Muscle and Muscular Dystrophy III Flashcards
How do Ca2+ pumps & ATPases contribute to malignant hyperthermia?
Because the RyR channels are constitutively open and releasing Ca2+, the Ca pumps and ATPases are constitutively active and utilize lots of ATP, adding heat to the system.
What is a tetanic contraction?
A muscle that receives a series of very frequent impulses has an excess of Ca2+ present in the sarcomeres and does not relax. This hyper contracted state is called a tetanic contraction.
What is a motor unit?
A motor unit is the collection of muscle cells that a single neuron innervates. Each muscle cell is only innervated by one neuron, but one neuron may innervate up to 500 muscle cells. The number of muscle fibers a neuron innervates changes with the degree of muscle control needed. A motor neuron in the ocular muscles may only innervate 2-3 muscle cells/fibers, and 10-20 muscle fibers in the hand. In the quads, one motor neuron may innervate 200 or 500 muscle cells.
How is muscle tension controlled in skeletal vs cardiac and smooth muscle?
Cutting a nerve to skeletal muscle destroys its contractibility. Cutting a nerve to cardiac and smooth muscle will only affect its modulation, it will still contract.
What gets added during muscular hypertrophy?
New myofibrils are created, each with its own SR. The myofibrils do not swell much in diameter because this causes the Ca2+ to diffuse across larger distances and affects the contractibility of the sarcomere.
What are muscle stem cells?
Muscle stem cells are called satelite cells. Satelite cells comprise 2-3% of the total nuclei of a muscle and lie on outside the plasma membrane of the muscle cells. They respond to molecular signals from the muscle cell to divide and fuse with the cell and add another myonucleus. Satelite cells are able to regenerate an entire muscle cell within a week (cell damaged by myotoxin).
How does muscle repair occur in the three muscle types?
Skeletal muscle is repaired via satelite cells. There are no satelite cells in cardiac muscle, and cardiac cell damage results in scar tissue. Smooth muscle de-differentiates and divides into new smooth muscle (very complex).
What effect can muscle cells have on adipocytes?
Muscle cells can secrete signals that trigger the adipocytes to transform into brown fat. Muscle cells have widespread effects on the body, most poorly understood.
What are the basic clinical features of Duschene Muscular Dystrophy?
X-linked disease (mostly affects males), Dystrophin gene/protein, Calf pseudohypertrophy and toe walking, Gowers’ sign/maneuver, very high creatine kinase (1000-10000, vs normal <200) 100% have cardiomyopathy by 18 yo. Death usually due to cardiopulmonary failure in 20’s. Very low reproductive rates.
What function does the dystrophin gene perform?
Dystrophin connects the actin in a muscle cell to plamsa membrane structures which connect to extracellular matrix and then to other muscle cells. This forms the framework for cohesive muscle contraction. Many muscular dystrophies involve mutations in the other proteins involved in this network.
What are the molecular/genetic differences between DMD and Becker Syndrome and how does this affect their survival/transplant chances?
DMD results from big deletions or frameshifts in the gene. Becker results from smaller, in-frame deletions and less severe manifestation. Becker patients have better survivals in part because they are more likely to receive a heart transplant than are DMD patients. DMD patients have heart & lung problems and their outcomes are not likely to improve with a transplant. Becker only have heart problems.
What is the most testable drug treatment option available for DMD patients?
Corticosteroids. The administration of steroids may not prolong life, but may delay the need for wheelchairs. It prolongs active life.
