Muscle Contraction

Question 1

Slow twitch fibres

Answer 1

• contract slower
• less powerful contractions
• contract over longer periods of time
  Eg: long distance running

Question 2

Adaptations of slow twitch fibres

Answer 2

• large store of myoglobin ( stores oxygen)
• good blood supply
• lots of mitochondria

Question 3

Fast twitch fibres

Answer 3

• contract faster
• more powerful contraction
• only work for short period of time
  Eg: weightlifting

Question 4

Adaptations of fast twitch fibres

Answer 4

• thicker = more powerful contractions
• more myosin filaments
• high conc of glycogen
• high conc of enzymes involved in anaerobic respiration
• contains phoshphocreatine = generates ATP from ADPin anaerobic conditions

Question 5

How many proteins make up muscle myofibrils + muscle Fibre

Answer 5

2
Actin + myosin

Question 6

Actin

Answer 6

• thin filament
• light coloured
• 2 strands twisted together

Question 7

Myosin

Answer 7

• thicker filament
• dark coloured
• rod shaped fibres with bulbous heads on side

Question 8

What are myofibrils

Answer 8

• cylindrical organelles that run along length of muscle fibres
• site of muscle contraction
  ( make up muscle fibres)

Question 9

What are muscle fibres

Answer 9

• long specialised cells
• made of myofibrils
• share nucleus + sarcoplasm (cytoplasm)

Question 10

What is a sarcolemma

Answer 10

• the shared membrane of muscle fibres

Question 11

What is the sarcoplasmic reticulum

Answer 11

• organelle In shared cytoplasm (sarcoplasm)
• store of Ca2+ ions

Question 12

What is the sarcoplasm

Answer 12

• shared cytoplasm around circumference of muscle fibres
• share nuclei + mitochondrial

Question 13

What are sarcomeres

Answer 13

• units that make up myofibrils
• made up of myofilaments (actin)

Question 14

What is a H band

Answer 14

• only thick myosin
• dark

Question 15

What is a I band

Answer 15

• only thin actin
• light

Question 16

What is a A band

Answer 16

Contains areas of both:
1- only myosin
2- myosin + actin overlap

Question 17

What is the M line

Answer 17

• middle of sacromere
• where Actin filaments overlap with myosin

Question 18

What is muscle contraction

Answer 18

• Myofilaments sliding past one another

Question 19

What is sliding filament theory

Answer 19

How muscle contraction is coordinated in myofibrils

Question 20

What is the z line

Answer 20

• end of a sacromere

Question 21

Sliding filament theory

Answer 21

• depolarisation of sarcolemma by arriving action potential
  -depolarisation causes myosin + actin filaments to slide past each other= sarcomeres contract
• as many sarcomeres contract simultaneously = muscle fibres contract = whole muscle contracts
  -sarcomeres relax + filaments slide back as muscle relaxes

Question 22

What does myosin and actin have that allows muscle contraction

Answer 22

Myosin= bulbous heads
Actin= binding site

Allows filaments to bind together + movement of head allows filaments to slide past each other

Question 23

How many binding sites do myosin heads have and what do they bind to

Answer 23

2
- actin
- ATP

Question 24

What is tropomyosin

Answer 24

• protein located on actin filaments
• blocks Actin-Myosin binding site when at rest
• when muscle stimulated = protein moves revealing binding site

Question 25

3 ways to make ATP rapidly

Answer 25

1- oxidative phosphorylation in aerobic respiration
2- glycolysis in anaerobic respiration

3- phosphocreatine = store of phosphate
- donates phosphate to ADP to form ATP = anaerobic but no lactate

• during periods of low muscular activity ATP can give back phosphate = phosphocreatine

Question 26

Steps of muscle contraction

Answer 26

1- depolarisation of sarcolemma from arriving action potential
2- Sarcoplasmic reticulum release Ca2+ ions into sarcoplasm = tropomyosin changes shape revealing actin B sites
3- myosin head binds to actin
4- ATP hydrolysed to ADP = energy released cause myosin head to bend
5- filament “slide” past

Question 27

Forming a New Cross bridge

Answer 27

• Myosin head bends back to original position
• Myosin forms cross bridge with binding site further along actin filament

Question 28

Steps in halting muscle contraction

Answer 28

• No action potentials = sarcoplasm reticulum stops Ca2+ release
• Tropomyosin changes shape blocking actin binding site = myosin heads can no longer bind
  -filaments return to resting position

Question 29

Comparison between neuromuscular junction + synapse

Answer 29

Similarities
- neurotransmitters
- sodium potassium pump to maintain resting potential

Differences:
Neuromuscular:
- only excitatory
- only motor neurones
- neurotransmitter binds to membrane of muscle fibre (sarcolemma)

Synapse:
- inhibitory or excitatory
- can be any neurones
- neurotransmitter binds to post-synaptic neurone

Question 30

What molecule binds to myosin head causing it to detach from actin

Answer 30

ATP

Question 31

Why do slow twitch fibres need good blood supply and fast twitch fibres a high glycogen conc

Answer 31

1- slow twitch respire aerobically = need good O2 supply
2- fast twitch respite anaerobically at high intensity= need immediate energy source
3- slow twitch are low intensity = they have time for glucose to be supplied via blood/ don’t need their own store

Question 32

Role of ATP hydrolyse

Answer 32

• activated by Ca2+ ions
• ATP to ADP + P
• for energy for muscle contraction