PSYC1004 Lecture Notes - Lecture 10: Resting Potential, Electrochemical Gradient, Depolarization
26 Oct 2018
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Action potential
Depolarisation: the membrane potential becomes less negative than at rest.
Hyperpolarisation: the membrane potential becomes more negative than at rest.
Repolarisation: membrane potential returning to the resting membrane potential after either
depolarisation or hyperpolarisation.
An electrical signal - described as a brief, large depolarisation in a neuron
Threshold - A particular membrane potential that will elicit an action potential (~-50mV)
All-or-none principle - subthreshold – no action potential occurs suprathreshold – action potential
occurs (same amplitude every time)
The action potential and ion movement
Ions moving in and out of the neuron cause the action potential.
Important ions channels for AP:
- Na+ channels
- K+ channels
Na+ and K+ channels are voltage-gated - This means that they will open and close depending on the
membrane potential!
Voltage-gated Na+ channels (needs to reach a certain voltage for the gate to work which is -50mV)
Na+ channels Open/Close/Inactivate depending on the membrane potential
When channels open: Na+ ions move into the cell (influx, along electro-chemical gradient) - leads to
large membrane depolarisation AKA Action Potential (AP).
Na+/K+ pumps (needed for repolerization… restoring membrane potential)
Na+/K+ pumps are active transporters that require energy (ATP) to work.
At rest: The pumps work slowly to maintain the membrane potential at ~-70mV
Peak AP, Na+/K+ pumps are working at maximum speed to: - remove 3Na+ from the cell; bring 2K+
into the cell
• More + ions leaving the cell than entering.
• This allows neurons to repolarize to the resting membrane potential after an AP has occurred
Voltage-gated K+ channels
Different to Na+ channels – do not have inactivation gates!
- K+ channels can open (opens at threshold of -50vM) and close only (starts to close slowly at the AP
peak +30mv and then is closed at repolarization).
- K+ channels are much slower compared to Na+ channels
Sodium ions want to leave the cell due to the concentration gradient, but wants to stay inside due to
the electrical gradient
When channels open: K+ ions move OUT of the cell (efflux, along chemical gradient) - leads to
membrane repolarisation
Summary of AP and ion movement
Document Summary
Depolarisation: the membrane potential becomes less negative than at rest. Hyperpolarisation: the membrane potential becomes more negative than at rest. Repolarisation: membrane potential returning to the resting membrane potential after either depolarisation or hyperpolarisation. An electrical signal - described as a brief, large depolarisation in a neuron. Threshold - a particular membrane potential that will elicit an action potential (~-50mv) All-or-none principle - subthreshold no action potential occurs suprathreshold action potential occurs (same amplitude every time) Ions moving in and out of the neuron cause the action potential. Na+ and k+ channels are voltage-gated - this means that they will open and close depending on the membrane potential! Voltage-gated na+ channels (needs to reach a certain voltage for the gate to work which is -50mv) Na+ channels open/close/inactivate depending on the membrane potential. When channels open: na+ ions move into the cell (influx, along electro-chemical gradient) - leads to large membrane depolarisation aka action potential (ap).
