7. When an action potential arrives via a neurone, at nmj, calcium ions are released from the sarcoplasmic reticulum - these calcium ions diffuse through the sarcoplasm and bind to troponin molecules (bead structure on tropomyosin) - this binding
Changes the shape of the troponin, which moves the tropomyosin away from the binding sites on the actin - this means cross bridges can form allowing the power stroke and muscle contraction to occur
A myosin head group can't attatch to any such binding site, cross bridges can't form and muscle contraction can't occur
8. In striated muscle, each muscle is attached to the skeleton by tendons and is under voluntary control, each muscle is composed of a series of bundles, these are
Groups of muscle fibres surrounded by connective tissue containing blood vessels and nerves
Contractile units of the muscle and are arranged end to end for the entire length of the myofibril
A large number of myofibrils within the sarcoplasm they, like fibres, exhibit a striated pattern under the microscope
9. Calcium ions allow muscles to contract, without them, the binding sites for the myosin head group on the actin fibre are covered by tropomyosin subunits, this means that
A myosin head group can't attatch to any such binding site, cross bridges can't form and muscle contraction can't occur
Changes the shape of the troponin, which moves the tropomyosin away from the binding sites on the actin - this means cross bridges can form allowing the power stroke and muscle contraction to occur
10. The pattern of banding on myofibrils is caused by the sarcomeres, these are the smallest
A large number of myofibrils within the sarcoplasm they, like fibres, exhibit a striated pattern under the microscope
Contractile units of the muscle and are arranged end to end for the entire length of the myofibril
Groups of muscle fibres surrounded by connective tissue containing blood vessels and nerves
11. In the second stage of 'The power stroke', upon binding to the actin, the myosin heads change shape, pulling the thin actin filaments towards the centre of the sarcomere, so they
Attaching themselves to the binding sites on actin
Overlap more with the thick filament. This stage is specifically known as the power stroke
ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
12. Tropomyosin is
Wound around the actin, reinforcing it
bound to tropomyosin, each complex consists of three polypeptides, one binds to actin, one to tropomyosin (wound around actin) and one to calcium ions
13. In the first stage of 'The power stroke', myosin head groups on the myosin filaments form cross brigdes with the surrounding filaments by
Attaching themselves to the binding sites on actin
ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
Overlap more with the thick filament. This stage is specifically known as the power stroke
14. A cross bridge is
The name given to the attatchment formed by a myosin head binding to a binding site on an actin filament
Wound around the actin, reinforcing it
15. Outline the structure of actin
The actin filament is formed from a helix of actin sub-units, each contains a binding site for the myosin heads, two other proteins, tropomyosin and troponin are attached to the actin fibre
ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments
16. Myofibrils contained two different types of filaments: thin filaments made predominantly of actin, and
Found at the centre of the myosin filaments, no myosin heads are in this region of myosin filaments
Thick filaments made of myosin
Together shortening the sarcomere which is the basis of muscle contraction
17. Outline the structure of myosin
The myosin filament is formed from a number of myosin proteins wound together, each ends in a myosin head, which contains an ATPase
ADP and Pi, this entire process repeats, causing the sarcomere to contract fully
18. The structure of skeletal muscle goes from muscle, to bundle, to fibre, to myofibril, to sarcomeres to
Protein filaments
Together shortening the sarcomere which is the basis of muscle contraction
19. ATP supply is maintained by aerobic respiration, anaerobic respiration and transfer from creatine phosphate in the muscle cell sarcoplasm -
The phosphate group from creatine phosphate can be transfered to ADP to form ATP quickly by the enzyme creatine phosphotransferase - this enables muscle contraction for a further 2 - 4 seconds
1-2 seconds worth of contraction
20. There is only sufficient ATP available in a muscle fibre for around
1-2 seconds worth of contraction
The phosphate group from creatine phosphate can be transfered to ADP to form ATP quickly by the enzyme creatine phosphotransferase - this enables muscle contraction for a further 2 - 4 seconds
