MUSCLE CONTRACTION

Question 1

what are the 2 types of muscle fibres

Answer 1

type 1

type 2

Question 2

Describe the events of a muscle contraction

Answer 2

Action potential arrives at a neuromuscular junction
Neurotransmitter diffuses across gap and opens gated Na+ channel
Wave of depolarisation triggers calcium to be released from the sarcoplasmic reticulum by opening calcium ion channel and therefore diffuse out (low calcium in cytoplasm)
Calcium binds to tropomyosin causing it to change shape and expose myosin binding sites on actin
ADP attaches to myosin head = powerstroke
ATP attaches to myosin head = causing it to detach
Calcium activates ATPase which hydrolyses ATP–> ADP therefore providing energy for myosin to return to original position.
ADP reattaches and mason attaches further down actin filament

Question 3

How are muscles attached to bones

Answer 3

tendons

Question 4

What attaches bone to bone

Answer 4

ligaments

Question 5

what is the agonist

Answer 5

the contracting muscle

Question 6

what is the antagonist

Answer 6

the relaxing muscle

Question 7

what are skeletal muscle fibres made up of

Answer 7

large bundles of long cells called muscle fibres

Look STRIATED due to alternating dark and light bands

Question 8

what is the sarcolemma

Answer 8

the cell membrane of muscle fibres

Question 9

What is the sarcoplasm

Answer 9

a muscle cells cytoplasm

Question 10

what are the folds called that stick into the cytoplasm

Answer 10

T tubules

Question 11

What is the function of a T tubule

Answer 11

help to spread electrical impulses throughout the sarcoplasm so they reach all parts of the muscle fibre

Question 12

what is the sarcoplasmic reticulum

Answer 12

a network of internal membranes that runs through the sarcoplasm

Question 13

what is the function of the sarcoplasmic reticulum

Answer 13

stores and releases calcium ions that are needed for muscle contraction

Question 14

wha organelle do muscles have lots of and why

Answer 14

mitochondria for aerobic respiration

Question 15

a muscle fibre is multinucleate- what does that mean

Answer 15

it has many nuclei

Question 16

what do muscle fibres have lots of

Answer 16

long cylindrical organelles called myofibrils

made up of proteins and highly specialised for contraction

Question 17

what 2 filaments do myofibrils contain

Answer 17

thick myosin filaments

thick actin filaments

Question 18

what does a myofibril look like under an electron microscope

Answer 18

alternating dark and light bands
dark bands - thick myosin filaments, and some overlapping thin actin filaments
light bands - thin actin filaments ONLY

Question 19

what are the dark bands called

Answer 19

A bands

Question 20

what are the light bands called

Answer 20

I bands

Question 21

what is each myofibril made up of

Answer 21

many short units called sarcomeres

Question 22

what is at the end of each sarcomere

Answer 22

a Z line

Question 23

what is in the middle of each sarcomere

Answer 23

an M line

The M line is the middle of the myosin filaments

Question 24

What is the H zone

Answer 24

The H zone is around the M line and only contains myosin filaments

Question 25

Explain the sliding filament theory

Answer 25

Myosin and actin filaments slide over one another to make the sarcomeres contract The simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract Sarcomeres return to their original length as muscle relaxes

Question 26

what changes occur when the sarcomeres contract

Answer 26

A bands stay same length I bands get shorter H zones get shorter Sarcomeres get shorter

Question 27

What do myosin filaments have

Answer 27

globular heads that are hinged so can move back and forth | binding sites - one for actin and one for ATP

Question 28

what do activists filaments have

Answer 28

a binding site for myosin heads called an actin-myosin binding site

Question 29

what protein is found between actin filaments and what does it do

Answer 29

tropomyosin | it helps filaments move past each other

Question 30

what happens to the binding sites in resting muscles

Answer 30

the binding sites in resting muscles are blocked by tropomyosin

Question 31

what happens to calcium when the muscle stops being stimulated

Answer 31

when muscle stops being stimulated calcium ions leave their binding sites and are moved back to sarcoplasmic reticulum via active transport This causes the tropomyosin to move back too So they block the bonding sites Actin filaments slide back to their relaxed position which lengthens the sarcomere

Question 32

what is it called when the myosin head is attached to the actin filaments

Answer 32

a cross bridge

Question 33

ATP-PC system, how long does PC last

Answer 33

a few seconds

Question 34

state some properties of slow twitch muscle fibres

Answer 34

``` endurance activites can work for a long time without fatigue energy released slowly aerobic respiration lots of mitochondria red in colour as rich in myoglobin (red coloured protein that stores oxygen) ```

Question 35

state some properties of fast twitch muscle fibres

Answer 35

``` used for fast movement short bursts of energy - speed or power get tired very quickly anaerobic respiration less mitochondria fatigue quickly due to lactic acid white in colour as less myoglobin (so can't store much oxygen) ```