Four Stages of Muscle Contraction, Sliding Filament Theory

________ allow for the rapid transmission of action potentials throughout the muscle fibre.

‘T’ tubules

Energy released from ________ is used to pull the actin filaments towards the centre of the sarcomere.

ATP

________ has a high affinity for calcium ions.

Troponin

The ________ bind to troponin molecules on actin filaments.

calcium ions

The ________ action potential travels from the brain via a motor neurone to the motor end-plate, which creates a muscle action potential over the muscle fibres sarcoplasm.

neural

What are the four stages of muscle contraction following rest?

Excitation, contraction, recharge, relaxation.

Myosin is the ________ protein filament found in the myofibril

thick

Actin is the ________ protein filament found in the myofibril.

thin

Exam Question: Using the sliding filament theory, summarise the process of a muscle contraction. (6-8 marks).

Acetylcholine is released from neurotransmitters in the synapse as a response to a nervous impulse. These bind to acetylcholine receptors. This allows sodium ions, Na+ to diffuse across the sarcolemma and down the T tubules which depolarises the muscle cell (action potential). This triggers the release of calcium ions (Ca++) which bind to troponin, causing tropomyosin to leave the actin binding sites. Energy is released from the dissociation of ATP. This allows it to cock and bind to the actin, forming actomyosin cross-bridges. This is known as a power stroke, which results in the muscle shortening. This process repeats as long as there is sufficient Ca++ and ATP.

The binding of calcium ions to troponin results in ________ leaving the actin binding sites.

troponin