Action Potential Flashcards
(20 cards)
What is an action potential?
A nerve impulse - how information is travelling along a neuron
What does an action potential allow?
Communication within the neuron, along an axon
Where is an action potential generated?
At the axon hillock - below the soma
How is an action potential generated?
By the summation of converging impulses from the dendrites or by electrical stimulation - experimentally
What does hyperpolarisation mean?
Makes the membrane potential more negative tan the RMP:
injection of small negative current, positive ions move out (K)
negative ions move in (cl)
What does depolarisation mean?
Makes the membrane potential more positive than the RMP:
injection of small positive current
positive ions move in (Na+)
What is decremental conductance?
A small degree of depolarisation due to a small stimulation, decays along the length of the neuron - stimulation at one point will cause a positive potential but will eventually go down
How do you elicit an action potential?
Increase the size of the stimulation and the amount of depolarisation - need to meet the threshold of -50mV - there is no point of return
What are voltage gated ion channels?
They are channels which are opened when the membrane becomes depolarised - different degrees of depolarisation open the channels
eg. positive membrane potentials (lots of depolarisation) usually results in inactivation of sodium channels
How can you create a steady membrane potential?
Inject a current into the axon - record the membrane current
What does conductance mean?
The rate of ion travel through the channel
What do voltage clamp experiments reveal?
Membrane current - transient inward current, followed by a small outward current
Sodium current - fast, movements of ions into the neuron through the Na channels, fast conductance
Potassium - slow, movement of ions out of the neuron through the K channels - very slow conductance
What does refractory mean?
When there is loads of depolarisation, there is a refractory period where the gate cannot be reactivated it till the MP goes back to a resting state
What gates do we have at rest?
An activation gate
Inactivation gate
What happens if we have just enough depolarisation?
The activation gate opens
When does the K+ channel open?
Needs lots of depolarisation for it to open, not just a little bit
Steps of an action potential
- At rest, the majority of the channels are closed
- Small depolarisation opens a few NA channels, Na moves in (diffusion and electrostatic forces) leading to further depolarisation
- If the stimulation is large enough (above the threshold) the majority of the Na channels open, more Na moves into the neuron, leading to further depolarisation
- As the neuron continue to depolarise, some K+ channels are opened, allowing K+ to leave the neuron (diffusion). More sodium channels are open than K
- At positive potentials the Na+ channels become deactivated (refractory) so that no Na can pass through. The remaining K+ channels open and K continues to leave the neuron driven by both diffusion and electrostatic forces - K wants to be the boss
- K continuous to leave the neuron - the membrane potential decreases and becomes negative - repolarisation
- The K channels begin to close, Na return to their closed normal state. The membrane potential drops to below the resting membrane potential due to a few open K channels and the high concentration of K outside the neurons. This is known as hyperpolarisation. Hard for another AP
- The final K channels close, external K diffuses away. Membrane potential returns to normal using the pump - works like mad
What does hyper polarisation mean?
When the membrane potential drops below the resting potential
Is the action potential different sizes?
It is the same size along the whole axon, all or nothing response
What is propagation of the action potential along the axon?
Unidirectional - unmyelinated
It is like a waveform - all happens at once - like waving a piece of string
