Download Pg. 109 Action Potentials

Pg. 109 Resting Potentials
Think back to chemistry!
 Opposites attract!
Potentials
 Key Point #1: All cells exhibit a membrane potential
 Difference in electrical charge
 Cytoplasm (-) and ECM (+)
 Represent this as voltage
Resting Potential
 Key Point #2: The resting potential of the cell (inside) is the
membrane potential when NOT transmitting signals
 -70 mV
 Sodium/potassium pumps maintains the potential
 Active transport
 ATP
 AGAINST the gradient
 Key Point #3: At rest, Na+ and K+ are constantly moving
 The membrane is more permeable to K+
 Key Point #4: Ion Channels
 K+ and Na+ move through ungated ion channels (free flowing)
 Gated ion channels- open/close in response
 Ligand-gated
 At synapses
 Open/close when a specific chemical binds
 Voltage gated
 axons
 Open/close when the potential changes
 30 second break
 Find a classmate and ask them what their favorite
book is and why.
Pg. 110 Action Potentials
 Key Point #1: Action potential




A response/impulse
All or none
Generated at the axon hillock
Carry information along the axons
 Very brief- lasting only 1-2 milliseconds. This allows
neurons to produce them at high frequency
Generation of Action Potentials:
A Closer Look
Key Point #2: At resting potential
 Voltage-gated Na+ and K+ channels are closed
Key Point #3: When an action potential is
generated Voltage-gated Na+ channels open first and Na+
flows into the cell K+
 Decrease in voltage- depolarization
 From -70 mV to -60 mV
 Key Point #3 continued Na+ influx causes more Na+ channels to open and
diffuse into the cell
 Causes further depolarization
 -60 mv to -50 mv
 POSITIVE FEEDBACK!
 Key Point #4: Threshold
 The voltage needed for an action potential to fire.
Action Potential
 Action potentials propagate impulses along neurons.
 Membranes of neurons are polarized by the
establishment of electrical potentials across the
membranes.
 In response to a stimulus, Na+ and K+ gated channels
sequentially open and cause the membrane to become
locally depolarized.
 Na+/K+ pumps, powered by ATP, work to maintain
membrane potential.
15
Label the graph of the action potential as we go through the next
several slides.
16
Key
Na
K
Membrane potential
(mV)
50
0
50
2
Depolarization
OUTSIDE OF CELL
INSIDE OF CELL
Inactivation loop
1
Resting state
100
Sodium
channel
Potassium
channel
Threshold
2
1
Resting potential
Time
 KP#5: Once the threshold is met, Na+ continues to
rush inside the cell, raising the voltage into the
positive region (~+40)
Key
Na
K
50
Rising phase of the action potential
Membrane potential
(mV)
3
Action
potential
50
2
Depolarization
OUTSIDE OF CELL
INSIDE OF CELL
Inactivation loop
1
Resting state
100
Sodium
channel
Potassium
channel
3
0
Threshold
2
1
Resting potential
Time
Key
Na
K
50
Rising phase of the action potential
Membrane potential
(mV)
3
Depolarization
OUTSIDE OF CELL
INSIDE OF CELL
Inactivation loop
1
Resting state
Potassium
channel
3
0
100
Sodium
channel
Falling phase of the action potential
Action
potential
50
2
4
Threshold
2
4
1
Resting potential
Time
 Key Point #6: When the neuron’s voltage is high
enough, the Na+ channels will close
 During the falling phase, voltage-gated K+ channels
open, and K+ flows out of the cell

Repolarizing the cell

Making the cell negative again
Key
Na
K
50
Rising phase of the action potential
Membrane potential
(mV)
3
Depolarization
OUTSIDE OF CELL
3
0
100
Sodium
channel
Falling phase of the action potential
Action
potential
50
2
4
Threshold
2
4
1
5
Resting potential
Time
Potassium
channel
INSIDE OF CELL
Inactivation loop
1
Resting state
5
Undershoot
1
 KP#7: Undershoot More K+ flows out the cell, making the cell
even more negative (-75 mV)
 Eventually the K+ channels close to restore
the resting potential (homeostasis)
Figure 48.11a
50
Membrane potential
(mV)
Action
potential
3
0
2
50
4
Threshold
1
5
Resting potential
100
Time
1
Refractory Period
 During the refractory
period after an
action potential, a
second action
potential cannot be
initiated
 KP #8: The refractory
period is a result the
closing of Na+
channels and a
second impulse
cannot be fired.
Axon
Action
potential
1
Na
Plasma
membrane
Cytosol
Axon
Plasma
membrane
Action
potential
1
Na
K
2
Cytosol
Action
potential
Na
K
Axon
Plasma
membrane
1
 KP#9: Impulses travel
Na
in one directiontowards the synapses.Action
potential
Moves down the axon K
in a wave like motion 2 Na
to prevent
K
diminishing.
Cytosol




K
3
K
Action
potential
Na
Sequence the following in order of occurrence
Depolarization
Resting state
Repolarization
Hyperpolarization
Resting state
Depolarization
Hyperpolarization
Repolarization
Resting state
50
?
Membrane potential
(mV)
3
0
Resting state
2
Depolarization
50
Hyperpolarization
1
Repolarization
Resting state
100
Time
4
5
1
Tell me what you know!
a. increase; increase
b. increase; decrease
c. decrease; increase
d. decrease; decrease
Tell me what you know!
Adding a poison that specifically disables the Na+/K+
pumps to a culture of neurons will cause:
a. the resting membrane potential to drop to 0 mV.
b. the inside of the neuron to become more negative relative to the
outside.
c. the inside of the neuron to become positively charged relative to
the outside.
d. sodium to diffuse out of the cell and potassium to diffuse into the
cell.
Homework
 Read and outline 48.4 Synapses
 Neurotransmitters-next slide
Homework
 In most animals, transmission across synapses involves chemical
messengers called neurotransmitters: Choose one





Acetylcholine
Epinephrine
Norepinephrine
Dopamine
Serotonin