Muscle Contraction Flashcards
Describe the function of calcium ions and ATP in muscle contraction.
- Calcium ions diffuse into myofibrils from sarcoplasmic reticulum;
- Calcium ions cause tropomyosin to move, exposing the binding sites on the actin;
- Myosin heads attach to binding sites on actin, forming crossbridge;
- Ca activates ATPase, leading to ADP formation
- Hydrolysis of ATP on myosin heads causes myosin heads to bend;
- Bending pulls actin molecules;
- 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
- Myosin head binds to actin, and pulls actin past;
- Myosin head detaches from actin and moves further along actin, forming another crossbridge
- 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)
- Entry of calcium ions in presynaptic membrane
- Causes Vesicles to fuse with membrane, leading to exocytosis
- Neurotransmitter diffuses across the cleft and binds to receptors on postsynaptic membrane
- Depolarisation occurs as sodium ions enter;
- Release of calcium ions within the muscle
- Removes tropomyosin by Ca binding to troponin;
- Exposing binding sites on the actin;
- Cross bridge formation as myosin binds;
- Myosin head moves and pulls the actin along;
- Head detach and reattach;
- 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;
