Muscle and Muscular Dystrophy I Flashcards
What are the major functioning myofilaments?
Actin and myosin. (There are other myofilaments. These are just the major types.)
What is myofiber?
Another term for a skeletal muscle cell.
What is a myocyte?
Another term for a cardiac muscle cell.
What causes the shifting of some striation lines in muscle fibers?
The fixation process. These are myofilaments that have been slightly damaged in the preparation process.
How are myotubes formed?
By the fusion of myoblasts, individual muscle cells that fuse to form functional muscle cells. Individual cells are about 10 microns in length, but muscle cells can be up to 2.5 cm. This requires multi nucleation in order to supply sufficient RNA for cellular processes.
How many main muscle fiber types are there?
Three. Two fast twitch, one slow twitch. Fast/slow refers to relative contraction speeds. Two fast twitch types are differentiated by fatigue rates, one fatigues quickly, one slowly. Slow twitch and fatigue resistant fast twitch have high concentrations of mitochondria.
What is different in smooth muscle versus striated?
Smooth muscle still has the same actin and myosin filaments, but it is not organized the same way and does not appear striated, and it is regulated differently. Contraction is still based on Ca2+. Smooth muscle cells are mono nucleated, small, thin (5um, 10-20x thinner than striated), and long.
What is different in cardiac muscle versus skeletal muscle?
Nuclei locate in the center of the cell, and cells are mostly mononucleated (some are dinucleated)
What are intercalated disks in cardiac cells and what function do they perform?
Intercalated disks are the dark staining lines in cardiac cells that delineate the myocytes. They form very strong junctions between cells that hold the cells together while they all contract. They also propagate action potentials from cell to cell through gap junctions located in the intercalated disks. Gap junctions allow for electrical continuity.
What muscle types have gap junctions and which do not?
Cardiac and smooth muscle have gap junctions. Skeletal muscle does not.
What is the basic mechanical unit of a muscle cell, what is it constructed of, and how long is it?
The sarcomere. Sarcomere’s extend from Z to shining Z (Z-lines/disks separate sarcomeres). Thick filaments are myosin and thin filaments are actin. A relaxed sarcomere spans approximatly 2.5 microns.
What are two regulatory proteins that are found on actin filaments?
Troponin and Tropomyosin. Tropomysosin binds to 6-7 actin molecules and covers the binding site of myosin. Troponin attaches to the end of tropomyosin and senses Ca2+. When troponin senses Ca2+, it moves and tropomyosin moes with it, allowing myosin to contact the actin filament. Troponin is similar in form and funciton to calmodulin in that it binds multiple Ca2+ ions.
What is a simple antibody test for cardiac damage?
Cardiac troponin antibodies will bind to any available cardiac troponin in the blood, detecting relatively small amount of cardiac damage.
What is the basic structure of myosin filaments?
They are composed of 400 individual myosin fibers, each with a head region containing an actin binding site and an ATP binding site that allows movement of the head. The heads are arranged at 60 degree intervals around the filament and concentrated near the ends of the filaments, the central areas are generally devoid of heads.
Mutations in which proteins may lead to muscle diseases?
Mutations in any proteins associated with the sarcomere may cause muscle disesases. This includes troponin, tropomyosin, actin, and myosin. It also includes many proteins not covered here, including Titin, which keeps the myosin filament centered between the Z-disks.
What structure do most of the mutations in Hypertrophic Cardiac Myopathy affect, and what four pathways affect the overall patient condition?
The sarcomere. Most mutations are missense and their mechanisms are not completely understood. Myocyte hypertrophy leads to cardiac hypertrophy (big cells = big organ), myocyte disarray leads to disorganized firing, interstitial and replacement fibrosis leads to arrhythmias, and dysplastic intramyocardial arterioles leads to ischemia.
