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Questions and Answers
If the sarcomere is too short, actin filaments will collide, leading to increased tension.
If the sarcomere is too short, actin filaments will collide, leading to increased tension.
False
The velocity of muscle contraction increases with the load on the muscle.
The velocity of muscle contraction increases with the load on the muscle.
False
Isometric contraction occurs when muscle length changes but tension remains constant.
Isometric contraction occurs when muscle length changes but tension remains constant.
False
Cardiac muscle has a built-in pacemaker known as the sinoatrial node.
Cardiac muscle has a built-in pacemaker known as the sinoatrial node.
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The action potential in cardiac muscle is shorter than that of skeletal muscle, preventing tetany.
The action potential in cardiac muscle is shorter than that of skeletal muscle, preventing tetany.
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All muscle cells in the heart work independently of one another due to their structure.
All muscle cells in the heart work independently of one another due to their structure.
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Isotonic contraction is characterized by constant muscle length while moving an object through a distance.
Isotonic contraction is characterized by constant muscle length while moving an object through a distance.
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The heart's pump function is enhanced by the regular occurrence of tetany.
The heart's pump function is enhanced by the regular occurrence of tetany.
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Smooth, cardiac, and skeletal muscles all share the same contraction mechanism.
Smooth, cardiac, and skeletal muscles all share the same contraction mechanism.
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Gap junctions allow for rapid spread of action potentials in cardiac muscle tissue.
Gap junctions allow for rapid spread of action potentials in cardiac muscle tissue.
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Tetanus in skeletal muscle refers to a sustained muscle contraction resulting from high-frequency stimulation.
Tetanus in skeletal muscle refers to a sustained muscle contraction resulting from high-frequency stimulation.
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A motor unit consists of multiple alpha motor neurons and one muscle fiber.
A motor unit consists of multiple alpha motor neurons and one muscle fiber.
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The force of skeletal muscle contraction can be increased only through temporal summation.
The force of skeletal muscle contraction can be increased only through temporal summation.
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An overstretched sarcomere can develop maximum tension due to optimal overlap of actin and myosin.
An overstretched sarcomere can develop maximum tension due to optimal overlap of actin and myosin.
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Smaller motor units are recruited first to increase the force of contraction during skilled movements.
Smaller motor units are recruited first to increase the force of contraction during skilled movements.
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The optimal resting length of a sarcomere allows for maximum strength of contraction.
The optimal resting length of a sarcomere allows for maximum strength of contraction.
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During prolonged muscle contraction, all motor units remain active without rotation.
During prolonged muscle contraction, all motor units remain active without rotation.
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Temporal summation results in multiple Action Potentials occurring in quick succession to increase muscle contraction force.
Temporal summation results in multiple Action Potentials occurring in quick succession to increase muscle contraction force.
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Smooth muscle contraction is primarily controlled by voluntary nervous impulses.
Smooth muscle contraction is primarily controlled by voluntary nervous impulses.
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Calcium plays no significant role in the contraction process of cardiac muscle.
Calcium plays no significant role in the contraction process of cardiac muscle.
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Study Notes
Muscle Fiber Components
- Muscle fibers consist of a number of myofibrils surrounded by the sarcolemma, a plasma membrane.
- Myofibrils are made up of sarcomeres which are the functional units of muscle contraction.
- Each sarcomere consists of thin filaments (actin) and thick filaments (myosin).
- The arrangement of these proteins gives skeletal muscle its striated appearance.
Relationship Between Resting Length and Force
- A muscle fiber can generate the most force at its optimal resting length.
- Above or below this length, the force generated is reduced.
- This is due to the overlap of actin and myosin filaments, which is optimal at the optimal length.
- If the overlap is too small or too large, the force generation is reduced.
Force/Strength of Contraction of Skeletal Muscle
- The force of contraction can be varied by adjusting the frequency of stimulation and the number of motor units recruited.
- Tetanus is a sustained muscle contraction that occurs when the frequency of stimulation is increased.
- Increasing the frequency of action potentials leads to a sustained rise in intracellular calcium, resulting in a greater force than a single twitch.
- Motor units consist of an alpha motor neuron and all the muscle fibers it innervates.
- Smaller motor units are recruited before larger ones.
- As more force is needed, more motor units are recruited to increase the force.
- Motor units rotate during prolonged contraction, allowing for sustained contraction without fatigue.
Effect of Sarcomere Length on Force
- The length-tension curve shows the relationship between sarcomere length and the force it can generate.
- A sarcomere at its optimal length (B) generates the maximum force.
- If the sarcomere is stretched too far, the force generating potential is reduced.
- If the sarcomere is too short, the force generated is also reduced as the actin filaments collide with each other.
- The velocity of muscle contraction varies inversely with the load on the muscle.
Main Types of Muscle Contraction
- Isotonic contraction occurs when the muscle length changes while maintaining a constant tension.
- This is the type of contraction that is used to move objects through a distance.
- Isometric contraction occurs when the muscle length is constant and the tension does not exceed the load.
- This is the type of contraction that is used to hold an object in place.
Cardiac Muscle
- Cardiac muscle is striated and distributed across the atria and ventricles of the heart.
- It is able to generate its own action potentials due to the presence of a pacemaker, the sinoatrial node.
- Action potentials in cardiac muscle are longer than those in skeletal muscle, preventing tetany and ensuring the heart functions as a pump.
- Once an action potential is generated, it spreads through the atria and ventricles via gap junctions.
- The heart functions as an electrical syncytium, meaning that all muscle cells behave as one, ensuring coordinated contraction.
- The coordinated contraction of cardiac muscle is essential for efficient blood pumping.
Cardiac Muscle Contraction Mechanism
- Cardiac muscle contraction is initiated by calcium influx through L-type calcium channels.
- The calcium influx triggers the release of more calcium from the sarcoplasmic reticulum, leading to a rise in intracellular calcium levels.
- Calcium binds to troponin, causing a conformational change that exposes the myosin binding site on actin, allowing for crossbridge formation and muscle contraction.
- The relaxation of cardiac muscle occurs when calcium is pumped back into the sarcoplasmic reticulum.
Smooth Muscle
- Smooth muscle is found in the walls of hollow organs like the digestive tract, blood vessels, and urinary bladder.
- Smooth muscle is not striated and is controlled by the autonomic nervous system, hormones, and local factors.
- Smooth muscle has a slower contraction speed compared to skeletal and cardiac muscle.
- Smooth muscle can contract over a wider range of lengths than skeletal muscle and can sustain contractions for longer periods.
- The contraction of smooth muscle is regulated by calcium, but the mechanism is different than in skeletal and cardiac muscle.
Smooth Muscle Contraction Mechanism
- Calcium binds to calmodulin, activating myosin light chain kinase.
- The activated kinase phosphorylates myosin, enabling it to bind to actin and initiate contraction.
- Relaxation of smooth muscle occurs when myosin light chain phosphatase removes phosphate from myosin, reducing its ability to interact with actin.
Key Differences Between Smooth, Cardiac, and Skeletal Muscle
- Skeletal muscle is striated, voluntary, and contracts rapidly and forcefully.
- Cardiac muscle is striated, involuntary, and has a longer action potential than skeletal muscle, preventing tetany.
- Smooth muscle is non-striated, involuntary, and contracts slowly over a wide range of lengths.
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Description
Test your knowledge on the components of muscle fibers, the relationship between resting length and force generation, and the dynamics of muscle contraction strength. This quiz covers the key concepts of muscle physiology, including sarcomeres, actin, myosin, and tetanus.
