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Flashcards in Exam 1 Histology Deck (14):

Collagen Fibers

High tensile strength


Elastic Fibers

Allows tissues/organs to stretch & return to size
Elastin fibers incorporate bundles of microfibrils that act as a scaffold during development and consist of the Glycoprotein Fibrillin.
Elastin, an amorphous component, is added later and forms the major part of the fiber.


Reticular Fibers

Provides delicate framework of support


A bands

(Anisotrophic) are dark bands (myosin, overlaps actin)


I bands

(Isotrophic) are light bands (actin, tropomyosin, troponins)


H band

the center of the A band (myosin with no overlap of actin; slightly lighter portion of middle of A band)



is the basic contractile unit of striated muscle.

Sarcomere repeats are represented by myofibrils.



Myofibrils are held in place with each another by desmin, which is an intermediate filament proteins.
These proteins hold adjacent Z-lines (disks) together



bound to the Z disk and acts like a spring to limit amount of contraction and prevent myosin form reaching Z disk



extends form Z disk and acts as guide for actin direction and length



* consists of T, C, and I subunits
* T binds to tropomyosin
* C binds to calcium
* I inhibits actin-myosin interaction
When the C unit of troponin binds to calcium, it triggers a shape change moving tropomyosin away from the binding site for actin-myosin interaction



found in shallow grooves of double stranded actin; runs along actin and blocks the actin-myosin interaction sites


Cardiac Muscle

* Differences from skeletal muscle
* mononucleated
* Central nuclei
* Diad vs triad of the sarcoplasm and the T tubule
* Have intercalated disks that have gap junctions between adjoining cells that allow transmission of action potentials between cells
* Also have bifurcation’s between the cells due to the branching patterns of the tissue
* Also can have lipofuscin granules due to incomplete lysosomal degradation of the dye
* Incapable of regeneration after tissue death*


Smooth muscle

* Single, elongated, oval central nucleus with torpedo/submarine shape
* Capable of division
* Z disks are not in register, so do not form striations; gives smooth appearance
* In cross section, there are not nuclei in every cell*
* Contraction is regulated by calmodulin
* Calcium bods to calmodulin when activates myosin light chain kinase (MLCK)
* MLCK phosphorylates light chains in myosin and increases myosin ATPase activity; myosin slides along actin filaments and creates muscle tension