Skeletal Muscles, Muscles, Nervous System

• What's a myofibril?

  Large,cell structure in a muscle that contains myosin and actin
• Sarcolemma


  The membrane of the muscle fibre
• Sarcomere


  Z line to Z line
• Sarcoplasm


  cytoplasm of a muscle cell
• How is the energy used in muscle contraction?

  For the movement of myosin heads For the reabsorption of calcium ions to the sarcoplasmic reticulum using active transport
• How is phosphocreatine involved in muscles?

  For active muscles, it acts as a phosphate store to generate ATP by combining with ADP when the rate of supply of Oxygen and ATP is low compared to demand
• How do muscles relax?

  When muscle stimulation decreases. Calcium ions are actively transported back into the sarcoplasmic reticulum using the energy supplied by the hydrolysis of ATP. The myosin head cannot bind to the now hidden binding sites of actin due to tropomyosin So muscle does not contract.
• H Zone

  During a contraction this section gets narrower

  
• M line

  The middle point of a sarcomere, it doesn't change during contraction
• Z line

  The two ends of the myofibril, they get closer during contractions.

  
• A band

  The length of the myosin, does not change during contractions as it stays in the same place and the actin filaments are pulled over it.

  
• I band


  The area where there is only actin filament, gets narrower during contraction.

  
• Neuromuscular junction

  The synapse between a motor neurone and a skeletal muscle. An action potential from here stimulates muscle contraction/relaxation

  
• T-tubules

  In the sarcolemma, they run downwards and allow an action potential to reach the sarcoplasmic reticulum.

  
• Sarcoplasmic reticulum


  A storage and release area for ca2+ ions in muscle contraction.
• Role of Ca2+ ions in muscle contraction?

  Released from the sarcoplasmic reticulum. It binds to a protein attached to tropomyosin on the actin filament and causes the protein to change shape. This shape change moves tropomyosin out of the way of the actin-myosin binding site so muscle contraction can occur. It also stimulates the release of ATP hydrolase
• Phosphocreatine


  Can form ATP with ADP to make ATP and creatine. The store will last only a few seconds so mainly for rigorous exercise only. Some of the creatine forms creatinine which is broken down in the kidneys but high levels can cause kidney damage.
• Slow twitch muscles

  Postural muscles primarily found in the back and calf muscles. They release energy slowly through aerobic respirations because they contain lots of mitochondria and have a close connection to capillaries for gas exchange. They are rich in myoglobin, a red protein that stores oxygen. They are arranged in antagonistic pairs across joints to prevent fatigue as only a few fibres contract at a time.
• Fast twitch muscles

  Contract quickly but also fatigue quickly. Good for short bursts of speed and power e.g. sprinting and eye movement. High proportions of these are found in arms, legs and eyes. Energy is released quickly through anaerobic respiration using glycogen in the muscle fibres. They also have stores of PCr. They have few mitochondria and blood vessels. They don't have much myoglobin either so they can't store much oxygen, this gives them a more whiteish colour.