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.
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.
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.
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.