Muscle Tissue Overview

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Questions and Answers

During muscle contraction, what is the functional unit where this process occurs?

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

What distinguishes skeletal muscle from smooth and cardiac muscle?

  • Skeletal muscle cells are joined by intercalated discs.
  • Skeletal muscle contains a single, centrally located nucleus.
  • Skeletal muscle fibers are multinucleated. (correct)
  • Skeletal muscle is under involuntary control.

What is the role of satellite cells in muscle tissue?

  • To regulate the calcium concentration within the sarcoplasm
  • To transmit action potentials throughout the muscle fiber
  • To repair and regenerate damaged muscle fibers (correct)
  • To provide structural support to the extracellular matrix

How do myoblasts contribute to skeletal muscle fiber formation?

<p>They fuse together to form multinucleated muscle fibers. (B)</p> Signup and view all the answers

What structural component is primarily found within the I-band of a sarcomere?

<p>Actin filaments only (C)</p> Signup and view all the answers

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

<p>Storing and releasing calcium ions (D)</p> Signup and view all the answers

What connective tissue layer directly surrounds individual muscle fibers?

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

What event marks the initiation of skeletal muscle contraction?

<p>The release of calcium ions from the sarcoplasmic reticulum (C)</p> Signup and view all the answers

What is the role of T-tubules in muscle contraction?

<p>To transmit action potentials from the sarcolemma into the muscle fiber (A)</p> Signup and view all the answers

What is the functional significance of the arrangement of actin and myosin filaments within the sarcomere?

<p>It enables the sliding filament mechanism of muscle contraction. (C)</p> Signup and view all the answers

Flashcards

Muscle Tissue

One type of tissue specialized for contraction and movement.

Epimysium

Dense connective tissue surrounding the entire muscle.

Perimysium

Bundles of muscle fibers (fascicles); allows nerves and blood vessels to reach fibers.

Endomysium

Basal lamina of loose connective tissue surrounding individual muscle fibers.

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Sarcoplasm

Muscle cell organelles; cytoplasm.

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Sarcolemma

Plasma membrane of a muscle cell.

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Sarcoplasmic Reticulum

Muscle (smooth) endoplasmic reticulum.

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Myofibrils

Contractile threads within muscle fibers.

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Sarcomere

Functional unit of muscle contraction

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I-Band

Contains only thin filaments (actin, tropomyosin, troponin).

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Study Notes

  • Muscle tissue is specialized for contraction/movement

Types of Muscles

  • Skeletal muscle
  • Cardiac muscle
  • Smooth muscle

Muscle Cell Organelles

  • Cytoplasm is also known as sarcoplasm
  • Plasma membrane also known as sarcolemma (plasmalemma)
  • Smooth endoplasmic reticulum also known as sarcoplasmic reticulum
  • Mitochondrion are called sarcosome

Skeletal, Cardiac, and Smooth Muscle Characteristics

  • Cell shape for skeletal muscle is long elongated, cardiac muscle arranged in irregular parallel, and smooth muscle is cylindrical
  • Nucleus for skeletal is multinucleated and peripheral; cardiac is mononuclear; and smooth muscle has only one nucleus
  • Striations are present/due to sarcomere in skeletal muscle; cardiac muscle has present due to binding to troponin; smooth muscle is absent

Contraction

  • Skeletal muscle is voluntary and controlled via somatic nervous system and innervation
  • Requires Ca+ to initiate contraction
  • Muscle contains motor neuron

Skeletal Muscle Details

  • Skeletal muscle fibers/cells/myocytes are formed by the fusion of multiple myoblasts.
  • A single muscle fiber contains hundreds of nuclei.
  • Myofilaments: Actin (thin) and Myosin (thick).

Connective tissue framework

  • Epimysium: dense connective tissue surrounding the entire muscle.
  • Perimysium: surrounds bundles of muscle fibers (fascicles); loose connective tissue.
  • Endomysium: basal lamina of connective tissue surrounding individual muscle fibers.

Diagram of Muscle fibers

  • Muscle fiber contains myofibrils, contractile thread-like structures
  • Cross striations result from sarcomeres arranged end to end.
  • Sarcoplasm contains myofibrils.
  • Sarcomere is a functional unit of contraction.
  • Myofibrils contain thick and thin filaments arranged into repeating units called sarcomeres.

Sarcomere Bands

  • Contains both actin & myosin.
  • A-band (anisotropic band) is the dark band.
  • I-band (isotropic band, light band) contains only thin filaments (actin, troponin, tropomyosin).
  • Z-line (Z-disc) is the boundary between 2 sarcomeres
  • H-zone (Henson's zone) is the central region of A-band; contains only myosin thick filaments.
  • M-line is located in the center of Sarcomere.
  • Contraction occurs at sites along overlapping filaments of sarcomere past one another.

Thick Filaments - Myosin

  • Tail
  • Heads with Actin-binding site, ATP & ATPase binding site

Sarcomere

  • Myosin
  • F-actin
  • G-actin

Formation of skeletal muscles (myogenesis)

  • Differentiation & fusion of muscle precursor cells (myocytes) /myoblasts into mature muscle fibers (myocytes).
  • Origin: paraxial mesoderm from somites (blocks of mesoderm along neural tube).
  • Somites differentiate into myotomes.
  • Myoblasts align & adhere to each other leading to fusion and form myotubes.
  • Myotubes elongate & synthesize myofilaments (actin, myosin).
  • Mature muscle fibers (myofibers)

Activation of Satellite Cells

  • A portion of myoblast does not fuse so they do not differentiate; these are satellite cells stem
  • These cells remain around the muscle fibers for future repair/regeneration
  • Muscle injury/mechanical stress activates satellite cells to re-enter cell cycles
  • Satellite cells proliferate to produce myoblasts
  • Some fuse damaged myofibers to repair
  • Others remain as satellite cells for future regeneration
  • Muscle fibers grow by hypertrophy (increase in size not number)
  • Satellite cells reside around sarcolemma basal lamina of muscle fibers

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