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1

two of the greatest neuroscientists of the last
century

Alan Hodgkin and Andrew Huxley

2

they were awarded the Nobel Prize in Medicine or
Physiology in 1963

Alan Hodgkin and Andrew Huxley

3

The Hodgkin and Huxley experiments were conducted on a most unusual animal, the ___

squid

4

The Hodgkin and Huxley experiments were conducted on a most unusual animal, the squid,
and used a newly developed electronic method called the

voltage clamp

5

The reason they used
the squid for their experiments is because

the squid has giant axons that are used for escape

6

a typical axon in your body has a diameter of
about

2 μm

7

diameter of a giant axon

800-1000
μm, almost a full millimeter.

8

Hodgkin and Huxley used a new technique called

voltage clamp

9

evaluate the ion currents
that generate an action potential.

voltage clamp

10

is where the fibers
from the brain make synaptic
contacts with the giant axons.

giant
stellate ganglion

11

relates voltage, current and conductance

Ohm’s law

12

the degree of negativity (or
positivity) inside the cell relative to the outside and is measured in millivolts (mV).

Membrane potential

13

flow of ions through the channels in the
membrane

Current

14

“when positive ions flow into the cell

“inward current

15

when positive ions flow out of the cell

“outward current

16

Current is in units of

Amperes

17

is the symbol for current in
equations.

I

18

is the ease with which an ion can pass through a channel.

Conductance

19

means the same thing as permeability, but it can be measured, represented quantitatively, and is
used in equations

Conductance

20

symbol for conductance is

g

21

is the net force acting on an ion that drives it into or out of a cell.

Driving force

22

is the difference between the equilibrium potential for the ion and the
membrane potential, (Eion - Vm).

driving force

23

four terms are related and linked together by Ohms law

membrane potential (Vm)
current (I)
Conductance (g)
Driving force

24

Ohms law

Current (I) =conductance (g) x driving force (Eion -Vm) or I=g x (Eion -Vm).

25

When the
driving force is 0, as occurs when the
membrane potential is at

ENa (+55 mV),

26

conductances for Na+ and K+ are not constant during the action potential.
T/F

T

27

we have three dependent
variables

time, conductance and voltage, all of which are changing together

28

This method has the advantage of holding the membrane potential
constant over the entire length of an axon while recording the currents that flow into and out of
the axon through ion channels.

voltage clamp technique

29

is inserted down a length of a squid giant axon.

voltage-sensing electrode

30

voltage-sensing electrode
connected to the ______that measures the membrane potential.

oscilloscope