skeletal muscles

Question 1

how do muscles work

Answer 1

antagonistic pairs
pull in opposite directions
one muscle contracts the other relaxes
skeleton incompressible so muscles can transmit force to bone

Question 2

microscopic structure of skeletal muscle

Answer 2

many bundles of muscle fibres packaged together
attached to bone by tendons
the muscle fibre has sarcomella myofibrils mitochondria etc

Question 3

ultrastructure of myofibril

Answer 3

two long protein filaments arranged in parallel
myosin thick filament
actin thin
arranged in sarcomeres
end z line
middle m line
H zone only contains myosin

Question 4

banding pattern in myofibrils

Answer 4

I band light only actin filaments
A band dark band thick myosin
h zone only myosin
darkest region overlapping myosin and actin

Question 5

overview muscle contraction

Answer 5

myosin head slide along myosin - sarcomere contract
simultaneous contraction of many sarcomeres = myofibrils and muscle fibres to contract
sarcomeres contract
H zone shorter
I band shorter
A band same
Z line closer

Question 6

muscle full contraction

Answer 6

depolarisation spreads down sarcomella via t tubules causing Ca ions release from sarcoplasmic reticulum which diffuse to myofibrils
calcium ions bind to tropomysoin causing it to move and expose binding sites on actin
allowing myosin head with ADP attached to bind to binding site on actin forming actin myosin crossbridge
myosin head changes angle pulling actin along myosin - ADP released using energy from atp hydrolysis
new atp binds to myosin head causing it to detach from binding site
hydrolysis of atp nay atp hydrolase releases energy for myosin head to return to original position
myosin reattaches to Dif binding sites further along actin
process repeated as long as ca conc high

Question 7

during muscle relaxation

Answer 7

ca AT back to ER using energy from ATP
tropomyosin moves back to block myosin binding site on actin again so no actin myosin cross bridges

Question 8

phosphocreatine role in muscle contraction

Answer 8

source of Pi
rapidly phosphorylates ADP to regenerate ATP
ADP + phosphocreatine produces ATP and creatine
runs out after a few seconds so used in short bursts of vigorous excercise
anaerobic

Question 9

slow twitch muscles

Answer 9

specialised for slow sustained contractions
obtain ATP minly drom aerobic reopsirationg so release energy slow and fatigue slow
high prop in muscles used for posture legs of long distance runners
high conc of myoglobin which stores o2 for aerobic respiration
many mitochondria for high rate of aerobic respiration
many capillaries supply high conc of oxygen and glucose for aerobic respiration and prevent build up of lactic acid causing muscle fatigue

Question 10

fast twitch muscles

Answer 10

specialised for brief intensive contraction
obtain atp mainly from anaerobic respiration releasing energy fast and fatigue fast due to high lactate conc
high prop in biceps
low level myoglobin
lots glycogen hydrolysed to provide glucose for anaerobic respiration which is inefficient so lots of glucose required
high condo of enzymes involved in Ana
store phosphocreatine