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127 Cards in this Set
- Front
- Back
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what are the other names for muscle cells?
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muscle fibers
myofibers |
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which filament is composed primarily of actin?
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thin filament
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which filament is composed primarily of myosin?
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thick filament
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what type of contractions do skeletal muscles undergo?
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quick, voluntary
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what type of contractions do cardiac muscle cells undergo?
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quick, rhythmic, involuntary
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what type of contraction do smooth muscle cells undergo?
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slow, involuntary
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what types of cells compose skeletal muscle?
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elongated
unbranched cylindrical multinucleated |
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where are the nuclei of skeletal muscle cells?
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in the periphery of the cell
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what feature can you see well in a longitudinal section of skeletal muscle?
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striations of pink-stained myofilaments
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where do skeletal myofibers originate?
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mesoderm
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what is the name for precursor cells of skeletal myofibers?
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myoblasts
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what is the name for the structure produced by the fusion of several myoblasts?
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myotubes
(multinucleated with relative lack of myofilaments) |
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what are the two methods by which skeletal muscle grows?
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hypertrophy
hyperplasia |
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as a method of skeletal muscle growth, how does hypertrophy occur?
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increase in size of muscle cell
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as a method of skeletal muscle growth, how does hyperplasia occur?
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increase in number of cells
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which method of muscle growth is more common in skeletal muscle?
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hypertrophy
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which method of muscle growth is more common in cardiac muscle?
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hyperplasia
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what is the name for the dense connective tissue sheath which surrounds the entire muscle?
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epimysium
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what is the name for the connective tissue sheath surrounding each muscle fassicle?
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perimysium
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what is the name for the delicate connective tissue sheath which surrounds each myofiber?
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endomysium
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what is the endomysium composed of?
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external lamina (type of basal lamina)
loose mesh of reticular fibers |
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how are muscle cells repaired, since they are terminally differentiated and cannot replicate?
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satellite cells in external lamina divide and differentiate into myoblasts which fuse to form new fibers
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what is in each skeletal muscle fiber?
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sarcolemma
multiple nuclei cytoplasm with multiple myofibrils |
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what organelles are abundant in skeletal muscles?
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sarcoplasmic reticulum
mitochondria glycogen granules (for anaerobic glycolysis) myoglobin |
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which band (staining color) is the A band?
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dark
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which band (staining color) is the I band?
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light band
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what is the thin dark line within the I band in skeletal muscle?
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Z disc
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what does the A band consist of?
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center - thick, myosin filaments
peripheral portions - thick and thin filaments |
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what does the H band consist of?
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thick filaments only
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what does the I band consist of?
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thin filaments only
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where does the sarcomere go between?
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Z lines
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what is the functional unit of contraction in skeletal muscle?
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sarcomere
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how many thin filaments are around each thick filament in skeletal muscle?
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6
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what are thick filaments composed of primarily?
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myosin II
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what is on the globular head of the myosin II molecules?
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binding sites for ATP and actin
myosin ATPase activity |
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what are the three main components of the thin filament?
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F-actin (two helical strands)
Tropomyosin Troponin |
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what polymerizes to form F-actin?
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G-actin
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what is the purpose of tropomyosin?
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provides structural support for F-actin
blocks myosin binding |
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what are the three components of troponin?
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TnT
TnC TnI |
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What does TnT do?
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binds to tropomyosin
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what is the purpose of TnC?
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binds calcium ions
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what is the purpose of TnI?
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inhibits actin-myosin interaction
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what is the molecule that binds and anchors thin filaments to the Z line?
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alpha-actinin
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what molecule connects the thick filaments to the Z lines?
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titin
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if cytokeratin is present in a tumor cell, where did the tumor originate?
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epithelial cells
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if vimentin is present in a tumor, where did the tumor originate?
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endothelial cells
vascular smooth muscle fibroblasts chondroblasts macrophages (mesenchymal tumor) |
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if the intermediate filament, desmin is present in a tumor, where did the tumor originate?
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skeletal muscle
nonvascular smooth muscle (muscle tumor) |
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if neurofilament is present in a tumor, where did the tumor originate?
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neurons
(neuronal tumor) |
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if glial fibrilar acidic protein (GFAP) is present in a tumor, where did the tumor originate?
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astrocytes
oligodendroglia microglia Schwann cells ependymal cells pituicytes (gliomatous tumor) |
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if Lamins A, B, and/or C are present in a tumor, where did the tumor originate?
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inner membrane of nuclear envelope
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what does the intermediate filament, desmin do in muscle fibers?
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surrounds the Z line and links myofibrils together and to the sarcolemma
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how well developed is the sarcoplasmic reticulum in skeletal muscle cells?
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very well developed
ensheaths each myofibril |
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what is the invagination of the sarcolemma of a muscle cell which carries the electrical signal into the interior of the the cell?
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T tubule
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what is the site of initiation of muscle contraction?
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triad
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what is a triad composed of?
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two terminal cisternae
one T tubule |
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where are the T tubules located in skeletal muscle?
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A-I junction
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what is a terminal cisternae?
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expansion of the sarcoplasmic reticulum
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what are the three types of skeletal muscle fibers found in every muscle in varying amounts?
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Type I fibers - aerobic - slow oxidative
Type IIa fibers - intermediate Type IIb fibers - anaerobic - glycolytic |
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compare myoglobin content in three types of skeletal muscle fibers
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Type I > Type IIa > Type IIb
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compare number of mitochondria in three types of skeletal muscle fibers
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Type I > Type IIa > Type IIb
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compare glycogen content in Type I and Type IIb skeletal muscle fibers
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Type IIb > Type I
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which skeletal muscle fibers are the slow-twitch fatigue-resistant fibers?
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Type I fibers
react slowly to nerve stimulation, but maintain sustained contraction |
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which skeletal muscle fibers are the fast-twitch fatigue-prone fibers?
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Type IIb fibers
react quickly to nerve stiumulation, but fatigue rapidly b/c of lactic acid production |
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what is the predominant skeletal muscle type in postural muscles and limbs?
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Type I fibers
(also predominant in marathon runners) |
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what are the predominant skeletal muscle fibers in extraocular muscles and digits?
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Type IIb fibers
(also predominant in sprinters and weightlifters) |
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what type of skeletal muscle fiber is predominant in 400m- and 800-m sprinters?
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Type IIa fibers
(also predominant in hockey players) |
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what shortens as muscles contract?
what lengthens? |
H bands and I bands
overlap between thick and thin filaments |
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what causes the "rigor state" of muscle contraction?
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myosin head bound to actin
absence of ATP |
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what causes myosin to uncouple from actin?
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binding of ATP to myosin
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what causes a conformational change in myosin head, causing it to extend?
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hydrolysis of ATP to ADP and Pi
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what causes a strong binding of myosin to actin?
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release of Pi from myosin head
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what causes the myosin head to bend, forcing the movement of the thin filament along the thick filament?
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release of ADP from myosin head
(aka power stroke) |
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what molecule partially covers the myosin-binding site on the actin filament in the inactive state?
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tropomyosin
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what causes the positional shift of tropomyosin, which exposes the myosin-binding site on the actin filament?
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binding of Ca2+ to troponin C
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in addition to Ca2+, what is required for muscle contraction?
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ATP
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what type of disorder leaves the innervation to a muscle intact, but affects the muscle itself?
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myopathy
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what type of disorder is duchenne muscular dystrophy?
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myopathy
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what causes Duchenne muscular dystrophy?
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mutation in dystrophin gene
leads to replacement of degenerating muscle fibers by fat cells |
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what is the purpose of dystrophin?
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links cytoskeleton to dystrophin-associated complex and then to extracellular matrix
actually attaches microfilaments to sarcolemma & basal lamina, which actually allows contraction |
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what type of disorder leaves the muscle fibers intact, but disturbs or eliminates the innervation of the muscle?
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neuropathy
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what type of disorder is Guillain-Barre syndrome?
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neuropathy
(acute idiopathic polyneuritis) |
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what are the symptoms of Guillain Barre?
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begins as parasthesias of feet, followed by paralysis of legs, progressing rapidly upwards
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What does Guillain-Barre cause?
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abnormal myelin sheath
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what type of disorder is Myasthenia gravis?
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disorder of the neuromuscular junction
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what causes Myasthenia gravis?
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autoantibodies to the ACh receptor block binding of ACh
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what are the symptoms of Myasthenia gravis?
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muscle weakness and atrophy, most active ones first
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what is ptosis?
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drooping eyelids
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what type of cells are cardiac muscle fibers?
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long
branched one (rarely two) nucleus (centrally placed and ovoid) |
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what cells commonly accumulate lipofuscin granules with age?
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neurons
cardiac muscle fibers |
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what are two prominent organelles in cardiac muscle fibers?
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mitochondria
glycogen granules |
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how well is the sarcoplasmic reticulum developed in cardiac muscle?
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less so than skeletal muscle
does not ensheath every myofibril |
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where do T tubules occur in cardiac muscle cells?
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Z line
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what does a diad consist of?
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one T tubule
one terminal cisterna |
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what type of muscle cell contains diads?
what type of muscle cell contains triads? |
diads - cardiac muscle
triads - skeletal muscle |
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what are the specialized junctional complexes unique to cardiac muscle?
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intercalated discs
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what are the three parts of an intercalated disc?
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fascia adherens (zonula adherens)
macula adherens (desmosome) gap junctions |
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what is the function of the fascia adherens (zonula adherens) in cardiac muscle fibers?
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anchors actin filaments of sarcomere to sarcolemma via alpha-actinin
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what is the function of the macula adherens (desmosome) in cardiac muscle fibers?
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binds cardiac fibers together
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what is the function of gap junctions in cardiac muscle fibers?
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permits electrotonic coupling of adjacent fibers, allowing heart to work as a functional synctium
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what are the types of cardiac muscle fibers?
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atiral fibers
ventricular fibers pacemaker cells pukinje fibers |
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what are the small cardiac cells with few T tubules, that produce polypeptide hormones?
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atrial fibers
fewer T tubules than ventricular cells cytoplasmic granules containing hormones like atrial natriuretic factor |
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when is atrial natriuretic factor secreted by the heart?
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in response to increased blood volume
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what are the effects of atrial natriuretic factor?
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increases sodium and water excretion
relaxes smooth muscle overall effect: lower blood volume & pressure |
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How do ventricular fibers appear?
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larger than atrial fibers, with more T tubules and no cytoplasmic granules
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which specialized cardiac muscle fibers are in the SA node and generate the intrinsic rhythm of the heart?
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pacemaker cells
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which specialized cardiac muscle fibers convey the SA rhythm to other cardiac fibers?
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Purkinje fibers
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how do purkinje fibers appear?
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paler, larger, fewer myofibrils, more gap junctions
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what type of tissue "repairs" lesions of the heart?
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connective tissue
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what is the effect of infarctions on remaining cardiac muscle fibers?
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compensatory hypertrophy
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how do smooth muscle fibers appear?
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spindle-shaped cells with a single, ovoid, centrally placed nucleus
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what organelles are present in smooth muscle cells?
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abundant mitochondria
some RER large Golgi apparatus |
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what surrounds smooth muscle cells?
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external lamina (basal lamina)
reticular fiber network (endomysium) |
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what types of collagen are produced by smooth muscle cells?
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type IV and type III collagen
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how do smooth muscle cells attach to one another?
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fuse endomysial sheaths
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what two ways can smooth muscle cells grow?
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increase cell size/number
regenerate in response to injury or physiological demand (like myometrium of uterus) |
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how many thin filaments surround a thick filament in smooth muscle?
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12
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how does the nucleus of a smooth muscle cell appear when contracted?
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spiralled
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what are the actin filaments in smooth muscle anchored to? what anchors them to these things?
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dense bodies
alpha-actinin |
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how are the myosin filaments associated with the actin filaments in smooth muscle?
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bind to actin during contraction cycle
in staggered arrangement, rather than bipolar arrangement |
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which enzyme converts smooth-muscle myosin into the active form?
how is this enzyme activated? |
myosin light chain kinase (MLCK)
MLCK is activated by the binding of calmodulin, which has already picked up calcium released from SR |
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how well developed is the sarcoplasmic reticulum in smooth muscle?
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poorly developed
SR is only on cell surface, associated with caveolae well developed SR is not necessary due to small size and slow contractions |
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how are signals transmitted across visceral smooth muscles?
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via the abundant gap junctions, b/c innervation is poor
allows for slow, wave-like contractions |
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where is vascular smooth muscle derived from?
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mesoderm
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how is vascular smooth muscle contraction different from visceral smooth muscle contraction?
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waves of contraction are more localized
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where is the smooth muscle of iris found?
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in the sphincter and dilator pupillae of eye
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where is smooth muscle of iris derived from?
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ectoderm
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how does smooth muscle of iris differ from other types of smooth muscle?
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rich nerve supply
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