13.13 Muscles Flashcards
Describe how smooth muscle contracts and where it is found. Give examples of smooth muscle.
Contracts without conscious control.
Found in walls of internal organs (apart from heart)
E.g. stomach, intestine and blood vessels.
Describe how cardiac muscle contracts and where it is found.
Contracts without conscious control (myogenic)
Only found within the heart.
What type of muscle is used in locomotion- movement? Give an example of how muscles can work together.
Skeletal muscle
E.g. biceps and triceps move the lower arm antagonistically (oppositely)
Explain how skeletal muscles work.
- Attached to the bones by tendons
- Contracts in response to acetylcholine from motor neurone (neuromuscular junction).
- Muscles can only pull- opposing muscles groups are needed to pull in opposite directions at a joint. One contracts, one relaxes.
What is muscles group contracting referred to as?
Agonist
What is muscles group relaxing referred to as?
Antagonist
Describe and explain the structure of skeletal muscles.
- Highly specialised muscle fibres= long thin cells containing several nuclei.
- Muscle cell surrounded by a thin cell membrane called a sarcolemma.
- Cell contains cytoplasm called sarcoplasm, contains large number of mitochondria.
- Fibres contain large number of myofibrils- run parallel along length of cell.
- Myofibril surrounded by sarcoplasmic reticulum
- Myofibril made of myofilaments- myosin and actin
What does skeletal muscle look like under a light microscope?
Often called striated muscle as under the light microscope, dark bands are visible across muscle fibres.
What does skeletal muscle look like under a electron microscope?
Dark bands are visible across each myofibril.
Each sarcomere has a distinctive banding pattern due to presence or absence of myosin and actin.
Actin is the ______ filament
Thin
Myosin is the ______ filament
Thick
H zone contains
Only myosin with no overlap
M line is
Myosin anchored
A band is
Only myosin
I band is
Only actin
Z disk/line is
Actin anchored
What is the sarcomere and what happens when muscles contract?
One Z disc to another.
When muscle contracts, Z lines get closer together, thicken and shorten.
Briefly describe what happens to areas in the myofibril during muscle contraction?
Each sarcomere shortens, bringing Z lines closer together, as the actin is pulled over myosin filaments (slide over each other), increasing the amount they overlap.
What happens to A band as the muscle contracts?
Stays the same
What happens to I band as the muscle contracts?
Shortens
What happens to H zone as the muscle contracts?
Shortens
What happens to Z discs as the muscle contracts?
Come closer together
What happens to the sarcomere as the muscle contracts?
Shortens
What happens when a myofibril is relaxed?
Tropomyosin covers sites on actin filament to which myosin attach.
Explain what happens if the muscle fibre is excited by a motor neurone according to the sliding filament theory?
- Ca2+ are released from the sarcoplasmic reticulum into the sarcoplasm.
- Ca2+ diffuse and bind to tropomyosin so it moves exposing the myosin head binding sites on actin filament.
- Myosin heads bind to actin binding sites forming cross bridges.
- The myosin head pulls actin filament a short distance OVER the myosin- POWER STROKE
- ADP and Pi are released from myosin head (changes shape)
- A new ATP binds to myosin head, breaking cross bridges and separating it from the actin.
- ATP is hydrolysed into ADP and Pi by ATP hydrolase, the energy released re-cocks the myosin head- RECOVERY STROKE
- Process repeats, pulling actin along myosin filament more each time.
Role of Ca2+ ions in sliding filament theory
- Ca2+ ions are actively transported back into sarcoplasmic reticulum.
- Ca2+ ions also activate ATP hydrolase.
What is ATP required for in muscles?
Sliding of filaments during contraction
Active transport of calcium ions into sarcoplasmic reticulum
Why do muscle fibres require an alternative biochemical pathway to allow the regeneration of ATP?
Fibre can only store enough ATP to allow for contraction for 3-4 seconds.
Regen of ATP by anaerobic respiration takes about 10 seconds
Regen of ATP by aerobic respiration takes longer
Which molecule does muscle fibres use to allow the regeneration of ATP?
Phosphocreatine
Use of phosphocreatine in muscles
- Provides a phosphate (Pi) group to ADP
- To regenerate ATP short term
How can phosphocreatine be regenerated?
Regenerated using ATP when it is supplied via aerobic respiration
ADP + phosphocreatine <——> ATP + creatine
How can the energy released in hydrolysis of phosphocreatine be used in muscle contraction?
Energy released from hydrolysis not used directly.
It is used in phosphorylation of ATP, which is then used in muscle contraction
Properties of slow twitch muscles
- Slow, sustained and less powerful contractions over long periods of time.
- Slow to fatigue.
- Found in calves muscles involved in maintaining posture.
Adaptations of slow twitch muscles
- Specialised to use aerobic respiration energy system to regenerate ATP
- Have many large mitochondria- some just under the sarcolemma to provide ATP for active transport, and some deep between the myofibrils
- High cones of myoglobin- protein that acts as oxygen store in muscles (gives muscle fibres their red colour)
- Very closely associated with a large number of capillaries- provides a good oxygen supply
- Less extensive sarcoplasmic reticulum as less calcium ions required at one time
- Less glycogen as glucose broken down fully via aerobic respiration
Properties of fast twitch muscles
- Produce rapid, strong and more powerful contractions over short periods of time.
- Fast to fatigue.
- Found in bicep muscles
Adaptations of fast twitch muscles
- Specialised to use PC-ATP anaerobic respiration systems to regenerate ATP
- Have fewer, smaller mitochondria.
- Low concentration of myoglobin- as primary energy systems are anaerobic.
- Fewer capillaries associated with fibres.
- Extensive sarcoplasmic reticulum as more calcium ions required at one time for rapid intense contraction.
- More glycogen as more glucose required as anaerobic respiration yields less ATP per glucose.
Describe the banding pattern in striated muscle
- Lightest band is I band, actin only
- Darkest band is overlapping region, actin and myosin
- Medium shading is H zone/band is myosin only.
Describe the sliding filament theory
- Attachment / cross bridges between actin and myosin heads;
- ‘Power stroke’ / movement of myosin heads / pulling of actin (over myosin);
- Detachment of myosin heads (requires ATP binding);
- (Energy from ATP) Myosin heads move back/to original position / ‘recovery stroke’;
Describe the function of calcium ions in muscle contraction.
- Ca2+ Binding/changing shape/removing tropomyosin;
- Exposes actin binding sites;
- Myosin head attaches/cross-bridge formation;
- Activates ATP hydrolase;
Describe the function of calcium ions in muscle contraction.
- Ca2+ Binding/changing shape/removing tropomyosin;
- Exposes actin binding sites;
- Myosin head attaches/cross-bridge formation;
- Activates ATP hydrolase;
Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction
result in shortening of sarcomeres. Describe how.
- Entry of calcium ions (presynaptic membrane);
- Vesicles fuse with membrane / exocytosis /release Ach (Acetylcholine);
- Neurotransmitter diffuses;
- Binds to receptors, postsynaptic / membrane / muscle membrane;
- Depolarisation / sodium ions enter;
- Release of calcium ions (from within the muscle);
- Removes tropomyosin / bind to troponin;
- Exposing binding sites on the actin;
- Actinomyosin cross bridge formation / myosin binds;
- Myosin head moves / pulls the actin along;
- Rachet mechanism / description /detach and reattach;
- ATP hydrolase activated;
Nerve impulses arriving at the presynaptic membrane at the neuromuscular junction
result in shortening of sarcomeres. Describe how.
- Entry of calcium ions (presynaptic membrane);
- Vesicles fuse with membrane / exocytosis /release Ach (Acetylcholine);
- Neurotransmitter diffuses;
- Binds to receptors, postsynaptic / membrane / muscle membrane;
- Depolarisation / sodium ions enter;
- Release of calcium ions (from within the muscle);
- Removes tropomyosin / bind to troponin;
- Exposing binding sites on the actin;
- Actinomyosin cross bridge formation / myosin binds;
- Myosin head moves / pulls the actin along;
- Rachet mechanism / description /detach and reattach;
- ATP hydrolase activated;
Explain the importance of ATP hydrolase during muscle contraction.
- Hydrolysis of ATP releasing energy;
- used to form / break actinomyosin cross-bridges;
Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race?
- Aerobic respiration releases more energy /produces more ATP;
- Little/no lactate produced / does not accumulate;
- Avoids cramp / muscle fatigue;
- CO2 easily removed from the body / CO2 removed by breathing;
Muscle contraction requires ATP. What are the advantages of using aerobic rather than anaerobic respiration to provide ATP in a long-distance race?
- Aerobic respiration releases more energy /produces more ATP;
- Little/no lactate produced / does not accumulate;
- Avoids cramp / muscle fatigue;
- CO2 easily removed from the body / CO2 removed by breathing;
A muscle fibre contracts when it is stimulated by a motor neurone. Describe how transmission occurs across the synapse between a motor neurone and a muscle fibre.
- Ca2+ channels / gates open;
- Ca2+ ions enter (pre-synaptic neurone);
- Vesicles move towards / fuse with presynaptic membrane;
- Release / exocytosis of transmitter substance / of acetylcholine;
- Diffusion (of transmitter) across gap / cleft;
- (Transmitter) binds to receptors in postsynaptic membrane;
- Na+ channels open / Na+ ions enter (postsynaptic side);
After death, cross bridges between actin and myosin remain firmly bound resulting in rigor mortis. Explain what causes the cross bridges to remain firmly bound.
- respiration stops;
- no ATP produced;
- ATP required for separation of actin and myosin/cross bridges;
Describe slow twitch muscle fibres
- have lots of mitochondria/ (slow fibres) respire aerobically;
- More myoglobin
Describe fast twitch muscle fibres
- used for rapid/brief/powerful/strong contractions;
- Phosphocreatine used up rapidly during contraction/to make ATP;
- Anaerobic respiration involved;
- ATP used to reform phosphocreatine;
- Lots of phosphocreatine in fast twitch fibres;
- No myoglobin
Describe fast twitch muscle fibres
- used for rapid/brief/powerful/strong contractions;
- Phosphocreatine used up rapidly during contraction/to make ATP;
- Anaerobic respiration involved;
- ATP used to reform phosphocreatine;
- Lots of phosphocreatine in fast twitch fibres;
- No myoglobin
Describe the role of phosphocreatine
- Provides (energy and) phosphate / phosphorylates;
- To make ATP from ADP & Pi;
