A summary of muscles in the Human Biology A2 module - Bodies and Cells in and out of Control.

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Muscles - Anatomy

STRATED MUSCLE; also skeletal as attached to bones and voluntary as you can control when it contracts for movement.

Sarcolemma = membrane of fibres  Myosin = thick with hooks  Actin = two strands and thin

Antagonistic - work together with opposite jobs

Synergistic - work together with same aim

Fast twitch - quick spurts of activity, anerobic repiration, little myoglobin, few mitochondria. e.g. eyelid movement

Slow twitch - endurance activity, arobic respiration, large amounts of myoglobin, many mitochondria. e.g. posture muscles.

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Muscles - Bonding within a myofibril

Myosin filaments lie in a line parallel to each other, bases attached at the M - line. Actin filaments alignat the Z - line. Both overlap producing a striped appearance in the myofibril.

Upon contraction: 

A band (actin & myosin) stays the same length as always the length of myosin. 

H zone (myosin) shortens as more actin slides into A band.    

I band (actin) shortens as actin slides into A band.

Z lines (run through centre of I band) move closer together as  ore actin slides under myosin.

Sarcomere is the distance between the Z lines.

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Muscles - Sliding Filament Theory

  • Tropomyosin cover myosin head binding sites. Mysosin head has been energised by ATP (ADP remains).
  • Ca2+ travel from t tubules + pull away tropomyosin, exposing the binding sites on the actin.
  • Myosin head then binds to site on actin.
  • Myosin head swivels to a different angle, pushing actin into A band + releases ADP.
  • New ATP detaches head.
  • Myosin head resumes normal position as it is re-energised (ATP ==> ADP + Pi).
  • Ca2+ activates ATPase for the above reaction.
  • The process repeates.
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