Sliding Filament Theory

Pre-Stages

  1. A muscle contraction starts in the brain where a signal is sent to the motor neuron.

  2. The impulse travels moves into the transverse tubules which causes calcium to be released from the sarcoplasmic reticulum

  3. Calcium binds to the actin and causes it to change shape so that it can interact with myosin

  4. The change in the shape allows myosin heads to form cross-bridges between the actin and myosin.

  5. Energy from the ATP is used to create a “power stroke“ between the two filaments. The actin filament slides inward and shortens or contracts the whole muscle

Questions:

  1. The motor unit consists of muscle fibers and a neuron.

  2. What neurotransmitter is needed to initiate a muscle contraction? acetylcholine

  3. What substance causes the actin to change shape? calcium

  4. How does myosin and actin interact with each other? cobine, the trigger for SF theory

  5. What substance provides the energy for muscle contraction? ATP

  6. Where is calcium released from? sarcoplasmic reticulum

  7. What is the gap between the neuron and muscle fiber called? neuromuscular junction

  8. Where are the two filaments found in muscles? actin & myosin

On the actin filament

  1. Calcium ions released from the sarcoplasmic reticulum bind to troponin and change tropomyosin’s shape. This exposes the actin-binding sites.

  2. Tropomyosin blocks actin binding sites so the muscle is relaxed.

  3. Calcium ions remain present so actin binding sites are still exposed.

On the myosin filaments

  1. ADP + Pi are bonded to the myosin heads. This means they are active and ready to bond if actin-binding sites are exposed.

  2. Active myosin heads are now able to bind with the newly exposed actin binding sites. This produces tension in the muscle.

  3. The myosin head changes shape as a result of binding to the actin filament This pulls the two filaments along one another. ADP + Pi are released as a result of this shape change

  4. ATP can now bind to the myosin head. This causes it to release from the actin.

  5. ADP breaks down to ADP + Pi and the cycle is able to repeat if provided with a ready supply of ATP.