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Physiology 1 > Muscle Physiology Part 4 > Flashcards

Muscle Physiology Part 4 Flashcards

1
Q

What kind of mechanism helps muscle contraction to occur?

A

Sliding filament mechanism

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2
Q

What is the sliding filament mechanism?

A

The interaction of the cross-bridges from the myosin and actin filaments

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3
Q

What are thick filaments composed of?

A

Multiple myosin molecules

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4
Q

What do myosin molecules consist of?

A
  1. Tail
  2. 2 Heads (that can bind ATP and ACTIN)
    - The head uses ATP as an energy source for contraction (ATPase)
    - the head flexes and relaxes
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5
Q

What are thin filaments composed of?

A
  1. Actin
  2. Tropomyosin
  3. Troponin (globular protein)
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6
Q

What are Titin filamentous molecules?

A

They keep the actin and myosin filaments in place

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7
Q

What do titin fliamentous molecules attach to?

A

One end attaches to the z disk

One end attaches to myosin

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8
Q

In the relaxed state of a muscle fiber, what happens to the myosin binding sites on an actin filament?

A

The myosin binding site becomes covered by the troponin-tropomyosin complex.
- calcium binding exposes the site

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9
Q

What is an ATPase?

A

An enzyme that uses ATP as an energy source for contraction

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10
Q

During resting stage, before muscle contraction begins, what configuration is the myosin heads in? What is bound to it?

A

The myosin heads are in the “low energy configuration” and is bound by ATP

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11
Q

What does ATPase do to the myosin head? What configuration does it cause the myosin head to form?

A

ATPase cleaves the ATP which leaves ADP + Phosphate attached to the myosin head
-This causes the head to become “energized” and form a high energy “cocked position”

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12
Q

When calcium ions bind to the troponin-tropomyosin complex, what happens?

A
  1. The myosin biding sites on the actin molecules are revealed and
  2. The myosin heads bind to the active sites
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13
Q

The binding of the myosin heads to actin form what?

A

Forms “cross bridges”

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14
Q

What are cross bridges?

A

Cross bridges are formed by the binding of myosin heads to the myosin binding sites on actin filaments

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15
Q

What does the forming of the cross bridge do?

A

THe cross bridge causes a conformational change in the myosin head

  • the heads bend toward the center of the sarcomere
  • causing the actin to slide towards the M-line-“power stroke”
  • Phosphate followed by ADP are released giving energy to stroke.
  • another ATP replaces them
  • the binding of the ATP detaches the myosin head from actin
  • cycle restarts
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16
Q

What is the “power stroke”

A

The power stroke occurs when the bound myosin head bends toward the center o the sarcomere causing actin to move toward the M-line

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17
Q

How is the power stroke activated?

A

Phosphate is released which initiates the power stroke. ADP is also released which has the stored energy needed for stroke.

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18
Q

Is an action potential needed for muscle shortening? GIve an example, and what is it called?

A

No. It is called “Contracture” when an action potential is not needed for contraction.

  • an example is RIGOR MORTIS
  • actin and myosin remain in continuous contracted or active state because there is not enough ATP to bind again and bring about relaxation
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19
Q

What do muscles need energy for? (3 things)

A
  1. “Walk along mechanism”
  2. Calcium pump in the SR
  3. Sodium -potassium pump in the sarcolema
20
Q

Is rephosphorylation needed in muscles? Why or why not?

A

Yes phosphorylation is needed because ATP in muscles is limited, and you need more for contraction.

21
Q

What are the 3 sources of energy for muscle contraction?

A
  1. Phosphocreatine
  2. Glycolysis
  3. Oxidative Metabolism
22
Q

What molecule is used to turn ADP to ATP in muscle?

A

Phosphocreatine

23
Q

How is phosphocreatine created?

A
  • Creatine is produced from amino acids in the liver

- In the muscle “creatine kinase” binds phosphate and creatine to produce phosphocreatine.

24
Q

How does phosphocreatine create ATP from ADP?

A

Phosphocreatine is cleaved, releasing energy that is used to bond a new phosphate ion to ADP. ATP created

25
Q

Is there a large amount of phosphocreatine in muscle?

A

NO, there is a small amount of phosphocreatine in muscles

26
Q

What are the two tissues that can store glycogen?

A
  1. The liver

2. Muscles

27
Q

How does glycolysis contribute to the energy needed for muscle contraction?

A
  1. Glycogen is broken down into glucose
  2. Glucose is broken into pyruvic acid and lactic acid
  3. The energy releases of bonds broken reconstituted ATP and phosphocreatine
    4.
28
Q

Can the glycolysis breakdown and reconstitution of ATP and phosphocreatine be done without oxygen?

A

YES

29
Q

Which rate of ATP formation is faster and by how much? Glycolysis or Oxidative metabolism

A

Glycolysis by 2.5 x

30
Q

Which energy source is responsible 95% of the energy used for contraction?

A

Oxidative metabolism

31
Q

How does oxidative metabolism produce ATP for muscle contraction?

A

By combining O2 with the end products of Glycolysis, and other sources of energy like proteins, lipids and carbohydrates

  • for short periods: carbohydrates
  • for long periods: fatty acids
32
Q

What is tension?

A

The pulling force

33
Q

What does the magnitude of tension (pulling force) depend on?

A

The amount of tension depends on the length of the sarcomere before contraction happens

34
Q

When is contraction optimal?

A

When the sarcomere length is in the optimal resting len

35
Q

When does tension decrease in the muscle?

A

When there is over contraction, too much overlap of actin and myosin, which shows as a decrease in length

decrease tension=decease length=over contraction

36
Q

When there is increased length in actin seperation, is there less or more tension?

A

Less tension

37
Q

What do no cross bridges signify in terms of tension?

A

No tension

38
Q

How do muscles change the strength of their contraction?

A

Change their strength of contraction by varying the number of ACTIVE motor units

39
Q

What is the rate of motor unit activation called?

A

Summation

40
Q

How many ways can summation occur? What are they?

A
  1. Multiple fiber summation

2. Frequency summation

41
Q

What is multiple fiber summation?

A

Is the increase of the number of motor units contracting at onc

More motor units contracting= stronger contracting force

42
Q

What is the size principle?

A

When more motor units are activated at the same time the contraction is stronger

43
Q

What is frequency summation in relation to contraction?

A

An increase in the frequency of contraction

44
Q

In frequency summation do all the “action potentials” arrive at the muscles one after the other?

A

No, however at LOWER frequency stimulation, CONTRACTIONS occur one after the other!

45
Q

What happens when the frequency increases?

A

There comes a point where each new contraction occurs BEFORE the preceding contraction. There is an overlap and the force of contraction is stronger.

46
Q

What is “tetanization” in relation to muscle contraction?

A

Tetanization is when you reach such a high frequency of stimulation that the muscle contraction almost merge together and the contractions become “SMOOTH” and “CONTINUOUS”

47
Q

What happens with Puerperal Tetany

A
  1. Calcium ions do not flow into the presynaptic terminal when voltage gated calcium channels open
  2. So spontaneous action potentials are generated causing contraction of peripheral skeletal muscles
  3. Can occur after calving (milk fever)

Physiology 1 (10 decks)

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