Skeletal Muscle Physiology Quiz
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Questions and Answers

What percentage of total body weight do skeletal muscles typically make up in males?

  • 25%
  • 40% (correct)
  • 50%
  • 32%
  • Which property of muscle refers to its ability to respond to a stimulus?

  • Contractility
  • Extensibility
  • Elasticity
  • Excitability (correct)
  • Which of the following describes the ability of a muscle to shorten with force?

  • Elasticity
  • Contractility (correct)
  • Extensibility
  • Excitability
  • What is the main characteristic that defines voluntary muscles?

    <p>Their actions can be directed by thoughts</p> Signup and view all the answers

    What property of muscle allows it to recoil to its original resting length after being stretched?

    <p>Elasticity</p> Signup and view all the answers

    What occurs when action potentials cease during muscle relaxation?

    <p>Ca2+-ATPase pumps move Ca2+ back into the sarcoplasmic reticulum</p> Signup and view all the answers

    Which statement is true regarding motor units?

    <p>All muscle fibers within a motor unit contract when the motor neuron is activated</p> Signup and view all the answers

    How does the number of muscle fibers in a motor unit affect muscle control?

    <p>Finer muscle control requires smaller motor units with fewer muscle fibers</p> Signup and view all the answers

    What is the relationship between motor unit recruitment and contraction strength?

    <p>Increased motor unit recruitment leads to greater contraction strength</p> Signup and view all the answers

    Which type of muscles is likely to have more muscle fibers per motor unit?

    <p>Larger, stronger muscles with thousands of fibers</p> Signup and view all the answers

    What type of muscle tissue is characterized by having multiple nuclei that are peripherally located and is under voluntary control?

    <p>Skeletal muscle</p> Signup and view all the answers

    Which muscle tissue type comprises the walls of hollow organs and blood vessels?

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

    What structure in cardiac muscle facilitates communication between cells?

    <p>Intercalated disks</p> Signup and view all the answers

    What is the role of the autonomic nervous system in muscle tissue?

    <p>Regulates involuntary muscle function</p> Signup and view all the answers

    What is the primary structural unit of skeletal muscle?

    <p>Muscle fiber</p> Signup and view all the answers

    Which connective tissue layer surrounds individual muscle fibers?

    <p>Endomysium</p> Signup and view all the answers

    What characteristic distinguishes smooth muscle from other types of muscle?

    <p>Single nucleus centralized</p> Signup and view all the answers

    What type of muscle is classified as involuntary and striated?

    <p>Cardiac muscle</p> Signup and view all the answers

    Which of the following is NOT a characteristic of muscle fibers?

    <p>Centrally located nuclei</p> Signup and view all the answers

    What symbol represents the smallest functional unit of muscle contraction?

    <p>Sarcomere</p> Signup and view all the answers

    Which layer of connective tissue surrounds a bundle of muscle fibers known as a fascicle?

    <p>Perimysium</p> Signup and view all the answers

    What is the primary function of the sarcoplasmic reticulum in muscle cells?

    <p>Releasing calcium ions for contraction</p> Signup and view all the answers

    Which component is primarily responsible for the striated pattern seen in skeletal muscle?

    <p>Sacromeres</p> Signup and view all the answers

    How are muscle fibers adapted for their function?

    <p>Containing more than one nucleus</p> Signup and view all the answers

    What is the role of satellite cells in muscle repair?

    <p>They can fuse to damaged muscle cells.</p> Signup and view all the answers

    Which type of muscle fibers typically experience reduced mass with aging?

    <p>Type II fibers</p> Signup and view all the answers

    What happens to myostatin levels and satellite cell quantity with age?

    <p>Increase in myostatin and decrease in satellite cells.</p> Signup and view all the answers

    What is the primary function of the agonist muscle during movement?

    <p>To cause movement in a specific direction.</p> Signup and view all the answers

    Which part of the muscle is referred to as the belly?

    <p>The fleshy portion between the tendons.</p> Signup and view all the answers

    In relation to muscle attachment, what is an origin?

    <p>The fixed or stationary bone attachment of a muscle's tendon.</p> Signup and view all the answers

    What is the function of myostatin?

    <p>Inhibit muscle recovery.</p> Signup and view all the answers

    What can endurance training help mitigate in aging individuals?

    <p>Reduction in capillary blood supply.</p> Signup and view all the answers

    What defines the load in a lever system involving muscles?

    <p>The resistance that opposes the movement.</p> Signup and view all the answers

    Which of the following describes a muscle spasm?

    <p>A sudden involuntary contraction of a single muscle.</p> Signup and view all the answers

    What is the primary role of myofibrils in muscle fibers?

    <p>To facilitate the sliding filament mechanism</p> Signup and view all the answers

    Which structure corresponds to the light bands observed in skeletal muscle?

    <p>I band</p> Signup and view all the answers

    What causes the shortening of I bands during muscle contraction?

    <p>Thin filaments slide over thick filaments</p> Signup and view all the answers

    What is the function of titin in muscle fibers?

    <p>To provide structural support and elasticity</p> Signup and view all the answers

    How do the A bands change during contraction according to the sliding filament theory?

    <p>They remain the same length</p> Signup and view all the answers

    What role does the troponin-tropomyosin system play in muscle contraction?

    <p>It serves as a switch regulating cross bridge attachment</p> Signup and view all the answers

    During muscle relaxation, how does tropomyosin affect the binding sites on actin?

    <p>It blocks binding sites to prevent crossbridges</p> Signup and view all the answers

    What happens to crossbridge cycling when calcium ions are released into the muscle?

    <p>Troponin changes shape to expose binding sites</p> Signup and view all the answers

    What is the H zone in skeletal muscle Anatomy?

    <p>Region where only thick filaments are present</p> Signup and view all the answers

    What is the significance of the Z line within the sarcomere?

    <p>It anchors thin filaments during contraction</p> Signup and view all the answers

    Which component is primarily responsible for the contraction of skeletal muscle fibers?

    <p>Actin and myosin interactions</p> Signup and view all the answers

    What is the primary function of M lines in sarcomeres?

    <p>To anchor thick filaments during contraction</p> Signup and view all the answers

    What is formed when ATP binds to myosin during the crossbridge cycle?

    <p>Myosin detaches from actin</p> Signup and view all the answers

    What happens to the length of the sarcomere during muscle contraction?

    <p>It shortens as Z discs are pulled together</p> Signup and view all the answers

    What is the main purpose of muscle tone in skeletal muscles?

    <p>To maintain muscle firmness without producing movement</p> Signup and view all the answers

    What condition results in decreased muscle tone and flaccid muscles?

    <p>Hypotonia</p> Signup and view all the answers

    Which type of muscle fibers are considered slow-twitch?

    <p>Type I fibers</p> Signup and view all the answers

    What characterizes fast-twitch muscle fibers (Type IIX)?

    <p>Large stores of glycogen</p> Signup and view all the answers

    What happens to the reflexes during hypertonia?

    <p>They are enhanced and become pathological</p> Signup and view all the answers

    Which statement is true regarding the role of the brain and spinal cord in muscle tone?

    <p>They excite motor neurons which help establish muscle tone.</p> Signup and view all the answers

    What distinguishes isometric contractions from isotonic contractions?

    <p>Isometric contractions do not produce muscle shortening.</p> Signup and view all the answers

    What is a characteristic of type II A muscle fibers?

    <p>They are red fast oxidative fibers.</p> Signup and view all the answers

    What effect does hypertonia have on muscle reflexes?

    <p>It enhances reflexes but does not cause spasms.</p> Signup and view all the answers

    What role do satellite cells play in skeletal muscles?

    <p>They aid in muscle repair.</p> Signup and view all the answers

    Which type of muscle contraction involves a change in muscle length while generating force?

    <p>Isotonic contraction</p> Signup and view all the answers

    What is the primary fiber type responsible for endurance activities?

    <p>Type I fibers</p> Signup and view all the answers

    What distinguishes spastic paralysis from flaccid paralysis?

    <p>Spastic paralysis involves increased muscle tone and reflexes.</p> Signup and view all the answers

    In which type of muscle fibers would you find an abundance of mitochondria and rich capillary supply?

    <p>Type I fibers</p> Signup and view all the answers

    Which condition describes an increased muscle tone resulting in stiff and rigid muscle?

    <p>Hypertonia</p> Signup and view all the answers

    Study Notes

    Support and Movement 3: Muscular System

    • Muscle is one of four basic tissue types in the human body
    • Skeletal muscles comprise 40% of male body weight, about 32% of female body weight
    • Muscle tissues perform a variety of functions
    • Skeletal muscles are voluntary, controlled consciously via nervous system
    • Cardiac and smooth muscles are involuntary, controlled by autonomic nervous system

    Outline

    • Skeletal Muscles Structure
    • Mechanisms of Contraction
    • Contractions of Skeletal Muscle
    • Motor Unit
    • Types of skeletal muscle

    Properties of Muscle

    • Contractility: Ability of muscle to shorten with force
    • Excitability: Capacity of muscle to respond to a stimulus
    • Extensibility: Muscle can be stretched to its normal resting length, and beyond, to a limited degree
    • Elasticity: Ability of muscle to recoil to original resting length after stretched

    Classification of Muscle

    • Voluntary (skeletal): actions directed by thoughts via nervous system.
    • Involuntary (cardiac and smooth): actions directed by autonomic nervous system

    Types of Muscle Tissue

    • Skeletal muscle:
      • Attached to bones
      • Multiple, peripheral nuclei
      • Striated, voluntary, and involuntary (reflexes)
    • Smooth muscle:
      • Walls of hollow organs, vessels, glands, skin
      • Single, central nuclei
      • Not striated, involuntary, with gap junctions (visceral smooth)
    • Cardiac muscle:
      • Heart
      • Single, central nuclei
      • Striated, involuntary, with intercalated disks

    Skeletal Muscle Structure

    • Most distinctive feature is striations and multinucleate nature
    • Muscle fibers are muscle cells ensheathed by thin connective tissue (endomysium)
    • The plasma membrane is called sarcolemma
    • Muscle fibers are similar to other cells, but are multinucleate and striated

    Skeletal Muscle Structure (Connective Tissue)

    • Fibrous connective tissue from tendons forms sheaths (epimysium) that extend around and into muscle
    • Inside the muscle, connective tissue divides muscle into columns called fascicles
    • Connective tissue around fascicles is called perimysium

    Skeletal Muscle Structure (Internal)

    • Muscle fibers are muscle cells
    • Ensheathed by thin connective tissue layer called endomysium
    • Plasma membrane is called sarcolemma
    • Muscle fibers are similar to other cells except are multinucleate and striated

    Mechanisms of Contraction

    • The sliding filament theory of muscle contraction describes how thin filaments (actin) slide past thick filaments (myosin), shortening the sarcomere.
    • This process requires energy (ATP)

    Structure of Muscle Fiber

    • Each fiber contains myofibrils
    • Myofibrils contain myofilaments (thick and thin filaments)
    • Thick and thin filaments give rise to striations

    Structure of Myofibril

    • A band- is dark, corresponds to the length of thick filaments.
    • I band- spans the distance between the A bands of successive sarcomeres
    • H zone- light area in the center of A band where actin and myosin don't overlap
    • Z disc- at center of I band where actins attach

    Sarcomeres

    • The contractile units in skeletal muscle.
    • Structural elements are M lines (anchor myosin); titin attaches myosin to Z disc.

    Sliding Filament Theory of Contraction

    • Thin (actin) filaments slide over thick (myosin) filaments, shortening the sarcomere and producing muscle shortening.
    • The lengths of the filaments do not change; the filaments slide past each other.

    Cross-Bridge Cycle

    • A series of steps demonstrating how ATP powers the movement of the myosin head relative to actin.
    • The cycle involves cross-bridge attachment, myosin head pivoting, cross-bridge detachment, and myosin reactivation.

    Control of Contraction

    • Troponin-tropomyosin system controls cross-bridge attachment to actin.
    • In relaxed muscle, tropomyosin blocks binding sites on actin.

    Summary of the sliding filament theory of contraction

    • A myofibril shortens by movement of the insertion toward the origin of the muscle.
    • Sarcomere shortening is achieved by sliding of the myofilaments.
    • Sliding of the filaments occurs via asynchronous myosin cross-bridge power strokes.
    • Length of the filaments remains constant.
    • A bands remain constant in length.

    Excitation-Contraction Coupling (NMJ)

    • Motor neuron ending at sarcolemma where a motor end plate (NMJ) occurs.
    • ACh binds to receptors, triggering an action potential.
    • Action potential propagates down T tubules opening calcium release channels
    • Ca²+ activates the contraction mechanism
    • Relaxation: Ca²+ pumped back into sarcoplasmic reticulum

    Relationship of the Action Potential

    • The action potential triggers an increase in intracellular Ca²+, leading to muscle contraction.

    Muscle Relaxation

    • Action potentials cease.
    • Ca²+-ATPase pumps return Ca²⁺ into the SR.
    • No more Ca²⁺ is available to bind to troponin C.

    Motor Unit

    • A motor neuron and all the muscle fibers it innervates.
    • Number of muscle fibers per motor unit varies with degree of fine control.
    • Contraction strength results from motor unit recruitment.

    Muscle Tone

    • Skeletal muscle exhibits muscle tone (tension) at rest.
    • Involuntary contractions of motor units maintained by neurons in the brain and spinal cord.
    • Important in maintaining posture and support
    • Flaccid condition occurs when motor neurons are damaged or cut, reducing muscle tone

    Muscle Tone Imbalance

    • Hypotonia: decreased or lost muscle tone. Muscles loose, flattened.
    • Hypertonia: increased muscle tone. Tendon reflexes and pathologic reflexes may occur, rigidity.

    Types of Muscle Contractions

    • Reflexive: involuntary
    • Tonic: Maintenance of steady tension (muscle tone).
    • Isometric: Muscle changes tension but not length.
    • Isotonic: Muscle changes length but not tension
      • Concentric: Muscle shortens whilst generating force; muscle length decreases
      • Eccentric: Muscle lengthens whilst generating force; muscle length increases.

    Types of Skeletal Muscle

    • Type I (Slow oxidative):
      • Adapted to contract slowly, without fatigue
      • Utilizes mostly aerobic metabolism
      • High in myoglobin content, rich capillary supply and many mitochondria
      • Gives fibers red color
      • Have small motor neurons
    • Type II (Fast glycolytic):
      • Adapted to contract rapidly; fatigues quickly
      • Utilizes mostly anaerobic metabolism
      • Low in myoglobin content, poor capillary supply and few mitochondria
      • Gives fibers white color
      • Have larger motor units
    • Type IIA (Fast oxidative- glycolytic):
      • Intermediate characteristics between Type I and Type IIX

    Muscle Repair

    • Skeletal muscles have stem cells (satellite cells) located near muscle fibers
    • Satellite cells fuse to damaged muscle cells repair damage or fuse with each other to form new muscle fibers
    • Myostatin inhibits satellite cells

    Muscle Decline With Aging

    • Reduced muscle mass (primarily type II fibers)
    • Reduction in capillary blood supply
    • Fewer satellite cells, increased myostatin production

    Production of Movement by Muscles

    • Muscle attachments include insertion and origin points; belly
    • Biceps brachii is an example: origin, insertion, nerve supply, and actions

    How Skeletal Muscles Produce Movements

    • Lever system and leverage: rigid structures moving around fixed points (fulcrum)
    • Effort causes movement, load opposes movement

    Muscle Shapes

    • Parallel, fusiform, parallel with tendinous bands, convergent, unipennate, bipennate, multipennate, and circular muscles.

    Nomenclature (How muscles are named)

    • Shape, Size, Location, Action, Attachment

    Homeostatic Imbalance Disorders

    • Abnormal contractions
      • Spasm: involuntary contraction of a single muscle → spasms in a group.
      • Cramp: prolonged periods of muscle use, inadequate blood flow → painful
      • Spasmodic twitching
      • Tremor: rhythmic involuntary muscle movements
    • Exercise-induced muscle damage
      • Delayed onset muscle soreness (DOMS), 12-48 hours after exercise, swelling, stiffness, accompanied by soreness, microscopic muscle damage

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    Description

    Test your knowledge on skeletal muscle physiology with this quiz. Questions cover topics like muscle properties, motor units, and muscle control mechanisms. Ideal for students studying human anatomy and physiology.

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