Muscle Structure

Question 1

How many types of muscle are there?

Answer 1

Skeletal, Cardiac and smooth

Question 2

Which types of muscle are striated?

Answer 2

skeletal and cardiac

Question 3

What is most skeletal muscle attached to?

Answer 3

bone

Question 4

what attaches skeletal muscle to bonds?

Answer 4

tendons

Question 5

what are the 2 main functions of skeletal muscle?

Answer 5

• movement

- generation of heat

Question 6

Is muscle contraction endothermic or exothermic?

Answer 6

exothermic

Question 7

What are muscle cells called? (2 names)

Answer 7

• myocytes

- muscle fibres

Question 8

What covers muscle fibres?

Answer 8

a layer of connective tissue called endomysium

Question 9

is the endomysium part of the myocyte membrane or not?

Answer 9

not- it’s distinct

Question 10

what is the name of muscle fibre membrane?

Answer 10

sarcolemma

Question 11

are muscle cells multinucleate?

Answer 11

yes (each cell has several nuclei)

Question 12

what makes muscle cells multinucleate?

Answer 12

cell fusion during development

Question 13

How are muscle fibres grouped?

Answer 13

into bundles called Fascicles

Question 14

what covers fascicles?

Answer 14

a sheath called the epimysium (forms the muscle)

Question 15

what is an individual muscle fibre made up of?

Answer 15

bundles of protein filaments called myofibrils

Question 16

what are myofibrils composed of?

Answer 16

bundles of protein filaments called myofilaments

Question 17

what are the Tunnels in muscle fibres called?

Answer 17

T-tubules

Question 18

where are the T-tubules?

Answer 18

in muscle fibres leading off from the sarcolemma into the interior of the muscle fibre

Question 19

where is the sarcoplasmic reticulum found?

Answer 19

wrapped around the myofibrils

Question 20

What forms a triad?

Answer 20

specialised parts of the sarcoplasmic reticulum called terminal cisternae and T-tubules

Question 21

What is the function of a triad?

Answer 21

couples membrane excitation with contraction

Question 22

What are the 2 main structural features of the sarcomere?

Answer 22

thin and thick filaments

Question 23

what are thick filaments made up of? (2)

Answer 23

myosin and titin

Question 24

what are thin filaments made up of?

Answer 24

actin and nebulin

Question 25

what do both the thick and the thin filament connect to?

Answer 25

the Z-disk

Question 26

what is the z-disk?

Answer 26

the part of the sarcomere which joins 2 sarcomeres together

Question 27

what are only the thick filaments connected to?

Answer 27

proteins of the M-line

Question 28

what is the M-line?

Answer 28

the centre of a sarcomere

Question 29

what’s the name of the model suggesting how muscle contraction occurs?

Answer 29

sliding filament theory

Question 30

what type of myosin is found in skeletal muscle?

Answer 30

Type II

Question 31

What activity does a myosin head have?

Answer 31

ATPase

Question 32

What controls the movement in sliding filament?

Answer 32

hydrolysis of ATP

Question 33

how many forms does actin exist in?

Answer 33

2

Question 34

what 2 forms does actin exist in?

Answer 34

• Globular (G)

- Filamentous (F)

Question 35

which form of actin is found in proteins?

Answer 35

Filamentous (F)

Question 36

Describe tropomyosin

Answer 36

runs along the actin chain and consists of 2 alpha helical chains that coil around each other. 1 tropomyosin interacts with 7 actin monomers

Question 37

describe troponin

Answer 37

a complex of 3 proteins- troponin T, I and C

Question 38

What does Troponin T do?

Answer 38

binds to tropomyosin

Question 39

what does Troponin I do?

Answer 39

binds to actin and inhibits contraction

Question 40

what does Tropnin C do?

Answer 40

binds calcium

Question 41

In terms of just Actin and Myosin interaction, what happens during muscle contraction?

Answer 41

• Myosin is found to actin
• Myosin head binds ATP and the myosin-actin cross-bridge dissociates
• Myosin head has built-in ATPase activity- breaks down ATP to ADP+ Pi - changing myosin conformation (cocked state)
• new bridge forms between actin and myosin
• phosphate is released and power stroke occurs- myosin returns to uncocked state. ADP is released and system is back at starting point- but the actin and myosin have moved relative to eachother- contraction

Question 42

What happens in terms of Troponin and Troppomyosin to trigger contraction?

Answer 42

• At rest, the troponin trimer sits so that TnI inhibits the formation of actin-myosin bridges (covers myosin binding site)
• When contraction is signaled, Ca2+ conc. increases, Ca2+ can now bind to troponin C- triggering a change in conformation of troponin and tropomyosin
• Tropomyosin moves deeper into the actin groove, whilst troponin complex shifts up, revealing the myosin binding sites for actin- cross bridges and contraction can occur

Question 43

describe the chain of events at the NMJ?

Answer 43

• Motor neurons release ACh into synapse which bind to nAChR at the muscle membrane, which open, allowing Na+ ions to flood in to the muscle and depolarise the membrane
  this depolarisation causes a calcium signal which can start the actin-myosin bridge formation

Question 44

where in the muscle fibre is Calcium high?

Answer 44

the sarcoplasmic reticulum

Question 45

How does calcium get into the sarcoplasmic reticulum in the first place?

Answer 45

SERCA (sarcoplasmic/endoplasmic reticulum calcium ATPase) actively pumps it in

Question 46

describe the movement of calcium when muscle contraction occurs

Answer 46

An AP spreads down the T-tubule, cuasing a change in Dihydropyridine/ DHP/ L-type VSCC
this pulls open the ryanodine receptor, releasing Ca2+ from the sarcoplasmic reticulum into the cytoplasm
after contraction has taken place, SERCA pumps calcium ions back into SR, restoring low Ca2+ concentration in the cytoplasm