muscles Flashcards
general roles of skeletal muscle and structure?
voluntary movements of bones
inspiration and contraction of diaphragm
skeletal muscle ‘pump’ helps return venous blood to the heart
structure break down - muscle fascicle - muscle fibre - myofibril - sarcomeres
sarcomeres - what are the lines and bands and stuff?
they appear striated
z line at each end
I bind = just actin (the lighter one) - gets smaller as muscle contracts
A band = overlapping of actin and myosin, appears darkest
how is contraction initiated?
Motor neurons carry electrical impulse to the muscle.
AP causes release of ACh.
Depolarises sarcolemma, passes along T tubules and right to the sarcoplasmic reticulum.
Depolarises it and releases Ca2+ from stores
what are T tubules?
These are invaginations in the plasma membrane.
Form a triad with sarcoplasmic reticulum
how quick is contraction?
5 cycles of the whole thingy per head (myosin head)
explain how the contraction mechanism works
(Starting with the myosin bound to actin strongly) ATP binds to myosin head, reducing affinity of myosin head for the actin, breaking crossbridge.
Second ATP is hydrolysed for head straightening. The ADP and phosphate actually stay bound to the myosin heads, phosphorylation causes a conformational change, and the myosin head straightens out.
Then makes a weak link to actin = actin myosin cross bridge.
Phosphate is released from the myosin head, strengthening the cross bridge. Head bends, pulls it along = contraction. ADP is released, we’re back to a tight binding with a bent head
what is summation?
when action potentials in quick succession cause an increase in strength of contraction
what are the three kinds of muscle fibres (speed-wise) and their colour?
slow/type I = red due to myoglobin which stores oxygen, has a rich blood supply to provide this oxygen, slow levels of sustainable force like posture
fast oxidative/type IIa = middle man, typically more forceful so needs more ATP and has glycogen stores
fast glycolytic/type IIb = anaerobic so rely on glycolysis
neuromuscular junction? botox?
we kind of know this - nicotinic Ach receptors (LGICs) , let in Na+, activates Ca2+ voltage gated channels etc…
botox effects snares, preventing docking and therefore exocytosis of ACh, causing paralysis/muscle weakness
inhibitors?
literally at every possible point/step of muscle contraction
aerobic training is and does what?
aerobic - long distance running/swimming = sustained low level exercise, stimulating slow fibres
type IIx fibres may be converted into IIa
this increases resistance to fatigue, also causes changes in capillaries to improve blood suppy
no increase in strength
anaerobic training is and does what?
contraction of type IIa and IIb fast twitch muscle fibres like wright lifting
results in an increase in strength as more myofilaments are added to myofibrils to increase diameter of muscle fibres (not more muscle fibres just bigger ones)
energy delivery when we exercise - how fast is oxygen delivery and what does this mean for the beginning of exercise?
increase in O2 demand cannot be met immediately, it takes a few minutes for oxygen delivery and uptake to reach it’s maximum
this means in the earlier (2) minutes of exercise we rely on stored energy
what stored energy is sued in early exercise?
ATP and phosphocreatine stores - used up very quickly
must change to anaerobic glycolysis
what are the three immediate stores of energy that don’t last long?
ATP to ADP + Pi
ADP + PCr in presence of creatinine kinase makes ATP + creatinine
adenylate kinase ADP + ADP forms ATP and AMP