6.3 Skeletal muscles

• muscles act in antagonistic pairs
• tendons attach skeletal muscles to bones
• ligaments attach bones to other bones
• pairs of skeletal muscles contract and relax to move bones at a joint
• in an antagonistic pairs what does the agonist muscle do?

  contracts
• in an antagonistic pairs what does the antagonist muscle do?

  relax
• skeletal muscle is made up of long muscle fibres
• the sarcolemma is the cell membrane of muscle fiber cells
• the sarcoplasm is a muscle cell's cytoplasm
• transverse tubules are bits of the sarcoplasm that fold inwards
• the sarcoplasmic reticulum stores and releases calcium ions
• what does multinuleate mean?

  Having multiple nuclei
• thick myofilaments are made up of myosin
• thin myofilaments are made up of actin
• A -bands are dark bands of myofibril that contain thick myosin filaments and some overlapping thin actin filaments
• I-bands are light bands that contain thin actin filaments
• a myofibril is made up of many short units called sarcomeres
• a Z-line marks the end of each sarcomere
• a M-line is at the middle of each sarcomere
• The H-zone only contains myosin filaments
• sarcomeres contract by myosin and actin filaments sliding over each other
• thick myofilaments are made up of myosin
• thin myofilaments are made up of actin
• dark bands contain some thick myosin filaments and some actin
• dark bands are called A-bands
• light bands contain only thin actin filaments
• light bands are called I-bands
• a myofibril is made up of many short units called sarcomeres
• the ends of each sarcomere are marked with a z-line
• the middle of each sarcomere has a M-line
• the H-zone contains only myosin filaments
• what theory explains muscle contraction?

  sliding filament
• in a contracted sarcomere what happens to the A bands?

  stays the same length
• in a contracted sarcomere what happens to the I bands?

  Shorten
• in a contracted sarcomere what happens to the H zone?

  gets shorter
• in a contracted sarcomere what is the overall effect on the size of the sarcomere?

  gets shorter
• myosin filaments have globular heads and binding sites
• each myosin has a binding site for ATP and for actin
• in a resting muscle binding sites are blocked by tropomyosin
• slow twitch muscle fibres contract slowly, fast twitch muscle fibres contract quickly