6.Local response and electronic potential. Action potential

Question 1

What are the 2 responses a neuron or excitable tissue can produce

Answer 1

Slow/ graded- electrically non excitable membranes

Action potential- electrically excitable membrane

Question 2

In terms of distance of signal, what are the differences in responses

Answer 2

Action potential can conduct impulses over long distances

Slow can conduct impulse for short distance, conduction with decrement

Question 3

Which response requires a threshold

Answer 3

Action potential

Threshold of -50mv must be met for it to occur and to open voltage gated channels

No threshold for slow

Question 4

What happens to amplitude in each of the responses

Answer 4

Action potential- amplitude standard, always the same despite bigger/smaller stimulus

Slow- Amplitude corresponds to stimulus

Question 5

Which response can be summated

Answer 5

Only slow responses can be summated
Action potentials cant be summated BECAUSE THEY HAVE ANSOLUTE REFRACTORY PERIOD!!!!!!

Question 6

What is absolute refractory period

Answer 6

During this period, no matter how big the stimulus, a action potential will not occur

Closure of the inactivation
gates of the Na+ channel in response to depolarization.

These inactivation gates are in the closed position until the cell is repolarized back to the resting membrane potential

Question 7

What is relative refractory period

Answer 7

Begins at the end of the absolute r.p and overlaps with the hyperpolarization afterpotential

An action potential will only occur if the depolarizing current applied is GREATER

There is higher permeability for K+ here than at rest

Question 8

What is accommodation

Answer 8

If depolarization happens slowly or depolarization is held for a long time, action potential will fail to fire despite being above threshold

This is because depolarization closes inactivation gates on Na+ channels

Question 8

Give an example of accommodation

Answer 8

Hyperkalemia

Elevated blood serum K+ concentration

At rest, nerve and muscle cell membranes are very permeable to K+ an increase in extracellular K+ concentration causes depolarization of the resting membrane

The sustained depolarization closes the inactivation gates on Na+ channels making it less likely to fire an active potential