The Muscular System Overview
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Questions and Answers

What role does calcium play in muscle relaxation?

  • It replaces structural proteins in muscle tissue.
  • It causes muscle fibers to thicken.
  • It is pumped back into the sarcoplasmic reticulum. (correct)
  • It activates the myosin binding sites on actin.

What happens to skeletal muscle fibers as a result of resistance exercise?

  • The muscle fibers lose their structural proteins.
  • The thickness of the muscle fibers increases. (correct)
  • The fibers become thinner and less dense.
  • The number of fibers increases significantly.

Which of the following is a consequence of muscle atrophy?

  • No changes in the appearance of muscle tissue.
  • Increase in muscle mass due to tissue replacement.
  • Improvement in muscle performance and appearance.
  • Replacement of muscle tissue with connective and adipose tissue. (correct)

What is indicated by the phrase 'use it or lose it' in relation to muscles?

<p>Regular use of muscles prevents atrophy. (A)</p> Signup and view all the answers

What is the typical percentage of skeletal muscle mass loss in humans between the ages of 30 and 50?

<p>10% (B)</p> Signup and view all the answers

What initiates muscle contraction?

<p>Nerve impulse signaling (C)</p> Signup and view all the answers

Which connective tissue layer surrounds an entire skeletal muscle?

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

What is the primary function of muscle tone?

<p>To stabilize body positions (C)</p> Signup and view all the answers

Which of the following statements about muscle properties is correct?

<p>Muscle can contract forcefully when stimulated (C)</p> Signup and view all the answers

How does fascicular arrangement impact a muscle's capabilities?

<p>It influences the muscle's power and range of motion. (B)</p> Signup and view all the answers

What type of muscle fascicle arrangement has fibers arranged parallel to one another?

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

Which type of muscle has fascicles arranged in concentric circles?

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

What role does the perimysium serve in skeletal muscle structure?

<p>It surrounds the bundles of muscle fibers (C)</p> Signup and view all the answers

What is the primary characteristic of pennate muscles?

<p>They have short fascicles relative to muscle length. (A)</p> Signup and view all the answers

Which characteristic is true about fusiform muscles?

<p>They are similar to parallel muscles but have a spindle-shaped belly. (B)</p> Signup and view all the answers

What is a primary function of the muscular system?

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

Which type of connective tissue insulates individual muscle fibers?

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

What do myoblasts fuse to form?

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

What role do satellite cells play in muscle tissue?

<p>They assist in muscle repair during adulthood. (D)</p> Signup and view all the answers

What is the function of the sarcoplasmic reticulum in muscle fibers?

<p>It stores, releases, and retrieves calcium. (C)</p> Signup and view all the answers

Which factor contributes most to muscle power?

<p>The total cross-sectional area of the muscle (A)</p> Signup and view all the answers

What is the primary structural component of thick filaments in a sarcomere?

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

What is a sarcomere primarily recognized as?

<p>The basic functional unit of muscle contraction (D)</p> Signup and view all the answers

Which proteins are found in thin filaments?

<p>Actin, tropomyosin, and troponin (A)</p> Signup and view all the answers

What initiates the muscle contraction process in skeletal muscle fibers?

<p>Release of calcium from the sarcoplasmic reticulum (B)</p> Signup and view all the answers

What is the function of the myosin binding site on actin?

<p>To allow myosin to bind for contraction (D)</p> Signup and view all the answers

Which of the following best describes the sliding filament theory?

<p>Thin filaments slide over thick filaments toward the center of the sarcomere (B)</p> Signup and view all the answers

What is the role of the sarcoplasmic reticulum in muscle contraction?

<p>Releases and stores calcium ions (B)</p> Signup and view all the answers

What are myofilaments primarily composed of?

<p>Protein structures forming muscle fibers (D)</p> Signup and view all the answers

Which type of muscle tissue is characterized by striations?

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

What type of muscle tissue primarily comprises the heart wall?

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

Which statement about smooth muscle is true?

<p>It lines the walls of internal organs. (C)</p> Signup and view all the answers

What is the fundamental contractile unit of a muscle called?

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

How do cardiac muscle cells function during contraction?

<p>They are fused together by cell junctions. (B)</p> Signup and view all the answers

Which of the following best describes the properties of skeletal muscle tissue?

<p>It shows striations and is voluntary. (B)</p> Signup and view all the answers

What happens to skeletal muscle tissue when it is inactive for a prolonged period?

<p>It begins to atrophy. (D)</p> Signup and view all the answers

What is a key characteristic of smooth muscle fibers?

<p>They have no visible striations. (B)</p> Signup and view all the answers

Flashcards

Types of Muscle Tissue

The human body has three types of muscle tissue: skeletal, cardiac, and smooth.

Skeletal Muscle

A type of striated muscle tissue that moves bones of the skeleton.

Cardiac Muscle

Striated muscle tissue found only in the heart.

Smooth Muscle

Non-striated muscle tissue that lines internal organs.

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Myocardium

The contractile tissue of the heart.

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Muscle Contraction

The process by which a muscle shortens to produce movement.

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Sarcomere

The basic functional unit of skeletal muscle.

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Muscle Tissue Properties

Muscles have properties like excitability, contractility, extensibility, and elasticity, enabling movement.

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Muscle Fascicle Arrangement

The way muscle fibers are bundled together, impacting muscle power and range of motion.

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Parallel Muscle

Muscle fibers run parallel to the long axis of the muscle, allowing for greater range of motion.

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Fusiform Muscle

Spindle-shaped muscle with a central belly, providing both power and range of motion.

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Circular Muscle

Muscle fibers arranged in a circle, closing and opening openings.

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Convergent Muscle

Muscle fibers converge from a broad origin to a single tendon.

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Pennate Muscle

Muscle fibers attach at an angle to a tendon, allowing for more force generation but less range of motion.

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Unipennate Muscle

Muscle fibers attach to one side of a tendon, like a feather with a single vane.

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Bipennate Muscle

Muscle fibers attach to both sides of a tendon, like a feather with two vanes.

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Muscle Contraction Mechanism

The process by which muscle fibers shorten, generating force, involving interactions between myosin and actin filaments.

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Muscle Relaxation

The return of muscle fibers to their resting length after contraction, involving the detachment of myosin from actin.

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Muscle Tone

A state of slight, continuous muscle contraction, even when the muscle is not actively moving.

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What is Excitability?

The ability of muscle tissue to respond to a stimulus, such as a nerve impulse, by changing its membrane potential.

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What is Contractility?

The ability of muscle tissue to shorten forcefully when stimulated.

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What is Extensibility?

The ability of muscle tissue to stretch beyond its resting length without being damaged.

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What is Elasticity?

The ability of muscle tissue to return to its original length after being stretched.

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Epimysium Function

A dense connective tissue sheath surrounding the entire muscle, allowing it to contract powerfully while maintaining its structural integrity.

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Muscle Fiber Growth

Resistance exercise increases the formation of myofibrils, making muscle fibers thicker.

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Muscle Atrophy

The loss of muscle mass and structural proteins due to lack of use, leading to decreased performance and appearance.

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Age-Related Muscle Loss

Between ages 30 and 50, humans naturally lose about 10% of skeletal muscle mass.

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What happens during muscle relaxation?

Calcium is pumped back into the sarcoplasmic reticulum, causing tropomyosin to cover the myosin binding sites on actin, relaxing the sarcomere and the muscle.

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How does physical training affect muscles?

Although the number of muscle fibers is genetically determined, physical training can increase muscle size by adding structural proteins, resulting in performance improvements.

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What are myofibrils?

Myofibrils are bundles of myofilaments within a muscle fiber, arranged in repeating units called sarcomeres. They are responsible for muscle contraction.

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What are myofilaments?

Myofilaments are the contractile proteins within myofibrils. They are of two types: thick filaments (myosin) and thin filaments (actin, tropomyosin, and troponin).

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What is a sarcomere?

A sarcomere is the basic functional unit of a muscle fiber, a highly organized arrangement of contractile myofilaments. It's the smallest unit that can contract.

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What is the sliding filament theory?

The sliding filament theory explains muscle contraction. It states that actin filaments slide past myosin filaments, shortening the sarcomere and thus the muscle fiber.

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What is the role of calcium in muscle contraction?

Calcium ions released from the sarcoplasmic reticulum bind to troponin, which then shifts tropomyosin, exposing the myosin-binding sites on actin. This allows myosin to bind to actin and initiate contraction.

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What is the sarcoplasmic reticulum?

The sarcoplasmic reticulum is a specialized type of endoplasmic reticulum in muscle fibers. It stores, releases, and retrieves calcium ions, crucial for muscle contraction.

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What is the sarcolemma?

The sarcolemma is the plasma membrane of a muscle fiber. It acts as a barrier and transmits nerve impulses.

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What is sarcoplasm?

Sarcoplasm is the cytoplasm of a muscle fiber. It contains the organelles and enzymes needed for muscle function.

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Study Notes

The Muscular System

  • The muscular system comprises all muscles in the body.
  • Objectives include discussing muscle tissue types, functions, and properties; describing skeletal muscle structure and function; defining the sarcomere; understanding muscle contraction and relaxation; analyzing the effects of exercise and inactivity on skeletal muscle tissue.

Types of Muscle Tissue

  • Skeletal muscle: Found mostly in the body, moves bones; voluntary control; striated.
  • Cardiac muscle: Forms most of the heart; involuntary control; striated.
  • Smooth muscle: Found in internal organs; involuntary control; non-striated.

Skeletal Muscle Structure

  • Skeletal muscles are anchored to bones via tendons.
  • Striated fibers are packed together in parallel bundles.
  • Connective tissue sheaths surround these bundles.

Smooth Muscle

  • Located in internal organ walls (stomach, intestines, blood vessels).
  • Non-striated and spindle-shaped.
  • Cell junctions hold them together.
  • Involuntary control.

Myocardium

  • A contractile tissue unique to the heart.
  • Cell plasma membranes are fused, functioning as a unit.
  • Stimulation of one cell triggers neighboring cells to contract.

Skeletal Muscle Contraction

  • Voluntary controlled.
  • Rapid contractions and relaxations.
  • Contractile activity relies on neural input.
  • Troponin binds calcium for contraction.
  • Fast-acting, easily fatigues.

Smooth Muscle Contraction

  • Involuntary.
  • Slow or prolonged contractions/relaxations.
  • Response to neural, hormonal, or chemical changes.
  • Calmodulin binds calcium for contraction.
  • Slow-acting, less prone to fatigue.

Muscle Contraction

  • Muscle contraction begins from signals.
  • Tension-producing sites in muscle cells activate for contraction.
  • Myosin and actin filaments work together to create movement.
  • Followed by relaxation, muscle cells return to low tension state

Functions of the Muscular System

  • Produce movement.
  • Stabilize body positions.
  • Store and move substances.
  • Produce heat.

Muscle Tissue Properties

  • Contractility: The ability of muscle to forcefully contract when a nerve impulse occurs.
  • Excitability: The ability of muscle to respond to stimuli, such as nerve impulses, by changing membrane potential.
  • Extensibility: The ability of muscle to stretch within limits without being damaged.
  • Elasticity: The ability of muscle to return to its original length after stretching.

Structure of a Skeletal Muscle

  • Epimysium: A sheath of dense irregular connective tissue that surrounds the entire muscle.
  • Perimysium: A layer of dense irregular connective tissue that surrounds bundles (fascicles).
  • Endomysium: A layer of areolar connective tissue surrounding individual muscle fibers, electrically insulating them.
  • Tendon: Connects muscle to bone; formed from the connective tissue layers extending to the periosteum of a bone.

Muscle Shapes and Fascicle Arrangement

  • Muscle fibers are usually parallel within a fascicle.
  • Fascicle arrangement patterns relate to tendons. Common types are parallel, fusiform, circular, convergent, and pennate.
  • Fiber length correlates to range of motion (longer = greater range).
  • Cross-sectional fiber area influences power. More fibers = greater power.

Muscle Cells (Skeletal Muscle Fibers)

  • Long, cylindrical, multinucleated cells.
  • Myofibrils (arranged as sarcomeres) composed of myofilaments (both thick and thin filaments).
  • Sarcomeres are considered the functional units of muscle fibers; they are highly organized.
  • Sarcolemma: plasma membrane of a muscle fiber.
  • Sarcoplasmic reticulum: specialized smooth endoplasmic reticulum, which stores, releases, and retrieves calcium ions within a muscle fiber.
  • Sarcoplasm: cytoplasm of a muscle fiber.

The Sarcomere

  • The smallest functional unit of striated muscle tissue.
  • Fundamental contractile unit of a muscle fiber.
  • Contains thick filaments (myosin) and thin filaments (actin, tropomyosin, troponin).

The Sliding Filament Theory

  • Skeletal muscle contraction results from the sliding of actin on myosin filaments, shortening the muscle fiber.

Skeletal Muscle Relaxation

  • Calcium is pumped back into the sarcoplasmic reticulum.
  • Tropomyosin covers myosin-binding sites on actin.
  • The sarcomere relaxes, and the muscle relaxes.

Exercise and Skeletal Muscle Tissue

  • Number of skeletal muscle fibers in a muscle is genetically determined, it doesn't change.
  • Mature muscle cells cannot divide; physical training modifies appearance not number.
  • Exercise promotes changes in muscle performance and appearance.

Effect of Resistance Exercise on Skeletal Muscle Tissue

  • Increases myofibril formation, increasing muscle fiber thickness.
  • Enlarges muscles due to structural protein additions.
  • Athletes often take extra protein supplements to add muscle mass.
  • Loss of structural proteins and muscle mass due to inadequate use.
  • Muscle tissue is replaced by connective tissue and fat.
  • Age-related muscle loss occurs, particularly between 30-50 years of age, around 10% loss.
  • This loss can be partially due to lack of physical exercise.

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