29 Questions
What is responsible for the actual muscle contraction?
Actin and myosin filaments
Which part of the muscle fibers contains both myosin and actin filaments?
A bands
How many myofibrils does each muscle fiber typically contain?
Several hundred to several thousand myofibrils
Which type of filaments are found in the light bands of myofibrils?
Only actin filaments
What causes the myofibrils to have alternate light and dark bands?
Actin and myosin filaments partially interdigitating
Which part of the muscle fibers is isotropic to polarized light?
I bands
What happens to the ends of actin filaments in the contracted state according to the sliding filament mechanism of muscle contraction?
They overlap one another to their maximum extent
What is the primary cause of actin filaments sliding inward among the myosin filaments during muscle contraction?
Force generated by the interaction of cross-bridges from myosin filaments with actin filaments
Where are the Z discs positioned in the contracted state according to the sliding filament mechanism of muscle contraction?
Pulled up to the ends of the myosin filaments by the actin filaments
Why are the forces generated by cross-bridges from myosin filaments with actin filaments inactive under resting conditions?
The forces are not needed when muscles are at rest
What factor determines whether the actin filaments begin to overlap one another in the relaxed state according to the sliding filament mechanism of muscle contraction?
Proximity to the Z discs
What is the initial trigger for contraction in muscle fibers?
Presence of calcium ions
What is the major source of energy for the contractile process in muscle fibers?
ATP molecule degradation
How many polypeptide chains make up a myosin molecule?
Six
Which molecular characteristic describes the structure of myosin tails?
Double helix formation
What occurs when myosin and actin filaments interact in muscle contraction?
Cross-bridge formation
In the sliding filament model, what is the role of calcium ions in muscle contraction?
Activation of myosin-actin forces
What part of the myosin molecule forms the body of the filament?
Tails
Which component of the myosin head is involved in controlling its function during muscle contraction?
Light Chains
What is the approximate total length of each myosin filament?
1.6 micrometers
Which part of the myosin filament extends outward to the sides?
Heads
What is the role of the hinged heads in muscle contraction?
Participate in the actual contraction process
Why are there no cross-bridge heads in the center of the myosin filament for a distance of about 0.2 micrometers?
Because of hinged arms extending away from the center
What is the function of cross-bridges in muscle contraction?
Interact with actin filaments to cause contraction
What is the role of titin molecules in muscle contraction?
Anchor myosin and actin filaments in place
Where are the Z-discs located in relation to muscle contraction?
At the ends of actin filaments
What is the primary function of the sarcomere in muscle physiology?
Mediate the interaction between myosin and actin filaments
Why is titin described as a 'springy' molecule?
It changes length as the sarcomere contracts and relaxes
Which organelle supplies contracting myofibrils with energy in the form of adenosine triphosphate (ATP)?
Mitochondria
Test your knowledge of muscle anatomy and composition, including tendon fibers, myofibrils, actin and myosin filaments. Learn how muscles are composed of bundles of tendon fibers that insert into bones, and the structure of myofibrils at a microscopic level.
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