6.4 - Skeletal muscles

Question 1

Describe features of skeletal muscles (sometimes called striped or striated)

Answer 1

• voluntary
• joined to bones by tendons

Question 2

What feature do all muscles share?

Answer 2

pairs are antagonistic

Question 3

Name the two main proteins present in a myofibril and describe them

Answer 3

actin: thin and myosin: thick

Question 4

What is the sarcolemma?

Answer 4

membrane of a muscle fibre

Question 5

What is the sarcoplasm?

Answer 5

cytoplasm of a muscle fibre

Question 6

What is the sarcomere?

Answer 6

one contractile unit of a muscle fibre

Question 7

What is the A band?

Answer 7

total width of myosin

Question 8

What is the H zone?

Answer 8

where there is myosin only

Question 9

What is the I or light band?

Answer 9

where there is actin only

Question 10

What is the M line?

Answer 10

middle point of myosin

Question 11

What do Z lines indicate?

Answer 11

the parameters of one sarcomere

Question 12

Describe what happens to the parts of a myofibril during contraction

Answer 12

• A band stays same
• H zone and I band shorten
• Z lines move closer together

Question 13

Does the A band ever change?

Answer 13

no, it always stays constant

Question 14

Fast twitch muscles fibres

Answer 14

• fast contractions
• rapid release of energy
• lots of thick myosin filaments
• high glycogen conc -> hydrolysis of glycogen to glucose
• high conc of enzymes involved in anaerobic respiration (uses mainly anaerobic)
• high conc of phosphocreatine to rapidly generate ATP from ADP

Question 15

Slow twitch muscle fibres

Answer 15

• slow contractions
• long periods of exercise
• large store of myoglobin
• rich blood supply
• lots of mitochondria
• mainly aerobic respiration

Question 16

Role of phosphocreatine

Answer 16

combines with ADP to form ATP for muscle contraction

Question 17

Describe how skeletal muscle contracts

Answer 17

• Ca2+ ions diffuse into myofibrils from sarcoplasmic reticulum
• causing movement of tropomyosin on actin, exposing actin’s actin-myosin binding sites
• myosin heads attach to binding sites on actin, forming actinomyosin cross bridges
• hydrolysis of ATP on myosin heads causes them to bend, pulling actin molecules
• new ATP molecule attaches to each myosin head
• so myosin heads detach from sites

Question 18

What else is ATP needed for?

Answer 18

active transport of Ca2+ ions into sarcoplasmic reticulum