18 Questions
What does the top of the contraction illustration represent?
Beginning of the contraction
How does the size of the motor unit vary?
According to the size of the neuron's cell body
In which type of muscle units does a stimulus take longer to reach muscle fibers?
Muscle units with small-diameter axons
What determines the size of the motor unit?
Size of the motor nerve axon
How can the magnitude of a muscle contraction be altered?
By activating more motor units or changing their frequency
Which factor influences how quickly nerve impulses travel through axons?
Diameter of the axons
What initiates muscle contraction by initiating the release of calcium ions?
Z line
What happens during an eccentric muscle contraction?
Thin filaments are pulled away from the thick filaments
What causes troponin to reposition tropomyosin molecules?
Release of calcium ions
In an isometric contraction, what does the muscle fiber do?
Does not change length
What happens in a shortening crossbridge contraction?
Cross-bridges are re-formed
What is the process called when the thin filaments slide past the thick filaments in a sarcomere?
Sliding filament theory
Which type of muscle contraction results in the shortening of the muscle fiber?
Concentric contraction
What occurs when a muscle actively resists motion created by an external force?
Eccentric contraction
What is the role of ATP in generating tension during muscle contraction?
Hydrolysis leading to ADP release
During an eccentric contraction, how is tension generated by the muscle?
Cross-bridges are re-formed
In muscle contraction, what binds with actin when receptor sites on actin are free?
Myosin
What happens in a muscle fiber when the force created by cross-bridge cycling matches the external force?
Isometric contraction happens
Study Notes
Muscle Contractions
- There are two main types of muscle contractions: concentric (shortening) and eccentric (lengthening).
- In a concentric contraction, thin filaments are pulled toward thick filaments, and tension is generated as cross-bridges are formed and re-formed.
- In an eccentric contraction, thin filaments are pulled away from thick filaments, and cross-bridges are broken and re-formed as the muscle lengthens.
Cross-Bridge Cycle
- The cross-bridge cycle involves the formation and re-formation of cross-bridges between myosin and actin filaments.
- The cycle consists of rest, coupling, and contraction stages.
- ATP is attached near the head of the cross-bridge, and calcium ions are stored in the sarcoplasmic reticulum.
Muscle Structure and Function
- Muscle contraction is initiated by a nerve impulse at the motor end plate, which evokes an action potential that travels along the muscle fiber.
- The action potential releases calcium ions, which cause troponin to reposition tropomyosin molecules, making receptor sites on actin available for myosin to bind.
Types of Muscle Contraction
- Isometric contraction: muscle contracts without changing length, generating tension as cross-bridges are re-formed.
- Concentric contraction: muscle shortens as thin filaments slide toward thick filaments, accompanied by the formation and re-formation of cross-bridges.
- Eccentric contraction: muscle lengthens as thin filaments are pulled away from thick filaments, with cross-bridges breaking and re-forming.
Motor Units
- Motor units vary in size, structure, and function from muscle to muscle.
- The size of the motor unit is determined by the number of muscle fibers and the type of muscle fibers.
- The contraction of the entire muscle is the result of many motor units firing asynchronously and repeatedly.
Test your knowledge on muscle contractions where thin filaments are pulled away from thick filaments in an eccentric contraction. Understand the process of cross-bridges being broken and reformed as muscles lengthen, generating tension.
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