Excitation Contraction Coupling

Question 1

What does the Nernst equation tell us?

Answer 1

It gives a formula that relates the numerical values of the concentration. gradient to the electrical gradient that balances it

Question 2

What is the resting membrane potential?

Answer 2

-60mV

Question 3

What effect does increasing extracellular K+ concentration have on membrane potential?

Answer 3

Becomes less negative

Question 4

Briefly explain the events at the synapse

Answer 4

ACh stored in vesicles
Influx of Ca2+ triggers vesicle fusion with presynaptic membrane and the release of ACh into synaptic cleft
ACh binds to its post-junctional membrane receptor
Receptors are called nicotinic acetylcholine and when bound, they open briefly to allow a passage of Na+ and K+
Therefore membrane depolarisation
ACh degraded into choline and acetate by acetylcholinesterase
Choline recirculated to presynaptic junction

Question 5

What are the names of the receptors on the T tubule and on the SR?

Answer 5

DHP receptor; RyR

Question 6

What happens to the wave of depolarisation?

Answer 6

It travels along the T tubule, activates voltage sensitive DHP receptor and stimulates the RyR to open the Ca2+ channel
Allows cytoplasmic Ca2+ to rise

Question 7

How is muscle relaxed again?

Answer 7

Ca2+ is removed back into SR using SERCA, and the Ca2+ forms a complex with a low affinity Ca2+ binding protein: calsequestrin

Question 8

What do the number of crossbridges affect?

Answer 8

Force

Question 9

What does the rate of cross bridge cycling affect?

Answer 9

Velocity