4. Muscle contraction Flashcards
What are the three types of muscle?
Skeletal
Smooth
Cardiac
What is meant by the term contraction?
The ability of a muscle to actively shorten and develop tension
What are the structures that make up the muscle?
Muscle Fasciculus Fibre/cell Myofibril Sarcomere Filaments
Describe the actin filaments in the relaxed state?
The ends of actin filaments from Z discs barely overlap
Describe the actin filaments in the contracted state?
Actin filaments pulled inward, overlap to maximum extent
What are the features of the actin filaments?
Double stranded F-actin molecules comprising of polymerised G-actin molecules
2 strands of tropomyosin molecules
Troponin complex on each tropomyosin for contraction (binds to Ca2+)
How many myosin and actin filaments on each myofibril?
1500 myosin
3000 actin
Describe the first three steps of the sliding-filament mechanism
- Low Ca2+ conditions, tropomyosin blocks access to the myosin binding site of the actin
- In high Ca2+ conditions, Ca2+ binds to troponin
- The positions of troponin and topomyosin are altered on actin + myosin can now access its binding site on actin
complete the full theory
Describe what happens when the sarcomere length decreases
Unstretched muscle
Describe what happens when the sarcomere is at optimal resting length
Muscle can develop maximal tension
Describe what happens to increased sarcomere length?
Actin is pulled to end of myosin with no overlap. No tension
Describe excitation-contraction coupling in skeletal muscles
Action potential travels along a motor nerve to the neuromuscular junction
Nerve secretes small amount of acetylcholine
ACh opens channels on muscle membrane
Na+ flows into the cell – initiates an action potential
AP travels along muscle fibre membrane
Describe the T-tubule endoplasmic reticulum system?
Muscle membrane depolarized, AP flows rapidly through centre of fibre via the T-tubules. Sarcoplasmic Reticulum releases Ca2+
Rise in intracellular Ca2+ enables Ca2+-binding to troponin, tropomyosin moves and cross-bridge cycling occurs
Ca2+ actively pumped back into SR store. Relaxation
What causes the release of Calcium ions?
Action potential from Sarcoplasmic reticulum
What causes re-uptake of calcium ions?
Calcium pump