Sliding Filament theory Flashcards
What is a myofibril?
Muscles are made up of thin fibres called myofibrils and each myofibril contains a series of sarcomeres which are the basic unit of muscle fibres.
What is in a sarcomere?
Sarcomeres contain two proteins called Actin and Myosin.
What happens in a sarcomere during muscle contraction?
Myosin heads attach to Actin to form cross bridges. The myosin filaments then pull the Actin filaments towards them using a power stroke.
What makes up a sarcomere?
Sarcomeres also contain a:
H ZONE - the centre of the sarcomere that has only myosin filaments.
Z LINE - the lines that separate each sarcomere from the next that attach to actin filaments.
A BAND - the area in between actin and myosin filaments where contraction takes place.
I BAND - the are at the end of the sarcomere where only actin filaments and the z line exist.
What happens pre-contraction?
At rest, the troponin and tropomyosin cover the actin so the myosin cannot bind to the actin. There are no calcium ions as they are regulated by the sarcoplasmic reticulum. Then, the nervous system sends an impulse to create action potential, acetylcholine is released and calcium is then released into the sarcomeres.
What happens during contraction?
Calcium binds to the troponin which pulls the tropomyosin away from Actin, allowing the myosin heads to attach to the action, making cross bridges. The myosin heads then conduct a power stroke using ATP and this movement pulls the actin towards the myosin. As the sarcomeres contract, the length of the myofibrils reduce bringing the muscle ends together. The H zone and I band disappear and the Z lines move closer together.
What happens at the end of contraction?
The nerve impulse stops which stops the release of acetylcholine and calcium. This means the troponin and tropomyosin recover the actin filaments. The muscle returns to its resting state causing the H zone, I bands and Z lines to expand and return to their original position.
