Topic Eleven - Action Potential Flashcards
Kahoot on neuron anatomy and action potential*
What is an action potential?*
An action potential is an electrical signal that travels along a neuron.
It is how neurons communicate and transmit messages.
Describe the sequence of conductance changes that occur before, during and after an action potential*
- A neuron has a membrane potential of -70 mV with a greater concentration of potassium inside the cell and sodium outside the cell.
- An event occurs that causes sodium channels to open.
- If the cell reaches threshold at -55 mV, an action potential is triggered
- More sodium channels open and more sodium comes into the cell depolarizing it further.
- At +40 mV, the sodium channels close and the potassium channels open.
- Potassium goes out of the cell, repolarising it.
- The cell becomes hyperpolarised.
- The potassium channels close
- The cell returns to resting membrane potential.
What is a refractory period and what impact does it have on the spike-rate code?*
There are two refractory periods, the absolute refractory period and the relative refractory period.
During the refractory periods, it is either impossible (absolute refractory period) or much more difficult (relative refractory period) for action potentials to be initiated.
Describe the sequence of events that occurs before, during and after a synaptic transmission*
Pre-synaptic
- Action potential moves along the axon and deploarised the nerve terminal
- Calcium-dependent exocytosis: calcium enters terminal because voltage=gated calcium-channels open, and causes neurotransmitter-filled vesicles to merge with cell membrane
Synaptic
- Release of neurotransmitter from vesicles
- Diffusion across synaptic cleft
- re-uptake of neurotransmitter
Post-synaptic event
- Neurotransmitter opens ligand-gated sodium channels on post-synaptic dendrite
- Create either EPSP or IPSP
- Generation of action potential in cell body if threshold is reached.
What are EPSPs and IPSPs?
Inhibitory post-synaptic potential
- A IPSP makes the post-synaptic neuron less likely to fire.
- It brings the neuron further away from threshold
Excitatory post-synaptic potential
- An EPSP makes the post-synaptic neuron more likely to fire an action potential.
- It brings the neuron closer to threshold
How do EPSPs and IPSPs integrate temporally and spatially?*
Temporal:
- When there is a short time constant, the signal dies away quickly
- When there is a long time constant (two signals occurring close together), the signals can “ride on top of each other” and make it easier to reach threshold.
Spatial:
- Things that are far apart spatially will not add
- Things that are close together spatially will add
What is the role of the myelin sheath?*
The myelin sheath increases conductance velocity by 10x to 1000x as the depolarization “leaps” between these nodes.
This is called saltatory conduction
What is the potassium and sodium concentration of a neuron?
High potassium on the inside of the cell
High sodium on the outside of the cell
The inside of the cell is negative, usually around -70mV
Why is it more difficult/impossible to initiate another action potential during the refractory periods?
Absolute refractory period:
- Sodium channels are open or recovering
Relative refractory period:
- Voltage-gated potassium gates are opened which makes the cell hyperpolarised. This means a greater depolarization is required.
What is the threshold needed to reach to initiate an action potential?
-55 mV
