30 Questions
Which type of muscle fibers are resistant to fatigue and used in activities involving endurance and continuous contraction?
Type I/slow fibers
Which type of muscle fibers have a larger diameter and are used in activities for power and speed for a short duration?
Type II/fast fibers
Which type of muscle fibers have a high oxidative and glycolytic capacity and are resistant to fatigue?
Type IIa fibers
Which type of muscle fibers have a low oxidative and glycolytic capacity and are resistant to fatigue?
Type IIb fibers
What is the equation for work output during muscle contraction?
W = L x D
What is the main source of energy for muscle contraction?
Adenosine triphosphate (ATP)
What is the function of ATP in muscle contraction?
All of the above
Which of the following molecules is NOT involved in the sliding filament theory?
Tropomyosin
What triggers the release of calcium ions in a muscle cell?
Arrival of action potential at the ends of the T system
Where is calcium stored in resting muscle fibers?
Endoplasmic (sarcoplasmic) reticulum
What is the role of the T system in muscle contraction?
To propagate action potentials
How is calcium pumped back into the sarcoplasmic reticulum after muscle contraction?
By ATPase
What is the shape of an individual myosin molecule?
Golf club
What role do calcium ions play in muscle contraction?
Linking action potentials to contraction
During exercise, what is the first source of energy used by the muscles?
Phosphocreatine
What is the total amount of phosphocreatine compared to ATP in the muscle?
Five times as much as ATP
What is the next important source of energy after phosphocreatine during exercise?
Glycogen
What is the main end product of the enzymatic breakdown of glycogen?
Lactic acid
What is the final source of energy used by muscles for sustained, long-term contraction?
Oxidative metabolism
Which macromolecule contributes half of the energy for a 2 to 4-hour period during oxidative metabolism?
Carbohydrates
Which macromolecule provides the greatest proportion of energy produced during oxidative metabolism?
Fats
When are proteins utilized as a source of energy for muscle contraction?
When carbohydrates and fats are used up
What is a motor unit composed of?
A motor neuron and a group of muscle fibers
Which of the following is true about the cross bridge in muscle contraction?
The cross bridge is responsible for the power stroke in muscle contraction
What is the role of tropomyosin in muscle contraction?
Tropomyosin covers the binding sites on actin to prevent myosin cross bridge binding
What causes the conformational change in the tropomyosin-troponin complex during muscle contraction?
The binding of calcium ions to troponin
What is the role of ATP in muscle contraction?
ATP transfers energy to the myosin cross bridge
What happens during the power stroke of the cross bridge?
The cross bridge flexes, pulling the actin inward
What triggers the exposure of the binding sites on actin during muscle contraction?
The release of calcium ions from the terminal cisterns
How is the myosin cross bridge re-energized during muscle contraction?
The release of the cross bridge from actin triggers the hydrolysis of ATP into ADP and inorganic phosphate
Study Notes
Muscle Fiber Types
- Slow-twitch muscle fibers are resistant to fatigue and used in activities involving endurance and continuous contraction.
- Fast-twitch muscle fibers have a larger diameter and are used in activities for power and speed for a short duration.
- Oxidative muscle fibers have a high oxidative and glycolytic capacity and are resistant to fatigue.
- Glycolytic muscle fibers have a low oxidative and glycolytic capacity and are resistant to fatigue.
Muscle Contraction
- The equation for work output during muscle contraction is Work = Force x Distance.
- The main source of energy for muscle contraction is ATP.
- ATP provides the energy for muscle contraction by binding to the myosin head.
Sliding Filament Theory
- The molecule NOT involved in the sliding filament theory is DNA.
- The release of calcium ions is triggered by an action potential.
- Calcium ions are stored in the sarcoplasmic reticulum in resting muscle fibers.
- The T system plays a role in transmitting the action potential to the muscle fiber.
Muscle Fiber Structure
- Calcium is pumped back into the sarcoplasmic reticulum after muscle contraction by the Ca2+-ATPase pump.
- An individual myosin molecule is shaped like a golf club.
- Calcium ions play a role in muscle contraction by binding to troponin and tropomyosin.
Energy Sources
- During exercise, the first source of energy used by the muscles is ATP.
- Phosphocreatine is present in a 3-4:1 ratio compared to ATP in the muscle.
- After phosphocreatine, the next important source of energy during exercise is anaerobic glycolysis.
- The main end product of the enzymatic breakdown of glycogen is pyruvate.
- The final source of energy used by muscles for sustained, long-term contraction is fatty acid oxidation.
- Fat contributes half of the energy for a 2 to 4-hour period during oxidative metabolism.
- Carbohydrates provide the greatest proportion of energy produced during oxidative metabolism.
- Proteins are utilized as a source of energy for muscle contraction during prolonged fasting or starvation.
Motor Unit
- A motor unit is composed of a motor neuron and the muscle fibers it innervates.
Muscle Contraction Mechanism
- The cross bridge forms between the myosin head and actin during muscle contraction.
- Tropomyosin blocks the binding sites on actin in resting muscle fibers.
- The conformational change in the tropomyosin-troponin complex during muscle contraction is triggered by calcium binding.
- The power stroke of the cross bridge occurs when the myosin head binds to actin and releases Pi.
- The binding sites on actin are exposed during muscle contraction when tropomyosin is moved away.
- The myosin cross bridge is re-energized during muscle contraction by ATP binding.
Test your knowledge on red muscle fibers and the sliding filament theory of muscle contraction. Learn about the characteristics of slow fibers (type I, red muscle) and their role in muscle contraction.
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