Podcast
Questions and Answers
Which of the following best describes the relationship between a motor neuron and muscle fibers within a motor unit?
Which of the following best describes the relationship between a motor neuron and muscle fibers within a motor unit?
- A single motor neuron innervates multiple muscle fibers, but each muscle fiber is generally innervated by only one motor neuron. (correct)
- Multiple motor neurons converge to innervate a single muscle fiber, creating a complex network of control.
- Motor neurons and muscle fibers operate independently; the number of connections varies greatly.
- Each muscle fiber receives input from multiple motor neurons to allow for fine motor control.
A muscle requiring high precision movements would likely have:
A muscle requiring high precision movements would likely have:
- As few as one muscle fiber per motor neuron. (correct)
- Several hundred muscle fibers per motor neuron.
- An equal distribution of muscle fibers across all motor neurons.
- A variable number of muscle fibers per motor neuron depending on the task.
What happens when a stimulus triggers an action potential in a motor neuron?
What happens when a stimulus triggers an action potential in a motor neuron?
- Only some of the muscle fibers in the motor unit contract, depending on the strength of the stimulus.
- The motor neuron does not affect the contraction of the muscle fibers.
- The motor neuron stimulus causes the muscle fibers to contract asynchronously.
- All of the muscle fibers in the motor unit contract synchronously. (correct)
Which of the following statements is true regarding force gradation in a motor unit?
Which of the following statements is true regarding force gradation in a motor unit?
The amount of force generated in a single muscle fiber is most directly dependent on:
The amount of force generated in a single muscle fiber is most directly dependent on:
Which of the following is NOT a primary factor influencing the force generation of a group of muscles?
Which of the following is NOT a primary factor influencing the force generation of a group of muscles?
Repetitive stimuli that reach a muscle before it relaxes will:
Repetitive stimuli that reach a muscle before it relaxes will:
Which motor unit type will generate the greatest force?
Which motor unit type will generate the greatest force?
Which of the following best describes the relationship between the frequency of stimuli and force production in muscle fibers?
Which of the following best describes the relationship between the frequency of stimuli and force production in muscle fibers?
During an isometric muscle action, what is the primary characteristic that differentiates it from isotonic or isokinetic contractions?
During an isometric muscle action, what is the primary characteristic that differentiates it from isotonic or isokinetic contractions?
Which of the following accurately describes the movement of sarcomere filaments during a concentric muscle action?
Which of the following accurately describes the movement of sarcomere filaments during a concentric muscle action?
In the context of muscle actions, what distinguishes an eccentric action from a concentric action?
In the context of muscle actions, what distinguishes an eccentric action from a concentric action?
Consider a scenario where a weightlifter is holding a barbell at a fixed position during a lift. Which type of muscle action is primarily occurring?
Consider a scenario where a weightlifter is holding a barbell at a fixed position during a lift. Which type of muscle action is primarily occurring?
How does the capacity to generate force typically differ among concentric, eccentric, and isometric muscle actions?
How does the capacity to generate force typically differ among concentric, eccentric, and isometric muscle actions?
Why do normal body movements rely on sustained muscle contractions rather than simple twitches?
Why do normal body movements rely on sustained muscle contractions rather than simple twitches?
An athlete is performing squats. Which type of muscle action is primarily occurring in the quadriceps during the descent (lowering) phase of the squat?
An athlete is performing squats. Which type of muscle action is primarily occurring in the quadriceps during the descent (lowering) phase of the squat?
Flashcards
Sustained Contractions
Sustained Contractions
Sustained muscle activity, not simple twitches, underlies normal body movements.
Summation
Summation
Increased frequency of stimuli prevents muscle fiber relaxation, leading to increased force production. Think summation.
Static (Isometric) Muscle Action
Static (Isometric) Muscle Action
Muscle generates force without changing length; no change in joint angle.
Concentric Contraction
Concentric Contraction
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Eccentric Muscle Action
Eccentric Muscle Action
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Dynamic Muscle Action
Dynamic Muscle Action
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Isometric Contraction
Isometric Contraction
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Isokinetic Contraction
Isokinetic Contraction
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Motor Unit
Motor Unit
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Muscle Fiber: Neuron Ratio
Muscle Fiber: Neuron Ratio
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Motor Neuron Action Potential
Motor Neuron Action Potential
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Motor Unit Force Gradation
Motor Unit Force Gradation
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Force in Single Muscle Fiber
Force in Single Muscle Fiber
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Motor Unit Recruitment
Motor Unit Recruitment
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Motor Unit Discharge Frequency
Motor Unit Discharge Frequency
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Motor Unit Type
Motor Unit Type
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Study Notes
- Motor unit consists of an anterior motor neuron and the specific muscle fibers it innervates
- Each muscle fiber generally receives input from only one neuron
- A single motor neuron may innervate several muscle fibers
- The number of muscle fibers per motor neuron generally relates to a muscle's particular movement function
- Muscles requiring less precision may have several hundred fibers served by a single motor neuron
- Muscles needing great precision may have as few as one muscle fiber per motor neuron
All-or-None Principle
- A strong enough stimulus to trigger an action potential in the motor neuron activates all accompanying muscle fibers in the motor unit to contract synchronously
- There is no such thing as a motor neuron stimulus that causes only some fibers to contract
- A motor unit does not exert a force gradation; the impulse either elicits an action or it does not
- A stronger action potential cannot produce a stronger contraction
Gradation of Force (Acute)
- The amount of force generated in a single muscle fiber relies on the number of crossbridges
- Force generation of a group of muscles relies on five factors:
- The number of motor units recruited: a muscle generates considerable force when activated by all of its motor units
- Frequency of motor unit discharge: repetitive stimuli that reach a muscle before it relaxes increases the total tension
- Type of motor unit recruited: larger/Type II motor units generate greater force
- Preloading the muscle (activating the stretch reflex)
- Speed of contraction
Summation of Force
- Normal body movements are not made up of simple twitches, but sustained contractions
- Increasing frequency of stimuli increases until fibers do not have time to relax, then "summation" and increased force production occurs
Muscle Actions
- Static (isometric) muscle action ("contraction"):
- Muscle produces force but does not change in length
- Joint angle does not change
- Myosin cross-bridges form and recycle, with no sliding
- Isotonic contractions: same force
- Isokinetic contractions: speed of the movement does not change
- Dynamic muscle action:
- Muscle length and joint angle change
- Includes both isotonic and isokinetic actions
- Concentric contraction: when a muscle shortens while producing force and sarcomeres shorten as filaments slide towards the center
- Eccentric muscle action: when a muscle lengthens while producing force and cross-bridges form but the sarcomere lengthens
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Description
The motor unit comprises a motor neuron and the muscle fibers it innervates. Each muscle fiber typically receives input from a single neuron, though one neuron can innervate multiple fibers. The all-or-none principle dictates that a stimulus triggers all fibers in a motor unit to contract synchronously.
