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Physiology - Jourdan > Lecture 04 Skeletal Muscle > Flashcards

Lecture 04 Skeletal Muscle Flashcards

0
Q

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

A

A Band

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1
Q

What refers to a chain of sarcomeres?

A

Myofibril

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2
Q

Dihydropyridine (DHP) channels are part of what structure?

A

T tubules

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3
Q

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

A

Sarcoplasmic reticulum

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4
Q 
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
A

Calcium Ion Influx into Axon Terminal

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5
Q 
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
A

100

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6
Q 
Which of the following maintains an optimum calcium concentration gradient to facilitate return of calcium to SR
Calsequestrin
SERCA
DHP
Ryanodine
A

Calsequestrin

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7
Q

Fast twitch fibers have what characteristics?

A

More fatigable than slow twitch fibers

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8
Q

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
A

3

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9
Q

What is epimysium

A

Connective tissue surrounding entire muscle

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10
Q

What is a muscle?

A

Made up of multiple fascicles

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11
Q

What is perimysium?

A

Connective tissue surrounding individual fascicle

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12
Q

What is a fascicle

A

A bundle of myofibers

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13
Q

What is endomysium

A

Delicate connective tissue around each myofiber

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14
Q

What is sarcolemma

A

The plasmalemma or cell membrane of a muscle fiber

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15
Q

What is myofiber

A

Individual multinucleated muscle cell

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16
Q

What is myofibril

A

A chain of sarcomeres within a myfiber

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17
Q

What is myofilament

A

Actin and myosin filaments that make up a sarcomere

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18
Q

What creates a triad?

A

Two cisternae with t tubule in between

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19
Q

What is a T-tubule?

A

Invaginations of sarcolemma

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20
Q

What are the four sections of sarcomeres?

A

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

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21
Q

What is a Z disc?

A

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

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22
Q

What are I bands?

A

Composed entirely of actin and the width changes during contraction

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23
Q

What are A bands?

A

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

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24
Q

What are H bands?

A

Composed of entirely myosin and width changes during contractions

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25
Q

When sarcomeres are aligned what pattern is produced?

A

Banding pattern characteristic of striated muscle. Bands are lined up

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26
Q

Where is the nucleus in a muscle fiber?

A

Nucleus pushed to the outside of the of the sarcomeres

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27
Q

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

A
  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
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28
Q

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

A
  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
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29
Q

What is DHP?

A

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

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30
Q

What happens once calcium is released into the cytosol?

A

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
Q

What activates the myosin head?

A

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
Q

What are the cross bridge steps?

A
  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
Q

When will the myosin sliding stop?

A

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
Q

Between what bands are the T tubules located?

A

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

35
Q

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

A

Out of the sarcoplamic reticulum

36
Q

When does the ryanodine channels close?

A

When the sarcolemma repolarizes

37
Q

What does calsequestrin do?

A

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
Q

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

A

Active transport

39
Q

What are ryanodine receptors?

A

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

40
Q

What is SERCA?

A

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

41
Q

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

A

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

42
Q

When is tension maximum in a sarcomere?

A

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

43
Q

At what point is no more tension possible?

A

Max point occurs when acting filaments touch

44
Q

What happens when actin filaments overlap?

A

Tension drops toward 0 because no more sliding can occur

45
Q

True or False

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

A

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

46
Q

What is muscle tone?

A

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

47
Q

Where is ATP required for muscle contraction?

A

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

48
Q

What is the concentration of ATP in muscle fiber?

A

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

49
Q

How does phosphocreatine restore ATP?

A

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
Q

What are three methods of rephosphorylation of ATP?

A

Phosphocreatine, Glycolysis, oxidative metabolism

51
Q

How does Glycolysis rephosphorylize ATP?

A

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
Q

What rephosphorylizes ATP the best for long-term contractions?

A

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
Q

What are two main types of muscle contractions?

A

Isometric and isotonic

54
Q

What is isometric muscle contraction?

A

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
Q

What is isotonic muscle contraction?

A

When muscle length changes

56
Q

What are the two types of isotonic contractions?

A

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

57
Q

What are the two types of myofibers?

A

Dark, slow fibers (red)

Light, Fast fibers (white)

58
Q

What are fast muscle fibers?

A

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

59
Q

What are slow fibers?

A

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
Q

True or False

In adulthood, one cane increase the number of myofibers?

A

False. Mass of myofiber can increase by increasing myoFRIBRILS

61
Q

What happens if there is a lost of muscle tissue?

A

It will be replaced by scar tissue. Fibrous connective tissue

62
Q

What muscle is predominantly composed of dark fibers in mammals?

A

Soleus

63
Q

What muscle is predominantly composed of light fibers?

A

Gastrocnemius

64
Q

What is a motor unit?

A

Neuron and the myofibers it innervates

65
Q

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

A

A motor unit

66
Q

What is summation?

A

Electrical events occur faster than mechanical events

67
Q

How does summation work in skeletal muscle fibers?

A

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
Q

What is tetany?

A

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

69
Q

How does the bone-muscle system often transmit forces?

A

Levers

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

70
Q

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

A

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

71
Q

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

A

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
Q

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

A

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
Q

Where do machines transmit forces?

A

From one place to another

74
Q

What two forces involve machines?

A

Force applied to the machine (in-force (Fi) or effort)

Force derived from the machine (out-force (Fo) or resistance)

75
Q

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

A

Mi=FiLi
Mo=FoLo
Equilibrium = FiLi = FoLo

76
Q

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

A

Speed.

Physiology - Jourdan (10 decks)

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