muscle contraction

Question 1

what is skeletal muscle

Answer 1

the type of muscle you use to move, e.g. biceps and triceps

Question 2

what to tendons do

Answer 2

attach skeletal muscle to bones

Question 3

what do ligaments do

Answer 3

attach bones to other bones

Question 4

how do bones work as levers

Answer 4

because bones are incompressible so they can act as a lever to give the muscle something to pull against

Question 5

what are antagonistic pairs

Answer 5

muscles that work together, one muscle contracts and one muscle relaxes, the contracting one is called agonist and the relaxing one is called antagonist

Question 6

give an example of how antagonistic pairs of muscles work

Answer 6

when your bicep contracts, your tricep relaxes and when your tricep contract your bicep relaxes.

Question 7

what is the cell membrane of the muscle fibres called

Answer 7

sarcolemma

Question 8

the muscle fibre membrane has folds on it, what are these called and what’s its purpose

Answer 8

transverse t tubules, they help spread the electrical impulse throughout the sarcoplasm so they reach all parts of the muscle fibre

Question 9

what’s the network of internal membranes called and what’s its purpose

Answer 9

sarcoplasmic reticulum, stores and releases calcium ions which are needed for muscle contraction

Question 10

what do muscle fibres have plenty of

Answer 10

mitochondria to provide ATP for contractions

Question 11

muscle fibres are multinucleate, what does this mean

Answer 11

they have many nuclei

Question 12

muscle fibres have long, cylindrical organelles, what are these called, what are they made of and what is their purpose

Answer 12

myofibrils, they’re made of proteins and are highly specialised for contraction

Question 13

what 2 things do myofibrils contain in them and what are each of them made of

Answer 13

1) thick myofilaments made of the protein myosin

2) thin myofilaments made of the protein actin

Question 14

if you look at a myofibril under a microscope what 2 things do you see, and are they called

Answer 14

1) dark bands that contain thick myosin myofilaments and some thin actin filaments - called A bands
2) light bands that contain thin actin filaments ONLY - called I-bands

Question 15

myofibrils are made up of small units called what

Answer 15

sarcomeres

Question 16

what marks the middle and end of each sarcomere and what does the middle also mark

Answer 16

middle - M-line. the m-line is also the middle of the myosin filaments
end - Z-Line

Question 17

what is around the middle line of the sarcomere and what does this contain

Answer 17

H-zone, the H-Zone only contains myosin filaments

Question 18

what slides over one another to make the muscle contract

Answer 18

the myosin and actin filaments slide over each other to make the sarcomeres contract, the actual myofilaments don’t contract themselves

Question 19

what does the simultaneous contraction of lots of sarcomeres mean

Answer 19

the myofibrils contract which means the muscle fibres contract

Question 20

myosin filaments have globular heads, what does this mean

Answer 20

this means they’re hinged so they can move back and forth

Question 21

what 2 things does each myosin head have

Answer 21

1) binding site for actin

2) binding site for ATP

Question 22

what do actin filaments have on their surface and what are they called

Answer 22

binding sites for myosin heads called actin-myosin binding sites

Question 23

what is found between actin filaments and what does it help

Answer 23

a protein called tropomyosin which helps myofilaments move past each other

Question 24

in resting muscles what blocks the actin-myosin binding site and what does this mean

Answer 24

the actin-myosin binding site is blocked by tropomyosin which means myofilaments cannot slide past each other because the myosin heads cant bind to the actin-myosin binding site

Question 25

how is a muscle contraction triggered by an influx of calcium ions (5 steps)

Answer 25

1) when depolarization spreads down the T-tubules is causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm
2) these bind to a protein attached to tropomyosin, causing the protein to change shape which pulls the tropomyosin out of the actin-myosin binding site and exposes the binding site which allows the myosin head to bind
3) the bond formed is called actin-myosin cross bridge, calcium ions also activate the ATP hydrolase which hydrolyses ATP into ADP and Pi to provide energy, this energy causes myosin head to bend, which pulls the actin filament in a rowing action
4) another ATP molecule provides energy to break the actin-myosin cross bridge so the myosin head detaches and then reattaches to a different binding site further along the actin filament so a new cross bridge is formed and the cycle is repeated
5) many cross bridges form and break very rapidly which pulls the actin filament along which shortens the sarcomere causing the muscle to contract, this cycle will keep happening as long as calcium ions are present

Question 26

what happens in terms of calcium ions when the muscle stops being stimulated, what does this cause and why does this mean muscles aren’t stimulated anymore

Answer 26

when the muscle stops being stimulated the calcium ions leave their binding sites and move back by active transport into the sarcoplasmic, this causes tropomyosin molecules to move back, so they block actin-myosin binding sites so the muscles aren’t contracted because no myosin heads are attached to actin filaments

Question 27

what are the 3 ways ATP is generated when muscles are contracted

Answer 27

1) aerobic respiration
2) anaerobic respiration
3) ATP-Phosphocreatine system

Question 28

how does the PCr system work (3 steps)

Answer 28

1) ATP is made by phosphorylating ADP by adding a phosphate group taken from PCr
2) PCr is stored inside cells and the ATP-PCr system generates ATP very quickly
3) PCr runs out after a few seconds so its used in short bursts of exercise
4) the ATP-PCr system is anaerobic and its alactic