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Questions and Answers
If the sarcomere is too short, the actin filaments collide into each other and tension is also reduced ___ is optimal.
If the sarcomere is too short, the actin filaments collide into each other and tension is also reduced ___ is optimal.
B
The velocity of muscle contraction varies ___ with the load on the muscle.
The velocity of muscle contraction varies ___ with the load on the muscle.
inversely
Isotonic contraction involves constant tension while the muscle length ___ .
Isotonic contraction involves constant tension while the muscle length ___ .
changes
A sustained muscle contraction is referred to as ______.
A sustained muscle contraction is referred to as ______.
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In isometric contraction, the muscle length remains constant while the tension ___ the load.
In isometric contraction, the muscle length remains constant while the tension ___ the load.
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Cardiac muscle is striated and distributed across the atria on top and ___ on the bottom.
Cardiac muscle is striated and distributed across the atria on top and ___ on the bottom.
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The mechanism by which the strength of contraction can be varied in skeletal muscle includes ______ and recruitment of motor units.
The mechanism by which the strength of contraction can be varied in skeletal muscle includes ______ and recruitment of motor units.
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The sinoatrial node in cardiac muscle acts as a built-in ___ capable of spontaneous depolarization.
The sinoatrial node in cardiac muscle acts as a built-in ___ capable of spontaneous depolarization.
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A motor unit consists of an α motor neurone and all the muscle fibres ______ by that neurone.
A motor unit consists of an α motor neurone and all the muscle fibres ______ by that neurone.
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Cardiac action potentials are much longer than those for skeletal muscle, preventing the heart from entering a state of ___.
Cardiac action potentials are much longer than those for skeletal muscle, preventing the heart from entering a state of ___.
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During prolonged contraction of a muscle, motor units ______ to prevent fatigue.
During prolonged contraction of a muscle, motor units ______ to prevent fatigue.
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The optimal resting length of a sarcomere is crucial for achieving maximum ______ of contraction.
The optimal resting length of a sarcomere is crucial for achieving maximum ______ of contraction.
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Once an action potential is generated in the cardiac muscle, it spreads rapidly via ___ through the atria and into the ventricles.
Once an action potential is generated in the cardiac muscle, it spreads rapidly via ___ through the atria and into the ventricles.
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In cardiac muscle, all cells behave like one cell, forming an electrical ___.
In cardiac muscle, all cells behave like one cell, forming an electrical ___.
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As muscle length increases, there is initially an increase in ______ developed until a limit is reached.
As muscle length increases, there is initially an increase in ______ developed until a limit is reached.
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The key differences between smooth, cardiac, and skeletal muscle include variations in structure, function, and ___ .
The key differences between smooth, cardiac, and skeletal muscle include variations in structure, function, and ___ .
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Skeletal muscle contraction can be altered through mechanisms such as ______ signaling.
Skeletal muscle contraction can be altered through mechanisms such as ______ signaling.
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The strength of contraction is graded appropriately by recruiting ______ motor units as needed.
The strength of contraction is graded appropriately by recruiting ______ motor units as needed.
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Smooth muscle contraction differs from skeletal muscle in that it is typically ______ coordinated.
Smooth muscle contraction differs from skeletal muscle in that it is typically ______ coordinated.
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The ______ is responsible for the precise control of muscle movements depending on the size of the motor unit.
The ______ is responsible for the precise control of muscle movements depending on the size of the motor unit.
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Study Notes
Muscle Fiber Components
- Each muscle fiber contains many myofibrils
- Myofibrils are composed of sarcomeres
- Sarcomeres are the basic functional unit of skeletal muscle, composed of thin and thick filaments
Skeletal Muscle Force Generation
- Resting length of muscle dictates force generated during contraction.
- Optimal resting length: allows for maximum overlap between actin and myosin filaments, yielding maximum force.
- Overstretched sarcomere: reduces force due to decreased actin and myosin overlap.
- Shortened sarcomere: reduces force due to actin filament collision.
Skeletal Muscle Contraction Strength
- Tetanus: Sustained muscle contraction achieved by high-frequency stimulation leading to sustained rise in intracellular calcium levels.
- Motor Unit Recruitment: Graded increase in force achieved by recruiting additional motor units (alpha motor neuron and all muscle fibers it innervates).
- Smaller motor units recruited first, followed by larger ones as more force is required.
- During prolonged contraction, motor units alternate activity, preventing fatigue.
Skeletal Muscle Contraction Types
- Isotonic Contraction: Constant tension, muscle length changes. Used for moving objects.
- Isometric Contraction: Constant length, tension does not overcome load. Used for maintaining posture.
Cardiac Muscle
- Striated muscle found in the walls of the heart.
- Self-excitable muscle, generating its own rhythm through the sinoatrial (SA) node, also known as the pacemaker.
- Cardiac action potential is much longer than skeletal muscle action potential, preventing tetany and ensuring proper blood pumping.
- Action potential spreads throughout the heart via gap junctions, allowing coordinated contraction as a single unit (electrical syncytium).
Smooth Muscle
- Not striated, found in walls of hollow organs, blood vessels, and airways.
- Contraction is generally slow and sustained, controlled by various factors including hormones and neurotransmitters.
- Calcium plays a key role in smooth muscle contraction, but the mechanism differs from skeletal muscle.
- Myosin phosphorylation is critical for smooth muscle contraction.
Muscle Types Comparison
- Skeletal Muscle: Striated, voluntary, rapid and forceful contraction, controlled by somatic nervous system.
- Cardiac Muscle: Striated, involuntary, rhythmic contractions, specialized for pumping blood, controlled by autonomic nervous system.
- Smooth Muscle: Non-striated, involuntary, slow and sustained contractions, controlled by autonomic nervous system, hormones, and local factors.
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Description
Test your understanding of skeletal muscle components and force generation with this quiz. Explore topics such as myofibrils, sarcomeres, and the mechanisms behind muscle contraction strength. Perfect for students studying muscle physiology.
