Skeletal Muscles (15)

Question 1

What are the 3 types of muscle?

Answer 1

cardiac muscle
smooth muscle
skeletal muscle

Question 2

Where are cardiac muscles found?

Answer 2

only in the heart

Question 3

Where are smooth muscles found?

Answer 3

walls of blood vessels and intestines

Question 4

Where are skeletal muscles found?

Answer 4

attached to incompressible skeleton by tendons

Question 5

What is meant by antagonistic pair of muscles?

Answer 5

muscles can only pull, so they work in pairs to move bones around joints by pulling in opposite directions

Question 6

What are the names of the muscles in antagonistic pairs, and what do they do?

Answer 6

agonist contracts
antagonist relaxes

Question 7

What 2 things happen during muscle contraction?

Answer 7

1) Calcium ions are actively transported back into the endoplasmic reticulum
2) tropomyosin blocks the actin binding site

Question 8

What is the gross structure of skeletal muscles?

Answer 8

• muscle cells are fused together to form myofibrils
• arrangement ensures there’s no point of weakness between cells
• each bundle is surrounded by endomysium

Question 9

What are myofibrils?

Answer 9

bundles of parallel muscle fibres

Question 10

What is endomysium?

Answer 10

loose connective tissue with many capillaries

Question 11

What are the 3 features of the microscopic structure of skeletal muscles?

Answer 11

myofibrils
sarcoplasm
sarcolemma

Question 12

What is the role of myofibrils?

Answer 12

site of contraction

Question 13

What is the sarcoplasm?

Answer 13

shared nuclei and cytoplasm with lots of mitochondria and endoplasmic reticulum

Question 14

What is the sarcolemma?

Answer 14

folds inwards towards sarcoplasm to form transverse tubules

Question 15

Draw the ultrastructure of myofibril, including its bands.

Answer 15

Look at notes.

Question 16

What are the 5 steps on how muscle contraction is stimulated?

Answer 16

1) at the neuromuscular junction, an action potentil causes voltage-gated calcium ion channels to open
2) vesicles move towards and fuse with the presynaptic membrane
3) exocytosis of acetylcholine which diffuses across synaptic cleft
4) acetylcholine binds to receptors on the sodium ion channel proteins on the skeletal muscle cell membrane
5) an influx of sodium ions causes depolarisation

Question 17

What is the role of calcium ions in muscle contraction?

Answer 17

1) action potential moves through transverse tubules in the sarcoplasm so calcium ion channels in the sarcoplasmic reticulum open
2) calcium ions bind to tropomyosin, triggering conformational change in tropomyosin
3) exposes binding site on actin filaments so actomyosin bridges can form

Question 18

What are the 5 steps of the sliding filament theory?

Answer 18

1) myosin head with ATP attached forms cross bridge with actin
2) this causes a power stroke where the myosin head changes shape, loses ADP and pulls actin over the myosin
3) ATP attaches to myosin head, causing it to detach from the actin
4) ATPase hydrolyses ATP so myosin head can return to original position
5) myosin head re-attaches to actin further along the filament

Question 19

What are the 4 pieces of evidence supporting the sliding filament theory?

Answer 19

1) H-zone narrows
2) I-band narrows
3) Z-lines get closer
4) A-zone remains the same width, proving myosin don’t shorten

Question 20

How does the sliding filament theory cause myofibril to shorten?

Answer 20

• myosin heads flex in opposite directions and so actin filaments are pulled towards each other
• distance between adjacent sarcomere Z lines shortens

Question 21

What is the role of phosphocreatine in muscle contraction?

Answer 21

it phosphorylates ADP directly into ATP (using its phosphate group) when O2 for aerobic respiration is limited (e.g. during vigorous exercise)

Question 22

Where do slow-twitches happen?

Answer 22

calf muscles

Question 23

Where do fast-twitches happen?

Answer 23

biceps

Question 24

What are the 3 steps in how to calculate the length of one sarcomere?

Answer 24

1) view thin slice of muscle under optical microscope
2) calibrate eyepiece graticule
3) measure distance from middle of 1 light band to another

Question 25

What is the function of slow-twitch?

Answer 25

• long-duration contraction
• well-adapted to aerobic respiration to prevent lactate buildup

Question 26

What is the function of fast-twitch?

Answer 26

• powerful, short-term contraction
• well-adapated to anaerobic respiration

Question 27

What are 4 structures/properties of slow-twitch?

Answer 27

• glycogen store
• contain myoglobin
• many mitochondria
• surrounded by many blood vessels

Question 28

How does having a glycogen store help with slow-twitches function?

Answer 28

many terminal ends can be hydrolysed to release glucose for respiration

Question 29

How does containing myoglobin help with slow-twitches function?

Answer 29

higher affinity for O2 than haemoglobin at lower partial pressures

Question 30

How does having many mitochondria help with slow-twitches function?

Answer 30

more ATP produced during aerobic respiration

Question 31

How does being surrounded by blood vessels help with slow-twitches function?

Answer 31

high supply of O2 and glucose

Question 32

What are 5 structures/properties of fast-twitch?

Answer 32

• large store of phosphocreatine
• more myosin filaments
• thicker myosin filaments
• high concentration of enzymes involved in anaerobic respiration
• extensive sarcoplasmic reticulum

Question 33

How does having an extensive sarcoplasmic reticulum help with fast-twitches function?

Answer 33

allows for rapid uptake and release of calcium ions