L5

Question 1

Purpose of the voltage clamp

Answer 1

Measure current flow across membrane and so determine current flow and conductance of ion channels responsible for the current.

Question 2

Erev

Answer 2

potential at which macroscopic current flow reverses direction
- changes from inwards to outwards

Question 3

Whole cell membrane channel

Answer 3

Advantage = currents don’t vary, they are reliable
onset and duration is constant, lets us estimate accurately

Question 4

single channel

Answer 4

only one or a few channels of same type
current flow small
Either inside out or outside out
NOT reliable

Question 5

What does it mean if a system is truly ohmic

Answer 5

cord = slope
both can be extrapolated back to Erev

Question 6

What did Hodgkin and Huxley conclude from their original data?

Answer 6

• activation range -50 to +20 mV for Na+
• fast activation, rapid & complete inactivation
  Same with K+
  identified underlying conductance using Ohm’s law