Action Potentials
“Salty banana in milky pools”
potassium on the inside, sodium chloride & calcium on the outside
Membrane potential
the difference in charge in outside vs inside the neuron
Action potential
a specific change in membrane potential
Propagation along the axon
Action potentials are all or nothing
always travel the same speed
Wether or not the cell sends an action potential is influenced by hundreds,
sometimes thousands, of other cells
Ion channels open & close
Keeps membrane and action potential in place
Depolarizing
A cell at rest is highly Polarized (-65 mv)
IPSP hyperpolarizes the neuron (more negative or move away from zero)
EPSP depolarizes (more positive and closer to 0)
threshold value
about -50mv
when reached an action potential is started
Action Potentials 1
, varies between neurons
Steps of Action potential
Rising Phase
1. If the depolarization (from EPSP) reaches the threshold value, then voltage-
gated sodium ion channels open
Voltage-gated sodium ion channels: along axon hillock and nodes of
Ranvier
Axon hillock can be called “spike initiation zone”
Summate incoming signals & decide if they meet the threshold
summation:
Spatial: From multiple different neurons at the same time
temporal: all info coming in from 1 location rapidly
2. Voltage-gated potassium channels open (more slowly) Shove potassium out &
lead to depolarization
Falling phase (Repolarization & absolute refractory period)
3. At top of potential voltage (highest point), sodium channels close, and
potassium stay open
Potassium goes out of cell due to concentration gradient and electrostatic
pressure
Peak positive voltage ( Overshoot)
AT rest they are naturally closed
after being opened for action potential, they are inactivated & closed (not
properly)
They will not open again for new signals for some time
Will close properly again when the membrane goes back to being at rest
Action Potentials 2
“Salty banana in milky pools”
potassium on the inside, sodium chloride & calcium on the outside
Membrane potential
the difference in charge in outside vs inside the neuron
Action potential
a specific change in membrane potential
Propagation along the axon
Action potentials are all or nothing
always travel the same speed
Wether or not the cell sends an action potential is influenced by hundreds,
sometimes thousands, of other cells
Ion channels open & close
Keeps membrane and action potential in place
Depolarizing
A cell at rest is highly Polarized (-65 mv)
IPSP hyperpolarizes the neuron (more negative or move away from zero)
EPSP depolarizes (more positive and closer to 0)
threshold value
about -50mv
when reached an action potential is started
Action Potentials 1
, varies between neurons
Steps of Action potential
Rising Phase
1. If the depolarization (from EPSP) reaches the threshold value, then voltage-
gated sodium ion channels open
Voltage-gated sodium ion channels: along axon hillock and nodes of
Ranvier
Axon hillock can be called “spike initiation zone”
Summate incoming signals & decide if they meet the threshold
summation:
Spatial: From multiple different neurons at the same time
temporal: all info coming in from 1 location rapidly
2. Voltage-gated potassium channels open (more slowly) Shove potassium out &
lead to depolarization
Falling phase (Repolarization & absolute refractory period)
3. At top of potential voltage (highest point), sodium channels close, and
potassium stay open
Potassium goes out of cell due to concentration gradient and electrostatic
pressure
Peak positive voltage ( Overshoot)
AT rest they are naturally closed
after being opened for action potential, they are inactivated & closed (not
properly)
They will not open again for new signals for some time
Will close properly again when the membrane goes back to being at rest
Action Potentials 2
