11. Structure + function of skeletal muscle Flashcards
Thick filaments
Myosin
Thin filaments
Actin F
Muscle spindles
used to detect changes in length of a muscle
(Golgi) tendons
used to detect changes in tension in tendons
Motor units
alpha motor neuron in the spinal cord and all of the muscle fibres it innervates
degree of contraction of a whole muscle relies on recruiting motor units in a particular order, from smallest to largest
allows fine control of movement at the lower end
more forceful contraction at upper end
Release of ACh at NMJ
depolarisation of the presynaptic memb
Ca2+ ions enter
Ca2+ ions promote fusion of the ACh-containing vesicles with the presynaptic memb
vesicles fuse with the memb
ACh released into the synaptic cleft by exocytosis
net influx of Na+ ions
depolarisation of the muscle fibre
Role of calcium in muscle contraction
binds to troponin C
causes conformational (shape) change in troponin
moves tropomyosin out of the way of the myosin binding sites on actin
Sliding filament theory
Myosin heads hydrolyse ATP - become reoriented and energised
Myosin heads bind to actin - forms crossbridges
Myosin heads rotate toward center of sarcomere - power stroke
crossbridges detach from actin
The importance of ATP
allows ‘cocking’ of the myosin head
needed to pump the calcium ions back into the SR
1) Slow oxidative fiber
2) Fast glycolytic fiber
3) Fast oxidative-glycolytic fiber
Skeletal muscle
Well developed system of T tubules and SR
Calcium ions from SR only
Calcium ions bind to troponin C
axial shortening of muscle
Cardiac muscle
Less well developed system of T tubules and SR
Calcium ions from ECF and SR
Calcium ions bind to troponin C; actin-linked regulation
shortening is less axial than in skeletal because cells are branched
Smooth muscle
No T tubules, very little SR
Calcium ions from ECF only
No troponins, calcium ions bind to calmodulin; myosin-linked regulation
no sarcomeres - cell contracts in several dimensions at once
