Muscle System Overview
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Questions and Answers

Which type of muscle is described as being voluntary and low endurance?

  • Smooth muscle
  • Striated muscle (correct)
  • Cardiac muscle
  • Involuntary muscle

What is a characteristic feature of cardiac muscle?

  • Hexagonal nuclei
  • Intercalated discs (correct)
  • Centrally placed nuclei in a hexagonal arrangement
  • Voluntary control

Which statement about smooth muscle is accurate?

  • It is involuntary and has high endurance. (correct)
  • It is directly controlled by the nervous system.
  • It has multiple nuclei per cell.
  • It contains striations.

What does a motor unit consist of?

<p>A single motor neuron and the group of muscle fibres it innervates (B)</p> Signup and view all the answers

How does the number of muscle fibres per motor unit relate to dexterity?

<p>Greater dexterity is associated with fewer muscle fibres per motor unit. (A)</p> Signup and view all the answers

What is the primary function of muscle tissue?

<p>To contract and produce movement (D)</p> Signup and view all the answers

In which part of the body would you primarily find smooth muscle?

<p>Digestive tract (C)</p> Signup and view all the answers

Which muscle type is responsible for involuntary movements in the organs?

<p>Smooth muscle (D)</p> Signup and view all the answers

Which characteristic is NOT associated with striated muscle?

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

What do the terms 'origin' and 'insertion' refer to in muscle anatomy?

<p>The points where a muscle connects to two different bones (B)</p> Signup and view all the answers

What are hexagonal nuclei a characteristic feature of?

<p>Striated muscle (C)</p> Signup and view all the answers

What role do tendons play in the musculoskeletal system?

<p>They connect muscle to bone (C)</p> Signup and view all the answers

How many skeletal muscles are estimated to be present in the human body?

<p>Approximately 650 (D)</p> Signup and view all the answers

Which statement best describes the arrangement of muscle fibers?

<p>Muscle fibers extend the entire length of the muscle. (D)</p> Signup and view all the answers

What type of contraction occurs when a muscle exerts force without changing its length?

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

What do myofibrils contain that enables muscle contraction?

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

What is the primary role of a neuromuscular junction (NMJ)?

<p>It connects motor neurons to muscle fibers. (A)</p> Signup and view all the answers

Which of the following is true about the all-or-nothing response of muscle fibers?

<p>It means a muscle fiber either contracts fully or not at all. (A)</p> Signup and view all the answers

In the context of motor units, which muscle has the highest number of fibers per motor unit?

<p>Biceps muscles (A)</p> Signup and view all the answers

What type of contraction results in a muscle lengthening while maintaining constant tension?

<p>Eccentric contraction (D)</p> Signup and view all the answers

During which type of isotonic contraction does the muscle shorten?

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

What is a potential consequence of heavy eccentric loading on muscles?

<p>It can cause greater muscle necrosis. (B)</p> Signup and view all the answers

How does asynchronous firing of motor units benefit muscle contraction?

<p>It allows for a smooth and graded contraction. (C)</p> Signup and view all the answers

What is the average number of muscle fibers per motor unit in the human body?

<p>150 fibers (D)</p> Signup and view all the answers

What is the duration of the contraction period in muscle physiology?

<p>0.04 sec (A)</p> Signup and view all the answers

Which phase of muscle contraction occurs immediately after the stimulus?

<p>Latent period (D)</p> Signup and view all the answers

What is the consequence of stimulation at a frequency shorter than the twitch time?

<p>Summation occurs (C)</p> Signup and view all the answers

How can summation in muscle contraction be achieved?

<p>By increasing both the number of motor units and the contraction rate (A)</p> Signup and view all the answers

What happens when impulses are sent at a higher frequency of over 40 pulses/sec?

<p>Muscle undergoes tetanus (D)</p> Signup and view all the answers

During which period does the muscle not respond to further stimulation?

<p>Refractory period (D)</p> Signup and view all the answers

In terms of muscle response, what does wave summation entail?

<p>Superimposing twitches for stronger contractions (B)</p> Signup and view all the answers

What is the duration of the relaxation period in the frog's muscle physiology?

<p>0.05 sec (D)</p> Signup and view all the answers

Flashcards

Striated Muscle

A type of muscle tissue characterized by visible stripes (striations) under a microscope. It's also known as skeletal muscle because it's typically attached to bones.

Striated Muscle: Voluntary

Striated muscles are under conscious control, meaning you consciously decide to move them.

Striated Muscle: Low Endurance

Striated muscles tire more quickly than other muscle types.

Muscle Biopsy

Collecting a small sample of muscle tissue for microscopic examination to diagnose conditions or assess muscle damage.

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Cardiac Muscle

The specialized muscle tissue of the heart that is striated and highly endurance oriented with unique specialized junctions.

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Cardiac Muscle: Involuntary

Heart muscle works continuously and independently of conscious effort.

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Cardiac Muscle: High Endurance

Cardiac muscle is continuously active and can operate for extended periods without fatigue.

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Smooth Muscle

Involuntary muscle found in organs like the digestive tract, blood vessels, and airways.

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Smooth Muscle: Involuntary

Smooth muscle functions without conscious control.

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Smooth Muscle: High Endurance

Smooth muscle can sustain contractions for longer periods of time than other muscle types.

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Motor Unit

A motor neuron and all the muscle fibers it controls, forming the basic functional unit of skeletal muscle.

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Motor Unit: Variable Fiber Number

The number of muscle fibers per motor unit can vary depending on the required level of fine motor control.

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Skeletal Muscle

Muscle tissue attached to bones, responsible for movement.

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Cardiac Muscle

Muscle found in the heart, responsible for pumping blood.

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Smooth Muscle

Muscle found in organs, responsible for involuntary actions.

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Muscle Fiber

Individual muscle cell within a muscle.

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Myofibril

Contractile part of a muscle fiber and contains sarcomeres.

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Sarcomere

The basic unit of contraction within a muscle, containing actin and myosin filaments.

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Tendon

Connects muscle to bone.

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Ligament

Connects bone to bone.

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Motor Unit

A motor neuron and all the muscle fibers it controls.

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Muscle Twitch

A single, brief contraction of a muscle fiber in response to a stimulus.

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Muscle Summation

The combination of multiple muscle twitches to create a stronger contraction.

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Isometric Contraction

Muscle tension increases but the muscle does not shorten.

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Isotonic Contraction

Muscle tension remains constant while the muscle shortens.

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Origin

Fixed attachment point of a muscle that doesn't move during contraction.

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Insertion

Movable attachment point of a muscle that moves during contraction.

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Flexor

Muscle that closes a joint.

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Extensor

Muscle that opens a joint.

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Motor Unit

A motor neuron and all the muscle fibers it controls.

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Neuromuscular Junction (NMJ)

The connection point between a motor neuron and a muscle fiber.

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Motor Unit Fiber Ratio

The number of muscle fibers controlled by a single motor neuron

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Isometric Contraction

Muscle contracts, but the length of the muscle stays the same.

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Isotonic Contraction

Muscle contracts and changes length.

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Concentric Contraction

Muscle shortens when contracting.

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Eccentric Contraction

Muscle lengthens when contracting while maintaining tension.

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All-or-None Response

A muscle fiber contracts completely or not at all when stimulated.

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Muscle Fiber Recruitment

Increasing strength in a muscle by activating more motor units.

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Frog Gastrocnemius Twitch Duration

A single stimulation of the frog gastrocnemius muscle results in a quick twitch lasting approximately 0.1 seconds.

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Human Muscle Twitch Duration

A single stimulation of a human muscle produces a twitch that lasts about 0.05 seconds.

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Muscle Latent Period

The delay (0.005 seconds) between a stimulus and the muscle's visible response.

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Muscle Contraction Period

The period (0.04 seconds) during which the muscle shortens in response to a stimulus.

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Muscle Relaxation Period

The period (0.05 seconds) where the muscle returns to its original length after contracting.

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Refractory Period

A brief period following initial stimulation where the muscle is unresponsive to further stimuli (0.002 seconds).

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Muscle Summation

A greater shortening of a muscle produced by multiple stimuli delivered before muscle relaxation.

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Multiple Motor Unit Summation

Increasing the number of motor units involved to produce a stronger muscle contraction. Think “recruitment”

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Wave Summation

Increasing the rate of stimulation of individual motor units leading to greater muscle contraction.

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Muscle Tetanus

A state of maximal muscle contraction resulting from high-frequency stimuli, fusing individual twitches together.

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Study Notes

Muscle System Overview

  • 40% of the body is skeletal muscle
  • There are approximately 650 skeletal muscles
  • Over 150 surface (anatomical) muscles

Learning Outcomes

  • Discuss the three main muscle types: cardiac, smooth, and striated
  • Describe the structure and arrangement of anatomical muscles
  • Outline the innervation of the motor unit
  • Describe the physiology of whole muscle action including twitch and summation
  • Differentiate between isometric and isotonic contraction

Muscle Types

  • Skeletal muscle: Attached to bones, voluntary, low endurance
  • Cardiac muscle: Walls of the myocardium, involuntary, high endurance
  • Smooth muscle: Lines digestive tract, bronchi, and blood vessels, involuntary, high endurance

Striated Muscle

  • Also called striped or skeletal muscle
  • Voluntary, under direct nervous control
  • Low endurance

Muscle Biopsy

  • Wide-bore needle inserted into muscle to remove a small sample
  • Muscle is analyzed using a microscope and histological stains

Striated Muscle Microscopic Details

  • Hexagonal
  • Nuclei on the outside (peripheral)
  • Fibers are the same size

Cardiac Muscle

  • Only in the heart
  • Striated, intercalated discs (gap junctions)
  • 1-2 nuclei per cell
  • Centrally placed
  • High endurance
  • Innervated by the pace-maker

Smooth Muscle

  • 1 centrally placed nucleus per cell
  • No striations
  • Sustained contraction

Motor Unit

  • The functional unit of skeletal muscle (MU)
  • Composed of a single motor neuron and the group of muscle fibers innervated by it
  • More muscle fibers than motor neurons, some motor neurons innervate more than one fiber
  • Fiber number varies with control needed (e.g., larynx 2-3/MU, eye 10/MU, biceps 1000+/MU)

Neuromuscular Junction (NMJ)

  • Also known as the motor endplate
  • The connection between the muscle fiber and motor neuron
  • Membranes of the nerve and muscle cells come into close contact
  • One NMJ per fiber

Motor Unit Function

  • When a muscle fiber is stimulated at the NMJ, it contracts ("all or nothing" response)
  • The degree of contraction of a muscle is determined by the number of stimulated motor units
  • Maximal contraction occurs when all motor units are firing together
  • In practice, asynchronous firing of motor units results in a graded response for a smooth contraction

Types of Muscle Contraction

  • Isometric contraction: Muscle contracts but does not shorten; length is maintained; tension increases
  • Isotonic contraction: Muscle changes length; tension remains constant
    • Concentric: Muscle shortens
    • Eccentric: Muscle lengthens

Concentric Isotonic Contraction

  • Force generated by muscle is greater than the load to be lifted
  • Muscle shortens in length

Eccentric Isotonic Contraction

  • Muscles slow joint movement
  • Heavy eccentric loading can damage muscle when overloaded (muscle necrosis)
  • Muscles are approximately 10% stronger during eccentric than concentric contractions

Muscle Physiology (Laboratory Preparations)

  • Whole muscle function studied using laboratory preparations (e.g., frog gastrocnemius)
  • Muscle responds with a 'twitch' (quick contraction) when stimulated electrically
  • Twitch duration: 0.1 sec in frogs, 0.05 sec in humans
  • Requires specialized equipment for analysis

Phases of Muscle Contraction

  • Latent period: Delay between stimulus and visible response
  • Contraction period: Muscle shortens
  • Relaxation period: Muscle returns to resting length
  • Refractory period: Brief period after stimulation when muscle can't respond further

Twitch Summation

  • Muscle can respond to a second stimulus while still contracting
  • Second stimulus superimposed on first, resulting in greater shortening (summation)

Types of Summation

  • Multiple motor unit summation (recruitment): Increased motor unit involvement
  • Wave summation: Increasing rate of contraction

Tetanus

  • High frequency stimulation fuses successive contractions into a sustained maximal contraction (tetanus)
  • Further increased stimulation will not shorten muscle more

References

  • Solomon et al, Ch 40
  • Alberts et al, Ch 17, pp 599-604

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MNB.05 Muscle Anatomy and Physiology PDF

Description

Explore the intricacies of the muscle system, including the three main types of muscles: skeletal, cardiac, and smooth. Understand their structure, function, and physiology, along with key concepts like muscle contraction types and the motor unit's innervation. This quiz covers essential aspects necessary for a comprehensive understanding of human muscular anatomy.

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