Lecture 04 Skeletal Muscle Flashcards Preview

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Flashcards in Lecture 04 Skeletal Muscle Deck (77):
0

What refers to a chain of sarcomeres?

Myofibril

1

what sarcomeric band does not undergo a change in length during the contraction of a skeletal muscle?

A Band

2

Dihydropyridine (DHP) channels are part of what structure?

T tubules

3

Ryanodine-sensitive calcium ion release channels are part of what structure?

Sarcoplasmic reticulum

4

Which of the following events occurs first during the transmission of a signal from an alpha motor neuron to a skeletal muscle fiber?
End-plate Depolarization
Calcium Ion Influx into Axon Terminal
Exocytosis of synaptic vesicles
Sarcolemma action potential

Calcium Ion Influx into Axon Terminal

5

Which of the following represents the factor by which the concentration of calcium ion increases in the cytosol after release from the sarcoplasmic reticulum
10
50
100
1000

100

6

Which of the following maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
Calsequestrin
SERCA
DHP
Ryanodine

Calsequestrin

7

Fast twitch fibers have what characteristics?

More fatigable than slow twitch fibers

8

Which of the following represents an example of an eccentric contraction?
1. The triceps muscle during the throwing of a ball
2. The triceps muscle while raising the body from the floor during a push-up
3. The triceps muscle while lowering the body to the floor during a push-up
4. The biceps muscle while raising the body during a pull up

3

9

What is epimysium

Connective tissue surrounding entire muscle

10

What is a muscle?

Made up of multiple fascicles

11

What is perimysium?

Connective tissue surrounding individual fascicle

12

What is a fascicle

A bundle of myofibers

13

What is endomysium

Delicate connective tissue around each myofiber

14

What is sarcolemma

The plasmalemma or cell membrane of a muscle fiber

15

What is myofiber

Individual multinucleated muscle cell

16

What is myofibril

A chain of sarcomeres within a myfiber

17

What is myofilament

Actin and myosin filaments that make up a sarcomere

18

What creates a triad?

Two cisternae with t tubule in between

19

What is a T-tubule?

Invaginations of sarcolemma

20

What are the four sections of sarcomeres?

Z lines, I bands, A bands, and H bands

21

What is a Z disc?

Anchor actin filaments and are loacted at each end of a sarcomere

22

What are I bands?

Composed entirely of actin and the width changes during contraction

23

What are A bands?

Composed of actin and myosin and width does not change during contraction

24

What are H bands?

Composed of entirely myosin and width changes during contractions

25

When sarcomeres are aligned what pattern is produced?

Banding pattern characteristic of striated muscle. Bands are lined up

26

Where is the nucleus in a muscle fiber?

Nucleus pushed to the outside of the of the sarcomeres

27

What steps happen in the synaptic cleft and terminal end of nerve fiber?

1. Arrival of action potential at terminal end of nerve fiber
2. Opening of voltage-gated calcium channels on nerve fiber ending. Ca diffuse into the terminal
3. Neurotransmitter (Ach) are released from synaptic vesicles into synaptic cleft (exocytosis) and diffuses
4. 2 Ach attach to ligand-gated sodium channels of the sarcolemma

28

What happens once the ligand-gated sodium channels of the sarcolemma open?

1. There is a sodium ion influx that causes End - plate Depolarization and thus opens voltage-gated sodium channels (Sarcolemma action potential)
2. Voltage-gated channels on T tubules (DHP) interact with ryanodine receptors on the SR membrane
3. Opeing of ryanodine - releases calcium
4. Increase Calcium ion in cytosol activates the sliding filament mechanism

29

What is DHP?

Dihydropyridine receptors that are voltage sensitive. L - type calcium channels arranged in quadruplets. Causes conformation change in the ryanodine receptors

30

What happens once calcium is released into the cytosol?

Calcium binds to troponin C on the actin filament.
Troponin then conforms and cause tropomyosin to expose active sites on actin
Myosin heads bind to actin active sites

31

What activates the myosin head?

ATP bound to the myosin hydrolyzed to ADP and inorganic phosphate. Energy liberated from the hydrolysis of ATP activates the myosin forcing it to the cock position.

32

What are the cross bridge steps?

1. Activated myosin head binds to actin forming a cross bridge
2. Inorganic phosphate is released and the bond between actin and myosin becomes stronger
3. ADP is released and the activated myosin head power strokes.
4. When another ATP binds to myosin head, the link between myosin and actin weakens and the myosin detaches

33

When will the myosin sliding stop?

As long as the active sites are exposed the process will repeat. When Calcium ions are actively transported back into the Sarcoplasmic reticulum causing the troponin to return to original shape allowing tropomyosin to glide over and cover myosin binding sites on actin

34

Between what bands are the T tubules located?

Between the A-I interface. Because of that they can have cisterni on each side of the t tubules and become triads.

35

Once ryanodine channels open where does the Ca ions flow out of?

Out of the sarcoplamic reticulum

36

When does the ryanodine channels close?

When the sarcolemma repolarizes

37

What does calsequestrin do?

Binds the Ca within the sarcoplasmic reticulum so that when the ATP calcium pumps are uptaking Ca they are not working so hard. Controls the concentration of free calcium with in the SR.

38

The calcium pump on in the SR is what type of transport?

Active transport

39

What are ryanodine receptors?

(RyRs) calcium release channels that are located on the cisternae. Open in response to conformational change in DHP receptors

40

What is SERCA?

Sarcoplasmic reticulum calcium ATPase - Uses ATP to pump calcium back into the SR

41

Why is there no tension when the sarcomere is fully stretched out?

Because there is no interaction between the myosin and actin when fully stretched out

42

When is tension maximum in a sarcomere?

When there is interaction between actin and myosin. And actin filament has overlapped all the cross bridges.

43

At what point is no more tension possible?

Max point occurs when acting filaments touch

44

What happens when actin filaments overlap?

Tension drops toward 0 because no more sliding can occur

45

True or False
When our bodies are at rest on a couch our muscles are 100% relaxed

No. There is some tension in all of our muscle. Keeps us sitting.

46

What is muscle tone?

Keep muscles in a slightly contracted state. Allows us to be ready to have a muscle contraction when needed

47

Where is ATP required for muscle contraction?

Sliding filament mechanism, pumping Ca ions from sarcoplasm into SR, pumping Na and K ions through the sarcolemma to reestablish resting potential

48

What is the concentration of ATP in muscle fiber?

4mmol which is enough to maintain contraction for 1-2 seconds

49

How does phosphocreatine restore ATP?

Phosphocreatine can release energy rapidly to ATP. Add phosphates back to ATP. Provides enough energy for 5-8 seconds of contraction when phosphocreatine is used with ATP

50

What are three methods of rephosphorylation of ATP?

Phosphocreatine, Glycolysis, oxidative metabolism

51

How does Glycolysis rephosphorylize ATP?

Can produce ATP and sustain contraction for 1 minute but there is a build up of pyruvic acid and which is converted to lactic acid.

52

What rephosphorylizes ATP the best for long-term contractions?

Oxidative metabolism: provides more than 95% of all energy needed for long-term contraction
Electron transport chain and kreb's cycle in the mitochondrion provides a lot of ATP

53

What are two main types of muscle contractions?

Isometric and isotonic

54

What is isometric muscle contraction?

Occurs when there is an increase in tension but not in length. Achieved by pushing on wall and muscle length remains the same but tension builds up

55

What is isotonic muscle contraction?

When muscle length changes

56

What are the two types of isotonic contractions?

Eccentric: Muscle gets longer : Force is greater than tension
Concentric: muscle gets shorter : Force is less than the tension

57

What are the two types of myofibers?

Dark, slow fibers (red)
Light, Fast fibers (white)

58

What are fast muscle fibers?

They are fibers that contract rapidly but have less endurance. Fewer mitochondria, little myoglobin, use anaerobic respiration primarily. Larger concentration of ATPase

59

What are slow fibers?

Red fibers that contract more slowly but have more endurance. They have more mitochondria, use aerobic respiration, have more myoglobin, and have smaller concentration of ATPase

60

True or False
In adulthood, one cane increase the number of myofibers?

False. Mass of myofiber can increase by increasing myoFRIBRILS

61

What happens if there is a lost of muscle tissue?

It will be replaced by scar tissue. Fibrous connective tissue

62

What muscle is predominantly composed of dark fibers in mammals?

Soleus

63

What muscle is predominantly composed of light fibers?

Gastrocnemius

64

What is a motor unit?

Neuron and the myofibers it innervates

65

What does the all - or - none really refer to?

A motor unit

66

What is summation?

Electrical events occur faster than mechanical events

67

How does summation work in skeletal muscle fibers?

Before the Ca returns to the SR the remaining Ca causes another action potential. Continued cycling between myosin and actin which increases the muscle tension. Each additional spike adds to the effects of the previous spikes

68

What is tetany?

If the frequency of spikes is fast enough, there is no time for relaxation between spikes and the muscle remains at maximal contraction.

69

How does the bone-muscle system often transmit forces?

Levers
Bone is the lever. The joint is the pivot/fulcrum

70

What is an example of a First - class lever system? Explain the first - class lever system

Fulcrum is in the middle and raising chin using the sternocleidomastoids or similar muscles. In-force and out-force move in opposite directions

71

What is a second-class lever system? Give an example

Resistance (out-force) is in the middle. Example is raising the body on the ball of the foot. Fulcrum= ball of foot. Both in and out forces are on the same side of the fulcrum

72

What is a third - class lever system? Give an example

Effort (in-force) is in the middle. Lifting a weight in the palm of your hand. Both in and out forces are on the same side of the fulcrum. And both forces move in same direction

73

Where do machines transmit forces?

From one place to another

74

What two forces involve machines?

Force applied to the machine (in-force (Fi) or effort)
Force derived from the machine (out-force (Fo) or resistance)

75

The force times it lever arm is a moment. Functional lever must have at least two moments. What are the two equations?

Mi=FiLi
Mo=FoLo
Equilibrium = FiLi = FoLo

76

Is our bicep elbow lever system designed for weight or speed?

Speed.