Muscle Contraction

Muscle Contraction

Sliding Filament Model

• Muscle contraction happens due to the sliding action of actin and myosin filaments within sarcomeres.
• This process is known as the sliding filament theory.
• During muscle contraction, myosin heads form cross-bridges with actin filaments and change their shape.

Role of ATP

• ATP provides the energy required for muscle contraction by triggering the shape change in myosin heads.
• Myosin heads bind ATP and hydrolyse it to ADP and an inorganic phosphate, releasing energy.
• This energy enables the myosin to flex and pull the actin filament towards the centre of the sarcomere.

Regulation of Muscle Contraction

• The role of calcium ions and the proteins tropomyosin and troponin is crucial in regulating muscle contraction.
• In a resting muscle, the actin binding sites are covered by tropomyosin.
• Calcium ions bind to troponin on the tropomyosin molecule, causing tropomyosin to move from the actin active sites.
• This allows myosin heads to bind to actin, beginning muscle contraction.

Role of Neuromuscular Junctions

• Neuromuscular junctions are the synapses between a motor neuron and a skeletal muscle fibre.
• Action potentials in the motor neuron result in the release of acetylcholine, a neurotransmitter, at the neuromuscular junction.
• Acetylcholine binds to receptors on the muscle cell membrane, triggering an action potential in the muscle cell.
• This leads to the release of calcium ions into the cytoplasm, starting the process of muscle contraction.

Relaxation of Muscles

• The muscle relaxes once the action potential stops, and calcium ions are pumped out of the cytoplasm and back into the sarcoplasmic reticulum.
• Tropomyosin again covers the actin binding sites, preventing any interaction between actin and myosin. This results in muscle relaxation.