Muscle Fiber Types Flashcards
Mo3. Ch6. Ln5.
What are skeletal muscles composed of?
Various fibers each with distinct morphological and physiological characteristics.
What is the most common approach to the classification system of muscles?
The twitch time of the the fibers.
2. Using the term “slow-twitch” and “fast-twitch”
What do motor units consist of?
Muscle fibers of the same type.
What is a fast-twitch motor unit?
One that develops force and relaxes quickly, resulting in a short twitch time.
How does a slow-twitch motor unit work?
it develops force and relaxes more slowly, leading to a longer twitch time.
Describe the classification methods for classifying muscle fibers?
One common method is through histochemical staining for myosin ATPase content, which identifies fibers as slow-twitch (Type I) or fast-twitch (Type IIa and Type IIx).
Another more specific technique involves quantifying the amount of myosin heavy chain (MHC) protein in the fibers, with nomenclature similar to that used in myosin ATPase staining.
Describe the differences between Type I and Type II fibers?
Type I(slow-twitch) and Type II (fast-twitch) fibers have contrasting mechanical and metabolic properties.
1. Type I fibers and known for their efficiency, fatigue resistance, and high capacity for aerobic energy production, making them well-suited for endurance activities but, they have limited potential for rapid force development, characterized by low myosin ATPase activity and low anaerobic power.
2. Type II fibers, are loss efficient and more prone to fatigue but excel in rapid force development due to their high myosin ATPase activity and high anaerobic power.
What are the differences within the type II category?
Type IIa and Type IIx fibers differ mainly in their capacity for aerobic-oxidative energy supply. T
Type IIa fibers have a greater capacity for aerobic metabolism, more capillaries surrounding them, and therefore greater resistance to fatigue compared to Type IIx fibers.
Name the characteristics of Type I (slow-twitch) Muscle fibers.
- Contraction speed
- Myosin ATPase activity
- Force production
- Fatigue resistance
- Energy source
- Mitochondria density
- Capillary density
- Myoglobin content
Describe the contraction speed in Type I (slow-twitch) muscle fibers.
The have a slow contraction speed, meaning they contract more slowly than fast-twitch fibers.
Describe the myosin ATPase activity in Type I muscle fibers.
Low, this enzyme activity is responsible for the breakdown of ATP, the energy source for muscle contraction.
Describe the force production characteristic in the Type I (slow-twitch) muscle fibers.
It produces less force compared to fast-twitch fibers, making them ideal for endurance activities rather than explosive power.
Describe the fatigue resistance characteristic of the Type I (slow-twitch) muscle fibers.
They have high fatigue resistance. They can sustain prolonged activity without tiring.
Describe the energy source characteristic of Type I (slow-twitch) muscle fibers.
They primarily rely on aerobic metabolism (Oxidative phosphorylation) to produce ATP. This involves the use of oxygen to generate energy from carbohydrates and fats.
Describe the mitochondria density characteristic of Type I (slow-twitch) muscle fibers.
It is high, the abundance of mitochondria enhances the fibers’ ability to produce energy through aerobic pathways.
Describe the capillary density characteristic of Type I (slow-twitch) muscle fibers.
It is high, an extensive capillary network ensures a continuous supply of oxygen and nutrients to the muscle fibers.
Describe the myoglobin content characteristic of type I (slow-twitch) muscle fibers
It is high, myoglobin is a protein that stores oxygen within the muscle cells, aiding in airobic respiration.
What are the functions of Type I (slow-twitch) muscle fibers?
- endurance activities - type I fibers are well-suited for activities that require sustained, low-intensity efforts, such as long-distance running, cycling, and swimming.
- Postural control - these fibers are predominantly found in muscles responsible for maintaining posture, like the muscles of the back and logs (eg. the soleus muscle).
Name the characteristics of Type IIa (fast-twitch oxidative) muscle fibers
- contraction speed
- myosin ATPase activity
- force production
- fatigue resistance
- energy source
- mitochondria density
- capillary density
- myoglobin content
describe the contraction speed characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
They have faster contraction speed than Type I fibers, but slower than Type IIx fibers.
Describe the myosin ATPase activity of Type IIa (fast-twitch oxidative) muscle fibers.
They are intermediate - higher than type I but lower than Type IIx, allowing for quicker energy release.
Describe the force production characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
They have greater force production then Type I fibers but less than Type IIx.
Describe the characteristic of fatigue resistance of type IIa (fast-twitch oxidative) muscle fibers.
It is moderate - type IIa fibers are more resistant to fatigue than type IIx fibers but less so than type 1 fibers.
Describe the energy source characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
It utilizes both aerobic and anaerobic metabolism. these fibers can generate ATP through both oxidative (aerobic) and glycolytic (anaerobic) pathways.
Describe the mitochondria density characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
Moderate to high - type IIa fibers have enough mitochondria to support aerobic energy production, making them more fatigue-resistant then Type IIx fibers.
Describe the capillary density characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
Intermediate - sufficient to support aerobic activity, though not as dense as in type I fibers.
Describe the myoglobin content characteristic of Type IIa (fast-twitch oxidative) muscle fibers.
Intermediate - supports the fiber’s oxidative capacity.
What are the functions of Type IIa (fast-twitch oxidative) muscle fibers?
- Mixed activities - Type IIa fibers are ideal for activities that require a combination of endurance and power, such as middle-distance running, swimming, or cycling.
- Adaptability - these fibers are adaptable and can increase their oxidative capacity with endurance training or their glycolytic capacity with strength training.
