Muscle Physiology 2 and 3 Flashcards
what is the difference between different muscle cells regarding Ca2+?
skeletal and heart - Ca2+ channel flux stimulates SR Ca2+ release through the Ryr
smooth muscle - Ca2+ released from SR via RyR and also IP3R
THEREFORE smooth muscle cells rely on agonists and not just AP
describe the action of muscle contraction in skeletal and cardiac muscle
cytoplasmic Ca2+ binds to troponin C, this induces a conformational change in the troponin/tropomyosin that exposes the myosin-binding sites on actin filaments to the myosin heads. Myosin heads can then attach to actin, twist and pull and create contraction to shorten sarcomere and muscle
what is the function of the myosin head?
it retains all the motor functions of myosin and the ability to produce movement and force
describe vascular smooth contraction
1 - Ca2+ binds to calmodulin and changes configuration, 2 - Ca2+-calmodulin complex activates myosin light chain kinase (MLCK), 3 - MLCK phosphorylates myosin light chain to catalyse cross-bridge activation, 4 - rest of crossbridge cycle is similar to skeletal and cardiac muscle
what does smooth muscle contraction/relaxation determine?
vascular lumen dimensions
what does RyR abnormality lead to
Ca2+ sparks: aberrant Ca2+ release events from single RyR clusters, leads to loss of SR Ca2+ - ABNORMALITY AND FAILURE
what is the effect in the excitation-contraction coupling reaction of Ryr failure?
reduced SR Ca2+ and shift of Ca2+ from inside to outside the cell
what is the consequence in cardiac muscle of RyR failure
contraction reduced and HEART FAILURE caused
what are the 2 types of heart failure?
pump failure and sudden cardiac death
what is pump failure?
progressive haemodynamic deterioration leads to profound bradycardia or asystole as the terminal event. Not sudden nor unexpected
what is sudden cardiac death?
the abrupt onset of symptoms and death are within 1 hour generally indicates cardiac death
what is the consequence of RyR failure in skeletal muscle
muscular dystrophy
what is Duchenne muscular dystrophy
recessive X-chromosome linked mutation, muscle degeneration, loss of skeletal muscle function, loss of movement, paralysis including muscles for life support, no cure and leads to death at around 25
what is Limb-Girdle Muscular Dystrophy?
affects limb girdle muscules and less severe than Duchennes, reduce life span slowly
how are the masticatory muscles affected in muscular dystrophy?
masticatory pattern distorted but muscle wastes less than other skeletal muscles, reduced function and patients need more time for chewing before swallowing
