Muscles Tissues Part 3 Flashcards

1
Q

What are the sources of ATP for muscles?

A
  1. Stored in muscle fibers before contraction begins as 3mmol ATP, 20mmol CP (creatine phosphate) and 100mmol glycogen
  2. Generated in three ways in muscle cell
    a) direct phosphorylation ADP by creatine phosphate

creatine phosphate + ADP <-> Creatine + ATP

at rest: skeletal fiber produces more ATP and CP than it needs
at us: more ATP is made through
b) aerobic metabolism and c) glycolysis (anaerobic metabolism)

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2
Q

What are the sources of energy stored in a typical muscle fiber?

A

ATP, Creatine Phosphate, Glycogen

Energy source: ATP
Initial Quantity: 3mmol
Utilization process: ATP -> ADP + P
Number of twitches supported by each energy source alone: 10
Duration of isometric tetanic contraction supported by each energy source alone: 2 sec

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3
Q

Why is glucose the primary energy source for cells?

A
  • Glucose is a small, soluble molecule that is easily distributed through body fluids
  • Glucose can provide ATP anaerobically through glycolysis. Although only a small amount is produced, glycolysis is important during peak levels of physical activity, in red blood cells, or when a tissue is temporarily deprived of oxygen
  • Glucose can be stored as glycogen, which forms compact, insoluble granules
  • Glucose can easily be mobilized because the breakdown of glycogen occurs very quickly and involved only a single enzymatic step. Mobilization of other intracellular reserves involves much more complex pathways and takes considerably more time
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4
Q

What are the roles of other fuel molecules besides glucose?

A

Can be chopped up, modified, and enter aerobic pathway -> ATP

  • Fatty acids liberated from adipose tissue
  • Glucose broken down into pyruvic acid in glycolysis
  • Oxygen from hemoglobin in blood or from myoglobin muscle fibers
  • Amino acids from protein breakdown

> > cellular respiration in mitochondria

duration of energy provided: minutes -> hours

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5
Q

Explain the process of cellular respiration

A

1. Glycolysis (Occurs in the cytoplasm)
- breakdown of glucose into pyruvate

2 molecules of pyruvate (3 carbons each)
2 molecules of ATP (net gain)
2 molecules of NADH (electron carriers)
Oxygen requirement: Anaerobic (does not require oxygen)

2. Citric Acid Cycle (Krebs Cycle) (Occurs in the mitochondria)
Starting molecule: Pyruvate (converted to Acetyl-CoA)
Products (per 1 Acetyl-CoA):
3 molecules of NADH
1 molecule of FADH₂
1 molecule of ATP
2 molecules of CO₂ (carbon dioxide as waste)
Oxygen requirement: Aerobic (requires oxygen)

3. Electron Transport Chain (ETC) (Occurs in the inner mitochondrial membrane)
- established proton (H+) gradient used to supply ATP synthase protein channel

Starting molecules: NADH and FADH₂ (from previous stages)
Process: Electrons are transferred through protein complexes in the mitochondrial membrane, creating a proton gradient.

End products:
ATP: Large amounts generated by ATP synthase (about 34 ATP per glucose molecule)
Water: Oxygen accepts electrons and combines with protons to form water (H₂O).
Oxygen requirement: Aerobic (oxygen is the final electron acceptor)

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6
Q

How much of ATP generation does aerobic respiration account for?

A

95%

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7
Q

What is glycogenosis and glycogenolysis?

A

Anabolism and catabolism of glycogen -> glucose

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8
Q

How is glucose broken down into pyruvate?

A

Glycolysis

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9
Q

What is lipolysis and lipogenesis?

A

Catabolism and anabolism of triglyceride -> fatty acid

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10
Q

What is gluconeogenesis?

A

Formation of new glucose from non-carbohydrate

-ex. converted from fatty acids of amino acid to form new glucose

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11
Q

What is beta-oxidation?

A

Converting fatty acids to 2 carbon chains

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12
Q

What to do in the absence of O2?

A

Anaerobic respiration: glycolysis followed by lactic acid production

Muscle glycogen
>
Glucose (from blood)
> (undergoes glycolysis, produces 2 ATP)
2 pyruvic acid
>
2 Lactic acid -> diffuses into blood

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13
Q

What are the limits on use of anaerobic respiration?

A
  1. Lowered pH will disable key enzymes necessary for contraction and decrease Ca++ binding to troponin. Muscles will not be able to generate as much of a contraction
  2. Depletion of metabolic reserves within muscle fibers
  3. Damage to the sarcolemma and SR
  4. Muscle fatigue
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14
Q

What are the advantages of aerobic respiration?

A
  1. Produces 32 ATP / glucose molecule instead of 2
  2. No lactic acid produced
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15
Q

What are the limiting factors on using aerobic respiration?

A

Availability of O2 that can diffuse into muscle fiber

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16
Q

Describe energy use and the 3 levels of muscle activity: At rest

A

Mostly fatty acids and glucose used as fuel to generate ATP (aerobic) ATP used to build reserves of creatine phosphate and glycogen

Fatty acids are catabolized; the ATP produced is used to build energy reserves of ATP, CP, and glycogen

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17
Q

Describe energy use and the 3 levels of muscle activity: Moderate activity

A

Glucose and fatty acids used as fuel in aerobic respiration
- 32 molecules of ATP / molecules of glucose

Glucose and fatty acids are catabolized; the ATP produced is used to power contraction

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18
Q

Describe energy use and the 3 levels of muscle activity: Peak activity

A

Most (2/3) ATP through glycolysis (anaerobic)
- buildup of H+ ions leads to fatigue once sarcoplasm buffer system reaches its limit (enzymes become less functional)
- when blood pH drops = metabolic acidosis (or lactic acidosis)

Most ATP is produced through glycolysis, with lactic acid as a by-product. Mitochondrial activity now produces only about one-third of ATP consumed

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19
Q

Glycolysis and skeletal muscle contraction:

A

Enables skeletal muscles to continue contracting even when insufficient oxygen is available

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20
Q

Production of lactate during peak activity and its conversion to glucose in the liver, and rebuilding of glycogen reserves in muscles during recovery

A

This process continues after exertion has ended, because lactate levels within muscle fibers remain relatively high, and lactate continues to diffuse into the bloodstream. After the absorbed lactate is converted to pyruvate in the liver, roughly 30% of the new pyruvate molecules are broken down in the mitochondria, providing the ATP needed to convert the remaining 70% of the pyruvate molecules into glucose. The glucose molecules are then released into the circulation, where they are absorbed by skeletal muscle fibers and used to rebuild their glycogen reserves

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21
Q

Production of lactate during peak activity and its conversion to glucose in the liver, and rebuilding of glycogen reserves in muscles during recovery

A

Much of the large amounts of lactate produced during peak exertion diffuses out of the muscle fibers and into the bloodstream. The liver absorbs this lactate and begins converting it into pyruvate

22
Q

Where does glucose come from in muscle? (Resting)

A

Resting skeletal muscles primarily break down fatty acids for energy and absorb glucose to build up their glycogen reserves

In most tissues, the transport of glucose into the cell is dependent on the presence of a carrier protein stimulated by insulin

23
Q

What is the post exercise recovery period?

A

Post exercise recovery processes:
- remove lactic acid from muscle and convert to pyruvic acid in liver
- replace ATP, CP, and glycogen reserves in muscle

The oxygen debt: the amount of oxygen required to restore normal, pre-exertion conditions (restore ATP, CP, and glycogen reserves) and convert lactic acid to pyruvic acid or glucose

  • all processes ^^^ require ATP
  • generated by aerobic respiration
  • requires O2 above resting rates
24
Q

What is the O2 debt

A

The amount of oxygen required to restore normal, pre-exertion conditions (restore ATP, CP, and glycogen reserves) and convert lactic acid to pyruvic acid or glucose

25
Q

What occurs for heat production at rest?

A

85% of heat needed to maintain body temperature is produced by skeletal muscles

during aerobic respiration, 58% of released energy warms sarcoplasm, interstitial fluid and circulating blood

26
Q

What occurs for heat production during exercise?

A

During exercise, body temperature starts to rise, and anaerobic respiration releases 70% of energy as heat. Heat loss is accelerated at the skin level to compensate

27
Q

What is muscle fatigue?

A

When muscle fails to contract in spite of receiving stimuli

28
Q

What is psychological fatigue?

A

The desire to discontinue the activity due to the effect of low blood pH and feelings of pain on the brain

29
Q

What are causes of muscle fatigue?

A

Not well understood;

  • depletion of glycogen, lipid, and amino acid reserves
  • accumulation of lactic acid and other metabolites
30
Q

What are causes of muscle soreness? (DOMS)

A

Small damage that will be repaired

31
Q

What are the classifications of skeletal muscle? (3)

A
  1. Slow oxidative (slow fibers) = type 1
    - slow, small diameter, fewer myofibrils
    - lots of mitochondria, surrounded by capillaries = high O2 supply
    - contain myoglobin to bind O2

Generates slower contractions, fatigues slowly due to lots of mitochondria to replenish ATP and higher O2 availability for aerobic respiration

  1. Fast oxidative (intermediate fibers) = type 2a
    - fast, intermediate diameter
    - lots of mitochondria and capillaries
    - some myoglobin

Generates intermediate contractions, and fatigues at intermediate rate

  1. Fast glycolytic (fast fibers) = type 2b
    - fast, large diameter
    - large glycogen reserves
    - few mitochondria

Generates powerful contraction but fatigues quickly due to few mitochondria to replenish ATP

32
Q

What are the criteria (2) for the types of skeletal muscle cells?

A

Based on 2 criteria;

  1. speed of contraction: fast, intermediate, slow

result of differences in number of myofibrils, glycogen reserves, and number of mitochondria between fast and slow fibers

  1. major pathways used to form ATP: anaerobic, aerobic respiration
33
Q

Fast glycolytic fibers:

A

Fast glycolytic (fast fibers) = type 2b
- fast, large diameter
- large glycogen reserves
- few mitochondria

Generates powerful contraction but fatigues quickly due to few mitochondria to replenish ATP
- can reach peak twitch tension in 0.01 seconds
- dependent on anaerobic respiration

34
Q

Slow oxidative fibers:

A

Slow oxidative (slow fibers) = type 1
- slow, small diameter, fewer myofibrils
- lots of mitochondria, surrounded by capillaries = high O2 supply
- contain myoglobin to bind O2

Generates slower contractions, fatigues slowly due to lots of mitochondria to replenish ATP and higher O2 availability for aerobic respiration
- takes 3x as long to reach peak tension as fast twitch
- cross-bridges cycles are slower in these fibers, conserving ATP
- more capillaries + Mb mean more O2 available and more aerobic respiration possible

35
Q

Fast oxidative (intermediate) fibers:

A

Fast oxidative (intermediate fibers) = type 2a
- fast, intermediate diameter
- lots of mitochondria and capillaries
- some myoglobin

Generates intermediate contractions, and fatigues at intermediate rate

36
Q

Properties of Skeletal Muscle fiber types (chart): Slow fibers

A

Cross sectional diameter: small
Time to peak tension: prolonged
Contraction speed: slow
Fatigue resistance: high
Color: red
Myoglobin content: high
Capillary supply: dense
Mitochondria: many
Glycolytic enzyme concentration in sarcoplasm: low
Substrates used for ATP generation during contraction: lipids, carbohydrates, amino acids (aerobic)
Alternative names: Type 1, red, Slow oxidative, slow-twitch oxidative

37
Q

Properties of Skeletal Muscle fiber types (chart): Intermediate fibers

A

Cross sectional diameter: intermediate
Time to peak tension: medium
Contraction speed: fast
Fatigue resistance: intermediate
Color: pink
Myoglobin content: low
Capillary supply: intermediate
Mitochondria: intermediate
Glycolytic enzyme concentration in sarcoplasm: high
Substrates used for ATP generation during contraction: primarily carbohydrates (anaerobic)
Alternative names: Type 2-A, Fast resistance, fast-twitch oxidative

38
Q

Properties of Skeletal Muscle fiber types (chart): Fast fibers

A

Cross sectional diameter: large
Time to peak tension: rapid
Contraction speed: fast
Fatigue resistance: low
Color: white
Myoglobin content: scarce
Capillary supply: few
Mitochondria: high
Glycolytic enzyme concentration in sarcoplasm: high
Substrates used for ATP generation during contraction: carbohydrates (anaerobic)
Alternative names: Type 2-B, Fast fatigue, white, fast-twitch glycolytic

39
Q

What is the effect of exercise on muscles: Aerobic/endurance exercise

A

Ex. Cross-training

  • fast fibers change to resemble intermediate fibers (increased myoglobin and mitochondria for aerobic respiration)
  • improvements in cardiovascular performance
40
Q

What is the effect of exercise on muscles: Anaerobic/high intensity

A

Ex. sprinting, weightlifting

  • muscle hypertrophy (an enlargement of the stimulated muscle fiber through production of more actin and myosin to fill each cell)
41
Q

What is the effect of exercise on muscles: No exercise

A

Muscle atrophy: reduction in muscle size, tone, and power

42
Q

Where can smooth muscle be found?

A

Stomach, intestines, blood vessels, arrector pili (dermis), ureters, uterus, bladder

Allows for constriction and dilation

Arranged in sheets:
- some in bundles around other tissues
- some lining blood vessels and intestinal tract

43
Q

What are the structural characteristics of smooth muscle?

A

Spindle shaped, no T-tubules or myofibrils, no sarcomere, no striations

Thick and thin filaments
- thin filaments anchored to dense bodies in network of intermediate fibers (composed of desmin protein)
- dense bodies are anchored to the sarcolemma and to neighbouring cells
- no troponin in thin filaments

44
Q

What are the similarities in contraction of smooth muscle and skeletal muscle?

A
  • sliding filament mechanism and cross bridge cycling
  • ca++ entering cell is final trigger
  • contraction requires ATP
45
Q

What are the differences in contraction of smooth muscle and skeletal muscle?

A
  • Ca++ enters primarily from outside of the cell
  • Ca++ also released from SR
  • ending the contraction; Ca++ is pumped back out of the cell
46
Q

Regulation of Smooth muscle contraction:

A

Highly variable - smooth muscle in different parts of the body respond to different combinations of stimuli

1) Neural regulation
- some, but not all smooth muscle cells receive input from nerve cells (not under voluntary control)
- nervous input can be either multi-unit or visceral (single-unit)

2) Smooth muscle also influenced by local factors
- chemicals, hormones, O2 and CO2 levels
- these factors can either stimulate or reduce contraction

3) Pacemaker (=pacesetter) cells
- some cells generate regular action potentials without any external stimulus
- leads to contraction of entire muscular sheets

47
Q

What are the characteristics of smooth muscle contraction?

A

Slow compared to skeletal muscle due to scattered thick and thin filaments
- generates strong tension, uses little ATP, difficult to fatigue

Response to stretch
- when first stretched -> retains the ability to contract
- significant because it allows hollow organs to fill without losing ability to stretch

Can stretch up to 2 1/2 times normal length and still generate high tension

48
Q

Smooth muscle tone?

A

Typically partially contracted

49
Q

Visceral (single-unit) smooth muscle tissue vs Multiunit smoot muscle tissue

A

Visceral Smooth Muscle:
- Cells contract as a whole unit

Found in hollow organs like the digestive tract.
Contractions are typically rhythmic and synchronized.
Reacts to stretch and hormones.
One single autonomic neuron

Multi-Unit Smooth Muscle:
-Cells contract independently.

Found in places where fine control is needed, like the eyes and large blood vessels.
Contractions are localized and are controlled by precise nerve stimulation.
Multiple neurons

50
Q

Smooth muscle contraction process:

A
  1. intracellular Ca++ concentration increases when Ca++ enters the cell and is released by sarcoplasmic reticulum
  2. Ca++ binds to Calmodulin (CaM)
  3. Ca++ - calmodulin activates myosin light chain kinase (MLCK)
  4. MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity
  5. Active myosin crossbridges slide along actin and create muscle tension
51
Q

Smooth muscle relaxation process:

A
  1. Free Ca++ in the cytosol decreases when Ca++ is pumped out of the cell or back into sarcoplasmic reticulum
  2. Ca++ unbinds from calmodulin (CaM). MLCK activity decreases
  3. Myosin phosphatase removes phosphate from myosin light chaine, which decreases myosin ATPase activity
  4. Less myosin ATPase activity results in decreased muscle tension -> relaxation