Podcast
Questions and Answers
Which of the following best characterizes a motor unit?
Which of the following best characterizes a motor unit?
- A single muscle fiber and all the neurons that innervate it.
- A group of muscle fibers that contract independently.
- A sensory neuron and the muscle fibers it stimulates.
- An anterior motor neuron and all the specific muscle fibers it innervates. (correct)
What determines the degree of precision in a muscle's movement?
What determines the degree of precision in a muscle's movement?
- The size of the muscle itself.
- The speed at which the muscle contracts.
- The number of motor neurons in the muscle.
- The ratio of muscle fibers to motor neurons. (correct)
What happens when a motor neuron receives a stimulus strong enough to trigger an action potential?
What happens when a motor neuron receives a stimulus strong enough to trigger an action potential?
- The accompanying muscle fibers in the motor unit contract asynchronously.
- All of the accompanying muscle fibers in the motor unit contract synchronously. (correct)
- Only some of the muscle fibers in the motor unit contract.
- The action potential spreads to other motor units.
Why can't a stronger action potential produce a stronger contraction?
Why can't a stronger action potential produce a stronger contraction?
What immediately determines the amount of force generated in a single muscle fiber?
What immediately determines the amount of force generated in a single muscle fiber?
Which of the following is NOT a key factor in the force generation of a group of muscles?
Which of the following is NOT a key factor in the force generation of a group of muscles?
How does repetitive stimuli influence muscle tension?
How does repetitive stimuli influence muscle tension?
Which type of motor unit will typically generate greater force?
Which type of motor unit will typically generate greater force?
Which of the following best describes the force production during static (isometric) muscle action?
Which of the following best describes the force production during static (isometric) muscle action?
What is the primary characteristic of isokinetic contractions?
What is the primary characteristic of isokinetic contractions?
Which of the following is true regarding eccentric muscle actions?
Which of the following is true regarding eccentric muscle actions?
Which of the following is a characteristic of dynamic muscle action?
Which of the following is a characteristic of dynamic muscle action?
What happens when the frequency of stimuli to a muscle fiber increases?
What happens when the frequency of stimuli to a muscle fiber increases?
In concentric muscle actions, what occurs at the sarcomere level?
In concentric muscle actions, what occurs at the sarcomere level?
Which type of muscle action involves a muscle producing force without a change in muscle length?
Which type of muscle action involves a muscle producing force without a change in muscle length?
Consider a scenario where you are slowly lowering a heavy box to the floor. Which type of muscle action is primarily involved in controlling the descent?
Consider a scenario where you are slowly lowering a heavy box to the floor. Which type of muscle action is primarily involved in controlling the descent?
Flashcards
Sustained Contractions
Sustained Contractions
Continuous muscle contractions that produce force without complete relaxation.
Static Muscle Action
Static Muscle Action
Muscle produces force without changing its length or joint angle.
Isotonic Contraction
Isotonic Contraction
Muscle action where the force remains constant while muscle changes length.
Isokinetic Contraction
Isokinetic Contraction
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Dynamic Muscle Action
Dynamic Muscle Action
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Concentric Contraction
Concentric Contraction
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Eccentric Muscle Action
Eccentric Muscle Action
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Force-Velocity Relationship
Force-Velocity Relationship
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Motor unit
Motor unit
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Muscle fiber innervation
Muscle fiber innervation
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Precision in muscle function
Precision in muscle function
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Action potential in motor units
Action potential in motor units
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Force gradation
Force gradation
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Force generation factors
Force generation factors
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Motor unit recruitment
Motor unit recruitment
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Type II motor units
Type II motor units
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Study Notes
Motor Units
- Motor units consist of anterior motor neurons and specific muscle fibers they innervate.
- Each muscle fiber usually receives input from only one motor neuron.
- One motor neuron can innervate many muscle fibers.
- The number of muscle fibers per motor neuron relates to the muscle's function (precision).
- Muscles needing less precision might have hundreds of fibers per neuron, while those needing more precision might have only one.
All-or-None Principle
- A stimulus strong enough to trigger an action potential in a motor neuron activates all fibers in the motor unit at once.
- The motor unit either contracts fully or not at all.
- There is no partial activation for motor units.
- A stronger stimulus does not affect the force generated.
Gradation of Force (Acute)
- Force generation in a group of muscles depends on these factors:
- Number of motor units recruited: More recruited units, more force. All units working together create maximal strength.
- Frequency of motor unit discharge: Higher frequency, more tension as muscle does not fully relax, builds up tension.
- Type of motor units recruited: Larger/Type II motor units generate greater strength.
- Preloading the muscle: Activating stretch reflex to build force.
- Speed of contraction: Different speeds generate optimal force and power output.
Summation of Force
- Normal body movement involves sustained contractions, not simple twitches.
- Rapid stimuli do not allow time for fibers to relax and thus summate into higher tension for more forceful movements.
- More frequent stimuli leads to summation of force.
Muscle Actions
- Static (isometric): Muscle produces force, but length doesn't change, joint angle does not change. Examples: Holding a heavy weight, static plank.
- Isotonic: Muscle produces force AND changes length; joint angle changes.
- Concentric: Muscle shortens; force generation while shortening (e.g., bicep curl).
- Eccentric: Muscle lengthens, force generation while lengthening; e.g., lowering a weight during a bicep curl.
- Isokinetic: Movement speed remains constant, but force can vary; involves specialized equipment.
Force-Velocity Curve
- The force-velocity curve is a graphical representation showing the relationship of force generated against velocity of muscle shortening/lengthening. An important way to visualize and understand the concept of concentric/concentric/isometric muscle force generation.
Review Questions
- Five ways in which muscles increase force output
- Differentiating types of muscle actions
- Relationship between force & velocity of contraction: What speed = max force/power?
- Force generation/contraction abilities for concentric/eccentric/isometric muscle actions.
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