NB 8 Neuronal excitability

Question 1

signal propragation in nerve cells are________ becasause _______________

Answer 1

active propagation because no decrements over large distances

Question 2

1) What is meant by electronic responses are graded?

2) What is meant by electronic responses are summate?

Answer 2

1) bigger stimulus = bigger response (grades in an exam)

2) multiple stimuli= summed responce (UCAS points add)

Question 3

What happens when threshold level is reached?

Answer 3

external m gates of Na+ channel start opening, most h gates are open as well.
therefore there is an increase Na+ in cell
positive feedback= more m gates open
after 1msec of threhold depolatisation h gates shut= repolarisation, h gates close at a slower rate to m gates opening for otherwise threshold would never be reached
voltage-gated K+ channels start to open 1-2msec of threhold depol. , K+ flows out = repolarisaiton,
hyperpolarisaiton occurs as delayed rectifier K+ channels open
to return to resting membrane potential: K+ channels clsoe due to hyperpolarisaiton, Na+ ha gates open

Question 4

Why is their a refractory period?

Answer 4

hyperpolarisaiton occurs due to layed rectifier K+ channels open,
also Na+ h gate can’t open after closing for a certain period of time
therefore no action potential can be fired