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PHYSIOLOGY > WEEK 8 (Skeletal muscle metabolism and Fiber types) > Flashcards

WEEK 8 (Skeletal muscle metabolism and Fiber types) Flashcards

1
Q

What are the steps of the Myosin Power Stroke?

A

1) The active site on actin is exposed as Ca2+ binds to TROPONIN
2) The myosin head forms a CROSS-BRIDGE with actin
3) During the power stroke, the myosin head bends, and ADP and phosphate are released
4) A new molecule of ATP attaches to the myosin head, causing the cross-bridge to detach
5) ATP hydrolyses to ADP and phosphate, which returns the myosin to the “cocked” position

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2
Q

What are the four steps in the excitation, contraction and relaxation processes that require ATP?

A

1) Splitting of ATP by myosin ATPase provides the energy for the power stroke of the cross bridge
2) Binding of a fresh molecule of ATP to myosin lets the cross bridge detach from the actin filament at the end of the power stroke so that the cycle can be repeated; ATP is later split to provide energy for the next stroke of the cross bridge
3) Active transport of Ca2+ back into the lateral sacs of the SARCOPLASMIC RETICULUM during relaxation depends on energy derived from the breakdown of ATP
4) Sodium-Potassium pump actively transports ions (Na+ back out of the cell & K+ back into the cell)

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3
Q

What are the three pathways that supply additional ATP as needed during muscle contraction?

A
  • Transfer of a high-energy phosphate from CREATINE PHOSPHATE to ADP (immediate source)
  • Oxidative phosphorylation
  • Glycolysis
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4
Q

Describe how Creatine phosphate can be used to supply ATP

A

Creatine Phosphate contains a high-energy phosphate group; the energy released from the HYDROLYSIS of Creatine phosphate, along with the phosphate, can be donated directly to ADP to form ATP. This reaction is catalysed by CREATINE KINASE and is REVERSIBLE.

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5
Q

Describe the equilibrium between creatine phosphate and ATP in relaxed and contracted cells

A

As energy reserves are built up in a resting muscle, the INCREASED CONCENTRATION of ATP favours transfer of the high-energy phosphate group from ATP to form creatine phosphate. However, during contraction, when myosin ATPase splits the reserves of ATP, the resultant fall in ATP favours transfer of the high-energy phosphate group from stored creatine phosphate to form more ATP.

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6
Q

Why is Creatine Phosphate the first source for supplying additional ATP when exercise begins?

A
  • most energy is stored in muscle in creatine phosphate pools
  • only one enzymatic reaction is involved in this energy transfer thus ATP can be formed rapidly
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7
Q

What type of activity is Creatine used for?

A

Activities requiring short, explosive bursts of energy

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8
Q

What are the key properties of Oxidative Phosphorylation?

A
  • Multistep so produces ATP at a relatively slow rate
  • Oxygen is required to support the MITOCHONDRIAL ELECTRON TRANSPORT SYSTEM which together with CHEMIOSMOSIS by ATP SYNTHASE harnesses energy captured from the breakdown of nutrient molecules and uses it to generate ATP
  • Fueled by glucose or fatty acids (depending on the intensity and duration of the activity)
  • yields 32 ATP molecules
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9
Q

Define aerobic/endurance-type exercise

A

When exercising muscles depend on delivery of adequate oxygen and nutrients to maintain their activity

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10
Q

How is increased oxygen made available to muscles during exercise?

A
  • Deeper, more rapid breathing brings more O2 into the blood
  • Heart contracts more rapidly and forcefully to pump more oxygenated blood to tissues
  • More blood is diverted to exercising muscles by dilation of the blood vessels supporting them
  • Haemoglobin molecules release more O2 in exercising muscles
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11
Q

What are properties of muscle that aid with oxygen delivery to exercising cells?

A
  • MYOGLOBIN can store small amounts of oxygen & increases the rate of oxygen transfer from the blood into muscle fibers
  • Muscle cells store glucose in the form of GLYCOGEN
  • Liver can store excess ingested carbohydrates as glycogen but once muscle & liver glycogen stores are filled, excess ingested carbohydrates are converted to body fat
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12
Q

What are the advantages glycolysis alone has over the oxidative phosphorylation pathway?

A
  • glycolysis can form ATP in the absence of oxygen
  • it can proceed more rapidly than oxidative phosphorylation
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13
Q

What is Glycolysis and what are its properties?

A

Glycolysis is when a glucose molecule is broken down into two pyruvate molecules, yielding two ATP molecules in the process

  • extracts considerably fewer ATP molecules from each nutrient molecule processed
  • rate of ATP production can exceed the rate of generation of ATP by oxidative phosphorylation as long as glucose is present
  • activity supported in this way is ANAEROBIC or HIGH-INTENSITY EXERCISE
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14
Q

What are the disadvantages of Anaerobic exercise?

A
  • large amounts of nutrient fuel must be processed since glycolysis is LESS EFFICIENT than oxidative phosphorylation
  • can only be sustained for a short duration
  • PYRUVATE is converted to LACTATE which is implicated in ACUTE MUSCLE SORENESS and produces METABOLIC ACIDOSIS
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15
Q

What are the two types of fatigue?

A

Muscle fatigue & Central fatigue

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16
Q

When does Muscle fatigue happen?

A

When an exercising muscle can no longer respond to stimulation with the same degree of contractile activity

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17
Q

What is Muscle fatigue?

A

A defence mechanism that protects a muscle from reaching a point at which it can no longer produce ATP since an inability to produce ATP would result in RIGOR MORTIS

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18
Q

What are the primary implicated factors of muscle fatigue?

A
  • local increase in inorganic phosphate from ATP breakdown
  • inappropriate leakage of Ca2+ through the sarcoplasmic reticulum’s Ca2+ release channels
  • depletion of glycogen energy reserves
19
Q

Explain how the local increase in inorganic phosphate from ATP breakdown leads to muscle fatigue

A

Increased levels of Pi reduce the strength of contraction by interfering with the power stroke of the myosin heads. Moreover, increased Pi appears to decrease the sensitivity of the regulatory proteins to Ca2+ and to decrease the amount of Ca2+ released from the lateral sacs

20
Q

Explain how inappropriate leakage of Ca2+ leads to muscle fatigue

A
  • Ca2+ loss from the cell depletes the sarcoplasmic reticulum Ca2+ supply needed to sustain contractile activity, leading to weaker contractions
  • exposure to leaked Ca2+ during fatiguing exercise activates PROTEASES which cause TRANSIENT MUSCLE DAMAGE, which likely contributes to the weakening of contractions
21
Q

When does Central fatigue happen?

A

When the central nervous system (CNS) no longer adequately activates the motor neurons supplying the working muscles; the person slows down or stops even though the muscles are still able to perform (PSYCHOLOGICALLY BASED).

22
Q

What is the need for elevated oxygen uptake during recovery from exercise called?

A

EXCESS POSTEXERCISE OXYGEN CONSUMPTION (EPOC)

23
Q

What happens during the repayment of an oxygen deficit?

A
  • Fresh supplies of ATP are formed by oxidative phosphorylation
  • Accumulated lactate os converted back into pyruvate
  • Remainder of pyruvate is converted back into glucose by the liver
  • Creatine phosphate is resynthesises to restore its reserves
  • Glucose is used to replenish glycogen stores drained from the muscles and liver during exercise
24
Q

What are the three major types of muscle fibers?

A
  • SLOW-OXIDATIVE (TYPE I) FIBERS
  • FAST-OXIDATIVE (TYPE IIa) FIBERS
  • FAST-GLYCOLYTIC (TYPE IIx) FIBERS
25
Q

What are the two main differences among the major types of muscle fibers?

A
  • speed of contraction (slow or fast)
  • type of enzymatic machinery they primarily use for ATP formation (oxidative or glycolytic)
26
Q

Which two factors affect the speed with which a muscle contracts?

A

The load & the myosin ATPase activity of the contracting fibers

27
Q

Describe fast fibers in contrast to slow fibers

A

Fast fibers have higher myosin ATPase activity than slow fibers do

The higher the ATPase activity, the more rapidly ATP is split and the faster the rate at which energy is made available of cross-bridge cycling. The result is a fast twitch compared to slow twitches of fibers that split ATP more slowly.

28
Q

What are the characteristics of Oxidative fibers?

A
  • more resistant to fatigue than glycolytic fibers are
  • abundance of MITOCHONDRIA and CAPILLARIES
  • high myoglobin content (myoglobin supports oxidative fibers’ oxygen dependancy & gives them a red colour hence “RED FIBERS”
29
Q

What are the properties of Fast-Glycolytic fibers?

A
  • few mitochondria
  • high content of glycolytic enzymes
  • high level of stored glycogen
  • smaller capillary supply than oxidative fibers
  • contain little myoglobin so sometimes called “WHITE FIBERS”
30
Q

Where are high proportions of Slow-oxidative fibers found?

A

In muscles specialised for maintaining low-intensity contractions for long periods without fatigue

31
Q

Where are high proportions o fast-glycolytic fibers found?

A

In the arm muscles which are adapted for performing rapid, forceful movements

32
Q

What two types of changes can be induced in muscle fibers?

A
  • changes in their oxidative capacity
  • changes in their diameter
33
Q

What changes do regular aerobic endurance exercises promote (e.g swimming)?

A

It promotes metabolic changes within the oxidative fibers but does not change the size

34
Q

How can the actual size of the muscles be increased?

A

By regular bouts of anaerobic, short duration, high intensity resistance training such as weight-lifting

35
Q

Describe Hypertrophy

A
  • Muscle enlargement comes primarily from an increase in diameter (HYPERTROPHY) of the fast-glycolytic fibers
  • Fiber thickening results from increased synthesis of myosin and actin filaments, which permits a greater opportunity for CROSS-BRIDGE INTERACTIONS and increases the muscle’s contractile strength
  • Mechanical stress that resistance training exerts on a muscle fiber triggers signalling proteins, which turn on genes that direct the synthesis of more myosin and actin
36
Q

Why are men’s muscle fibers thicker and muscles larger and stronger than those of women?

A

Due to TESTOSTERONE, a steroid hormone secreted primarily in males, which promotes SYNTHESIS and ASSEMBLY of myosin and actin.

37
Q

What is distinguishable about fast-twitch fibers?

A

Fast-twitch fibers are INTERCONVERTIBLE

[fast-glycolytic fibers can be converted to fast-oxidative fibers and vice versa depending on training efforts and the types of demands repetitively demanded on them]

38
Q

What is the difference between slow-twitch fibers and fast-twitch fibers?

A

SLOW-TWITCH FIBERS are supplied by motor neurons that exhibit a LOW-FREQUENCY pattern of electrical activity

FAST-TWITCH FIBERS are innervated by motor neurons that display INTERMITTENT RAPID BURSTS of electrical activity

39
Q

What is Muscle Atrophy?

A

When a muscle is not used, its actin and myosin content decreases, its fibers become smaller and the muscle ATROPHIES and becomes weaker

40
Q

What are the ways muscle atrophy can take place?

A
  • DISUSE ATROPHY
    (occurs when a muscle is not used for a long period even though the nerve supply is intact)
  • DENERVATION ATROPHY
    (occurs after the nerve supply to a muscle is lost)
  • AGE RELATED ATROPHY/SARCOPENIA
    (a gradual loss of muscle mass, strength and speed of muscle contraction occurs in ageing individuals)
41
Q

What happens after muscle fiber damage?

A

1) Locally released factors activate the satellite cells which divide to give rise to MYOBLASTS (undifferentiated cells)
2) A group of myoblasts fuse to form a large, multinucleated cell
3) This immediately begins to synthesise and assemble the the intracellular machinery characteristic of the muscle, ultimately differentiating completely into a mature muscle fiber

42
Q

What are the characteristics of Slow fibers?

A
  • Smaller than fast fibers
  • Innervated by smaller nerve fibers
  • Have a more extensive blood vessel system and more capillaries to supply extra amount of oxygen than fast fibers
  • Greatly increased numbers of mitochondria to support high levels of oxidative metabolism
  • Contains large amounts of myoglobin giving it its RED colour
43
Q

What are the characteristics of Fast fibers?

A
  • Large for great strength of contraction
  • Extensive sarcoplasmic reticulum is present for rapid release of calcium ions to initiate contraction
  • Large amounts of GLYCOLYTIC ENZYMES are present for rapid release of energy by the glycolytic process
  • Less extensive blood supply
  • Fewer mitochondria
  • Deficit of red blood cells giving it its WHITE colour

PHYSIOLOGY (10 decks)

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