Lecture 15: From Neuromuscular Junction to Myocyte Flashcards
what does myosin look like and do
- has two heads, two necks and one body
- pulls actin by bending the neck
- called the power stroke
- myosin molecules aggregate with tail regions to form thick filaments
what happens to the sarcomere lines during cross bride cycling
- filaments are pulled towards the centre (M lines)
- overlap between thick and thin filaments increases, so Z lines come closer together
- I and H bands get progressively shorter with each round
- A band doesn’t change
label the bands on a diagram of the sarcomere
check
what do the thin filaments comprise of
- actin polymers which are structural
- tropomyosin which blocks actin-myosin activity
- troponin which controls tropomyosin
how does tropomyosin prevent actin-myosin activity
it blocks myosin binding sites on the actin molecule
what is troponin made up of
TN-I (inhibitory)
TN-C (calcium binding)
TN-T (tropomyosin binding)
what is excitation-contraction coupling
- link between the depolarisation of membrane (excitation)
- with the tiny influx of calcium
- and the consequent huge increase in cytosolic calcium
- that leads to contraction
where is the calcium stored
- mostly in sarcoplasmic reticulum
- a lot of it is stored next to actin and myosin
how does calcium get released from the sarcoplasmic reticulum
1) membrane depolarises
2) calcium channels undergo conformational change
3) sarcoplasmic reticulum release channels undergo conformational change
4) release channels open
5) calcium flows from sarcoplasmic reticulum to cytosol
describe the process of cross-bridge cycling
1) myosin head releases actin, binds to ATP releasing ADP. resets myosin head to 90°
2) myosin head cleaves ATP to ADP and phosphate. activates myosin head into high energy state, ready to bind to actin
3) if calcium is present, myosin head and ADP binds actin
4) power stroke happens, myosin head swivels from 90° to 45°
what are the types of acetylcholine receptors
- nicotinic
- muscarinic
muscarinic receptors
- found in parasympathetic nervous system
- second messenger is G protein
nicotinic receptors and their mechanism
- found in skeletal muscle, in neuromuscular junction
- when activated, increase in voltage inside the cell
- opens non-specific ion channel so sodium flows in and potassium flows out
- net effect is an inward current as more sodium goes in than potassium goes out
what is carbachol
- nicotinic receptor agonist
- causes miosis in the eye, treating glaucoma
what is rocuronium
- nicotinic receptor antagonist
- used for tracheal intubation in A&E
