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Questions and Answers
Myosin and actin filaments partially interdigitate causing myofibrils to have alternate light and dark bands (I bands and A bands) creating a ______ appearance.
striated
Each muscle fiber consists of ______ responsible for the actual muscle contraction.
myofibrils
The small projections from the sides of the myosin are called ______.
cross-bridges
In the relaxed state, the ends of the actin filaments extending from two successive Z discs barely begin to overlap one another. Conversely, in the contracted state, these actin filaments have been pulled inward among the myosin filaments, so that their ends overlap one another to their maximum extent. Also, the Z discs have been pulled by the actin filaments up to the ends of the myosin filaments. The “walk-along” mechanism for contraction of the muscle is driven by the interaction of ______ and myosin filaments.
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The portion of the myofibril that lies between two successive Z discs is called a ______.
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Most of the energy during muscle contraction is required to provide the walk-along mechanism by which the cross-bridges pull the ______ filaments.
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Some energy is also required for pumping calcium ions from the sarcoplasm into the sarcoplasmic reticulum after the contraction is over and for pumping sodium and potassium ions through the muscle fiber membrane to maintain appropriate ionic environment. The concentration of ATP in the muscle fiber is sufficient to maintain full contraction for only 1 to 2 seconds. This highlights the importance of ATP in the ______ process.
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The skeletal muscle fibers are innervated by large, myelinated nerve fibers and each nerve ending makes a junction, called the neuromuscular junction, with the muscle fiber near its midpoint. Both the nerve terminals with muscle fiber plasma membrane together are called the ______.
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Smooth muscle is composed of fibers that are both shorter and smaller than that of ______ muscle.
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There are two major types of smooth muscles: Multi-unit smooth muscle and Single-unit (unitary) smooth ______.
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Single unit smooth muscle is arranged in a mass of hundreds to thousands of smooth muscle fibers that contract together as a single ______.
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The chemical basis for smooth muscle contraction is similar to that of the ______ muscle.
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Study Notes
Muscle Structure and Contraction
- Myosin and actin filaments interdigitate, resulting in an alternating light and dark band appearance in myofibrils, creating a striated appearance.
- Each muscle fiber contains myofibrils responsible for actual muscle contraction.
- Small projections from the sides of myosin filaments are known as cross-bridges.
- In the relaxed state, actin filaments from adjacent Z discs show minimal overlap, whereas in the contracted state, their overlap with myosin increases significantly.
- The Z discs are pulled toward the ends of the myosin filaments during contraction.
- Muscle contraction follows a “walk-along” mechanism driven by the interaction of actin and myosin filaments.
- The segment of myofibril between two Z discs is referred to as a sarcomere.
- Most energy for muscle contraction is utilized for the cross-bridges pulling the actin filaments.
- Additional energy is needed for calcium ion transport into the sarcoplasmic reticulum post-contraction, as well as for maintaining ionic balances of sodium and potassium across the muscle fiber membrane.
- The concentration of ATP in muscle fibers supports sustained contraction for only 1 to 2 seconds, underscoring the critical role of ATP in muscle activity.
Neuromuscular Junction
- Skeletal muscle fibers are innervated by large, myelinated nerve fibers.
- Each nerve ending forms a neuromuscular junction with the muscle fiber, typically located near the fiber's midpoint.
- The combined structure of nerve terminal and muscle fiber plasma membrane is known as the motor end plate.
Smooth Muscle Characteristics
- Smooth muscle fibers are shorter and smaller than those of skeletal muscle.
- There are two primary types of smooth muscle: multi-unit and single-unit (unitary) smooth muscle.
- Single-unit smooth muscle consists of a mass of fibers that contract together as a single functional unit.
- The chemical mechanisms of contraction in smooth muscle are similar to those in skeletal muscle.
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Description
Test your knowledge about skeletal and smooth muscle contraction with this quiz. Explore the composition and innervation of skeletal muscles, as well as the distribution of smooth and cardiac muscle in the body.
