1. Action Potential – electrical signal
carried by an axon in a nerve
oCaused by ions
oIs an electrochemical response
oResult from the disturbance of the
potential difference across the axon
plasma membrane

2. Excitability – the ability to
create an action potential in
response to a stimulus
2 Types of excitable cells
in body are muscle and
nerve cells.

3. Potential difference
measure of the charge
difference across the
plasma membrane.
Measured in millivolts
(mV)

4. Neuron Resting potential –
electrical charge difference of -85
to - 70 mV.
outside
inside

5. A negative sign is used because
inside is negative compared to
outside of plasma membrane.

6. What creates the potential
difference:
1.Large negative proteins are
trapped inside the cell
2.Sodium-potassium pump -
Pumps 3 Na + out for every 2 K +
it pumps into the cell.

7. What creates the potential difference:
1. Large negative proteins
2. Sodium-potassium pump
3.Potassium channels allow K + to
diffuse out of the cell
3 2
1

8. Electrical properties of the axon at rest:
othere is no action potential
running down the axon
oOutside + and inside is -
comparatively
oWhen potential difference
greatest

9. Characteristics of an action
potential:
•All or none event
•There must be a stimulus

10. Characteristics of an action potential:
•Stimuli may include
•Moving cell (touch)
•Light (sight)
•Change in temperature
(hot/cold)
•Chemicals (taste)
•Electrical shock (not normal)

11. Steps of a nerve impulse:
1. Polarization
•Axon is at its resting potential.
• Axon is ready to do work, receive
a stimulus. (Has potential energy)

12. Steps of a nerve impulse:
1. Polarization
2. Depolarization
occurs in response to a
stimulus and is when there is
no more separation of charge
across the plasma membrane

13. Steps of a nerve impulse:
1. Polarization
2. Depolarization
How is a neuron depolarized?
A.Stimulus hits channel proteins
called gates located in the plasma
membrane
B. These gates open allowing Na+
to rush into the cell

14. Steps of a nerve impulse:
1. Polarization
2. Depolarization
How is a neuron depolarized?
C. The action potential changes
from -85mV to +30 mV
D. The inside of the plasma
membrane is now + and
outside – (reversed)

15. Depolarization

16. Steps of a nerve impulse:
1. Polarization
2. Depolarization
3. Repolarization – when the
potential difference across
the plasma membrane is
restored to resting potential.

17. Steps of a nerve impulse:
1. Polarization
2. Depolarization
3. Repolarization
How does repolarization occur?
A. Sodium gates close.
B. Potassium gates open; K+ rushes
out of the cell resting potential is
restored.

19. 3. Repolarization
How does repolarization occur?
NOTE: It takes less than 1
millisecond for
depolarization and
repolarization to take place.

20. Don’t write this!!!!
But wait!!! This is not what
was originally our resting
potential set up was it???

21. Don’t write this!!!
Very good! No it wasn’t. We
had more Na+ on outside, now
the sodium is on the inside.
Guess what will start to pump
now?

22. Steps of a nerve impulse:
1. Polarization
2. Depolarization
3. Repolarization
How does repolarization occur?
A. Sodium gates close.
B. Potassium gates open
Write now!!!
C.Sodium –potassium pump will re-
establish original ion
concentrations of resting potential.
• Takes 1 millisecond
• Axon can not receive next
stimulus

26. Types of stimuli
1. Threshold stimulus
Is strong enough to trigger the
action potential.
Once it is reached there is no
stopping the action potential from
traveling.

27. Types of stimuli
1. Threshold stimulus
2. Subthreshold stimulus –
Is a stimulus not strong
enough to trigger the action
potential.

28. Types of stimuli
1. Threshold stimulus
2. Subthreshold stimulus
3. Local potential –
Caused by a subthreshold
potential
Causes a depolarization in the
area of the stimulus but not strong
enough to create an action
potential to travel the axon

30. How does the action potential
travel down the axon?
The action potential is strong
enough to depolarize the
adjacent area of membrane
opening the sodium gates causing
a wave of depolarization.

31. Refractory period – pump is
bringing stimulate portion of
membrane back to original resting
potential ion concentration.
During this time this section
cannot respond to another
stimulus, keeps action potential
from traveling wrong direction.

32. Two types of refractory periods:
1.Absolute refractory period – no
matter how strong the stimulus
there is no action potential
2. Relative refractory period – if the
stimulus is strong enough it will
produce an action potential

33. Don’t write
Remember – action
potential is all or none –
so how do you feel
different levels of
intensity?

34. Level of intensity of senation is
determined by:
1.Frequency of action potentials.
The higher the frequency the
greater the intensity.
2. Whether or not the axon is
myelinated determines type of
conduction.

35. Level of intensity of senation is determined by:
1.Frequency of action potentials
2. Whether or not the axon is myelinated.
Continuous conduction –
unmyelinated
the wave of depolarization moves
down the complete plasma
membrane
dull, slow pain

38. Level of intensity of senation is determined by:
1.Frequency of action potentials
2. Whether or not the axon is myelinated.
Continuous conduction
Saltatory conduction
myelinated
impulse jumps from node to
node.
Sharper pain

41. Nerve impulses travel from
one neuron to the next when
the nerve impulse travels
across the synapse.

42. NS Synapse – junction between
two neurons
Synaptic cleft – space in the
synapse
Neurotransmitter –chemical that
stimulates the dendrite of the next
neuron to depolarize.

43. Pre -synaptic neuron – first
neuron in a series
Post – synaptic neuron – second
neuron in a series

44. How does action potential
travel across synapse?
1.Action potential reaches
the pre-synaptic terminal.
2.Ca +gates open and Ca+
rushes in.

45. How does action potential travel across synapse?
3.Ca+ trigger release of the
neurotransmitter from the
synaptic vesicles.
4. Neurotransmitter travels
across the synaptic cleft
and binds to receptors on
the post-synaptic neuron.

46. How does action potential travel across synapse?
5. This stimulates ion gates
to open.

48. 2 types of synapses
1.Excitatory –
•Neurotransmitter stimulates Na+
gates to open at post-synapse
•Enough Na + gates must open for
creation of an action potential in
the post-synaptic membrane

50. 2 types of synapses
1.Excitatory –
Types of summation:
A. Temporal summation – one
pre-synaptic axon has a high
enough frequency of action
potentials to send enough
neurotransmitter to open enough
Na+ gates to continue the nerve
impulse.

52. B. Spatial Summation –
•have several pre-synaptic
neurons that excite one post-
synaptic neuron.
•enough Na+ gates will open for
action potential to travel through
next neuron.

54. 2 types of synapses:
1.Excitatory
2.Inhibitory
Neurotransmitter opens K+
channels on post-synaptic
membrane
K + will rush out of cell
causing hyperpolarization; an
increase in potential
difference (-80mV to -90mV)

55. 2 types of synapses:
1.Excitatory
2.Inhibitory
 filters out unnecessary info
 Mostly this type in body

56. Types of Neuron Arrangement:
1.Convergent circuit– more than
one pre-synaptic neuron goes to
one post-synaptic neuron.

57. Ty pes of Neuron Arrangement:
1. Convergent circuit
2. Divergent circuit
 one pre-synaptic neuron sends a
signal to several post-synaptic
neurons.
This spreads the message to
different parts of the body.
Ex. To muscles and brain

58. Types of Neuron Arrangement:
3. Oscillating circuit – a neuron
sends the message back to itself.
A single stimulus can result in a
long lasting signal.
Ex. Alarm clock = stimulus, stay
awake due to oscillating circuit.
Circuit may stop due to fatigue of
neuron or interference.