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57 Cards in this Set
- Front
- Back
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Myofiber
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The skeletal muscle cell (skeletal myocyte). An elongate multi-nucleate syncytium from the fusion of hundreds of myoblasts.
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Endomysium
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External lamina and reticular fibers that surrounds myofibers. Contains capillaries and axons.
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Satellite Stem Cells (skeletal muscle)
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Mono-nucleate stem cells within the external lamina that can form new myofibers
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Muscle fascicle
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A functionally coordinated group of myofibers
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Perimysium
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A thick connective tissue sheath that surrounds a muscle fascicle. It contains small arteries, veins, and nerves
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Muscle
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Groups of fascicles
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Epimysium
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A connective tissue capsule that ensheathes the entire anatomical muscle.
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Myotendinous junction (and transduction of force)
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Transduction of force. Goes from myofibers to endomysium, then perimyseium, then epimysium, then tendon to bone.
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Red (type 1) skeletal muscle fiber
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Slow twitch. Oxidative, so lots of mitochondria. Uses fatty acids. Has high myoglobin and a large blood supply.
Fibers have a small diameter, many lipid droplets, and low glycogen levels. |
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White (type 2) skeletal muscle fiber
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Fast-twitch. Glycolytic (anaerobic), so have easy sources of energy - glucose, gycogen, and no lipids. Haslow myoglobin and few mitochondria. Low endurance and low blood supply.
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Z line
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adhesion point between two sarcomeres
Contains alpha actinin which links the actin of consecutive sarcomeres Z for Zwinschenscheibe (between) |
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Sarcomere
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contractile unit of striated muscle. Made up of thin and thick sliding myofilaments
Length ranges from1 to 4 microns, depending on whether it's contracted or not |
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I-band
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The area around the Z line that contains only thin actin filaments, plus regulatory proteins,tropomyosin, and troponin. Width decreases in contraction
I for isotropic (doesn't bend polarized light) |
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M-line
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Middle of sarcomere (and middle of H band). Joins myosin laterally to its myosin neighbor. Has creatinine phosphokinase to regenerate ATP from creatine phosphate
M for Mittel (middle of H band) |
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H-band
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Middle part around M-line. Contains only thick myosin filaments. Width decreases during contraction
H for Helle (lightpart of dark A band) |
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A-band
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Contains whole length of thick filaments, so also has the overlap of the thin actin filaments. Width is constant during contraction.
A for anisotropic (bends polarized light and appears dark) |
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Thick Myofilament
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Contains myosin II. Heavy heads contain ATPase and actin-binding sites.
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Titin
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Links thick filament to Z-line. It's the largest known gene product
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Thin Myofilament
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Made up of filamentous actin. Two F-actin strands form the double helix that associates with tropomyosin, troponin, nebulin, and alpha actinin
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Tropomyosin
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Lies in groves between actin strands, inhibiting actin-myosin interaction
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Troponin
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Tripeptide complex with three subunits.
TnT -binds to tropomyosin TnC - binds to Ca2+, initiating contraction TnI - binds to actin and inhibits actin-myosin interactin |
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Nebulin
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Non-elastic protein that helps alpha actinin anchor actin at the Z-lines
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Desmin
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Intermediate filament that links sacromeres at the Z-lines and transduces force to the sarcolemma (endomysium)
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Sarcolemma
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Plasma membrane of muscle cells. Has ion transport proteins, ion channels, dystrophin.
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Dystrophin
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In the sarcolemma. Links actin in sarcomeres to laminin in external connective tissue
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T tubules
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Invagination of the sarcolemma that interface with terminal cisternae of the sarcoplasmic reticulum, forming a triad. Brings PM depolarization signal deeply and quickly into the muscle.
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Triad
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Made up of a T tubule and two terminal cisternae. Present at each I-A band junction. ACh induces release of Ca2+ from cisterna into T-tubles, initiating contraction
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Neuromuscular Junction
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The motor end plate. PM invaginations form the post-synaptic membrane
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Motor unit
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alpha motor neuron plus skeletal fibers associated with its axonal brances
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Sarcoplasmic reticulum
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Internal smooth ER network that stores Ca2+
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Contraction
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begins at the triad.
Ca2+binds to troponin and exposes actin binding site Myosin head-ATP interaction with actin induces ATP hydrolysis, pulling actin into A band |
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Acetylcholinesterase
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degrades unbound ACh in the synaptic cleft
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Calsequestrin protein
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Helps with the re-uptake of Ca2+ back into the sarcoplasmic reticulum
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Cardiac Muscle structure
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Has branching cells, no distinct fascicular structure, and no sympatic innervation (no NMJs)
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Pacemaker
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Myocytes that initiate contraction in the heart
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Propagation of conduction in cardiac muscle
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Gap junctions between Purkinje fiber myocytes, then myocardial myocytes
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Diad
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Cardiac equivalent of a skeletal triad - has a T-tuble and one terminal cisterna
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Intercalated disks
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Overlapping endjoints that connect and transduce force between cardiac muscle cells at the plasma membranes of longitudinal ends
Have macula adherens at transverse end fascia adherens - transverse end. Has alpha actinin Gap junction - on lateral ends. Transmits depolarization |
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Smooth muscle cells
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No striations or sarcomeres. Spindle shaped cells with single, elongated nucleus, centrally located.
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Dense bodies of smooth muscle
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An analog of Z-lines. Anchors desmin and actin microfilaments to the sarcolemma
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Contraction in smooth muscle
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Activated by extracellular Ca2+ via calmodulin-activated myosin light-chain kinase phosporylation of myosin.
Has partial and extended contraction. Signal passes through gap junctions. |
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Calveolae
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Like the T-tubules of striated muscle - associates with SR. Pinocytic sarcolemmal invaginations.
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Utrophin
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Localized in myofibers at NMJ and MTJ, unlike dystrophin
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SNAP-25
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Required for synaptic vesicle fusion with axonal membrane (for pre-synaptic)
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Neuromuscular spindles
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Stretch receptors in the skeletal muscles that mediate both sensory and motor functions. Have intrafusal fibers
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Intrafusal fibers
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specialized muscle cells in the spindle in a fluid-filled periaxial space within the capsule with is anchored in the endomysium and perimysium.
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Afferent neurons
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Sensory 1a and II fibers that sense length and rate
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Efferent gamma motor neurons
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Regulate contraction of the intrafusal myfibers to potentiate spindle sensitivity
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Golgi tendon organ (neurotendinous spindle)
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Senses tension in myotendinous junction, protecting tendons from excessive muscle contraction. Has no gamma motor neuron
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New muscle fibers from satellite stem cells
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May proliferate into new myoblasts which fuse to form myotubes, then differentiate into new mature fibers upon formation of NMJ
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Myotube
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Multinucleate fusion of myoblasts which becomes a mature fiber. Cannot undergo mitosis, but can undergo hypertropy.
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Cardiac muscle regeneration
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has no satellite cells - no hyperplasia. Ischemia leads to necrosis
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Smooth muscle regeneration
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Smooth muscle cells can hypertrophy/hypotrophy as well as undergo hyperplasia via mitosis of exisiting cells or differentiation of pericytes
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Pericytes
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mesencymal stem cells in the basal lamina of capillaries and venules that can differentiate into smooth muscle cells
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Skeletal muscle cell dimensions
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10-100 microns x 3 cm (Average)
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Cardiac muscle cell dimensions
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10-15 microns x 80-100 microns
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Smooth muscle cell dimensions
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1-2 microns x 20-200 microns
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