Case 9 Flashcards
How do skeletal muscles develop?
The fusion of 100+ small mesodermal cells (myoblasts), this is why each skeletal muscle fiber has 100+ nuclei.
How do skeletal muscles grow?
Through hypertrophy, muscle fibers lose their ability to divide after fusion.
What is a sarcolemma?
Plasma membrane of a muscle cell
What are the two layers of sarcolemma?
True cell membrane called the plasma membrane and an outer thin layer of polysaccharide, containing collagen fibers, at each end this layer fuses with a tendon fibre.
What are transverse (T) tubules?
Invaginations of the sarcolemma which tunnel in from the surface toward the centre of each muscle fibre. They are open to the outside of the fibre and so contain interstitial fluid.
What is sarcoplasm?
Cytoplasm of a muscle fiber, it contains large quantities of potassium, magnesium, phosphate and multiple protein enzymes.
What are the sarcoplasmic reticulum?
Fluid-filled system of membranous sacs that encircle each myofibril. Composed of two parts: 1)large dilated chambers called terminal cisternae that touch the T tubules 2)longitundinal tubulesthat surround the actual surface of the myofibril.
Whats a triad?
Transverse tubule and two terminal cisterns on either side.
What ion is in abundance in the sarcoplasmic reticulum?
Ca2+
What are myofibrils composed of?
1500 adjacent myosin (thick) filaments and 3000 actin (thin) filaments.
What are the basic functional unit of a myofibril?
The filaments of a myofibril do not extend the entire length, they are arranged in compartments called sarcomeres, which are the basic functional units.
What are myosin molecules composed of?
6 polypeptide chains, 2 heavy and 4 light. The two heavy wrap around each other, the tail points towards the center of the sarcomere, parallel to neighboring molecules. The heads of the heavy chains fold bilaterally and 2 light chains are attached to each head. Part of the body hangs to the side, providing and arm, the head and arm together are called cross-bridges, which have two hinges, thus cross-bridges extend in all directions.
How many myosin molecules make up a filament?
200+
What are the tree portine components of actin filaments?
Actin, tropomyosin and troponin.
What is actin made up of?
Double-stranded F-actin protein molecule wound in a helix.
What are the F-actin molecules of actin made up of?
Polymerised G-actin molecules each of which is attached to a molecule of ADP (the active sites), which interact with the cross-bridges of myosin fibers in muscle contraction.
What are regualtory proteins?
Tropomyosin and troponin, they help switch contraction on and off.
Where is tropomyosin located?
Wrapped spirally around the sides of F-actin helix, in resting state they lie on top of the active sites.
What is troponin?
Attached intermittently along the tropomyosin moleculescomplex of three subunits that are thought to attach the topomyosin and the actin.
What are the three subunits in the troponin complex?
Troponin I - storng affinity for actin, Troponin T - strong affinity for tropomyosin, Troponin C - strong affinity for calcium ions, initiates contraction process.
What are structural proteins?
Keep thick and thin filaments in proper alignement, give the myofibril elasticity and extensibility, link the myofibrils to the sarcolemma and extracellular matrix.
What are the types of twitch fibers?
Type 1 - slow twitch, type 2a - intermediate of fast oxidative-glycolytic fibres. Type 2b - fast glycolytic fibers.
How do slow fibers compare to fast fibers?
Half the diameter and take 3 times aslong to reach peak tension after stimulation.Continue contracting long after fast fibers would fatigue.
What do slow twitch fibers contain large volumes of?
Mitochondria and myoglobulin, a globular protein similar to haemoglobin that reversibly binds to oxygen allowing a substantial reserve of oxygen. Slow twitch fib ers also have a great oxygen supply from capillaries.
What are fast glycolytic fibres?
Make up most skeletal fibres in the body, reach peak tension in 0.01s, large diameter, densly packed with myofibrils, large glycogen reserves, few mitochondria, fatigue rapidly as they use massive amounts of ATp during contraction.
What are fast oxidative-glycolytic fibers?
Hybrid of slow and fast fibers, contain little myoglobin with an intermediate capillary and mitochondrial supply.They utilise glucose and fats and maufacture and use ATP.