lecture 30 - Skeletal muscle 1

Question 1

which type of muscle tissue is pictured here?

Answer 1

skeletal

Question 2

what is shown by numbers 1 - 5 and by the red arrow?

Answer 2

1. Z disc
2. H zone
3. I band
4. A band
5. M line

arrow shows 1 sarcomere

Question 3

label number 1-7

Answer 3

Question 4

which muscle type if pictured here?

Answer 4

cardiac

Question 5

what muscle type is this?

Answer 5

skeletal

Question 6

what’s this mayne?

Answer 6

smooth muscle

Question 7

is this cardiac, smooth, or skeletal muscle? why?

Answer 7

smooth (no strirations)

Question 8

which muscle type is under voluntary control?

Answer 8

skeletal

Question 9

which muscle types are striated?

Answer 9

cardiac and skeletal

Question 10

in skeletal muscle the nuclei are ________ whereas in cardiac muscle there are 1-3 ______ nuclei. Smooth muscles are _____-shaped and u______d

Answer 10

in skeletal muscle the nuclei are _peripheral_ whereas in cardiac muscle there are 1-3 _central_ nuclei. Smooth muscles are _spindle_-shaped and uninucleated.

Question 11

structure of skeletal muscle

Answer 11

• attach to bones via tendons
• 1 muscle fibre/cell goes from tendon to tendon (up to 35cm)
• reasonably wide at 0.1mm
• composed of myofibrils, containing filaments

Question 12

protein of thick filament

Answer 12

myosin

Question 13

protein of thin filament

Answer 13

globular actin

Question 14

myofibrils connect at the…

Answer 14

Z-disc

Question 15

where would you find only myosin and no actin?

Answer 15

H-zone

Question 16

at the _-line thick filaments are held together by the protein ______.

Answer 16

at the _M_-line thick filaments are held together by the protein _myomesin_.

Question 17

T-tubules

Answer 17

deep invaginations, continuous with the sarcolemma, which circle each sarcomere at the junctions of the A and I bands.

Question 18

in skeletal muscle, how many tubules per sarcomere?

Answer 18

2

Question 19

function of transverse tubules

Answer 19

allow action potentials to be carried deep within the muscle cell.

Question 20

sarcoplasmic reticulum

Answer 20

calcium storage site. The terminal cisternae of the SR lie close to the T-tubules

Question 21

what does this image show

Answer 21

contracted myofibril

Question 22

order the follwing from smallest to largest

• myofibril
• muscle
• sarcomere
• myofilament
• myocyte

Answer 22

smallest

1. myofilament
2. sarcomere
3. myofibril
4. myocyte
5. muscle

largest

Question 23

How many myosin subunits?

Answer 23

• 2
• one globular head and one tail
• tails intertwine to form a helix

Question 24

Each myosin head is an enzyme that…

Answer 24

hydrolyses ATP (ATPase)

Question 25

where would you find the binding site to which actin attaches?

Answer 25

myosin head

Question 26

how is actin arranged in thin filaments

Answer 26

double stranded helical actin chains

Question 27

\_\_\_\_\_\_\_\_\_\_ and _________ are regulatory proteins associated with actin in skeletal/cardiac muscle

Answer 27

\_Troponin\_ and \_tropomyosin\_ are regulatory proteins associated with actin in skeletal/cardiac muscle

Question 28

label 1,2 and 3

Answer 28

1 .troponin 2. actin 3. tropomyosin

Question 29

sliding filament theory of muscle conrtaction

Answer 29

sarcomere shortens as thin filaments are pulled over thick filaments

Question 30

outline the 4 steps of the **cross-bridge cycle**

Answer 30

1. cross-bridge formation 2. power stroke 3. detachment 4. energization of myosin head

Question 31

what must be present for the cross-bridge to form? why?

Answer 31

Ca²⁺ makes the actin site available

Question 32

what is the one region of the sarcomere that doesn't change in length/size during contraction?

Answer 32

A bands

Question 33

what is happening when the crossbridge forms?

Answer 33

myosin binds to the actin binding site (to form the crossbridge)

Question 34

what is occuring in the power stroke

Answer 34

- ADP is released (energy has been used) - the myosin head rotates to its low energy state (45^o to the actin) = sarcomere shortens

Question 35

what must happen for myosin to detach from actin?

Answer 35

a new ATP molecule binds to the myosin. This weakens the actin-myosin binding.

Question 36

energization of the myosin head

Answer 36

- myosin head hydrolyses the ATP to ADP + P_i - myosin moves back to its high energy conformation (90^o to the actin)

Question 37

Calcium binds to the \_\_\_\_\_\_\_, inducing a conformational change which pulls _________ off the ______ binding site. Therefore these sites are now available. As long as _______ is present above its threshold of (\_\_\_\_-\_\_\_\_mM) the cycle will continue.

Answer 37

Calcium binds to the \_troponin\_, inducing a conformational change which pulls \_tropomyosin\_ off the \_myosin\_ binding site. Therefore these sites are now available. As long as \_calcium\_ is present above its threshold of (\_0.001\_-\_0.01\_mM) the cycle will continue.

Question 38

how does calcium enter the cytosol of muscle fibres/cells?

Answer 38

calcium moves down its electrochemical gradient when the calcium channels in the sarcoplasmic reticulum open

Question 39

how does Ca2+ return to the SR?

Answer 39

Ca2+ ATPase transport pumps are constantly working to move calcium from the cytoplasm to the SR.

Question 40

what is Isotonic muscle contraction? what stays the same and what changes?

Answer 40

- shortening - tension constant - velocity variable

Question 41

what is isomeric muscle contraction? what stays the same and what changes?

Answer 41

- no shortening - length constant - tension variable

Question 42

where would you find Intercalated discs?

Answer 42

in cardiac muscle, connecting the cells together

Question 43

where would you find the I-band and the A-band?

Answer 43

I band = 2 (notice how it has become much smaller in length during contraction) A band = 1 (same length always)

Question 44

calcium interact with troponin in ______ regulated muscle and interact with calmodulin in _______ regulated muscle.

Answer 44

calcium interact with troponin in \_actin\_ regulated muscle and interact with calmodulin in \_myosin\_\_ regulated muscle.

Question 45

what is rigor mortis and what causes it?

Answer 45

stiff muscles caused by the absence of ATP, so the cross bridge can't detach

Question 46

when does the cross bridge cycle end?

Answer 46

when Ca2+ is actively transported back into the sarcoplasmic reticulum

Question 47

which number shows... (a) active tension (b) passive tension (c) total tension

Answer 47

1. = total tension 2. = passive tension 3. = active tension

Question 48

length-tension relationship

Answer 48

maximum force produced by the sarcomere is dependent on the degree of actin and myosin overlap

Question 49

in which type of muscle contraction can the legth-tension relationship be observed?

Answer 49

isometric

Question 50

what happens when the sarcomere is less than 2.0μm?

Answer 50

filaments collide and interfere with each other, reducing the force developed

Question 51

what happens, in the sarcomere, at lengths greater than 2.2μm?

Answer 51

active forced decline because the extent of overlap between filaments reduces, reducing the number of cross-bridges that can form

Question 52

at which length is the sarcomere able to produce the greatest force?

Answer 52

2.0μm-2.2μm

Question 53

pasive force =

Answer 53

as muscle is streched, the connective tissue around the muscle fibres resist the stretch

Question 54

active tension is dependent on?

Answer 54

sarcomere legnth

Question 55

total tension =

Answer 55

passive tension + active tension

Question 56

myocyte

Answer 56

another name for a muscle cell