Neuromuscular signaling

Question 1

Nicotinic receptor (ACh receptor)

Answer 1

4 transmembrane domains
5 subunits
wide 0.6 nm at most narrow, 3 nm at widest

Question 2

Distance across the synaptic cleft

Answer 2

50 nm

Question 3

Nicotinic receptor action

Answer 3

2 ACH bind, then the non-specfic cation channel is open and Na and K flow in and out respectively. Greater Na flux leads to depolarization

Question 4

End Plate Potential (EPP)

Answer 4

local depolarization brought on by opening of nicotinic receptors

Question 5

Dihydropyridine receptor (skeletal)

Answer 5

In T-tubules, acts as a voltage sensor
In smooth and cardiac muscle, acts as a VGCC
Transiently open, voltage sensitivity is high

Question 6

Ryanodine receptor (skeletal)

Answer 6

Ca channel that is mechanically linked to the DHP receptor, allows massive Ca flow into the T-tubule from the SR.

Question 7

muscle movement steps

Answer 7

1 Ca binds troponin (TnC gets TnI out the way)
2 tropomyosin moves into the groove of actin
3 myosin head binds actin filament
4 ATP charges myosin head (releasing it from actin, if necessary)
5 hydrolysis and cocking
6 new binding site
7 P released, power stroke

Question 8

dantrolene

Answer 8

treatment (IV) for malignant hyperthermia; don’t use succinylcholine on people with a family history of malignant hyperthermia

Question 9

RyR (SR Ca receptors)

Answer 9

release calcium when acted upon by calcium (Ca induced Ca release) - very strongly inactivated and the end of one cycle - relative refractory period of cardiac cells

Question 10

RyR re-activation vs. L-type Ca Channel re-activation

Answer 10

RyR takes several seconds, L-type Ca channel is ready almost as soon as repolarization is complete