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BMS150 Test 2 > Skeletal Muscle Physiology II (Week 9) > Flashcards

Skeletal Muscle Physiology II (Week 9) Flashcards

1
Q

What are the steps of the cross-bridge cycle?

A

1) ATP hydrolysis
2) Cross-bridge formation
3) Power stroke
4) Detachment of myosin from actin

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2
Q

Describe step 1 of the cross-bridge cycle

A

ATP hydrolysis:

  • myosin heads have the capacity to work as an enzyme (ATPase) to hydrolyze the ATP, ripping the phosphate off and hold onto to both (the phosphate and the ADP)
  • hydrolysis causes the myosin head to pivot, lining up with a new actin monomer
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3
Q

Describe step 2 of the cross-bridge cycle

A

Cross-Bridge Formation

  • the energized myosin head attaches to the myosin-binding site on actin
  • phosphate is released
  • creates a myosin-actin cross-bridge
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4
Q

Describe step 3 of the cross-bridge cycle

A

Power Stroke:

  • as the myosin grabs the actin, it “pushes” the actin, causing the sarcomere to shorten (brings Z lines closer together)
  • ADP is released
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5
Q

Describe step 4 of the cross-bridge cycle

A

Detachment of myosin from actin:

  • if ATP is around, ATP distracts myosin, and it loses connection to actin
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6
Q

What happens when there is no more ATP to help myosin detach from actin?

A

rigor mortis

(several hours after death, all muscles of the body go into contracture)

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7
Q

What determines the amount of tension in a contracting muscle?

A

the amount of action and myosin filament overlap

Note: Up to a point… too much or too little overlap decreases tension

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8
Q

muscle creates tension when it contracts but the overall muscle length does not change

load > force generated by muscle

A

isometric contraction

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9
Q

muscle shortens against a fixed load

force generated by muscle contraction > the load

A

isotonic contraction

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10
Q

True or False: During muscle relaxation, calcium is re-sequestered into the SR, as L-type channels return to their resting membrane potential

A

True

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11
Q

__________ pumps calcium back into the SR

A

SERCA

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12
Q

____________ pumps calcium into the ECF

A

sodium/calcium exchanger

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13
Q

What binds/traps calcium within the SR?

A

calsequestrin and calreticulin

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14
Q

What are the two types of muscle fibers?

A

1) slow twitch fibers (type I)
2) fast twitch fibers (type II)

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15
Q

What are some characteristics of slow twitch muscle fibers?

A
  • generally smaller
  • smaller nerve fibers = slower action potentials
  • more capillaries to supply higher amounts of oxygen
  • lots of mitochondria to support high levels of oxidative metabolism
  • lots of myoglobin (gives reddish appearance)
  • major storage fuel = fat
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16
Q

What are some characteristics of fast twitch muscle fibers?

A
  • generally larger
  • larger nerve fibers = faster action potentials
  • lots of SR for rapid Ca2+ release
  • lots of glycolytic enzymes present
  • energy can be derived from oxidative metabolism and anaerobic metabolism, based on subtypes…

Type IIA = fast oxidative glycolytic fibers
Type IIB = fast glycolytic fibers (fastest)

  • major storage fuel = glycogen
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17
Q

True or False: Slow twitch fibers are very resistant to fatigue, whereas fast twitch fibers fatigue quickly

A

True

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18
Q

True or False: Fast twitch fibers are used for endurance activities

A

False.

Slow twitch fibres = low force/endurance (e.g., walking, jogging)

Fast twitch fibers = high force (e.g., jumping, sprint)

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19
Q

True or False: We are generally limited in how much we can change the number of muscle fiber types we have, as this is largely predetermined by our genetics. However, we can change the size of our muscle fibers (hypertrophy) with particular types of training

A

True

Ex: you can train your type I’s to hypertrophy by endurance training

Ex: you can train your type II’s to hypertrophy by heavy lifting

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20
Q

What are the three metabolic energy systems that allow us to recycle AMP and ADP back into ATP?

A

1) phosphagen system (or phosphocreatine system)

2) glycogen lactic acid system

3) aerobic system

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21
Q

True or False: Phosphorylated creatine molecule has a high energy phosphate bond, holding more energy than ATP. It serves as a rapidly mobilizable reserve of high energy phosphates.

A

True

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22
Q

Both _______ and _______ constitute the phosphagen system

A

phosphocreatine,

ATP

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23
Q

The phosphagen system provides _________ seconds of maximal power. After this, must be replenished.

A

8-10s

Ex: think of a 100m sprint

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24
Q

Once we run out of PCr, what can we use?

A

Glycogen

25
Q

What is the fate of glucose after consumption?

A

can be broken down immediately (via glycolysis) into energy for the cells OR stored in the form of glycogen

26
Q

True or False: All cells are capable of storing some glycogen, but some cells can store more (e.g., hepatocytes, muscle cells)

A

True

27
Q

What percent of the weight of hepatocytes is glycogen?

A

5-8%

28
Q

What percent of the weight of muscle cells are is glycogen?

A

1-3%

29
Q

The initial stage of the glycogen lactic acid system is what?

A

glycolysis

30
Q

REVIEW: During glycolysis, _________ is split into two __________ molecules, yield a net of ____ ATP

A

glucose,

pyruvate,

2

31
Q

If we have sufficient oxygen, what happens after glycolysis?

A

pyruvate gets converted to acetyl CoA

which goes on to the Kreb’s cycle/CAC

byproducts of CAC = NADH, FADH2 –> go on to ETC to generate lots of ATP

Note: we need lots of mitochondria for both the CAC and ETC

32
Q

If there is insufficient oxygen, what happens after glycolysis?

A

pyruvate breaks down into lactic acid

through this rxn, we also generate NAD+, which feeds back into glycolysis

Note: lactic acid leaves the muscle and goes into the interstitial fluid/blood –> travels to the liver as lactate, where it is repurposed (Cori cycle) into glucose, and gives it back to the muscle

33
Q

The glycogen-lactic acid system provides _______ minutes of maximal contraction

A

1.3-1.6 minutes

34
Q

How much ATP is lost during the Cori cycle?

A

4 ATP

35
Q

Review: In the presence of oxygen, pyruvate is broken down into CO2, H2O, and energy via the CAC and ETC.

True or False: As long as nutrients in the body last, the AEROBIC system can be used for unlimited duration

A

True

36
Q

What type of sports might the aerobic system be useful for?

A

Ex: marathon running, cross-country skiing

Note: athletic events over 4-5 hours deplete glycogen stores of the muscle and depend on energy from other sources (mainly fats)

37
Q

Phosphocreatine can be used to replenish levels of ______

A

ATP

38
Q

Glycogen-lactic acid system can be used to replenish both ________ and ________

A

phosphocreatine,

ATP

39
Q

Oxidative metabolism can be used to replenish _________________

A

all systems; ATP, phosphocreatine, and glycogen-lactic acid system

40
Q

True or False: After exercise is over, stored oxygen must be replenished by breathing extra amounts of oxygen above normal requirements

A

True

repaying “oxygen debt”

41
Q

How many liters of oxygen are needed to restore the phosphagen and lactic acid system?

A

9 litres

42
Q

total oxygen that must be “repaid” after stores are used up

A

11.5 litres

43
Q

During heavy exercise, how long does it take to use up our stored oxygen?

A

~ 1 minute

44
Q

What is muscle strength determined by?

A

size

note: maximum contractile force is between 3-4kg/cm^2 of muscle cross-sectional area

45
Q

measure of the amount of work the muscle can perform IN A GIVEN PERIOD OF TIME

A

muscle power

46
Q

What is muscle power determined by?

A
  • strength of the muscle
  • distance and rate of contraction
47
Q

What does muscular endurance depend on?

A

nutritive support

(e.g., how much glycogen has been stored in the muscle prior to the exercise period?)

Note: how much can be stored may depend on the type and size of muscle fibre (e.g., type II can store more glycogen than type I; and type II B can store more than type IIA)

48
Q

With respect to muscle hypertrophy, we are not increasing the number of muscle ________ but increasing the number of ___________

A

fibers,

myofilaments within a muscle fiber

Note: in very RARE circumstances, under extreme muscle force generation, the number of muscle fibers may increase due to linear splitting of previously enlarged fibers –> this is called HYPERPLASIA

49
Q

occurs when muscles are stretched to a greater than normal length, and causes new sarcomeres to be added at the ends of the muscle fibers

A

muscle lengthening

50
Q

True or False: If you haven’t stretched in a long time, you may lose your muscle length

A

True

51
Q

What can be caused by maximal force development (e.g., weight lifting) leading to an increase in actin and myosin?

A

hypertrophy

52
Q

formation of new muscle fibers (rare) that can occur with endurance training

A

hyperplasia

53
Q

True or False: Hypertrophy but not hyperplasia results in increased force generation. With both, there is NO change in shortening capacity or velocity of contraction.

A

False

Both result in increased force generation

Both result in NO change in shortening capacity nor velocity of contraction

54
Q

True or False: Muscle lengthening occurs with normal growth, results in NO change in force development, increases shortening capacity, and increases contraction velocity

A

True

55
Q

When a muscle no longer receives contractile signals (no longer being stimulated) to maintain normal muscle size, this can lead to ______________

A

muscle atrophy

Note: we are NOT losing muscle fibers (yet), but we are losing actin and myosin filaments

56
Q

What are some causes of muscle atrophy?

A
  • denervation/neuropathy
  • tenotomy (lose a tendon)
  • sedentary lifestyle
  • plaster cast
  • space flight (micro-gravity)
57
Q

True or False: Muscle atrophy leads to…

  • degeneration of contractile proteins
  • decreased max force of contraction
  • decreased velocity of contraction
A

True

58
Q

True or False: If contractile signals return and reverses muscle atrophy, full return to function can occur within 12 months

A

False

Full return to function can occur in as little as 3 months (e.g., someone starts exercising again) as nerve supply grows back

59
Q

Chronic disuse of muscle (over months/years) can lead to the loss of __________

A

muscle fibers

Note: A lot more challenging to recover from

Note: when this happens, we get shortening of the muscle and fibrosis; fibers are replaced by fibrous and fatty tissue with little contractile proteins… can lead to loss of mobility

BMS150 Test 2 (10 decks)

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