Action Potentials Flashcards
Define action potential:
- Fundamental unit of information in the nervous system
- short lasting event in which the electrical membrane potential of cell readily rise and falls
What cells do action potentials occur in?
- Neurons
- Muscle cells
- Cardiac cells
- Endocrine cells
Define action potential:
The difference in electric charge across a cell membrane
What resting potential do electrically excitable cells tend to be?
-40 to -90 mV
What do we call cells at their resting potential?
polarised
What do we call cells which are more positive than their resting potential?
Depolarisation
What do we call cells which are more negative than their resting potential?
Hyperpolarisation
How does a potential difference across a cell membrane arise relating to k+ ion?
From an in balance of k+ ions inside the cells than the outside
Finish the sentence:
Excitable cells must have a ….
negative (hyperpolarised) resting potenial
What do impermeable membranes mean relating to chemical gradient?
Cannot exist
What is an electrochemical equilibrium?
When the ions are balanced
What is an opposing electrical gradient?
Chemical gradient increasing whilst electrical gradient is decreasing
What can stop all k+ ions reaching a chemical equilibrium?
an opposing electrical gradient
What is another name for opposing electrical gradient?
-Reversal potential
or
-Nernst potential
What is a reversal potential?
Membrane potential where the chemical and electrical gradients of an ion across a biological membrane are in equilibrium
What is the net flow of ions across a membrane at reversal potential?
No net flow
What does the Nernst equation show?
Equilibrium potential of an ion dependent on intra and extra cellular concentrations
What is the Nernst equation?
Ex = RT/zF ln [X]out/[X]in
What does R mean in the Nernst equation?
The universal gas constant
What does Ex mean in the Nernst equation?
The equilibrium potential
What does T mean in the Nernst equation?
The temperature in Kelvin
What does z mean in the Nernst equation?
The valence of the ion
What does F mean in the Nernst equation?
The Farady constant
What does [X]out mean in the Nernst equation?
Concentration of ion outside cell
What does [X]in mean in the Nernst equation?
Concentration of ion inside cell
What is the universal gas constant equal to?
8.3145 JK-1mol-1
What is the temperature in Kelvin equal to at 37C?
310.15K
What is the faraday constant equal to?
96485 C mol-1
During depolarisation of membrane potential what opens?
Voltage-gated Na+ channels open
What does voltage-gated Na+ channel-mediated depolarisation trigger?
A chain reaction
When is a chain reaction triggered?
At an action potential threshold
Describe an action potential:
- Na+ flow into cell due to depolarisation opening voltage-gated Na+ channels
- Result in a region of positive charge across the membrane
- Local depolarisation causes Na+ channels nearby to open
- More Na+ ion can flow into cell
- Voltage-gated K+ channels also activated by depolarisation (much more slowly)
- K+ leave the cell
- Na+ channel inactivates
- More voltage-gated K+ channels open causing hyperpolarisation
- Resting membrane potential re-established
Finish the sentence:
Voltage-gated Na+ channels rapidly…
inactivate after activation
Finish the sentence:
Due to depolarisation voltage-gated K+ channels activate more…
Slowly than voltage-gated Na+ channels
Is electrical resistance within an axon higher or lower in thinner axons?
Higher
What is meant bu a higher electrical resistance in thinner axons?
Slower conduction of signal
What do myelin sheath do?
Insulate the axon from negative external charge
What are the effects on electrical transmission due to myelin sheath?
Faster transmission
Can myelinated axon store some of the charge?
Yes
What acts as signal boosters to prevent storage of charge?
Nodes of Ranvier
What are at Nodes of Ranvier?
Highly density of volt-gated Na+/K+ channels
How does a Nodes of Ranvier work?
When a propagating action potential reaches the Node a new action potential is initiated
What is the action at the Nodes of Ranvier called?
Saltatory conduction
What makes up myelin sheath in PNS?
Schwann cells
What makes up myelin sheath in CNS?
Oligodendrocytes
What initiates an action potential?
- Anything which causes a depolarisation beyond action potential threshold
- Under physiological conditions normally generated by ion channels
What are different types o d ion channels which can generate an action potential?
- Voltage-activated
- Extracellular-activated (Ligand/light/heat/cold -activated)
- Intercellular-activated
- Stretch-activated
Describe the role of action potential in synaptic transmission:
- Action potential reaches presynaptic neurones
- Ca2+ enter voltage-gated Ca2+ channels
- Causing Na+ neurotransmitters to be released across the synapse
- Na+ reaches postsynaptic neuron and initiated a new action potential
Is the size of action potential does change what does?
The number of frequency
Why is it important to calculate the equilibrium potential?
If we know what ion channel is permeable to, we can predict what opening that channel will do to the membrane potential
