MSKS Physiology Lecture 4_Nureomuscular Junction

Question 1

What is the relationship between dihydropyridine and ryanodine

Answer 1

dihydropyridine is a voltage gated protein located within the T-tubule. When dihydropyridine is activated it opens ryanodine, which is a Ca channel located within the SR, and increases cytosolic Ca levels.

Question 2

Describe how muscle contractions happen in smooth muscle

Answer 2

1) Nerve signal stimulates the release of Ca from the SR
2) Ca binds calmodulin. Ca-calmodulin complex activates myosine light chain kinase (MLCK)
3) MLCK phosphoralates the head of myosine light chain in preperation for the power stroke cycle (note that in cardiac and skeletal muscle, myosine light chain can auto phosphoralate).

Note: to down regulate contractions myosine light chain phosphatase deposphoralates myosine light chain.

Question 3

Describe the function of the activation gate and the inactivation gate on fast Na channles

Answer 3

Both activation gates and inactivation gates are attached to fast sodium channels. Activation gates are located on the extra cellular side remain closed until an action potential is triggered. The inactivation gate is on the intracellular side and remain open until the action potential reaches threshold at which point it closes and stops the influx of Na to the cell. Shortly after the inactivation gate closes, the activation gate closes and the inactivation gate will reopen.

Question 4

How does hyperkalemia effect the membrane potential of cells and the function of fast Na channels

Answer 4

hyperkalemia (high serum K levels) makes a cells resting membrane potential more positive (because the K gradient is reduced) and with chronic exposure the inactivation gate of fast Na channels will close. This closure reduces the functionallity of the fast Na channels because even when the activation gate opens, not Na will enter the cell.