Skeletal Muscle Fiber Types Quiz
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Questions and Answers

What is the issue associated with myosin cross bridges when they are too short?

  • Enhanced tension production
  • Increased number of pull forces
  • Undesirable overlapping affecting mechanics (correct)
  • Ideal mechanics for shortening

What occurs when myosin cross bridges are too long?

  • Efficient force generation
  • Optimal actin binding
  • Increased muscle tension
  • Non-utilization of cross bridges (correct)

Which situation results in the generation of no tension?

  • Actin is fully accessible for binding
  • Shortened muscle fibers
  • Excessively long cross bridges (correct)
  • Cross bridges are overlapping adequately

Which of the following best describes the mechanics of muscle shortening?

<p>Shortening requires overlapping actin and myosin (C)</p> Signup and view all the answers

In muscle mechanics, what is the consequence of excessive fatigue on cross bridges?

<p>Reduced number of accessible cross bridges (D)</p> Signup and view all the answers

Which type of skeletal muscle fibre is classified primarily as slow-twitch?

<p>Type I (B)</p> Signup and view all the answers

Which muscle fibre type has high amounts of enzymes for anaerobic glycolysis?

<p>Fast-glycolytic (C)</p> Signup and view all the answers

Which characteristic makes oxidative fibres more advantageous for endurance activities?

<p>Increased resistance to fatigue (A)</p> Signup and view all the answers

What structural feature is prevalent in slow-oxidative fibres that aids in their function?

<p>Large amounts of mitochondria (C)</p> Signup and view all the answers

Which of the following statements is true regarding fast-twitch fibres compared to slow-twitch fibres?

<p>They have a higher myosin-ATPase activity. (C)</p> Signup and view all the answers

Which skeletal muscle fibre type primarily uses aerobic pathways for energy generation?

<p>Type IIa (B)</p> Signup and view all the answers

Which statement correctly distinguishes between oxidative and glycolytic fibres?

<p>Glycolytic fibres primarily rely on anaerobic respiration. (C)</p> Signup and view all the answers

What is a key characteristic of fast-glycolytic fibres regarding energy production?

<p>They are primarily designed for high-intensity, short-duration activities. (C)</p> Signup and view all the answers

In isotonic contraction, what remains constant during the muscle contraction?

<p>Load remains constant (C)</p> Signup and view all the answers

Which type of contraction involves muscle length remaining constant while tension is generated?

<p>Isometric contraction (C)</p> Signup and view all the answers

Which type of muscle contraction is characterized by constant velocity?

<p>Isokinetic contraction (C)</p> Signup and view all the answers

What is a primary difference between eccentric and concentric contractions?

<p>Eccentric contractions lengthen the muscle under load. (B)</p> Signup and view all the answers

What is a common consequence of performing eccentric exercises?

<p>Greater likelihood of muscle damage occurs. (A)</p> Signup and view all the answers

Which statement about skeletal muscles is true?

<p>Some skeletal muscles can produce movement without an insertion. (A)</p> Signup and view all the answers

During normal human movement, which contraction type is not typically observed?

<p>Isokinetic contraction (A)</p> Signup and view all the answers

In which scenario will muscle fibers not shorten?

<p>During isometric contractions (D)</p> Signup and view all the answers

What role do muscle spindles play in the body?

<p>They convey information about muscle length. (B)</p> Signup and view all the answers

Which of the following statements is true about gamma motor neurons?

<p>They cause contraction of intrafusal muscle fibers. (D)</p> Signup and view all the answers

What is the function of Golgi tendon organs?

<p>To convey information regarding muscle tension. (D)</p> Signup and view all the answers

How do afferent neurons contribute to the understanding of muscle status?

<p>They send signals to the central nervous system when detecting stretch. (B)</p> Signup and view all the answers

The concept of alpha-gamma coactivation primarily relates to which function?

<p>Contributing to muscle spindle sensitivity. (B)</p> Signup and view all the answers

In terms of proprioception, what information do muscle spindles specifically convey?

<p>Muscle length. (A)</p> Signup and view all the answers

Which motor neurons are responsible for causing the contraction of extrafusal muscle fibers?

<p>Alpha motor neurons. (D)</p> Signup and view all the answers

What maintains tension in a muscle spindle during coactivation?

<p>Contraction of intrafusal fibers. (A)</p> Signup and view all the answers

What does proprioception primarily help an individual understand?

<p>Relative position and movement of the body. (D)</p> Signup and view all the answers

Rhythmic patterned outputs related to walking are driven by which mechanism?

<p>Central pattern generators. (B)</p> Signup and view all the answers

What role do muscle spindles play in the stretch reflex?

<p>They detect changes in muscle length. (A)</p> Signup and view all the answers

The stretch reflex is classified as what type of reflex?

<p>Monosynaptic. (B)</p> Signup and view all the answers

In the withdrawal reflex, what occurs simultaneously with the contraction of agonistic muscles?

<p>Flexion of the affected limb. (C)</p> Signup and view all the answers

Which of the following statements best describes the function of afferent fibers in muscle spindles?

<p>They transmit sensory information to the CNS. (B)</p> Signup and view all the answers

What is the primary purpose of the crossed extensor reflex?

<p>To maintain balance during withdrawal. (B)</p> Signup and view all the answers

Which muscle group is primarily involved in the stretch reflex when the patellar tendon is tapped?

<p>Extensor muscles of the knee. (D)</p> Signup and view all the answers

What triggers the withdrawal reflex upon stimulation?

<p>Pain and discomfort in a limb. (C)</p> Signup and view all the answers

In the context of reflex actions, what does the term 'agonistic muscles' refer to?

<p>Muscles that cause movement. (C)</p> Signup and view all the answers

What is the role of the motor neuron in reflex actions?

<p>To transmit information to the muscle. (A)</p> Signup and view all the answers

What initiates the somatic reflexes discussed?

<p>Involuntary reflex pathways. (A)</p> Signup and view all the answers

What determines the percentage of each type of muscle fiber in an individual?

<p>Genetic endowment and activity level (C)</p> Signup and view all the answers

What is muscle hypertrophy primarily a result of?

<p>High-intensity training and increased muscle fiber size (B)</p> Signup and view all the answers

Which factor is understood to influence muscle growth and protein synthesis?

<p>High levels of testosterone (C)</p> Signup and view all the answers

How does tension develop in whole muscles during contraction?

<p>By pulling of actin filaments by myosin within sarcomeres (A)</p> Signup and view all the answers

What role do bones serve in the lever system described?

<p>They function as levers that pivot at joints. (A)</p> Signup and view all the answers

What happens to the tension when muscle contraction occurs?

<p>Tension is first generated in the muscle fibers. (C)</p> Signup and view all the answers

What effect does the placement of a muscle's insertion point have on movement?

<p>Closer insertion points increase the force required to lift a load. (C)</p> Signup and view all the answers

Which muscle adaptation is associated with oxidative capacity?

<p>Muscle endurance training (A)</p> Signup and view all the answers

What does increased tension in muscles lead to during contraction?

<p>Transmission of force to the bones (A)</p> Signup and view all the answers

What happens during the interconversion of muscle fiber types?

<p>Muscle fibers adapt to specific training regimes. (D)</p> Signup and view all the answers

How does skeletal muscle provide force during movement?

<p>Skeletal muscles only pull bones to create movement. (C)</p> Signup and view all the answers

What is the primary function of tendons in the muscular system?

<p>To connect muscle fibers to bones. (B)</p> Signup and view all the answers

What is a significant outcome of high-intensity training?

<p>Increased muscle fiber size and strength (A)</p> Signup and view all the answers

Which system amplifies the velocity and distance of movements?

<p>The lever system (A)</p> Signup and view all the answers

Flashcards

Slow-oxidative muscle fibers (Type I)

Slow-twitch fibers that rely on aerobic pathways for energy production; have high mitochondria, capillary, and myoglobin content, resisting fatigue.

Fast-oxidative-glycolytic muscle fibers (Type IIa)

Fast-twitch fibers that use both aerobic and anaerobic pathways for energy; possess moderate mitochondria and myoglobin content, and are moderately resistant to fatigue.

Fast-glycolytic muscle fibers (Type IIx)

Fast-twitch fibers that rely primarily on anaerobic glycolysis for energy; have high enzyme levels for rapid energy production but fatigue quickly.

Aerobic energy production

Energy production using oxygen, creating more ATP than anaerobic methods, allowing for longer activities.

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Anaerobic energy production

Energy production without oxygen; creates ATP quickly but less efficiently, leading to fatigue.

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Myosin-ATPase activity

The rate at which myosin hydrolyzes ATP, impacting the speed of cross-bridge cycling and muscle contraction.

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Muscle fiber fatigue

The decline in muscle power output due to sustained or intense exercise, often linked to energy depletion or metabolic factors.

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Oxidative vs. Glycolytic Fibers

Muscle fibers categorized based on their primary energy production method, impacting their endurance and fatigue resistance.

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Isotonic Contraction

Muscle contraction where muscle length changes while tension remains constant. This is the most common type of contraction used in daily activities.

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Isometric Contraction

Muscle contraction where muscle length remains constant while tension increases. No visible movement is observed.

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Isokinetic Contraction

Muscle contraction where the speed of movement remains constant, regardless of the load.

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Eccentric Contraction

Muscle contraction where the muscle lengthens under load. This occurs when resisting gravity or slowing down a movement.

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Concentric Contraction

Muscle contraction where the muscle shortens under load. This is the most common type of contraction used in activities like lifting.

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Exercise-Induced Muscle Damage (EIMD)

Damage to muscle fibers caused by intense or unaccustomed exercise, primarily during eccentric contractions.

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How does EIMD occur more often during eccentric contractions?

Eccentric contractions involve more stress on muscle fibers, leading to greater damage compared to concentric or isometric contractions.

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What is the role of load in muscle contractions?

Load refers to the resistance against which a muscle contracts. It affects the type of contraction and the amount of force required.

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Muscle Contraction: Ideal Length

The ideal length for a muscle to generate maximum force is where there is optimal overlap between actin and myosin filaments. This allows for the maximum number of cross-bridges to form and efficiently pull the actin filaments.

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Muscle Contraction: Too Short

If a muscle is too short, the actin filaments overlap excessively, leading to inefficient force production. Cross-bridges cannot form optimally, resulting in a weaker contraction.

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Muscle Contraction: Too Long

When a muscle is too stretched, the actin and myosin filaments are too far apart, resulting in fewer cross-bridge formations and a weak contraction. The muscle can't generate much tension.

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Muscle Contraction: Optimal Length

The ideal length of a muscle fiber for maximum force generation is when there is a sufficient overlap of actin and myosin filaments. This allows for many cross-bridges to form and exert strong pulling forces.

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Muscle Fatigue: The Two Extremes

Muscle fatigue can be caused by either excessive use of the muscle or a lack of use. Extreme use can lead to energy depletion and metabolite buildup, while disuse can result in muscle atrophy and weakness.

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Genetic Endowment

The percentage of each muscle fiber type is largely determined by genes and partly by activity.

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Muscle Fiber Adaptation

Muscle fibers adapt to demands like increased oxidative capacity (aerobic endurance) or hypertrophy (increased size).

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Oxidative Capacity

The ability of muscles to use oxygen efficiently.

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Muscle Hypertrophy

Increase in muscle fiber size due to high-intensity training.

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Testosterone Influence

Testosterone promotes the synthesis and assembly of active myosin in muscle.

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Muscle Fiber Type Interconversion

Muscle fiber types can transform (change) with proper exercise.

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Whole Muscle Structure

Whole muscles are bundles of muscle fibers attached to bones by tendons.

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Muscle Contraction

Muscle contractions pull on bones to create movement. Tension is first generated internally within sarcomeres.

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Lever System

Bones act as levers, joints as fulcrums, and muscles provide force. This system amplifies velocity and distance.

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Fulcrum

The pivot point of a lever system. E.g., a joint is a fulcrum in the body.

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Tension Transmission

Tension produced within muscle fibers is transmitted through tendons to bones, leading to movement.

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Muscle Insertion

The attachment point of the muscle closer to a joint influences the force needed to move a load.

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Muscle Growth

High intensity exercise leads to increase in overall muscle size by increasing muscle fiber size (cross-sectional area).

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Central Pattern Generators

Neural circuits in the spinal cord that produce rhythmic patterns of muscle activity, like walking, without conscious effort.

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Afferent Inputs

Sensory information carried from the body to the central nervous system (brain and spinal cord).

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Proprioception

The sense of body position and movement, allowing us to understand where our body parts are in space.

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Muscle Spindles

Sensory receptors within muscles that detect changes in muscle length.

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Intrafusal Fibers

Specialized muscle fibers within muscle spindles that detect stretch and send signals to the central nervous system.

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Extrafusal Fibers

Regular muscle fibers that are responsible for generating force and movement.

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Alpha Motor Neuron

Nerve cells that stimulate the contraction of extrafusal muscle fibers.

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Gamma Motor Neuron

Nerve cells that control the tension within intrafusal fibers, ensuring accurate length sensing.

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Golgi Tendon Organ

Sensory receptors located in tendons that detect changes in muscle tension.

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Alpha-Gamma Coactivation

Simultaneous activation of alpha and gamma motor neurons, ensuring muscle spindle sensitivity during contraction.

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What are muscle spindles?

Specialized sensory receptors found within muscles that detect changes in muscle length (stretch) and rate of change.

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What's the role of muscle spindles in the stretch reflex?

Muscle spindles detect muscle stretch, transmitting signals to the spinal cord via sensory neurons, triggering an involuntary muscle contraction to resist further stretching.

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What is a monosynaptic reflex?

A reflex pathway involving only one synapse between the sensory neuron and the motor neuron, resulting in a rapid and direct response.

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How does the stretch reflex protect muscles?

By detecting and resisting sudden stretches, the stretch reflex protects muscles from overstretching and potential injury.

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What is the withdrawal reflex?

A reflex triggered by a painful stimulus, causing an involuntary withdrawal of the affected body part.

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How do agonistic and antagonistic muscles work together in the withdrawal reflex?

Agonistic muscles contract to create movement, while antagonistic muscles relax to allow for the movement. This coordinated action allows for effective withdrawal.

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What is the crossed extensor reflex?

A reflex that occurs simultaneously with the withdrawal reflex, where the opposite limb extends to maintain balance and support the body.

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How does the crossed extensor reflex contribute to balance?

By extending the opposite limb, the crossed extensor reflex helps to maintain balance and prevent falling during withdrawal reflexes.

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What are the 3 main types of reflexes?

The three main types of reflexes are: the stretch reflex (muscle stretch), the withdrawal reflex (painful stimulus), and the crossed extensor reflex (balance during withdrawal) .

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Why are reflexes important?

Reflexes are critical for survival, protecting the body from harm by triggering rapid, involuntary responses to stimuli.

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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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