation, resulting in power stroke. The filaments slide past each other.
• What are the two determinents of skeletal muscle force generation?

  1. Numbers of muscle fibre required.
  2. Rate which muscle is stimulated (frequency)
• Explain Number of Muscle fibres required?

  It is activated by the regulation of how many neurons are active at one time. A small number of neuron's tends tp produce low force from the muscle, which increases as more force is added.
• What is frequency of stimulation?

  It is a single action potential = a pulse of Ca2+ release into the cytoplasm and short period twitch.

  Many action potentials fired in rapid sequences = sustained release of Ca2+ from the SR.

  Eventually we reach maximal signalling and contraction capability of the muscle, which the force with plateau.
• What are the three types of length tension relationship?

  Optimal, Stretched and Slack.
• What is optimal of LTR?

  Each muscle has an optimal length where it will be strongest, and when either longer or shorter than that length, it will be weaker, which results of the changing overlap actin and myosin filaments.
• What fibre is this?

  A) Fibre

  
• What fibre is this?

  A) Slow fibres

  
• Fast fibres fatigue quick, Slow fibres are steady.