Neurons, Synapses, and Signaling

Page
3

Slide 17

OUTSIDE

CELL

Na+

Key

K+

Sodium-

potassium

pump

Potassium

channel

Sodium

channel

INSIDE

CELL

Slide 18

Modeling of the Resting Potential

Resting potential can be modeled by an artificial membrane that separates two chambers.

At equilibrium, both the electrical and chemical gradients are balanced.

In a resting neuron, the currents of K+ and Na+ are equal and opposite, and the resting potential across the membrane remains steady.

Slide 19

Action potentials are the signals conducted by axons

Neurons contain gated ion channels that open or close in response to stimuli.

Membrane potential changes in response to opening or closing of these channels.

When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative. This is hyperpolarization, an increase in magnitude of the membrane potential / increase in difference between sides / farther from threshold.

Slide 20

Graded potentials and an action potential in a neuron

Stimuli

+50

+50

Stimuli

0

0

Membrane potential (mV)

Membrane potential (mV)

–50

–50

Threshold

Threshold

Resting

potential

Resting

potential

Hyperpolarizations

–100

–100

0

1

2

3

4

5

Time (msec)

(a) Graded Hyperpolarizations

Time (msec)

(b) Graded Depolarizations

Depolarizations

0

1

2

3

4

5

Strong depolarizing stimulus

+50

0

Membrane potential (mV)

–50

Threshold

Resting

potential

–100

Time (msec)

0

1

2

3

4

5

6

(c) Action potential

Action

potential

Slide 21

Other stimuli trigger a depolarization, a reduction in the magnitude of the membrane potential.

For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell.

Graded potentials are changes in polarization where the magnitude of the change varies with the strength of the stimulus.

Slide 22

Stimuli

+50

Membrane potential (mV)

–50

Threshold

Resting

potential

Depolarizations

–100

0

2

3

4

Time (msec)

(b) Graded depolarizations – magnitude of the change varies

with the strength of the stimulus.

1

5

0

Slide 23

Production of Action Potentials