Muscles

Question 1

2 protein filaments in myofibrils

Answer 1

Actin and myosin

Question 2

I band

Answer 2

Light bands where actin is and does not cross over with myosin

Question 3

A band

Answer 3

Dark region where actin and myosin overlap

Question 4

H zone

Answer 4

Light coloured region in the middle of the A band (myosin)

Question 5

Sarcomere

Answer 5

Distance between adjacent Z lines

Question 6

Properties of slow twitch

Answer 6

Adapted for aerobic.
Large store of myoglobin
Rich supply of blood vessels and numerous mitochondria

Question 7

Properties of fast twitch

Answer 7

Thicker and more numerous myosin filaments.
Higher conc of glycogen.
High conc of enzymes involved in anaerobic for rapid ATP.
Phosphocreatine store (can rapidly generate ATP from ADP in anaerobic conditions)

Question 8

Motor unit

Answer 8

All the muscle fibres supplied by the same motor neurone

Question 9

Neuromuscular junction

Answer 9

When nerve impulse arrives calcium ion protein channels open and diffuse into knob, synaptic vesicle fuses with presynaptic membrane and releases acetylcholine. Diffuses to postsynaptic membrane and increases permeability to Na+ which enter and depolarise membrane, creating impulse. Acetylcholinesterase breaks it down to avoid overstimulation.

Question 10

Similarities between neuromuscular junction and synapse

Answer 10

Both neurotransmitters transported by diffusion.
Both have receptors that cause influx of Na+ when binded to.
Use Na+-K+ pump to repolarise axon.
Use enzymes to break down neurotransmitter

Question 11

Differences between neuromuscular junction and synapse

Answer 11

NMJ only links motor neurone to muscle

End of action potential.

Question 12

What happens to I band during muscle contraction

Answer 12

Becomes narrower

Question 13

What happens to Z lines during muscle contraction

Answer 13

Go closer together, sarcomere shortens

Question 14

What happens to H zone during muscle contraction

Answer 14

Narrower

Question 15

What happens to A band during muscle contraction

Answer 15

Same length as it is determined by length of myosin

Question 16

How does the action potential cause muscle contraction

Answer 16

Action potential travels into muscle fibre via T-tubules (extension of cell-surface membrane that branch into cytoplasm).
Tubules in contact with endoplasmic reticulum which actively transports Ca2+ into it from cytoplasm.
Action potential opens Ca2+ protein channels on ER causing Ca2+ to diffuse into cytoplasm down conc gradient.

Question 17

How does influx of Ca2+ into cytoplasm cause muscle contraction

Answer 17

Bind to troponin and cause tropomyosin molecules blocking binding sites on actin to move away.
ADP molecules on myosin head allow them to bind actin filament and form cross bridge.
Myosin heads bend and change their angle to perform a power stroke and release ADP.
The ATP binds to myosin heads which causes them to release from actin filament.
ATP hydrolase hydrolyses ATP which causes the myosin heads to move back to original position.
Repeats until full contraction

Question 18

Role of ATP in muscle contraction

Answer 18

Return movement of myosin heads to cause actin filament to slide.
Return of calcium ions to sarcoplasmic reticulum via active transport.

Question 19

Phosphocreatine

Answer 19

Molecule stored by muscles for rapid production of ATP as phosphate ion from phosphocreatine transferred to ADP to form ATP and creatine.