Sarcomere Structure

Question 1

What are the 3 layers that separate Muscles and what is contained in each of them?

Answer 1

Endomysium - separates muscle fibres

Perimysium - lies between fascicles/fasciculi

Epimysium - dense sheath on surface of bundles of fascicles

Question 2

What are the 3 components of muscles?

Answer 2

Muscle fibre (cell) -> Fascicle -> muscle

Question 3

Where is force from muscles transmitted to?

Answer 3

The force is transmitted from muscles through tendons to the bone

Question 4

What are the 3 components of a muscle fibre cell and their function?

Answer 4

Sarcolemma - true cell membrane that encloses the muscle fibre

Sarcoplasm - intracellular fluid that fills spaces between myofibrils

Myofibril - mainly composed of acting and myosin filaments

Question 5

Where does the nuclei of a muscle fibre cell sit?

Answer 5

On the outside on top of the sarcolemma

Question 6

What is the sarcomere?

Answer 6

The portion of myofibril that lies between two Z-disks

Question 7

Draw and label the structure of a sarcomere?

Answer 7

Question 8

How do you recognise the A band under a microscope?

Answer 8

Its quite dark

Question 9

What band is split half by the ends of 2 different sarcomeres? And what colour is this band?

Answer 9

I band

Light

Question 10

What is in the H-zone?

Answer 10

The very middle of the Sacromere

Question 11

What disks define the end of the sarcomere?

Answer 11

the 2 Z-disks

Question 12

What is a myofibril?

Answer 12

The name for the individual rod like strand of muscle tissue/cell which all bundle together to form a fasicle

Question 13

What is the M line?

Answer 13

The M line runs down the middle of the sarcromere and in the middle of the A band

Question 14

What is the purple partin the sarcromere?

Answer 14

Thin actin filament

Question 15

What is the dark proportion of the myofibril?

Answer 15

Thick myosin filament

Question 16

How does Myosin attach to Actin?

Answer 16

Via its cross bridges which have actin binding sites

Question 17

What does the myosin tails made from?

Answer 17

two intertwined heavy chains

Question 18

What are the 2 binding sites found on Myosin fillaments?

Answer 18

Actin binding sites and ATP binding sites

Question 19

What do cross bridges do?

Answer 19

Attach to Actin and move their chains

Question 20

What filaments are thick and what ones are thin?

Answer 20

Myosin filaments are thick

Actin filaments are thin

Question 21

Give 2 features of Actin?

Answer 21

Actin is a contractile protein

Each G actin has a binding site for myosin

Question 22

What 2 other molecules are found in actin filaments?

Answer 22

Tropomyosin and Troponin

Question 23

What is the function of Tropomyosin?

Answer 23

Tropomyosin is a regulatory protein which overlaps the binding sites on actin for myosin, so it inhibits interation with myosin when Tropomyosin is in its relaxed state

Question 24

What is the function of Troponin?

Answer 24

Troponin is a regulatory calcium binding protein which forms a complex with the other proteins of the thin filament (Actin. and Tropomyosin)

Troponin binds to calcium and once its bound it changes conformation to pull tropomyosin away from the myosin interaction sites which regulates skeletal muscle contraction because it moves tropomysin away allowing the myosin to bind to actin.

Question 25

What protein attaches to keep myosin and actin in place together?

Answer 25

Titin

Question 26

Where does Titin attach to?

Answer 26

The Z-line

Question 27

What is the function of Titin?

Answer 27

To provide elasticity and stabilise myosin

Question 28

What is the role of Nebulin?

Answer 28

Nebulin helps align actin

Question 29

What are the 4 stuctural proteins?

Answer 29

Titin Z line protein (alpha-actinin) M-line proteins (myomesin, M-protein) Nebulin

Question 30

What are the 4 contractile proteins, which are involved in contraction and movement of filaments?

Answer 30

Actin Myosin Tropomyosin Troponin complex

Question 31

What is responsible for giving skeletal and cardiac muscles their striated appearance?

Answer 31

The thick and thin arrangement in Myofibrils

Question 32

Draw the what a Myofibril looks like and 3 different cross sections of where thick, thin and mixed filaments would occur

Answer 32

Question 33

What would you expect to see in cross sections of the I band, H zone, M line and the outer edge of the A band?

Answer 33

Question 34

What kind of structures would you expect to see in an A-band?

Answer 34

Primarily myosin filaments in the region of overlap

Question 35

What kind of structures would you expect to see in an I-band?

Answer 35

Actin filaments bisected by Z-line

Question 36

What kind of structures would you expect to see in the H-zone?

Answer 36

Region of A-band which contains only myosin filaments

Question 37

What occurs when a muscle goes from being relaxed to contracted?

Answer 37

The myosin and actin filaments move closer together and overlap more H zone and the I band both shorten

Question 38

What are T-tubules and their function?

Answer 38

T-tubules are invagination of the sarcolemma of skeletal and cardiac muscle * Action potential is propagated from the end plate along the surface of the muscle fibre (sarcolemma) * Action potential is propagated into the fibre down the T-tubule membrane * Depolarisation of the T-tubule membrane is 'signalled' to the membrane of the terminal cisternae

Question 39

Draw how the T-tubules, Sarcoplamic reticulum and terminal cisternae interact with myofibrils?

Answer 39

Question 40

What is the Sarcoplasmic reticulum and its function?

Answer 40

Its the same as the endoplasmic reticulum found in most cells (contains tubules for sorting and transporting things) Calcium is stored and release from here following membrane excitation

Question 41

How do T-tubules and Sarcoplasmic reticulum interact?

Answer 41

They are connection with junctions made from 2 intergral proteins, one in the T-tubules membrane and one in the Sarcoplasmic reticulum The T-tubule protein is a modified voltage-sensitive calcium channel called dihydropyridine receptor (DHP) which acts as a voltage sensor The Sarcoplasmic reticulumprotein is called ryanodien receptor (RYR) which forms a calcium channel

Question 42

How does T-tubules transport the action potentials?

Answer 42

T-tubule brings action potentials into the interior of the muscle fibre

Question 43

Where is calcium stored in the muscle?

Answer 43

In the Sacroplasmic reticulum