Topic 6 Skeletal Muscles Flashcards
name the 3 types of muscle in the body and where they are located
cardiac: exclusively found in heart
smooth: walls of blood vessels and intestines
skeletal: attached to incomprehensible skeleton by tendons
what does the phrase antagonistic pair of muscles mean
muscles can only pull so they work in pairs to move bones around joints
pairs pull in opposite directions
describe the gross structure of skeletal muscle
muscle cells are fused together to form bundles of parallel muscle fibres myofibrils
arrangement ensures there is no point of weakness between cells
each bundle is surrounded by endomycium which is loose connective tissue with many capilleries
describe the microscopic structure of skeletal muscle
- myofibrils: site of contraction
- sarcoplasm: shared nuclei and cytoplasm with lots of mitochondria and ER
- sarcolemma folds inwards towards sarcoplasm to form transverse tubules (T tubes)
draw a diagram to show the ultrastructure of a myofibril
refer to source from google
how does each band appear under an optical microscope
I band is light
A band is dark
how is muscle contraction stimulated
- at the NMJ the action potential causes the voltage gated Ca2+ channels open
- vesciles move towards and fuse with presynaptic membrane
- exocytosis of ACh which diffuses across the synaptic cleft
- ACh binds to receptors on Na+ channel proteins on skeletal muscle cell membrane
- Influx of Na+ causes depolarisation
explain the role of Ca2+ ions in muscle contraction
- action potential moves through the T tubules in the sarcoplasm and this caises Ca+ channels in sarcoplasm reticulum open
- Ca2+ binds to troponin triggering conformational change in troposmyosin
- exposes binding sites on actin filaments so actinomyosin bridges can form
outline the sliding filament theory
- myosin head with ADP attached forms cross bridge with actin ‘
- myosin head changes shape and loses ADP, pulling actin over myosin
- ATP attaches to myosin head causing it to detach from actin
- ATP hydrolyse hydrolyses ATP–> ADP + Pi so myosin head returns to original position
- myosin head reattached to actin further along filament
how does sliding filament action cause a myofibril to shorten
myosin heads flex in opposite direction so actin filaments are pulled towards each other
distance between adjacent sarcomere Z lines shortens
sliding filaments action occurs up to 100x per second in multiple sarcomeres
state 4 pieces of evidence that support the sliding filament theory
- H zone narrows
- I band narrows
- Z lines get closer
- A zone remains the same width
what happens during muscle relaxation
- Ca2+ is actively transported back into ER
- Tropomyosin blocks actin binding site
explain the role of phosphocreatine in muscle contraction
phosphorylates ADP into ATP when oxygen is limited for aerobic resp
how could a student calculate the length of one sacromere
- view thin slice of muscle under optical microscope
- calibrate eyepiece graticule
- measure distance from middle of one light band to middle of another
where are slow and fast twitich muscle fibres found in the body
slow twitch sites of sustained contraction like the calf
fast twitch sites of short term rapid powerful contraction like biceps
explain the role of slow and fast twitch muscle fibres
slow twitch: long duration contraction so well adapted to aerobic respiration to prevent lactate buildup
fast twitch powerful short term contraction so well adapted to anaerobic respiration
explain the structure and properties of slow twitch muscle fibres
- glycogen store
- contain myoglobin
- many mitochondria
- surrounded by many blood vessels
what is a motor unit
one motor neuron supplies several muscle fibres which act simultaneously as one functional unit
explain the structure and properties of fast twitch muscle fibres
- large store of creatine
- more myosin filaments and thicker ones
- high conc of enzymes involved in anaerobic respiration
- extensive sarcoplasmic reticulum to allow rapid uptake and release of Ca2+
