muscle contraction- molecular mechanisms

Question 1

microstructure of muscles

Answer 1

muscle
fascicles
muscle fibres/cells
myofibrils
actin and myosin filaments

Question 2

what do motor units do?

Answer 2

innervate muscle fibres

Question 3

how does an action potential travel across a neuromuscular junction

Answer 3

1.motor neurones AP arrives at axon terminal and depolarises the plasma membrane
2. this opens calcium channels s calcium ions diffuse into axon terminal and they bind to proteins
3. synaptic vesicles release Ach
4. Ach diffuses from axon terminal to motor end plate, binding to nicotinic receptors
5. binding of Ach opens an ion channel so Na+ and K+ pass through with more Na+ moving in than K+ out
6. local depolarisation of motor end plate
7. muscle fibre AP initiated
8. propagation

Question 4

what is excitation- contraction coupling

Answer 4

the sequence of events by which an AP in the plasma membrane activates the force-generating mechanisms

Question 5

how do muscles contract

Answer 5

-when muscle is relaxed, tropomyosin blocks actin binding site
-when calcium is related it binds to troponin and uncovers the binding sites of the active filament so that cross-bridges can form
-binding of cross-bridges allows force to be generated and contraction to be produced
-when muscle is relaxed again calcium is removed from troponin and restored back to sarcoplasmic reticulum

Question 6

which proteins are responsible for linking the membrane action potential release with calcium release

Answer 6

dihydropyridine receptor
ryanodine receptor

Question 7

what is the cross-bridge cycle

Answer 7

1. energised myosin cross-bridges bind to actin
2. cross-bridge binding triggers release of ATP hydrolysis products from myosin. this produces angular movement
3. ATP binds to myosin, breaking the link between actin and myosin so the cross-bridge dissociates
4. ATP bound to myosin is split it energise the myosin cross-bridge