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Questions and Answers
During muscle contraction, what is the functional unit where this process occurs?
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?
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?
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?
How do myoblasts contribute to skeletal muscle fiber formation?
What structural component is primarily found within the I-band of a sarcomere?
What structural component is primarily found within the I-band of a sarcomere?
What is the primary function of the sarcoplasmic reticulum in muscle cells?
What is the primary function of the sarcoplasmic reticulum in muscle cells?
What connective tissue layer directly surrounds individual muscle fibers?
What connective tissue layer directly surrounds individual muscle fibers?
What event marks the initiation of skeletal muscle contraction?
What event marks the initiation of skeletal muscle contraction?
What is the role of T-tubules in muscle contraction?
What is the role of T-tubules in muscle contraction?
What is the functional significance of the arrangement of actin and myosin filaments within the sarcomere?
What is the functional significance of the arrangement of actin and myosin filaments within the sarcomere?
Flashcards
Muscle Tissue
Muscle Tissue
One type of tissue specialized for contraction and movement.
Epimysium
Epimysium
Dense connective tissue surrounding the entire muscle.
Perimysium
Perimysium
Bundles of muscle fibers (fascicles); allows nerves and blood vessels to reach fibers.
Endomysium
Endomysium
Basal lamina of loose connective tissue surrounding individual muscle fibers.
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Sarcoplasm
Sarcoplasm
Muscle cell organelles; cytoplasm.
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Sarcolemma
Sarcolemma
Plasma membrane of a muscle cell.
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Sarcoplasmic Reticulum
Sarcoplasmic Reticulum
Muscle (smooth) endoplasmic reticulum.
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Myofibrils
Myofibrils
Contractile threads within muscle fibers.
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Sarcomere
Sarcomere
Functional unit of muscle contraction
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I-Band
I-Band
Contains only thin filaments (actin, tropomyosin, troponin).
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- 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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