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.