Physiology Of Neurons Flashcards
What are leak channels?
They are ion selective channels
They are restricted so ions cannot flow freely, they slowly move through
They are used in membrane potential maintenance
What are voltage gated channels?
Selective channels that respond to a neuron’s membrane potential
Closed at rest
What are ligand gated ion channels?
Selective ion channels
Open in response to the binding of a specific ligand to a receptor
What are mechanically gated ion channels?
Selective ion channels
Open in response to a physical stimulus
What is the definition of “equilibrium potential”?
Voltage across a cell membrane that exactly balances the concentration gradient for a specific ion
What is the first part of an action potential?
Initial depolarisation
A stimulus causes the cell to become less negative within the cytoplasm
This stimulus could be: a signal received by dendrites, a nearby cell depolarising or a synaptic signal transmitted via neurotransmitters
What is the second step in an action potential?
Positive feedback depolarisation
Voltage gated Na channels open and Na floods into the cell
This is a rapid influx since it is driven by a strong electrochemical gradient
More Na entering causes depolarisation to accelerate
What is the third step of the action potential?
Depolarisation
This continues until the action potential reaches between 30 and 40 mV
This takes around 1 millisecond
Na gates then close completing depolarisation
What is the fourth step of the action potential?
Voltage gated K gates open while Na channels remain closed
K leaves the cell causing the membrane potential to drop
What is the fifth step of the action potential?
Hyperpolarisation and the refractory period
The outflux of K continues until the membrane potential becomes too low (-90 mV)
This means Na channels cannot open as they are voltage gated
The voltage will slowly raise due to the Na/K pump
Why can’t voltage gated Na channels open during hyperpolarisation?
There is a VS module on the Na channel which is involved in voltage sensing
The VS region has concentrated positive charge which is very sensitive to the transmembrane potential
During hyperpolarisation, the negative internal potential of the cell pulls on the charges in the VS module to keep the channel closed
What are the 2 types of synapses?
Chemical synapse
Electrical synpase
What are graded potentials and how do they differ from action potentials?
They are a small change in potential
They are deviations from the resting potential whereas APs are the direct result of a defined stimulus such as receiving the signal from a dendrite
GPs are found mainly in the dendrites and cell bodies of neurones
What is the clinical significance of carbamazepine in the physiology of synapses?
Carbamazepine is an anticonvulsant, used particularly in the treatment of epilepsy
It binds to and inhibits voltage gated Na channels (preferred if channel is currently inactive)
This raises the threshold required for an action potential to occur
30% of patients develop resistance, this is thought to be related to genetics
What is the clinical significance of Lidocaine in the physiology of synapses?
Lidocaine is used as a local anaesthetic (can be administered topically or as a local injection)
Lidocaine binds to and inhibits voltage gated Na channels
It raises the threshold required for an action potential and inhibits the generation of local action potentials
Therefore blocks local pain receptors are
