Lecture 5: Resting and action potentials Flashcards
Give an example of juxtacrine signalling.
Notch signalling pathway: important in neural development
What is the ligand involved in juxtacrine signalling?
The signalling molecule is attached to the surface of one cell
Why is juxtacrine signalling called direct signalling?
Attached ligand interacts with receptor molecule on immediate neighbour cell
Give an example of autocrine signalling.
T cells produce IL-2 which binds to its own receptors, activating the cell
What is autocrine signalling
The signal travels out of the cell and binds to the outer membrane of the same cell
Give examples of hormones involved in paracrine signalling.
Histamine, prostaglandins
What is paracrine signalling?
A signal molecule leaves one cell and interacts with a receptor molecule on the immediate neighbour cell
Give examples of neurotransmitters involved in neural signalling.
Acetylcholine, noradrenaline
List the 5 types of chemical communication from fastest to slowest.
Juxtacrine Neural Autocrine Paracrine Endocrine
What is the charge of a cell inside, relative to outside?
Negative due to high concentration of amino acids inside the cell
Where is a higher concentration of negative chloride ions found?
Outside the cell
What is the cell membrane leaky to
Sodium and potassium ions
How is the balance of ions kept in place with a leaky membrane?
Sodium-potassium pump
What does the sodium-potassium pump do?
Uses ATP to push 3 sodium ions out for every 2 potassium ions (against their chemical gradients)
What is GABA?
A neurotransmitter
What does GABA do?
Open ligand-gated chloride channels, changing post-synaptic membrane potential
What does the potential to do work come from?
Separation of charged particles
What is the typical resting potential of a cell?
-70mV
What is the difference between ligand-gated channel and a signal-gated channel?
Ligand channels opens/closes in response to extracellular signal. signal gated channel opens/closes in response to intracellular molecule
When is a leak channel open?
Always
When does a voltage gated channel open?
In response to change in the membrane potential
How do voltage gated channels change in response to voltage?
Charged region of the protein can change shape if the voltage across them changes
What covers the channel of a voltage channel when it is inactivated?
A ball-and chain region
What do ribbon models show?
The proteins backbone (without considering R groups_
What is a space filling model?
Shows the actual space taken up by all the atoms in the protein
What is the first stage of an action potential that takes the cell out of the resting state?
Depolarization
What happens after a cell is depolarised?
Rising phase of the action potential followed by the falling phase of the action potential
What occurs after the initial falling phase of the action potential, before the cell returns to resting state?
Undershoot
Why does the cell react differently to membrane potentials that are of the same magnitude but occur during different parts of the action potential cycle?
Two types of voltage gated ion channels allow their ions through at different rates
How do ions move when the voltage gated ion channels are open?
Down their electro-chemical gradient
Sodium and potassium channels are affected at the same time, so why are ions allowed through at different rates?
Sodium channels are very efficient, so permeability increases sharply, whereas potassium is slower
What happens during depolarising phase?
Sodium channels open, sodium moves into the cell
What happens during repolarising?
Sodium channels are inactivated, potassium channels open
What happens during hyperpolarisation?
Potassium channels remain open, sodium channels reset
On what principle are action potentials initiated?
All-or-none principle
What is the all-or-none principle?
Depolarisation reaches threshold or not, therefore there is an action potential or not
When is threshold of an action potential reached?
When the opening of the voltage-gated Na+ channels stimulates other channels to open in a + feedback loop
What is the name given when a new stimulus can have have no greater effect?
Absolute refractory period
How long does the absolute refractory period last?
1-2ms
What does the absolute refractory period determine?
Maximum action potential frequency
What is the relative refractory period?
Na channels can be reopened but permemability of sodium ions needs to exceed permeability of potassium ions
The relative refractory period has an _______ threshold
Increased
How long does the relative refractory period last?
3-15ms
