Muscular System Quiz
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Questions and Answers

Which type of muscle tissue is primarily under voluntary control?

  • Skeletal muscle tissue (correct)
  • Striated muscle tissue
  • Cardiac muscle tissue
  • Smooth muscle tissue

Which of the following muscles is striated and involuntary?

  • Smooth muscle
  • Both skeletal and smooth muscle
  • Cardiac muscle (correct)
  • Skeletal muscle

What is the primary function of the muscular system in stabilizing body positions?

  • Moving substances within the body
  • Maintaining posture (correct)
  • Guarding body entrances
  • Producing heat

What is the structure of skeletal muscle fibers?

<p>Long and cylindrical with multiple nuclei (C)</p> Signup and view all the answers

Cardiac muscle tissue is characterized by which of the following features?

<p>Striated and contains cardiocytes (B)</p> Signup and view all the answers

What component is NOT part of skeletal muscle tissue?

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

Which type of muscle tissue is found in the walls of internal organs?

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

What characteristic distinguishes smooth muscle tissue?

<p>Non-striated (smooth) appearance (B)</p> Signup and view all the answers

What triggers the muscle action potential in the motor end plate?

<p>Binding of acetylcholine to its receptors (A)</p> Signup and view all the answers

What role does calcium ion (Ca2+) play in muscle contraction?

<p>It binds to troponin, exposing myosin binding sites. (A)</p> Signup and view all the answers

What happens to acetylcholine in the synaptic cleft after triggering a muscle action potential?

<p>It is destroyed by acetylcholinesterase. (D)</p> Signup and view all the answers

What is the consequence of elevated calcium levels in the sarcoplasm?

<p>Power strokes occur as myosin heads bind to actin. (A)</p> Signup and view all the answers

During muscle relaxation, what restores low levels of calcium in the sarcoplasm?

<p>Ca2+ active transport pumps (C)</p> Signup and view all the answers

What initiates the opening of calcium release channels in the sarcoplasmic reticulum?

<p>Muscle action potential traveling along transverse tubule (C)</p> Signup and view all the answers

What primarily happens during the contraction phase of muscle action?

<p>Thin filaments are pulled toward the center of the sarcomere. (C)</p> Signup and view all the answers

Which structure directly releases acetylcholine into the synaptic cleft?

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

What begins the contraction of skeletal muscle?

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

What role does calcium play during muscle contraction?

<p>It binds to troponin to expose actin active sites (A)</p> Signup and view all the answers

Which statement best describes the sliding filament theory?

<p>Thick and thin filaments slide past each other during contraction (C)</p> Signup and view all the answers

What happens during the power stroke phase of muscle contraction?

<p>Myosin cross-bridges bend towards the H zone (B)</p> Signup and view all the answers

What is the result of acetylcholinesterase breaking down ACh?

<p>Limitation of neuromuscular transmission duration (B)</p> Signup and view all the answers

What occurs immediately after the release of calcium from the sarcoplasmic reticulum?

<p>Troponin moves tropomyosin from actin (A)</p> Signup and view all the answers

What is necessary for the continuation of the contraction cycle?

<p>High calcium levels and ATP availability (D)</p> Signup and view all the answers

Which phase represents the detachment of cross-bridges?

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

What triggers the release of acetylcholine at the neuromuscular junction?

<p>Nerve impulse arriving at axon terminal (D)</p> Signup and view all the answers

What is the primary function of myosin heads during muscle contraction?

<p>To hydrolyze ATP and generate force (B)</p> Signup and view all the answers

What primarily influences the amount of tension produced by muscle fibers?

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

What are the three phases of a muscle twitch?

<p>Lag, contraction, relaxation (C)</p> Signup and view all the answers

Which situation describes incomplete tetanus?

<p>Muscle never relaxes completely (D)</p> Signup and view all the answers

How many muscle fibers does a motor neuron typically connect to in a muscle?

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

What is the effect of fatigue on muscle contraction?

<p>Results in weaker contractions (B)</p> Signup and view all the answers

What characterizes isometric contractions?

<p>Tension in the muscle rises while the length remains constant (D)</p> Signup and view all the answers

What type of muscle fiber contracts more quickly but fatigues rapidly?

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

Which type of muscle fiber is characterized by a high concentration of myoglobin?

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

What is the term used for the enlargement of muscle fibers due to training?

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

Which muscles are referred to as white muscles?

<p>Muscles dominated by fast fibers (D)</p> Signup and view all the answers

What is the primary function of pacemaker cells in the heart?

<p>To send electrical signals for heart contraction (C)</p> Signup and view all the answers

What type of muscle tissue is not striated and is found in internal organs?

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

Which characteristic is true for skeletal muscle tissue?

<p>Is attached to bones for movement (A)</p> Signup and view all the answers

What is the role of tropomyosin in muscle contraction?

<p>To cover active sites on actin (A)</p> Signup and view all the answers

Which of the following describes the organization of connective tissues in skeletal muscle?

<p>Epimysium surrounds the entire muscle (A)</p> Signup and view all the answers

What is the starting point for skeletal muscle contraction?

<p>Excitation at the neuromuscular junction (B)</p> Signup and view all the answers

What is released from synaptic vesicles at the neuromuscular junction?

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

Which type of muscle tissue primarily exists in the heart and is involuntary?

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

What is the role of calcium ions in muscle contraction?

<p>They are released and facilitate the interaction between actin and myosin (B)</p> Signup and view all the answers

What function does skeletal muscle NOT typically perform?

<p>Regulate blood flow (B)</p> Signup and view all the answers

What initial process occurs after acetylcholine binds to its receptors at the neuromuscular junction?

<p>Action potential in the sarcolemma is triggered (B)</p> Signup and view all the answers

What is the composition of thick muscle filaments?

<p>Myosin fibers around titan core (C)</p> Signup and view all the answers

Which muscle component helps in transmitting action potentials into the muscle fibers?

<p>T-tubules (D)</p> Signup and view all the answers

Flashcards

Skeletal Muscle

Skeletal muscle is attached to bones, has a striated appearance, and is under voluntary control. It allows for movement and is the most abundant muscle tissue in the body.

Cardiac Muscle

Cardiac muscle is found only in the heart. It is striated like skeletal muscle but unlike skeletal muscle, it is not under voluntary control. Its rhythmic contractions pump blood throughout the body.

Smooth Muscle

Smooth muscle is found in internal organs, such as the digestive system and blood vessels. It is not striated and is involuntary. It helps move substances within the body, like food through the intestines or blood in the arteries.

Action Potential in Muscle Tissue

This process involves changes in the electrical charge across the plasma membrane of a muscle cell. It is how the nervous system signals muscles to contract.

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Neuromuscular Junction

The neuromuscular junction is the specialized area where a motor neuron communicates with a muscle cell. It is essential for muscle contraction to occur.

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Muscle Contraction

Muscle contraction involves the sliding of protein filaments (actin and myosin) within muscle fibers. This shortening of muscle fibers generates force.

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Muscle Relaxation

Muscle relaxation occurs when the signal to contract stops, and calcium ions are removed from the muscle fibers. This allows the muscle to return to its resting state.

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Muscle Bundles

These are bundles of muscle fibers that are held together by connective tissue. They allow for more efficient contraction and movement.

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Pacemaker cells

Specialized muscle cells in the heart responsible for sending electrical signals that cause rhythmic contractions and pump blood.

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Smooth muscle tissue

A type of muscle tissue found in internal organs like the abdomen and intestines, blood vessel walls, and the iris of the eye.

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Cardiac muscle tissue

Muscle tissue found in the heart walls, responsible for its rhythmic contractions and blood pumping.

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Skeletal muscle tissue

Type of muscle tissue attached to bones, responsible for voluntary movement, posture, and other functions.

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Epimysium

The outer layer of connective tissue that surrounds an entire muscle.

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Perimysium

A connective tissue sheath that surrounds bundles of muscle fibers within a muscle.

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Endomysium

A thin layer of connective tissue that surrounds individual muscle fibers.

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Sarcolemma

The cell membrane of a muscle fiber.

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Sarcoplasm

The cytoplasm of a muscle fiber.

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Sarcoplasmic reticulum

A specialized type of endoplasmic reticulum in muscle fibers that stores calcium ions and releases them during muscle contraction.

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T-Tubules

Transverse tubules, extensions of the sarcolemma that penetrate into the muscle fiber, helping to transmit the action potential into the cell.

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Myofibrils

Long, cylindrical structures within muscle fibers that contain the contractile proteins actin and myosin, responsible for muscle contraction.

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Sarcomere

The basic functional unit of a myofibril, responsible for muscle contraction.

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Actin

A protein found in thin filaments of muscle fibers, responsible for muscle contraction by interacting with myosin.

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Myosin

A protein found in thick filaments of muscle fibers, responsible for muscle contraction. It interacts with actin to slide filaments past each other.

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Sliding Filament Theory

The process where thick and thin filaments slide past each other within the muscle fiber, resulting in the shortening of the sarcomere and muscle contraction.

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Troponin

A protein complex that binds calcium ions and initiates the muscle contraction process.

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Tropomyosin

A protein that covers the active sites on actin filaments, preventing myosin from binding in a relaxed muscle.

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Active site

The binding site on actin where myosin heads attach during muscle contraction.

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ATP in muscle contraction

The energy molecule that powers muscle contraction by detaching myosin heads from actin, allowing for repeated muscle contraction cycles.

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Acetylcholine (ACh)

A chemical messenger released by a motor neuron at the neuromuscular junction, triggering muscle contraction.

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Muscle action potential

A rapid change in electrical potential across the muscle cell membrane, triggered by acetylcholine.

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Sarcoplasmic reticulum (SR)

A network of internal membranes within a muscle fiber that stores and releases calcium ions.

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Troponin-tropomyosin complex

A protein complex that binds to calcium ions, triggering the exposure of myosin binding sites on actin.

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Tension Production in Muscle Fibers

The amount of tension a muscle fiber generates depends on the number of cross-bridges formed between actin and myosin filaments.

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Twitch

A single contraction and relaxation cycle of a muscle fiber in response to a stimulus. It has three phases: lag, contraction, and relaxation.

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Summation

When muscle fibers are stimulated repeatedly before they fully relax, the contractions become stronger. This can lead to incomplete tetanus (partial relaxation) or complete tetanus (no relaxation).

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Motor Unit

A motor neuron and all the muscle fibers it innervates. The number of muscle fibers per motor unit varies depending on the precision of movement required.

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Motor Unit Recruitment

The process of increasing the number of motor units activated to generate more force. It allows for fine control of movement strength.

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Muscle Fatigue

Muscle fatigue occurs when a muscle can no longer contract due to a depletion of ATP. This leads to a decrease in contraction strength and eventually failure.

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Isometric Contraction

A contraction where muscle tension increases but the muscle length remains constant. For example, holding a heavy object.

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Isotonic Contraction

A contraction where muscle tension remains constant, but the muscle length changes, allowing for movement. This can be either concentric (muscle shortens) or eccentric (muscle lengthens).

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Fast Muscle Fibers (Type II)

These muscle fibers have a large diameter, abundant glycogen, and fewer mitochondria. They contract quickly but fatigue rapidly.

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Slow Muscle Fibers (Type I)

These muscle fibers are smaller, have more mitochondria, and are rich in myoglobin. They contract slowly but can sustain contractions for longer periods.

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Study Notes

Musculoskeletal System (Part 2)

  • Learning Outcomes: Students will be able to list muscle types and their characteristics, understand action potentials and neuromuscular junctions, and describe muscle contraction and relaxation.
  • Functions of Muscular System: Muscles produce movement, stabilize body positions, move substances within the body, produce heat, support soft tissues, guard entrances/exits of the body, and provide nutrient reserves.
  • Types of Muscle Tissues: Skeletal, cardiac, and smooth muscles.
  • Skeletal Muscle Tissue: Primarily attached to bones, it is striated and voluntary.
  • Cardiac Muscle Tissue: Forms the heart wall; striated and involuntary.
  • Smooth Muscle Tissue: Located mainly in internal organs; non-striated and involuntary.
  • Skeletal Muscle Tissue Details: The most abundant tissue in the human body, under voluntary control. Skeletal muscle tissue contains skeletal muscle cells, connective tissue, blood vessels, and nerves. Each cell is called a skeletal muscle fiber, which is a long, cylindrical cell containing multiple nuclei and striations (alternating light and dark bands). Muscle fibers bind together and with connective tissue, nerves, and blood vessels to form bundles, which further combine to form muscles.
  • Cardiac Muscle Tissue Details: Found only in the heart, composed of cardiac muscle cells (cardiocytes), striated, and usually contain a centrally located single nucleus. Not under voluntary control; a bundle of specialized muscle cells (pacemaker cells) in the upper part of the heart sends electrical signals through cardiac tissue, causing the heart to contract and pump blood.
  • Smooth Muscle Tissue Details: Found in internal organs and blood vessel walls, spindle-shaped, contains a single nucleus, non-striated, and involuntary. The contractions in smooth muscles move food through the digestive tract, control blood flow, and adjust pupil size.
  • Anatomy of Skeletal Muscle: The organization of connective tissues: Epimysium surrounds muscle; perimysium sheathes bundles of muscle fibers; perimysium and epimysium contain blood vessels and nerves; endomysium covers individual muscle fibers; tendons connect muscle to bone or another muscle.

Skeletal Muscle Fiber Structures

  • Sarcolemma (cell membrane)
  • Sarcoplasm (muscle cell cytoplasm)
  • Sarcoplasmic Reticulum (modified ER) with high Ca2+ concentration
  • T-tubules and myofibrils aid in contraction
  • Sarcomeres - regular arrangement of myofibrils

Muscle Fiber Components

  • Thin Filaments: Actin, tropomyosin (covers actin's active sites), and troponin (holds tropomyosin in place and binding site for Ca2+).
  • Thick Filaments: Myosin fibers (with tail and globular heads) that form cross-bridges during contraction. Interactions between actin and myosin are prevented by tropomyosin in a resting state.

Muscle Fiber Contraction

  • Triggered by nerve impulses at the neuromuscular junction.
  • Action potential travels along the sarcolemma, to the T-tubules, triggering the release of calcium ions from the sarcoplasmic reticulum.
  • Calcium binds to troponin, causing tropomyosin to shift, exposing actin binding sites.
  • Myosin heads attach to actin and contract (power stroke).
  • ATP binding to myosin heads allows cross-bridges to detach.

Sliding Filament Theory

  • Thick and thin filaments slide past each other during contraction.
  • Cyclical process beginning with calcium release from the sarcoplasmic reticulum.
  • Calcium binds to troponin, shifting tropomyosin.
  • Myosin heads form cross bridges and pull actin filaments closer.
  • ATP allows the release of cross bridges.

Muscle Contraction & Relaxation

  • Action potential along T-tubules triggers calcium release from sarcoplasmic reticulum cisternae. Attachment sites are exposed and cross-bridge formation occurs.
  • ATP binds myosin head causing cross-bridge release and recovery stroke.
  • Acetylcholinesterase breaks down acetylcholine, limiting the duration of contraction, facilitating relaxation.

Tension Production by Muscle Fibers

  • Tension depends on the number of cross-bridges formed.
  • Skeletal muscle contracts most effectively over a narrow range of resting lengths.
  • "Twitch" is a single contraction-relaxation cycle in response to a stimulus (lag, contraction, and relaxation phases) - repeated stimulation leading to summation.

Summation

  • Repeated stimulation before relaxation leads to wave summation (a second twitch added to the first).
  • Incomplete tetanus (muscle never fully relaxes).
  • Complete tetanus (relaxation phase eliminated).

Motor Units and Recruitment

  • Motor units are composed of a motor neuron and the muscle fibers it stimulates.
  • A motor neuron typically contacts about 150 muscle fibers.
  • Precision of movement depends on the number of small motor units involved. Strength of contraction relies on the size of motor units activated. Muscles controlling fine movements have fewer fibers per unit (e.g., eyes); those controlling large movements have more.

Muscle Fatigue

  • Muscle fibers use ATP faster than they can produce it, leading to weaker contractions.
  • New ATP binding is vital for breaking down cross-bridges.
  • Examples: Muscle cramps, rigor mortis (stiffness after death).

Types of Muscle Contractions

  • Isometric: Tension increases but the muscle length remains constant.
  • Isotonic: Tension increases, and the muscle length changes. Resistance and speed of contraction are inversely related.

Muscle Performance

  • Fast fibers (type II myosin): Large diameter, densely packed myofibrils, large glycogen reserves, relatively few mitochondria, rapid contractions, fatigue quickly (white muscle).
  • Slow fibers (type I myosin): Half the diameter of fast fibers, take longer to contract, abundant mitochondria, extensive capillaries, high myoglobin concentrations, long-duration contractions, greater resistance to fatigue (red muscle).

Muscle Performance & Fiber Distribution

  • Pale muscle (dominated by fast fibers) = white muscle. Dark muscle (dominated by slow fibers and myoglobin) = red muscle.

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Musculoskeletal System Part 2 PDF

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Test your knowledge on the muscular system with this quiz. Explore topics such as muscle tissue types, functionality, and structural characteristics. Challenge yourself with questions on voluntary and involuntary muscles, as well as their locations in the body.

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