Muscle Anatomy and Physiology Quiz
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Questions and Answers

Which of the following is NOT a key feature of muscle cells?

  • Excitability
  • Contractility
  • Invisibility (correct)
  • Extensibility

Which connective tissue layer directly surrounds a muscle fascicle?

  • Endomysium
  • Perimysium (correct)
  • Epimysium
  • Sarcolemma

What is the smallest contractile element within a muscle unit?

  • Myofibril
  • Sarcomere
  • Myofilament (correct)
  • Muscle Fiber

Which of these is the correct order of muscle structure from smallest to largest?

<p>Myofilament - myofibril - muscle fiber (D)</p> Signup and view all the answers

What is the primary function of tendons in relation to skeletal muscles?

<p>To attach muscles to bones (C)</p> Signup and view all the answers

Which structure is described as the functional unit of a muscle?

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

Which of the following is the layer that insulates individual muscle fibers?

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

Which of the following myofilaments directly binds to myosin?

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

What is the primary role of tropomyosin in muscle contraction?

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

What is the significance of the presence of numerous mitochondria in muscle cells?

<p>To provide the ATP needed for muscle contraction (B)</p> Signup and view all the answers

Which of the following best describes the composition of the A band in a sarcomere?

<p>Both thick and thin filaments (A)</p> Signup and view all the answers

What is the primary function of titin in muscle fibers?

<p>To prevent excessive stretching of the sarcomere (C)</p> Signup and view all the answers

Which protein connects the Z line to the cell membrane?

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

What function do T tubules perform within a muscle fiber?

<p>They transmit the action potential (C)</p> Signup and view all the answers

What is a 'triad' in skeletal muscle composed of?

<p>One T tubule and two terminal cisternae (B)</p> Signup and view all the answers

What is the role of the sarcoplasmic reticulum (SR) in muscle contraction?

<p>To release calcium ions into the sarcoplasm (C)</p> Signup and view all the answers

Which event directly facilitates the exposure of actin's active sites during skeletal muscle contraction?

<p>Calcium ion binding to troponin (A)</p> Signup and view all the answers

What is the primary role of acetylcholinesterase (AChE) in muscle relaxation?

<p>To degrade acetylcholine in the synaptic cleft (B)</p> Signup and view all the answers

According to the sliding filament theory, which event directly causes the power stroke?

<p>Release of ADP and phosphate from the myosin head (A)</p> Signup and view all the answers

What is the function of the SERCA (Sarcoplasmic Reticulum Calcium-ATPase) pump during muscle relaxation?

<p>To actively transport calcium ions into the sarcoplasmic reticulum (B)</p> Signup and view all the answers

Which of the following steps in the muscle contraction cycle requires ATP hydrolysis?

<p>The separation of the myosin head from actin (C)</p> Signup and view all the answers

What is the primary role of creatine phosphate in muscle contraction?

<p>To convert to creatine and provide phosphate, which is then used to replenish ATP. (D)</p> Signup and view all the answers

What is the role of tropomyosin in a resting muscle?

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

Which of the following best defines a motor unit?

<p>A single motor neuron and all the muscle fibers it innervates. (D)</p> Signup and view all the answers

In the sequence of events during muscle contraction, what process immediately follows the formation of acto-myosin cross-bridges?

<p>The release of phosphate, initiating the power stroke (C)</p> Signup and view all the answers

Which of the following describes how ATP is directly used to make muscle cells ready for a new contraction cycle?

<p>ATP is used to reset the sodium-potassium gradient. (D)</p> Signup and view all the answers

If a muscle contraction requires high precision, which type of motor units are likely to be activated?

<p>Small motor units with a few muscle fibers. (D)</p> Signup and view all the answers

What is the term for the progressive decrease in muscle tension despite consistent nervous stimulation?

<p>Muscle fatigue. (C)</p> Signup and view all the answers

What does the term 'recruitment' refer to in the context of muscle contraction?

<p>The activation of additional motor units to increase contraction strength. (B)</p> Signup and view all the answers

Which energy system is used first during a muscle contraction?

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

What is the immediate product of glucose breakdown in the process of anaerobic glycolysis, before entering the Krebs cycle?

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

Which of the following is NOT a determinant of the strength of a muscle contraction?

<p>The amount of oxygen available to the muscle (D)</p> Signup and view all the answers

Flashcards

Muscle Excitability

The ability of muscle cells to respond to stimuli by generating action potentials, similar to a nerve cell reacting to a signal.

Muscle Contractility

The unique characteristic of muscle cells to shorten and thicken, generating force for movement.

Muscle Extensibility

The ability of muscle cells to stretch or lengthen without getting damaged. This is essential for allowing muscles to return to their original state after contraction.

Muscle Elasticity

The ability of muscle cells to return to their original shape after being stretched or contracted. This helps muscles maintain their form and function.

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Endomysium

A single muscle cell (fiber) is surrounded by a thin layer of connective tissue called endomysium. This acts as an insulator, ensuring proper electrical communication between muscle cells.

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Perimysium

A bundle of muscle fibers is wrapped in a sheath of connective tissue called perimysium. This helps organize muscles into functional units.

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Epimysium

The entire skeletal muscle is covered by a thick layer of connective tissue called epimysium. This layer helps hold the muscle together and allows it to transmit force to tendons.

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Sarcomere

The functional unit of a muscle, responsible for contraction. It consists of repeating units of myofilaments (actin and myosin) organized in a specific pattern.

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Actin

A thin filament that binds to myosin, allowing muscle contraction.

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Tropomyosin

A thin filament that covers the active sites on actin, preventing myosin binding.

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Troponin

A thin filament that binds to both actin and tropomyosin, regulating myosin binding.

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Myosin

A thick filament responsible for muscle contraction, composed of two heavy chains and four light chains.

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I band

The region of a sarcomere containing only thin filaments (actin).

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A band

The region of a sarcomere containing both thick and thin filaments.

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Triad

A specialized structure in muscle cells consisting of T tubules and terminal cisternae.

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T tubules

Inward folds of the muscle fiber membrane that transmit action potentials.

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What prevents myosin from binding to actin in the resting state?

In the resting state, actin's active sites are blocked by tropomyosin, preventing myosin from binding.

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How does calcium initiate muscle contraction?

Calcium ions bind to troponin, causing it to change shape and pull tropomyosin away from the active sites on actin.

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What happens when myosin binds to actin?

Myosin heads bind to the active sites on actin, forming cross-bridges. This binding is driven by the hydrolysis of ATP.

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What causes the power stroke during muscle contraction?

The release of phosphate from the myosin head triggers the power stroke. This movement pulls the actin filament towards the center of the sarcomere.

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How is the myosin-actin bond broken to allow for muscle relaxation?

ATP binds to the myosin head, causing it to detach from actin. This allows the cycle to repeat.

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How is the signal to contract terminated?

Acetylcholinesterase breaks down acetylcholine in the synaptic cleft. This stops the nerve signal and prevents further muscle contraction.

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How does calcium concentration decrease in the cytosol?

Calcium ions are actively pumped back into the sarcoplasmic reticulum by SERCA. This reduces calcium concentration in the cytosol.

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What happens to the troponin-tropomyosin complex during muscle relaxation?

The troponin-tropomyosin complex returns to its resting position, blocking the active sites on actin. This prevents further interaction with myosin.

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ATP (Adenosine Triphosphate)

The first energy source used for muscle contraction, lasting 1-2 seconds. It's directly available within the muscle fiber.

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Creatine Phosphate

The second line of energy for muscle contraction, lasting 8-10 seconds. It's a molecule that rapidly transfers a phosphate group to ADP, replenishing ATP.

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Glycolysis

A metabolic pathway where glucose is broken down into pyruvate, producing a small amount of ATP. It's the main energy source for short-term, high-intensity activities.

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Krebs Cycle

A cycle of reactions that occurs in the mitochondria, utilizing pyruvate from glycolysis to produce ATP. This process requires oxygen and is the main energy source for sustained activity.

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Motor Neuron

A single nerve cell that transmits signals from the brain or spinal cord to a muscle, causing it to contract.

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Motor Unit

A group consisting of a single motor neuron and all the muscle fibers it innervates. Each motor unit acts independently.

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Recruitment

The process of activating more motor units to increase the strength of a muscle contraction. This allows for graded muscle control.

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Muscle Fatigue

A decrease in muscle tension that occurs after repeated stimulation, even when the stimulus continues. This is a result of the muscle's inability to sustain high levels of activity.

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Study Notes

Skeletal Muscle Contraction

  • Skeletal muscles are responsible for movement, posture maintenance, heat production, and protecting internal organs.
  • Key features of muscle cells include excitability (responding to stimuli), contractility (shortening and thickening to generate force), extensibility (extending without damage), and elasticity (returning to original shape).

Muscle Types

  • Skeletal muscle: Striated, voluntary, multi-nucleated fibers, usually attached to the skeleton.
  • Smooth muscle: Non-striated, involuntary, spindle-shaped, uninucleated fibers, found in internal organs.
  • Cardiac muscle: Striated, involuntary, branched, uninucleated fibers, found only in the heart.

Skeletal Muscle Structure

  • Organized into:
    • Myofilaments (actin and myosin).
    • Myofibrils.
    • Muscle fibers.
    • Muscle fascicles.
    • Skeletal muscle.
  • Connective tissue layers surround muscle units: Endomysium (surrounds individual muscle fibers). Perimysium (surrounds muscle fascicles). Epimysium (surrounds the entire skeletal muscle).

Sarcomere Structure

  • I band: Thin (actin) filaments.
  • H zone: Only thick (myosin) filaments.
  • A band: Both thick and thin filaments.
  • Z line: Region between two I bands.
  • M line: Middle of the H zone, where myosin filaments connect.

Muscle Proteins

  • Dystrophin, titin, actinin, desmin, nebulin are important intracellular skeletal proteins that maintain sarcomere structure and function.
  • Dystrophin connects actin to the extracellular matrix.
  • Titin stabilizes the sarcomere.

Sarcotubular System

  • T tubules: Inward folds of the muscle fiber membrane, allowing the action potential to travel through the cell.
  • Sarcoplasmic reticulum (SR): Stores Ca²⁺ ions.
  • The triad: A combination of one T-tubule and two terminal cisternae of SR.

Neuromuscular Junction

  • Junction between a motor neuron and a muscle fiber.
  • Acetylcholine (ACh) released from the motor neuron triggers an action potential in the muscle fiber, leading to muscle contraction.

Muscle Fatigue

  • Repeated stimulation of muscle fibers can lead to decreased tension.
  • Characteristics include reduced shortening rate and slower relaxation rate.

Skeletal Muscle Fiber Types

  • Slow-twitch fibers (Type 1): Longer twitch duration, involved in sustained contractions, high endurance, and use oxidative phosphorylation more than glycolysis for ATP production.
  • Fast-twitch fibers (Type 2): Rapid contractions, used for powerful movements, and use glycolysis more than oxidative phosphorylation for ATP production.
  • Fast-oxidative-glycolytic (Type 2A) fibers: Intermediate characteristics between slow and fast-twitch fibers.
  • Fast-glycolytic (Type 2X/2B) fiber: Fastest twitch duration, primarily anaerobic and fastest fatigue.

ATP Energy in Muscle Contraction

  • ATP is essential for several phases of muscle contraction and relaxation.
  • ATP binding to myosin allows the detachment of myosin from actin.
  • ATP hydrolysis powers the power stroke, which brings about shortening of the muscle fiber.
  • The SERCA pump uses ATP to re-establish the appropriate Na-K gradient in the muscle cell.

Skeletal Muscle Metabolism

  • Stored ATP is utilized first for brief contractions.
  • Creatine phosphate stores are used next.
  • Oxidative phosphorylation is the primary long-term energy source.
  • Anaerobic glycolysis is used for brief, powerful contractions or when oxygen availability is low, which can lead to muscle soreness or pain as byproducts are produced.

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Description

Test your knowledge on the structure and function of muscle cells with this comprehensive quiz. It covers key features, connective tissues, contractile elements, and the roles of various proteins in muscle contraction. Perfect for students of anatomy and physiology.

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