3.6.3 muscles Flashcards
explain antagonistic muscles
muscles are arranged on opposite sides of a joint.
when one muscle relaxes, the other contracts.
the contracting muscle gets shorter and the relaxing muscle gets longer, allowing movement
describe the composition of muscle tissue
composed of muscle cells which are connected by muscle fibres.
the muscle fibres share nuclei, mitochondria, sarcoplasmic reticulum, and sarcoplasm.
each muscle fibre is made from many myofibrils.
describe the composition of myofibrils
composed from 2 protein filaments (actin and myosin) which form a sarcomere
describe the structure of a sarcomere
made from 2 protein filaments, actin and myosin.
a band = the whole length of the myosin (appears medium darkness due to some overlap of both filaments)
h zone = the length of the myosin only, with no overlap of actin (darkest in colour)
m line = middle of the sarcomere, made from myosin
z line = at both ends of a sarcomere
i band = the actin only section, goes over two sarcomeres ( lightest in colour)
describe the structure of actin
thinner filament.
made from 2 entwined strands of actin.
tropomyosin covers myosin binding sites on the actin
troponin also found on the tropomyosin, binds to Ca2+
describe the structure of myosin
thicker filament.
has myosin heads on surface, which bind to myosin binding sites on actin.
how does each section of the myosin change during contraction
the a band remains the same length as the myosin doesnt change in length
the i band gets shorter as the actin filament are pulled in
the h zone gets shorter as there is more overlap between myosin and actin
the z lines get closer together as the actin is pulled in
fast twitch fibres
used for intense activity.
ATP is obtained from anaerobic respiration.
stores less myoglobin for a lower oxygen concentration.
there is less ATP produced so the muscles fibres fatigue faster.
there is a faster contraction of muscles.
less mitochondria as anaerobic respiration is used.
greater phosphocreatine store
slow twitch fibres
used for prolonged activity.
ATP is obtained from aerobic respiration.
stores more myoglobin for a greater oxygen concentration.
there is more ATP produced so the muscle fibres fatigue slower
there is slower contraction of muscles
more mitochondria stored as anaerobic respiration is used.
lower phosphocreatine store
how does muscle contraction begin
Na+ diffuse into the sarcolemma, causing depolarisation.
the action potential is transmitted along t-tubes.
the sarcoplasmic reticulum releases ca2+ into the sarcoplasm
step 1 of muscle contraction
ca2+ bind to troponin.
this causes the tropomyosin, which is blocking myosin binding sites, to move and expose the binding sites on the actin.st
step 2 of muscle contraction
myosin heads bind to the myosin binding sites on the actin, forming an actin myosin crossbridge.
step 3 muscle contraction
myosin heads are in high energy and the tension of the position will pull the actin filaments along (powerstroke) ADP and Pi attached are released
step 4 muscle contraction
an ATP molecule will bind to the myosin causing it to detach from the actin, ATPase is stimulated by Ca2+ which hydrolyses the ATP to provide energy to allow the myosin head to recock into the original position
phosphocreatine
supplies ATP for muscle contraction, PCr donates a phosphate to ADP to form ATP during intense activity
