Muscles: Skeletal muscle part 1

Question 1

Is skeletal muscle voluntary?

Answer 1

Yes

Question 2

What is the function of skeletal muscle

Answer 2

the physical movement of the body

Question 3

Features of skeletal muscle

Answer 3

It has multiple peripheral nuclei
It has single long cylindrical cells
Striated

Question 4

What attaches skeletal muscle to bones

Answer 4

tendons

Question 5

Length of skeletal muscle fibres

Answer 5

35cm

Question 6

Width of skeletal muscle fibres

Answer 6

0.1mm

Question 7

What are skeletal muscle fibres composed of that contract

Answer 7

Myofibrils (contractile filaments)

Question 8

What are the sections of myofibrils

Answer 8

Sacromeres

Question 9

Thick filaments

Answer 9

run the entire length of A band

Question 10

Thin filaments

Answer 10

run the entire length of the I band (only thin) and partway into the A band

Question 11

Z disc/line

Answer 11

coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another

Question 12

H Zone

Answer 12

lighter mid-region where filaments do not overlap (no thin filaments) ONLY thick

Question 13

M line

Answer 13

line of protein myomesin that holds adjacent thick filaments together

Question 14

Sacromeres

Answer 14

extend from the z line to the next z line. It can contract. Z disc comes closer to the M line. If the Z disc gets closer together,the H zone and I band will get smaller. A band stays the same length

Question 15

Structural features of T-tubules

Answer 15

deep invaginations continuous with the sarcolemma and circle each sarcomere at each of the junctions of the A and I bands.
Folding in of the sarcolemma, goes around twice per sarcomere (at ends of A band)

Question 16

Function of T-tubules

Answer 16

Allows action potentials to be carried deep within the muscle cell and allows extracellular fluid can be close to myofibrils

Question 17

What is the function of the Sarcoplasmic reticulum (SR)

Answer 17

It is a Ca storage site (Ca is on/off switch), takes up Ca so low [Ca] inside cell

Question 18

What is the terminal cisternae

Answer 18

The sacroplasmic reticiulm adjacent to the t-tubules. The terminal cisternae of the SR lie close to the T Tubules, means if AP comes down T tubule it can quickly tell SR to do something

Question 19

What is a triad

Answer 19

2 Terminal cisternae around T tubule

Question 20

What is thick filaments made of

Answer 20

myosin

Question 21

How many subunits does each myosin have?

Answer 21

2

Question 22

What are the features of the subunits in myosin

Answer 22

globular head and a tail - this intertwinses with the tail of the other subunit to form a helix

Question 23

Function of the myosin head

Answer 23

to act as a binding site for actin. It also is an enzyme that hydrolyses ATP (an ATPase) because it moves (with hinge)

Question 24

What is the resting state of the myosin head

Answer 24

Is being pulled in

Question 25

Arrangement of thick filaments

Answer 25

The myosin heads project away from the M-line while the tails of the two subunits are intertwined.

Question 26

Function of titin in thick filaments

Answer 26

Titin anchors the thick filament to the Z-line

Question 27

What are thin filaments mainly composed of?

Answer 27

Globular actin proteins

Question 28

Strucutural shape of thin filaments

Answer 28

double stranded helical actin chain

Question 29

The two regulatory proteins associated with actin in skeletal and cardiac muscle

Answer 29

Troponin and tropomyosin

Question 30

Function of tropomyosin

Answer 30

It interacts with the myosin binding sites. Initially on top of myosin binding sites (like a plug)

Question 31

Function of troponin

Answer 31

It is regulated by Ca2+ and pulls of tropomyosin off binding site

Question 32

Sliding filament theory of muscle contraction

Answer 32

Sarcomere shortens as THIN filaments are pulled OVER the thick filaments - Z-line is pulled toward the M-line - I band and H zone become narrower - Myosin stays still - Thin actin filaments are pulled OVER myosin

Question 33

What is the starting point of the cross bridge cycle?

Answer 33

There is no fixed starting point as it is a cycle

Question 34

What occurs in the "Cross bridge formation" stage of the cross bridge cycle

Answer 34

The myosin binding sites are available due to Ca so myosin binds to the myosin binding sites on actin forming a cross-bridge. Myosin has already hydrolyzed ATP (to ADP) (ENERGISED state), it “stretched out” - wants to relax to resting state = holding lots of energy

Question 35

What MUST be present for the cross bridge cycle to occur and why

Answer 35

free Calcium in the intercellular space!! so that the myosin binding site on actin is exposed

Question 36

What occurs in the "Power stroke" stage of the cross bridge cycle

Answer 36

ADP is released (causing myosin head to pull in: resting state). Myosin head rotates to its low energy state (45° to the actin) pulling with it the thin filament. This causes the sarcomere to shorten

Question 37

What occurs in the "Detachment" stage of the cross bridge cycle

Answer 37

A new ATP molecule binds to the myosin. The actin-myosin bond is weakened and the myosin detaches (head lets go of actin)

Question 38

What occurs without the presence of ATP in the cross bridge cycle

Answer 38

The myosin head cannot detatch from the myosin binding site in actin > Rigor mortis

Question 39

What occurs in the "Energization of the myosin head" stage of the cross bridge cycle

Answer 39

Myosin head hydrolyzes the ATP to ADP + Pi | The myosin head moves back to its “high energy (cocked)” confirmation ( 90° to actin)

Question 40

What is the role of calcium in the cross bridge cycle?

Answer 40

Ca ions provide the “on” switch for the cross-bridge cycle to begin. When Ca binds with troponin, the tropomyosin moves to expose the myosin binding sites on actin

Question 41

What is the Ca threshold for the cross bridge cycle

Answer 41

0.001-0.01 mM

Question 42

What will a high concenration of Ca in the intercellular space cause in skeletal muscle?

Answer 42

A contraction

Question 43

What are the two features of skeletal muscle that regulate calcium?

Answer 43

Ca channels and active transport pumps Ca2+ ATPase

Question 44

Where are Ca channels located and how do they function?

Answer 44

Ca channels in the sacroplasmic reticulum allow the movement of Ca ions into the cytosol, regulating Ca levels - when they are open = Ca release so contraction - when they are closed = Ca cannot be released so not enough Ca for a contraction

Question 45

Where are Active transport pumps (Ca2+ ATPase) located and how do they function?

Answer 45

They are in the sacroplasmic reticulum and are constantly moving Ca2+ from the cytoplasm back into the sarcoplasmic reticulum. As soon as Ca levels drop - contraction stops