Microscopic Anatomy of Skeletal Muscle
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Questions and Answers

What are the three types of muscle tissue?

Smooth, cardiac, and skeletal.

Describe the structural characteristics that differentiate skeletal muscle fibers from other types of muscle.

Skeletal muscle fibers are striated, multi-nucleated, cylindrical, and under voluntary control.

What is the role of the sarcolemma in skeletal muscle fibers?

The sarcolemma serves as the cell membrane that surrounds muscle fibers, containing the nuclei and myofibrils.

Define sarcomere and its significance in muscle contraction.

<p>A sarcomere is the functional contractile unit of a muscle cell, composed of actin and myosin, crucial for muscle contraction.</p> Signup and view all the answers

Differentiate between the A band, H zone, and I band in a sarcomere.

<p>The A band contains overlapping actin and myosin, the H zone has only myosin, and the I band consists of only actin.</p> Signup and view all the answers

What is the function of tendons in the muscular system?

<p>Tendons connect muscles to bones and provide pathways for nerves and blood vessels.</p> Signup and view all the answers

Explain the process leading to muscle fiber contraction at the neuromuscular junction.

<p>An action potential triggers the release of acetylcholine, which binds to the sarcolemma, causing depolarization and muscle contraction.</p> Signup and view all the answers

What comprises a motor unit and its significance in muscle function?

<p>A motor unit consists of a motor neuron and all muscle fibers it innervates, allowing for coordinated muscle contraction.</p> Signup and view all the answers

What is the role of calcium and troponin in muscle contraction?

<p>They move tropomyosin away from the active site, allowing myosin heads to attach.</p> Signup and view all the answers

Describe the principle of all or none in muscle fiber contraction.

<p>A muscle fiber either contracts fully or does not contract at all.</p> Signup and view all the answers

How does multiple motor unit summation enhance muscle contraction strength?

<p>It increases contractile strength by activating more muscle cells through greater stimulation intensity.</p> Signup and view all the answers

What occurs during the latent phase of a muscle twitch?

<p>It is the initial phase where no visible contraction occurs despite stimulus application.</p> Signup and view all the answers

Explain what is meant by 'treppe' in muscle contraction.

<p>Treppe refers to the staircase effect where successive contractions increase in strength due to heat and calcium buildup.</p> Signup and view all the answers

What characterizes tetanus in muscle activity?

<p>Tetanus is characterized by sustained contraction with no relaxation due to rapid stimulation.</p> Signup and view all the answers

What is muscle fatigue and what causes it?

<p>Muscle fatigue is the inability of a muscle cell to contract due to ATP depletion and lactic acid buildup.</p> Signup and view all the answers

Differentiate between isometric and isotonic contractions.

<p>Isometric contractions involve no change in muscle length, while isotonic contractions involve a change in muscle length.</p> Signup and view all the answers

How does calcium influence muscle contraction at the sarcomere level?

<p>Calcium binds to Troponin, leading to a shift in Tropomyosin, which exposes the active sites on actin filaments for myosin binding.</p> Signup and view all the answers

What are the characteristics of a muscle named 'Longus'?

<p>A muscle named 'Longus' is typically elongated in shape and is often associated with larger muscle groups.</p> Signup and view all the answers

Identify the primary role of agonist muscles in movement.

<p>Agonist muscles, or prime movers, are primarily responsible for generating the main force during a specific movement.</p> Signup and view all the answers

What occurs during the Absolute Refractory Period in muscle cells?

<p>During the Absolute Refractory Period, sodium gates are open but inactivated, preventing any new action potentials from being generated.</p> Signup and view all the answers

Explain the relationship between sodium and potassium ions during action potential.

<p>During action potential, sodium gates open causing depolarization, and subsequently, potassium gates open for repolarization, restoring resting potential.</p> Signup and view all the answers

What is the function of fixator muscles?

<p>Fixator muscles immobilize the origin of a prime mover, stabilizing the joint and allowing the prime mover to exert more force at the insertion.</p> Signup and view all the answers

How does the direction of muscle fibers affect muscle naming?

<p>Muscles can be named based on the direction of their fibers, such as Transverse (horizontal) or Rectus (vertical), indicating their orientation in the body.</p> Signup and view all the answers

What happens after calcium binds to Troponin?

<p>After calcium binds to Troponin, Tropomyosin moves away from the actin sites, allowing myosin heads to attach and initiate contraction.</p> Signup and view all the answers

Flashcards

Muscle Twitch

A single contraction of a skeletal muscle fiber, having three phases: Latent, Contraction, and Relaxation.

Graded Response

Different numbers of muscle cells activated in a muscle according to the contractile need.

Threshold Stimulus

The stimulus needed to cause a muscle contraction.

Multiple Motor Unit Summation

Increase in contractile strength due to more muscle cells being stimulated.

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Treppe

Progressive increase in muscle twitches, same stimulus, due to heat & calcium.

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Wave Summation

Increased contractile strength due to repeated stimulation before relaxation.

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Tetanus

Sustained muscle contraction - No relaxation.

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Muscle Fatigue

Inability of a muscle to contract due to ATP depletion and lactic acid buildup.

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Skeletal Muscle Naming

Skeletal muscles are named based on various characteristics, including direction, size, location, origin number, origin/insertion location, shape, and action.

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Skeletal Muscle

A type of muscle tissue that is responsible for voluntary movement, is striated, multi-nucleated, and arranged in cylindrical bundles.

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Sarcolemma

The cell membrane of a muscle fiber (cell).

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Prime Mover

The muscle primarily responsible for a specific movement.

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Myofibrils

Bundles of protein filaments within a muscle fiber.

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Antagonist Muscle

A muscle that opposes the action of a prime mover.

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Sarcomere

The functional unit of muscle contraction, made up of overlapping actin and myosin filaments.

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Synergist Muscle

A muscle that aids a prime mover by reducing unwanted movements.

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Neuromuscular Junction

The point of contact between a motor neuron and a muscle fiber.

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Fixator Muscle

Specialized synergists that stabilize the origin of a prime mover.

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Motor Unit

A single motor neuron and all the muscle fibers it controls.

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Resting Potential

The electrical charge difference across a muscle cell membrane when it's at rest, typically between -60 and -90 mV.

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Action Potential

A rapid change in electrical potential that travels along a neuron or muscle fiber. (Nerve impulse).

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Action Potential

A rapid change in membrane potential, triggered by a stimulus, involving sodium and potassium ions.

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Calcium's role in contraction

Calcium ions entering the sarcomere bind to troponin, causing tropomyosin to move and exposing actin-binding sites, triggering the contraction process.

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Acetylcholine

A neurotransmitter released at the neuromuscular junction to trigger muscle contraction.

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Study Notes

Microscopic Anatomy of Skeletal Muscle

  • Three types of muscle: smooth, cardiac, and skeletal
  • Skeletal muscle characteristics: voluntary control, striated, multi-nucleated, cylindrical, found in bundles
  • Sarcolemma: cell membrane of a skeletal muscle fiber
  • Myofibrils: bundles of filaments within muscle fibers
  • Sarcomeres: functional contractile units of myofibrils
  • Myosin and Actin: thick and thin filaments within sarcomeres
  • A band: zone of overlap of actin and myosin filaments
  • H zone: contains only myosin filaments
  • I band: contains only actin filaments
  • Muscle fiber: a muscle cell, formed by bundles of myofibrils and sarcolemma
  • Endomysium: areolar connective tissue surrounding individual muscle fibers
  • Fascicles: bundles of muscle fibers
  • Perimysium: connective tissue surrounding fascicles
  • Epimysium: Connective tissue surrounding bundles of fascicles (muscles)
  • Tendons/Aponeuroses: strong connective tissue that connects muscles to bones, providing a path for nerves and blood vessels
  • Neuromuscular Junction: junction between a motor neuron and a muscle fiber
  • Axon Terminal: end of the motor neuron that approaches the muscle fiber
  • Motor Unit: a motor neuron and all the muscle fibers it innervates
  • Synaptic Cleft: space between the axon terminal and the sarcolemma of the muscle fiber
  • Muscle Contraction: Action Potential/Nerve Impulse travels down the axon to the axon terminal, releasing Acetylcholine, triggering depolarization and contraction. Calcium enters the sarcomere triggering events.

Naming Skeletal Muscles

  • Muscles named by direction (transverse, oblique, rectus)
  • Muscles named by size (maximus, minimus, longus, brevis)
  • Muscles named by location (e.g., Extensor carpi ulnaris)
  • Muscles named by origin and insertion (e.g., Sternocleidomastoid)
  • Muscles named by shape (e.g., deltoid)
  • Muscles named by action (e.g., adductors)

Types of Muscles

  • Prime Movers/Agonists: primarily responsible for a particular movement
  • Antagonists: oppose or reverse the movement of a prime mover
  • Synergists: aid actions of agonists by reducing undesirable movements
  • Fixators: specialized synergists that immobilize the origin of a prime mover

Muscle Activity

  • Resting Potential: -60 to -90mV (-90 for skeletal muscle) due to potassium and sodium concentration difference and pumps

  • Action Potential: sodium gates open, depolarization occurs, polarity increases to +35, sodium gates close, potassium gates open, repolarization.

  • Absolute Refractory Period: time when sodium gates are open and inactivated, no other action potential.

  • Relative Refractory Period: time when the sodium gates close and potassium gates open, but another action potential may be possible.

  • Muscle Contraction: After calcium enters the sarcomere causing a series of events resulting in a Power Stroke and contraction.

  • Muscle Twitch: a single muscle contraction, 3 phases (latent, contraction, relaxation). Subthreshold stimulus does not lead to contraction.

  • Maximal Stimulus: causes all muscle fibers in a muscle to contract

  • Multiple Motor Unit Summation/Recruitment: increasing contraction strength by stimulating more muscle cells.

  • Treppe: staircase effect, progressive increase in contractile strength with same stimulus. Wave summation: stimuli with increased rate, increasing contractile strength, tetanus: sustained contraction with no relaxation, and muscle fatigue: loss of contractile ability due to ATP depletion, and oxygen debt, lactic acid buildup.

  • Isometric Contractions: muscle length stays the same, force generated can changes

  • Isotonic Contractions: muscle length changes, forces generated stays the same.

  • Tonus: constant state of slight muscle tension

  • Electromyography: detecting, amplifying, and recording skin voltage due to skeletal muscle contraction (electromyograph/ electromyogram).

  • Work is the application of muscle force needed to move an object.

  • Dynamometry is the study of power. A Dynogram is the recording obtained.

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Microscopic Anatomy of Muscular System Notes PDF

Description

Test your knowledge on the microscopic anatomy of skeletal muscle, including the characteristics of skeletal, cardiac, and smooth muscle types. Explore the structure and function of muscle fibers, myofibrils, and sarcomeres, along with their associated connective tissues and filaments.

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