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Questions and Answers
What is the issue associated with myosin cross bridges when they are too short?
What is the issue associated with myosin cross bridges when they are too short?
What occurs when myosin cross bridges are too long?
What occurs when myosin cross bridges are too long?
Which situation results in the generation of no tension?
Which situation results in the generation of no tension?
Which of the following best describes the mechanics of muscle shortening?
Which of the following best describes the mechanics of muscle shortening?
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In muscle mechanics, what is the consequence of excessive fatigue on cross bridges?
In muscle mechanics, what is the consequence of excessive fatigue on cross bridges?
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Which type of skeletal muscle fibre is classified primarily as slow-twitch?
Which type of skeletal muscle fibre is classified primarily as slow-twitch?
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Which muscle fibre type has high amounts of enzymes for anaerobic glycolysis?
Which muscle fibre type has high amounts of enzymes for anaerobic glycolysis?
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Which characteristic makes oxidative fibres more advantageous for endurance activities?
Which characteristic makes oxidative fibres more advantageous for endurance activities?
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What structural feature is prevalent in slow-oxidative fibres that aids in their function?
What structural feature is prevalent in slow-oxidative fibres that aids in their function?
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Which of the following statements is true regarding fast-twitch fibres compared to slow-twitch fibres?
Which of the following statements is true regarding fast-twitch fibres compared to slow-twitch fibres?
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Which skeletal muscle fibre type primarily uses aerobic pathways for energy generation?
Which skeletal muscle fibre type primarily uses aerobic pathways for energy generation?
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Which statement correctly distinguishes between oxidative and glycolytic fibres?
Which statement correctly distinguishes between oxidative and glycolytic fibres?
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What is a key characteristic of fast-glycolytic fibres regarding energy production?
What is a key characteristic of fast-glycolytic fibres regarding energy production?
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In isotonic contraction, what remains constant during the muscle contraction?
In isotonic contraction, what remains constant during the muscle contraction?
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Which type of contraction involves muscle length remaining constant while tension is generated?
Which type of contraction involves muscle length remaining constant while tension is generated?
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Which type of muscle contraction is characterized by constant velocity?
Which type of muscle contraction is characterized by constant velocity?
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What is a primary difference between eccentric and concentric contractions?
What is a primary difference between eccentric and concentric contractions?
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What is a common consequence of performing eccentric exercises?
What is a common consequence of performing eccentric exercises?
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Which statement about skeletal muscles is true?
Which statement about skeletal muscles is true?
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During normal human movement, which contraction type is not typically observed?
During normal human movement, which contraction type is not typically observed?
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In which scenario will muscle fibers not shorten?
In which scenario will muscle fibers not shorten?
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What role do muscle spindles play in the body?
What role do muscle spindles play in the body?
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Which of the following statements is true about gamma motor neurons?
Which of the following statements is true about gamma motor neurons?
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What is the function of Golgi tendon organs?
What is the function of Golgi tendon organs?
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How do afferent neurons contribute to the understanding of muscle status?
How do afferent neurons contribute to the understanding of muscle status?
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The concept of alpha-gamma coactivation primarily relates to which function?
The concept of alpha-gamma coactivation primarily relates to which function?
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In terms of proprioception, what information do muscle spindles specifically convey?
In terms of proprioception, what information do muscle spindles specifically convey?
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Which motor neurons are responsible for causing the contraction of extrafusal muscle fibers?
Which motor neurons are responsible for causing the contraction of extrafusal muscle fibers?
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What maintains tension in a muscle spindle during coactivation?
What maintains tension in a muscle spindle during coactivation?
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What does proprioception primarily help an individual understand?
What does proprioception primarily help an individual understand?
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Rhythmic patterned outputs related to walking are driven by which mechanism?
Rhythmic patterned outputs related to walking are driven by which mechanism?
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What role do muscle spindles play in the stretch reflex?
What role do muscle spindles play in the stretch reflex?
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The stretch reflex is classified as what type of reflex?
The stretch reflex is classified as what type of reflex?
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In the withdrawal reflex, what occurs simultaneously with the contraction of agonistic muscles?
In the withdrawal reflex, what occurs simultaneously with the contraction of agonistic muscles?
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Which of the following statements best describes the function of afferent fibers in muscle spindles?
Which of the following statements best describes the function of afferent fibers in muscle spindles?
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What is the primary purpose of the crossed extensor reflex?
What is the primary purpose of the crossed extensor reflex?
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Which muscle group is primarily involved in the stretch reflex when the patellar tendon is tapped?
Which muscle group is primarily involved in the stretch reflex when the patellar tendon is tapped?
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What triggers the withdrawal reflex upon stimulation?
What triggers the withdrawal reflex upon stimulation?
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In the context of reflex actions, what does the term 'agonistic muscles' refer to?
In the context of reflex actions, what does the term 'agonistic muscles' refer to?
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What is the role of the motor neuron in reflex actions?
What is the role of the motor neuron in reflex actions?
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What initiates the somatic reflexes discussed?
What initiates the somatic reflexes discussed?
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What determines the percentage of each type of muscle fiber in an individual?
What determines the percentage of each type of muscle fiber in an individual?
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What is muscle hypertrophy primarily a result of?
What is muscle hypertrophy primarily a result of?
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Which factor is understood to influence muscle growth and protein synthesis?
Which factor is understood to influence muscle growth and protein synthesis?
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How does tension develop in whole muscles during contraction?
How does tension develop in whole muscles during contraction?
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What role do bones serve in the lever system described?
What role do bones serve in the lever system described?
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What happens to the tension when muscle contraction occurs?
What happens to the tension when muscle contraction occurs?
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What effect does the placement of a muscle's insertion point have on movement?
What effect does the placement of a muscle's insertion point have on movement?
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Which muscle adaptation is associated with oxidative capacity?
Which muscle adaptation is associated with oxidative capacity?
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What does increased tension in muscles lead to during contraction?
What does increased tension in muscles lead to during contraction?
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What happens during the interconversion of muscle fiber types?
What happens during the interconversion of muscle fiber types?
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How does skeletal muscle provide force during movement?
How does skeletal muscle provide force during movement?
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What is the primary function of tendons in the muscular system?
What is the primary function of tendons in the muscular system?
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What is a significant outcome of high-intensity training?
What is a significant outcome of high-intensity training?
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Which system amplifies the velocity and distance of movements?
Which system amplifies the velocity and distance of movements?
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Study Notes
Skeletal Muscle Fiber Types
- Three types: slow-oxidative (Type I), fast-oxidative (Type IIa), and fast-glycolytic (Type IIx)
- Different proportions in different muscles
- Type I fibers: slow twitch, high oxidative capacity, high resistance to fatigue, many mitochondria, many capillaries, high myoglobin content, red color, low glycogen content.
- Type IIa fibers: fast twitch, intermediate oxidative and glycolytic capacity, intermediate fatigue resistance, many mitochondria, many capillaries, intermediate myoglobin and glycogen content, red color.
- Type IIx fibers: fast twitch, high glycolytic capacity, low oxidative capacity, low resistance to fatigue, few mitochondria, few capillaries, low myoglobin content, white color, high glycogen content
Characteristics of Skeletal Muscle Fibers
- Type I and Type IIa fibers rely on aerobic pathways for ATP generation
- Type IIx fibers rely heavily on anaerobic pathways for ATP generation
- Type IIx fibers contain high amounts of enzymes for anaerobic glycolysis
- Type I fibers contain high amounts of mitochondria, capillaries, and myoglobin
- Type I fibers store and release energy during muscle contraction
Comparing Muscle Fibers
- Fast fibers hydrolyze ATP faster than slow fibers, resulting in faster cross-bridge cycling and faster muscle contraction.
- Oxidative fibers are more resistant to fatigue than glycolytic fibers
- This allows oxidative fibers to produce more ATP for longer.
Muscle Adaptations
- Muscle fibers adapt to the demands placed on them
- Increased oxidative capacity with aerobic training
- Increased muscle hypertrophy with anaerobic training
Muscle Fiber Types, Interconversion & Satellite Cells
- Type I and Type II fibers do not typically convert between each other.
- Satellite cells repair damaged muscles.
- Satellite cells differentiate into new muscle cells.
Sarcopenia
- Age-related loss of skeletal muscle mass and strength, typically after the 40s
- Physical inactivity contributes to sarcopenia.
- Possible to regain some strength through proper exercise.
Contraction of Whole Muscles
- Muscle fibers are attached to bones by tendons
- Tension is first produced internally within sarcomeres by the pulling of actin filaments by myosin.
- Tension is transmitted to bones as tendon tightens.
- Muscle contractions only pull bones to create movement (lever system)
Types of Muscle Contraction
- Isotonic contractions: constant tension; muscle length changes
- Isometric contractions: constant length; muscle length remains constant as tension increases
- Isokinetic contractions: constant motion; velocity remains constant as muscle fibers shorten (not common in human movement)
Exercise Induced Muscle Damage
- Eccentric exercises are more likely to damage muscles.
- Tension is exerted when muscle lengthens.
- Damage to ultrastructure of the sarcomere is common during eccentric activity.
- Fast-twitch fibers are more susceptible to damage than slow-twitch fibers due to smaller sarcomeric proteins
Load-Velocity Relationship
- Higher load→lower shortening velocity
- Lifting light weights→more muscle fiber shortening velocity
Motor Unit Recruitment
- Many muscle fibers controlled by single motor neuron (motor unit)
- Recruit progressively more motor units with increasing force needs.
- Start with small units→ large units
- Least fatiguable fibers recruited→most fatiguable units
Factors Influencing Muscle Tension
- Frequency of stimulation
- Length of fiber at onset of contraction
- Extent of fatigue
- Thickness of fiber
Frequency of Stimulation
- Increasing stimulation frequency→larger muscle tension
- Rapid stimulation→maximal sustained contraction; allows for build-up of tension.
- Complete relaxation between stimulations results in smaller tension outputs, as the 2nd contraction adds on, but a complete relaxation results in a full first contraction output only.
Length of Fiber at Onset of Contraction
- Optimal length: maximum number of myosin-actin cross-bridges occur
- Too short: undesirable overlap, non-ideal mechanics for shortening
- Too long: unused cross-bridges, non-ideal mechanics for shortening
Extent of Fatigue
- Inability to maintain muscle tension at a given level
- Fatigue can be peripheral or central.
- Peripheral causes include decreased rate of energy production, leakage of potassium and glycogen production
- Central causes include reduced central drive.
Thickness of Muscle Fibers
- Increasing fiber thickness ↑ muscle strength and power
- Fiber hypertrophy (increase in fiber size) and hyperplasia (increase in fiber number) contribute to this increase in thickness.
Control of Motor Activity
- Voluntary movements, reflexes, and rhythmic movements (e.g., walking)
- Proprioception: understanding the relative position and movement of the body (muscle spindles and Golgi tendon organs)
- Muscle spindles: monitor muscle length; golgi tendon organs: monitor muscle tension
- Alpha motor neurons: cause contraction of extrafusal fibers
- Gamma motor neurons: cause contraction of intrafusal fibers
- Stretch reflex: monosynaptic reflex: response to muscle length changes
Withdrawal Reflex
- Agonistic muscles contract to create movement
- Antagonistic muscles relax to allow for movement
Cross-Extensor Reflex
- Reflex movement involving opposite limb to maintain balance.
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Description
Test your knowledge on the different types of skeletal muscle fibers, including their properties and functions. Learn about slow-oxidative, fast-oxidative, and fast-glycolytic fibers, along with their roles in muscle performance and metabolism.
