Muscle Tissue Quiz for Biology Class 11
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Questions and Answers

Which type of muscle tissue is categorized as involuntary?

  • Smooth muscle
  • Skeletal muscle
  • Both B and C (correct)
  • Cardiac muscle

What is the ability of muscle to respond to stimuli called?

  • Extensibility
  • Excitability (correct)
  • Contractility
  • Elasticity

Which connective tissue sheath directly surrounds individual muscle fibers?

  • Epimysium
  • Perimysium
  • Fascia
  • Endomysium (correct)

Which of the following is NOT a function of muscles?

<p>Produce exchange of gases (C)</p> Signup and view all the answers

What role do nerves play in skeletal muscle function?

<p>They control activity of muscle fibers. (A)</p> Signup and view all the answers

Which characteristic of muscle refers to its ability to return to its resting length after being stretched?

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

Which of the following muscle types is under conscious control?

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

What is the dense irregular connective tissue that surrounds an entire skeletal muscle called?

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

What primarily affects the force of muscle contractions?

<p>The number of cross bridges attached (B)</p> Signup and view all the answers

Which factor does NOT influence force of muscle contraction?

<p>Type of exercise performed (A)</p> Signup and view all the answers

Which statement regarding muscle fiber recruitment is true?

<p>It involves activating more motor units. (D)</p> Signup and view all the answers

How does the relative size of muscle fibers affect muscle contraction?

<p>Bulkier muscles can develop more tension. (C)</p> Signup and view all the answers

At what degree of muscle stretch do sarcomeres generate maximum force?

<p>Between 80% and 120% of resting length (D)</p> Signup and view all the answers

Which factor does NOT influence the speed of muscle contraction?

<p>Hydration levels in the muscle (D)</p> Signup and view all the answers

What role does the frequency of stimulation play in muscle contraction?

<p>Higher frequencies increase the contraction force. (D)</p> Signup and view all the answers

What happens when a sarcomere is stretched beyond 120% of its resting length?

<p>Force of contraction decreases. (C)</p> Signup and view all the answers

What is the primary attachment point of a muscle that is less movable?

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

What type of attachment is considered the most common for muscles?

<p>Indirect attachment (B)</p> Signup and view all the answers

Which structural feature of skeletal muscle accounts for approximately 80% of the muscle cell volume?

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

What is the smallest contractile unit of a skeletal muscle fiber?

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

What feature is characteristic of the A band in myofibrils?

<p>Dark region (D)</p> Signup and view all the answers

Which of the following is NOT a component of the myofilament structure within a sarcomere?

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

What provides the resistance against abrasion from rough bony projections in muscles?

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

What structure serves as the muscle fiber plasma membrane?

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

What initiates the process of cross bridge formation in muscle contraction?

<p>Attachment of the myosin head to actin (C)</p> Signup and view all the answers

What distinguishes smooth muscle from skeletal muscle regarding connective tissue?

<p>Smooth muscle contains only endomysium. (A)</p> Signup and view all the answers

During the working stroke of the cross bridge cycle, what movement occurs?

<p>Myosin head pivots and pulls the thin filament toward the M line (B)</p> Signup and view all the answers

In smooth muscle, how is calcium primarily sourced for contraction?

<p>From extracellular sources predominately. (A)</p> Signup and view all the answers

What causes the detachment of the myosin head from the actin filament?

<p>Attachment of ATP to the myosin head (C)</p> Signup and view all the answers

What is the arrangement of thick and thin filaments in smooth muscle?

<p>They have a diagonal arrangement. (D)</p> Signup and view all the answers

What role does Ca2+ play in muscle contraction?

<p>Ca2+ binds to troponin, exposing myosin-binding sites on actin (C)</p> Signup and view all the answers

What is the role of calmodulin in smooth muscle?

<p>It binds to calcium to regulate contraction. (A)</p> Signup and view all the answers

What is the primary mechanism for the cessation of contraction in muscle fibers?

<p>Pumping of Ca2+ back into the sarcoplasmic reticulum (D)</p> Signup and view all the answers

Which statement accurately describes the electrical connections between smooth muscle fibers?

<p>Smooth muscle fibers are connected via gap junctions. (D)</p> Signup and view all the answers

Which of the following correctly describes the cocking of the myosin head?

<p>It results from the hydrolysis of ATP, positioning myosin in a high-energy state (A)</p> Signup and view all the answers

What must occur before cross bridge cycling begins?

<p>Release of ACh at the neuromuscular junction (D)</p> Signup and view all the answers

Why does smooth muscle have a greater power despite having fewer thick filaments?

<p>Thick filaments have myosin heads along their entire length. (C)</p> Signup and view all the answers

What defines the bulging appearance of smooth muscle during contraction?

<p>The location of dense bodies. (B)</p> Signup and view all the answers

What is the sequence of events at the neuromuscular junction that leads to muscle contraction?

<p>Action potential, ACh release, Ca2+ influx, myosin binding (B)</p> Signup and view all the answers

Which feature is absent in smooth muscle that is typically found in skeletal muscle?

<p>Striations and sarcomeres. (D)</p> Signup and view all the answers

What is the role of calmodulin in smooth muscle contraction?

<p>It binds to calcium and activates myosin kinase. (C)</p> Signup and view all the answers

How does smooth muscle contraction differ from skeletal muscle contraction?

<p>Smooth muscle contraction is triggered by increased intracellular calcium levels. (B)</p> Signup and view all the answers

Which statement is true about the mechanism of relaxation in smooth muscle?

<p>Dephosphorylation of myosin allows relaxation. (B)</p> Signup and view all the answers

What characterizes unitary smooth muscle?

<p>It contains many gap junctions facilitating synchronous contraction. (D)</p> Signup and view all the answers

What is a key function of the stress-relaxation response in smooth muscle?

<p>It allows temporary storage of contents in organs. (A)</p> Signup and view all the answers

Which component is primarily responsible for initiating contraction in smooth muscle?

<p>Calcium ions from extracellular space. (D)</p> Signup and view all the answers

What distinguishes multiunit smooth muscle from unitary smooth muscle?

<p>Independent contraction of muscle fibers. (C)</p> Signup and view all the answers

What mechanism stops contraction in smooth muscle?

<p>Calcium detachment from calmodulin. (A)</p> Signup and view all the answers

What role does ATP play during smooth muscle contraction?

<p>It energizes the sliding process of actin and myosin. (C)</p> Signup and view all the answers

How do neural stimuli affect smooth muscle contraction?

<p>They can modify the rate and intensity of contraction. (C)</p> Signup and view all the answers

Flashcards

Muscle Types

Skeletal (voluntary), cardiac (involuntary), and smooth (involuntary) muscles.

Muscle Characteristics

Excitability (responsiveness), contractility, extensibility, and elasticity.

Muscle Functions

Produce movement, maintain posture, stabilize joints, and generate heat.

Skeletal Muscle Anatomy

Skeletal muscle is made up of muscle fibers, nerves, blood vessels, and connective tissues.

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Nerve and Blood Supply (Skeletal Muscle)

Nerves, arteries, and veins supply each muscle to enable control and deliver the nutrients and oxygen required for contraction.

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Connective Tissue Sheaths (Skeletal Muscle)

Epimysium (outer), perimysium (around fascicles), and endomysium (around fibers) layers that surround and support muscle fibers.

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Muscle Fiber

Individual muscle cell that make up skeletal muscles

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Voluntary Muscle

Muscle that can be consciously controlled.

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Muscle Attachment

Muscles attach to bones at two points: insertion (movable bone) and origin (immovable or less movable bone).

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Direct Attachment

The epimysium (outer layer of muscle) is directly fused to the periosteum (bone lining) or perichondrium (cartilage lining).

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Indirect Attachment

Connective tissue from the muscle (tendons or aponeuroses) extends beyond the muscle, attaching to the bone.

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Skeletal Muscle Fiber

Long, cylindrical cells with multiple nuclei; the basic functional units of skeletal muscle.

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Sarcomere

The smallest contractile unit of a muscle fiber. It is the area between two Z-discs.

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Myofibril

Long, rod-like structures inside muscle fibers that contain repeating units of sarcomeres.

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Actin Myofilaments

Thin filaments in a sarcomere, responsible for muscle contraction by interacting with myosin.

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Myosin Myofilaments

Thick filaments in a sarcomere that provides the binding sites for actin during muscle contraction.

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Actin Composition

Thin filaments composed primarily of actin, a protein, arranged in a helical structure, and involved in muscle contraction.

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Troponin's Role

Troponin, a protein complex, binds calcium (Ca2+), initiating a shape change that moves tropomyosin, exposing myosin-binding sites on actin during muscle contraction.

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Tropomyosin's Action

A protein that blocks myosin-binding sites on actin, preventing muscle contraction until calcium interacts with troponin.

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Cross-Bridge Formation

High-energy myosin head attaches to an exposed actin binding site, forming a cross-bridge.

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Power Stroke

Myosin head pivots and pulls the actin filament towards the center of the sarcomere, causing muscle shortening.

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Cross-Bridge Detachment

ATP binds to the myosin head, causing the detachment of the myosin head from the actin.

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Myosin Head Re-Cocking

Energy from ATP hydrolysis "cocks" the myosin head into its high-energy state, preparing it for the next cross-bridge cycle.

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Calcium Role in Contraction

Calcium is crucial for muscle contraction. It's released to expose the myosin-binding sites on actin.

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Muscle Contraction Force Factors

Forcefulness of muscle contraction is impacted by the number of cross-bridges connecting the muscle fibers, impacted by four key factors; number of activated muscle fibers, fiber size, stimulation frequency, and muscle stretch.

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Muscle Fiber Recruitment

Increasing the number of motor units activated to generate a stronger contraction.

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Muscle Fiber Size

Larger muscle fibers generate more tension and force.

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Stimulation Frequency

Faster stimulation frequency leads to a stronger muscle contraction.

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Muscle Stretch and Contraction

Muscle contraction force is greatest when sarcomeres are at an optimal length—not too stretched or too contracted.

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ATP-Generating Pathway

The metabolic process in working muscles to produce ATP required for contraction.

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Muscle Weakness Metabolic Cause

Metabolic byproducts, like lactic acid, potentially result in muscle fatigue and weakness.

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Velocity and Duration of Muscle Contraction

Muscle contraction speed and duration are affected by muscle fiber type, load, and recruitment.

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Smooth Muscle Structure

Smooth muscle lacks connective tissue sheaths (only endomysium), has varicosities instead of neuromuscular junctions (diffuse junctions), and is innervated by the autonomic nervous system.

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Smooth Muscle SR & T-tubules

Smooth muscle has a less developed sarcoplasmic reticulum (SR) and no T-tubules, relying on extracellular Ca2+ for most contraction.

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Smooth Muscle Intercellular Connections

Smooth muscle cells are electrically connected via gap junctions, allowing action potentials to spread rapidly between cells, unlike skeletal muscle.

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Smooth Muscle Filaments

Smooth muscle contains overlapping thick and thin filaments, but thick filaments are fewer and have myosin heads along their entire length.

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Smooth Muscle Contraction Mechanism

Smooth muscle lacks troponin, but contains tropomyosin and calmodulin, which interacts with Ca2+ for contraction. Filaments are arranged diagonally to produce a corkscrew-like contraction.

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Dense Bodies in Smooth Muscle

Smooth muscle features dense bodies, analogous to Z-discs in skeletal muscle, which anchor filaments and cause bulges in the sarcolemma during contraction.

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Smooth vs Skeletal Muscle Power

Although smooth muscle has a lower ratio of thick to thin filaments (1:13) than skeletal muscle (1:2), myosin heads along the entire length of thick filaments in smooth muscle enable it to generate as much power as skeletal muscle.

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Smooth Muscle Calcium Influx

Smooth muscle sarcolemma contains specialized infoldings with calcium channels that allow extracellular calcium to enter and initiate contraction. The influx of Calcium is necessary for contraction which is initiated within the cell itself, as well as extracellularly.

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Smooth Muscle Contraction Trigger

Increased intracellular calcium (Ca2+) levels are the key factor initiating contraction in smooth muscle.

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Smooth Muscle Calcium Source

Smooth muscle primarily obtains Ca2+ from the extracellular space, unlike skeletal muscle, where the sarcoplasmic reticulum is the major source.

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Smooth Muscle Calcium Binding

The calcium (Ca2+) in smooth muscle binds to calmodulin, not troponin like in skeletal muscle.

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Smooth Muscle Myosin Activation

Activated calmodulin activates myosin light chain kinase (MLCK), which then phosphorylates myosin heads, enabling cross-bridge formation with actin.

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Smooth Muscle Relaxation Steps

Relaxation requires detaching Ca2+ from calmodulin, actively transporting Ca2+ into the SR (sarcoplasmic reticulum) and extracellular space, and dephosphorylation of myosin, leading to inactivation.

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Stress-Relaxation Response

Smooth muscles briefly respond to stretch, then adapt to the new length, allowing organs like the stomach and bladder to temporarily store contents.

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Unitary smooth muscle

Visceral smooth muscle found in hollow organs except the heart; cells are electrically coupled and synchronized; exhibits slow, synchronized contractions.

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Multiunit smooth muscle

Located in the lungs (airways), large arteries, skin (hair follicles), and eyes (iris); fibers are independent and controlled by nervous stimuli, resembling skeletal muscle in some ways.

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Sliding Filament Mechanism Smooth Muscle

Smooth muscle contraction, like skeletal muscles, relies on the sliding filament mechanism, where actin and myosin filaments interact to shorten the muscle.

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Smooth Muscle Functional Differences

Smooth muscle contraction differs from skeletal muscle's in the source and interaction of calcium with binding proteins, as well as the activation process for myosin heads.

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Study Notes

Muscle Tissue Overview

  • Muscle tissue is responsible for movement, posture maintenance, and heat production.
  • Three types of muscle tissue exist: skeletal, cardiac, and smooth.

Types of Muscle Tissue

  • Skeletal muscle: Voluntary muscle attached to bones, responsible for locomotion and manipulation.
    • Cells (fibers) are long, cylindrical, multinucleated, and striated.
    • Controlled consciously.
  • Cardiac muscle: Involuntary muscle found only in the heart.
    • Cells are branching, uni- or binucleate, and striated.
    • Controlled involuntarily.
  • Smooth muscle: Involuntary muscle found in the walls of hollow organs (except the heart).
    • Cells are spindle-shaped, uninucleate, and non-striated.
    • Controlled involuntarily

Muscle Characteristics

  • Excitability (responsiveness): Ability to receive and respond to stimuli.
  • Contractility: Ability to shorten forcibly when adequately stimulated.
  • Extensibility: Ability to be stretched.
  • Elasticity: Ability to recoil and resume resting length after stretching.

Skeletal Muscle Anatomy

  • Nerve and blood supply: Skeletal muscle requires substantial oxygen and nutrients, and waste removal during contraction. Nerves control each fiber separately, enabling precise control.
  • Connective tissue sheaths: Sheaths of connective tissue (epimysium, perimysium, and endomysium) surround and support individual muscle fibers and groups of fibers (fascicles).
    • Epimysium: Dense irregular connective tissue surrounding the entire muscle.
    • Perimysium: Fibrous connective tissue surrounding fascicles (bundles of muscle fibers).
    • Endomysium: Fine areolar connective tissue wrapping each muscle fiber.
  • Attachments: Muscles attach to bones in at least two points:
    • Origin: Attachment to the less movable bone.
    • Insertion: Attachment to the movable bone. -Direct (fleshy): Epimysium fused to periosteum. -Indirect: Connective tissue wrappings extend beyond the muscle as a tendon or aponeurosis.

Skeletal Muscle Microscopic Anatomy

  • Sarcolemma: Muscle fiber's plasma membrane.
  • Sarcoplasm: Muscle fiber's cytoplasm, containing glycogen for energy storage and myoglobin for oxygen storage.
  • Myofibrils: Densely packed, rod-like elements that run the length of the muscle fiber.
  • Sarcomeres: Smallest contractile unit of a muscle fiber, organized as repeating sections along myofibrils.
  • Myofilaments: Actin (thin) and myosin (thick) filaments within sarcomeres, responsible for the sliding filament mechanism of contraction.
    • Actin filaments: Composed of actin, troponin, and tropomyosin.
    • Myosin filaments: Composed of the myosin protein with heads that bind to actin.
  • Sarcoplasmic reticulum (SR): Smooth endoplasmic reticulum surrounding myofibrils, storing and releasing calcium ions (Ca2+).
  • T tubules: Infoldings of the sarcolemma, extending deep into the muscle fiber to conduct electrical impulses to the SR.

Excitation-Contraction Coupling

  • Sequence of events linking electrical stimulation to muscle contraction.
  • Action potentials travel along the sarcolemma and down the T tubules to stimulate Ca2+ release from the SR.
  • Ca2+ binding to troponin exposes myosin-binding sites on actin, leading to cross-bridge formation.

Sliding Filament Model of Muscle Contraction

  • Overlapping actin and myosin filaments slide past each other during contraction.
  • Actin filaments move towards the center of the sarcomere (M line).
  • Z discs move closer together, causing sarcomere shortening.

Cross-Bridge Cycling

  • Cycle of events during muscle contraction.
  1. Cross-bridge formation: Myosin head binds to actin.
  2. Power stroke: Myosin head pivots, pulling actin.
  3. Cross-bridge detachment: ATP binds to myosin, causing detachment from actin.
  4. Myosin reactivation: ATP hydrolysis "recocks" myosin head.

ATP Usage in Muscle Contraction

  • ATP required for cross-bridge cycling, Ca2+ pump, and other cellular activities.
  • ATP is regenerated quickly through three mechanisms:
    • Creatine phosphate (CP) phosphorylation: Provides rapid ATP regeneration.
    • Anaerobic pathway (glycolysis): Generates ATP without oxygen but produces lactic acid.
    • Aerobic respiration: Provides most ATP during prolonged activity but requires oxygen.

Muscle Fatigue

  • Physiologic inability to contract despite continued stimulation.
  • Causes include: ionic imbalances, insufficient ATP, decreased glycogen, increased inorganic phosphate, and magnesium.

EPOC (Excess Postexercise Oxygen Consumption)

  • Extra oxygen needed to replenish ATP and CP, convert lactic acid, and resynthesis glycogen.

Types of Contractions

  • Isotonic contractions: Muscle changes length and moves a load.
    • Concentric: Muscle shortens and does work (e.g., lifting a weight).
    • Eccentric: Muscle lengthens while maintaining tension (e.g., lowering a weight).
  • Isometric contractions: Muscle develops tension but does not change length (e.g., pushing against a wall).

Other Important Factors

  • Motor units: A motor neuron and all the muscle fibers it innervates.
  • Muscle twitch: Simplest contraction resulting from a muscle fiber's response to a single action potential.
  • Graded muscle responses: Variations in the degree of muscle contraction, including temporal (wave) summation and recruitment, crucial for controlling skeletal movement.
  • Muscle fiber types: Skeletal muscle fibers are categorized by their speed of contraction (slow or fast) and primary metabolic pathways (oxidative or glycolytic); different types are specialized for different functions.
  • Smooth muscle: Differs from skeletal muscle in structure (e.g., no striations, less developed SR), mechanism of contraction (e.g., Ca2+ binding to calmodulin rather than troponin), and functional characteristics (e.g. stress-relaxation response).

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