Muscles Flashcards
what do muscles act as?
antagonistic pairs against an incompressible skeleton to create movement. either automatic or conscious
antagonistic meaning
2 muscles attached, working in opposites to either contract or relax
what are muscle fibres made up of and what are these made up of?
myofibrils, which are made up of fused cells sharing nuclei and a sarcoplasm with many mitochondria, due to lots of ATP being essential for contraction
what are the 2 proteins that myofibrils are made up of?
myosin and actin (they form a sarcomere)
is actin a thin or thick filament?
thin
is myosin a thin or thick filament?
thick
explain the process of the sliding filament theory (6)
-when an action potential reaches a muscle, a response is then stimulated.
-Ca2+ ions enter and cause tropomyosin (protein) to uncover binding sites for myosin, exposing them.
-ADP is attached to the myosin head and can bind to the binding sites on the actin to form a cross-bridge.
-the angle created here creates tension, so the actin filament is pulled and slides along the myosin, releasing an ADP molecule.
-an ATP molecule can then bind to the myosin head, causing a shape change, so it detaches.
-in the sarcoplasm, ATPase hydrolyses ATP to ADP on the myosin, releasing energy to return to normal position.
-the process repeats whilst Ca2+ conc remains high and muscle remains stimulated.
how is the enzyme ATPase activated?
by Ca2+ ions
what happens when not enough ATP is produced in aerobic respiration?
anaerobic respiration will occur and the chemical phosphocreatine assists by providing phosphate to regenerate ATP from ADP
where is phosphocreatine stored?
in the muscles
what does the A band show on a myofibril?
all of the myosin filament, whether or not it is overlapping
what does the I band show on a myofibril?
actin only (thin letter)
what does the H zone show on a myofibril?
myosin only (thick letter)
what does the M line show on a myofibril?
middle of the myosin filaments
what does the Z line show on a myofibril?
the end of the sarcomere (end of alphabet)
which bands/zones decrease during contraction and why?
I band and H zone, due to actin on both sides of sarcomere being closer together
which band/zone increases during contraction?
Z line
which band/zone doesn’t change during contraction?
A band
describe the structure of a slow-twitch muscle fibre
there’s a large store of myoglobin, a rich blood supply, and lots of mitochondria
describe the structure of a fast-twitch muscle fibre
they are thicker with more myosin filaments, a large store of glycogen and phosphocreatine (to make ATP), and a high conc of enzymes from anaerobic respiration
where are slow-twitch muscle fibres located?
the calf muscles
where are fast-twitch muscle fibres located?
the bicep muscles
describe the properties of slow-twitch muscle fibres
they contract slower and can respire aerobically for longer due to the rich blood supply and myoglobin store
describe the properties of fast-twitch muscle fibres
they contract faster to provide short bursts of contraction
what are slow-twitch muscle fibres adapted for?
endurance (e.g. marathons)
what are fast-twitch muscle fibres adapted for?
intensity (e.g. sprints and weightlifting)
which muscle fibre takes longer to fatigue?
slow-twitch muscle fibres
how does a neuromuscular junction work?
1) Impulses arriving at the neuromuscular junction cause vesicles to fuse with the pre-synaptic membrane and release acetylcholine into the gap.
2) acetylcholine binds to receptors on the sarcolemma (muscle fibre membrane), causing depolarisation.
3) the depolarisation wave travels down the tubules (T system).
4) T system depolarisation leads to release of Ca2+ ions from the sarcoplasmic reticulum.
5) Ca2+ binds to proteins in the muscle, leading to contraction.
6) acetylcholinerase in the gap rapidly breaks down acetylcholine, so contraction only occur when impulses arrive continuously.
what is the sarcolemma?
the muscle fibre membrane
is an action potential created in the post-synaptic membrane of a normal synapse?
yes
is an action potential created in the post-synaptic membrane of a neuromuscular junction?
no, it ends here
are neurotransmitters excitatory or inhibitory in a normal synapse?
either
are neurotransmitters excitatory or inhibitory in a neuromuscular junction?
excitatory
is summation possible in a normal synapse?
yes
is summation possible in a neuromuscular junction?
only temporal
what are the connections between in a normal synapse?
neurone and neurone
what are the connections between in a neuromuscular junction?
neurone and muscle fibre
describe the structure of myosin
-each myosin filament is made up of 200 myosin molecules
-each myosin molecule has 2 protruding heads and a long tail
-each head contains ATPase, to hydrolyse ATP for muscle contraction
describe the structure of actin
-each actin filament is made up of 2 actin molecules and a second protein called tropomyosin
-sites which can bind to myosin heads, but in a RELAXED muscle, tropomyosin blocks these
-Ca2+ ions cause tropomyosin to move to expose the binding sites on actin sop that contraction can occur
what happens to the sarcomere during contraction?
it shortens
what happens to the H zone during contraction?
it becomes narrower
what happens to the I band during contraction?
it becomes narrower
what happens to the Z lines during contraction?
they become closer together
what happens to the A band during contraction?
it stays the same
