Skeletal Muscles (15) Flashcards
What are the 3 types of muscle?
cardiac muscle
smooth muscle
skeletal muscle
Where are cardiac muscles found?
only in the heart
Where are smooth muscles found?
walls of blood vessels and intestines
Where are skeletal muscles found?
attached to incompressible skeleton by tendons
What is meant by antagonistic pair of muscles?
muscles can only pull, so they work in pairs to move bones around joints by pulling in opposite directions
What are the names of the muscles in antagonistic pairs, and what do they do?
agonist contracts
antagonist relaxes
What 2 things happen during muscle contraction?
1) Calcium ions are actively transported back into the endoplasmic reticulum
2) tropomyosin blocks the actin binding site
What is the gross structure of skeletal muscles?
- muscle cells are fused together to form myofibrils
- arrangement ensures there’s no point of weakness between cells
- each bundle is surrounded by endomysium
What are myofibrils?
bundles of parallel muscle fibres
What is endomysium?
loose connective tissue with many capillaries
What are the 3 features of the microscopic structure of skeletal muscles?
myofibrils
sarcoplasm
sarcolemma
What is the role of myofibrils?
site of contraction
What is the sarcoplasm?
shared nuclei and cytoplasm with lots of mitochondria and endoplasmic reticulum
What is the sarcolemma?
folds inwards towards sarcoplasm to form transverse tubules
Draw the ultrastructure of myofibril, including its bands.
Look at notes.
What are the 5 steps on how muscle contraction is stimulated?
1) at the neuromuscular junction, an action potentil causes voltage-gated calcium ion channels to open
2) vesicles move towards and fuse with the presynaptic membrane
3) exocytosis of acetylcholine which diffuses across synaptic cleft
4) acetylcholine binds to receptors on the sodium ion channel proteins on the skeletal muscle cell membrane
5) an influx of sodium ions causes depolarisation
What is the role of calcium ions in muscle contraction?
1) action potential moves through transverse tubules in the sarcoplasm so calcium ion channels in the sarcoplasmic reticulum open
2) calcium ions bind to tropomyosin, triggering conformational change in tropomyosin
3) exposes binding site on actin filaments so actomyosin bridges can form
What are the 5 steps of the sliding filament theory?
1) myosin head with ATP attached forms cross bridge with actin
2) this causes a power stroke where the myosin head changes shape, loses ADP and pulls actin over the myosin
3) ATP attaches to myosin head, causing it to detach from the actin
4) ATPase hydrolyses ATP so myosin head can return to original position
5) myosin head re-attaches to actin further along the filament
What are the 4 pieces of evidence supporting the sliding filament theory?
1) H-zone narrows
2) I-band narrows
3) Z-lines get closer
4) A-zone remains the same width, proving myosin don’t shorten
How does the sliding filament theory cause myofibril to shorten?
- myosin heads flex in opposite directions and so actin filaments are pulled towards each other
- distance between adjacent sarcomere Z lines shortens
What is the role of phosphocreatine in muscle contraction?
it phosphorylates ADP directly into ATP (using its phosphate group) when O2 for aerobic respiration is limited (e.g. during vigorous exercise)
Where do slow-twitches happen?
calf muscles
Where do fast-twitches happen?
biceps
What are the 3 steps in how to calculate the length of one sarcomere?
1) view thin slice of muscle under optical microscope
2) calibrate eyepiece graticule
3) measure distance from middle of 1 light band to another
What is the function of slow-twitch?
- long-duration contraction
- well-adapted to aerobic respiration to prevent lactate buildup
What is the function of fast-twitch?
- powerful, short-term contraction
- well-adapated to anaerobic respiration
What are 4 structures/properties of slow-twitch?
- glycogen store
- contain myoglobin
- many mitochondria
- surrounded by many blood vessels
How does having a glycogen store help with slow-twitches function?
many terminal ends can be hydrolysed to release glucose for respiration
How does containing myoglobin help with slow-twitches function?
higher affinity for O2 than haemoglobin at lower partial pressures
How does having many mitochondria help with slow-twitches function?
more ATP produced during aerobic respiration
How does being surrounded by blood vessels help with slow-twitches function?
high supply of O2 and glucose
What are 5 structures/properties of fast-twitch?
- large store of phosphocreatine
- more myosin filaments
- thicker myosin filaments
- high concentration of enzymes involved in anaerobic respiration
- extensive sarcoplasmic reticulum
How does having an extensive sarcoplasmic reticulum help with fast-twitches function?
allows for rapid uptake and release of calcium ions
