Explain how skeletal muscle contracts.

Muscle fibers are comprised of elongated myofibrils. A myofibril is made of repeating chains of sarcomeres which have no nucleus but have myosin and actin filaments which are able to slide past each other during muscle contraction. As a result, Z discs may move closer together and the H zone may shorten, but the actin and myosin filaments always remain the same size. Muscle contraction occurs when an action potential reaches the end of a motor neuron. Using neurotransmitters (primarily acetylcholine) at the neuromuscular junction, the action potential is transferred to the muscle fibre as the sarcoplasmic reticulum rapidly releases Ca 2+ ions. These calcium ions cause conformational changes in the myosin and actin, exposing binding sites. Myosin heads then bind to sites on the actin and form relatively stable cross-bridges. By reforming these cross-bridges at different spots on the actin filament using ATP, the actin filaments at either side of the H zone move closer together towards the M band. ATP causes the release of myosin heads from actin, whereas its conversion to ADP + Pi changes the angle of the myosin head. As this cycle repeats, the sarcomeres are shortened, allowing for movement of skeletal muscles.

Answered by Daniel R. Biology tutor

1398 Views

See similar Biology IB tutors

Related Biology IB answers

All answers ▸

Explain the events that occur in cells that result in the production of genetically identical nuclei (8 marks)


What are the differences between normal cells and cancer cells?


Explain the light-dependent reaction of photosynthesis


Explain what 5' and 3' ends mean in regards to DNA structure?


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences