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Flashcards in Muscle Contraction Deck (19)
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Describe the function of calcium ions and ATP in muscle contraction.

  1. Calcium ions diffuse into myofibrils from sarcoplasmic reticulum;
  2. Calcium ions cause tropomyosin to move, exposing the binding sites on the actin;
  3. Myosin heads attach to binding sites on actin, forming crossbridge;
  4. Ca activates ATPase, leading to ADP formation
  5. Hydrolysis of ATP on myosin heads causes myosin heads to bend;
  6. Bending pulls actin molecules;
  7. Attachment of a new ATP molecule to each myosin head causes myosin heads to detach (from actin sites);


Describe the role of myosin in muscle contraction

  1. Myosin head binds to actin, and pulls actin past;
  2. Myosin head detaches from actin and moves further along actin, forming another crossbridge 
  3. ATP provides energy to recock head


Advantages of having many glycogen molecules in fast muscle fibres

  • Glycogen broken down to produce many glucose
  • This is used for glycolysis (anaerobic respiration)
  • Glycolysis not very efficient as it only yields 2 ATP per glucose
  • So many glucose made means more ATP made
  • Anaerobic respiration is a quick source of ATP for explosive movement


What happens to A,H,Z, I and sarcomere during a contraction

  • A band stays the same
  • H band gets shorter
  • Z lines get shorter
  • I bands gets shorter 
  • Sarcomere gets shorter


Role of mitochondria in muscle contraction

  • Mitochondria produces of ATP
  • These are hydrolysed, allowing myosin head to move 
  • Reabsorption of acetyl + choline from cleft to make acetylcholine
  • Energy is used to move vesicles to membrane;
  • Synthesis of acetylcholinesterase.


Explain how an AP passes along the motor neurone to the neuromuscular junction

  • Depolarisation of axon membrane occurs due to the influx of Na+
  • Na+ diffuse to adjacent region
  • This opens Na+ gates of adjacent region as threshold met
  • Na+ influx in adjacent reflux (depolarises);
  • This process is repeated along axon
  • Saltatory conduction occurs as AP jumps from node to node


What is the role of ATP and Phosphocreatine in muscle contraction

  • Phosphocreatine allows reformation of ATP without respiration as it releases Pi to join ADP;
  • ATP provides energy for the movement of the myosin head 


Benefits of having a a lot of slow twich muscle for long-distance runners

  • Endurance athletes exercise for long periods of time;
  • Would need to release energy aerobically
  • Slow twitch are resistant to fatigue;
  • Slow twitch fibres have many mitochondria;
  • This is the site of Krebs cycle and electron transport chain;
  • Much ATP formed by  aerobic resp;


Explain the advantage of Slow muscle fibres having many capillaries in close contact.

  • Many capillaries give high concentration of oxygen
  • Close,so shorter diffusion pathway for diffusion of oxygen
  • Capillaries have good glucose supply as there's little glycogen present in slow MF;
  • Allows more aerobic respiration, prevents build-up of lactic acid
  • Removal of heat and CO2;


what causes the different bands seen in the muscle fibres

  • A (darker) band is due to myosin filaments and overlapping actin;
  • H zone only myosin filaments;
  • I band (light)  has only actin filaments;


Describe how Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction result in shortening of sarcomeres. (10 marks)

  1. Entry of calcium ions in presynaptic membrane
  2. Causes Vesicles to fuse with membrane, leading to exocytosis
  3. Neurotransmitter diffuses across the cleft and binds to receptors on postsynaptic membrane 
  4. Depolarisation occurs as sodium ions enter;
  5. Release of calcium ions within the muscle
  6. Removes tropomyosin by Ca binding to troponin;
  7. Exposing binding sites on the actin;
  8. Cross bridge formation as myosin binds;
  9.  Myosin head moves and pulls the actin along;
  10. Head detach and reattach;
  11. ATPase activated to hydrolyse ATP


Describe the role of tropomyosin during relaxation and muscle contraction

  • In relaxed muscle, tropomyosin covers binding site;
  • Tropomyosin is attached to troponin;
  • Calcium ions bind to troponin
  • Thus causes tropomyosin to move (from binding site)
  • Actin binding site free


Benefits of having both types of muscle fibres

  • fast fibres make fast contraction possible
  • most of the energy is anaerobically generated in fast twitch;
  • fast fibres used in explosive movement
  • slow fibres allow sustained contraction
  • most of the energy is aerobically generated in fast twitch;
  • slow also fibres used in maintaining posture 


Why do people who make insufficient ATP have weak muscle contractions?

Energy released by ATP is needed for:

  • formation of cross bridges between actin and myosin head;
  •  Pulling of actin (power stroke)
  • Detachment of myosin heads;
  •  Myosin heads move back to original position  (recovery stroke)


If myosin are unable to bind to other myosin, this prevents muscle contraction

  • Can’t pull actin along 
  • When the Myosin head bend, myosin moves instead of actin
  • So can’t move actin towards each other
  • Sarcomere does not shorten so no contraction possible


What causes the changes shown in the diagram as the myofibril contracts? 

  • A-band appears bigger due maximum overlap of actin and myosin filaments
  • Because actin slides past myosin;
  • Causing I-band to shorten, causing Z-lines to move closer;
  • H-zone disappears when actin filaments meet;


Why does phosphocreatine take longer to be remade as people get older 

  • As people get older slower metabolism/respiration rate so less ATP production.
  • ATP used to reform phosphocreatine;


What is the role of phosphocreatine (PC) in providing energy during muscle contraction?

1. provides phosphate (so phosphorylates);

2. To make ATP;


Use your knowledge of fast muscle fibres to explain why the time taken for phosphocreatine to be redfomed increases with age

1. From graph, phosphocreatine takes longer to remake as people get older;

2. Fast muscle fibres used for rapid/powerful contractions;

3. Phosphocreatine used up rapidly during contraction/to make ATP;

4. Anaerobic respiration involved;

5. As people get older slower metabolic rate/slower ATP production/slower respiration;

6. ATP used to reform phosphocreatine;

7. Lots of phosphocreatine in fast fibres;