NNN I Flashcards
what is the resting membrane potential of a neuron and why
-70mV
it is like this because the transporters and ion channels create a distribution of ions/ charges
what is depolarisation or excitation
Any entry or +ions (Ca, K, Na) or exit of - ions (Cl)
what is hyperpolarization of inhibition
any exit of +ions or entry of -ions.
This causes the membrane potential to be lower than the rmp
what is repolarisation
when the membrane potential returns to its resting state after depolarisation.
opening of channels for a neurone at rest typically
Na channels: flows inwards (depolarization, excitatory)
Ca channels: flows inwards (depolarization, excitatory)
Cl channels: flows inwards (hyperpolarization, inhibitory)
K channels: flows outwards (hyperpolarization, inhibitory)
what does an agonist of a Na channel do
opens channel, causes Na flow in cell, causes excitation
what does a Na channel antagonist do
closes channel, stops Na ion flow, favours inhibition…. e.g. local anaesthetics like lidocaine
what does an agonist of of K channel do
opens K channel, causes K flow out of the cell, makes more negative and is therefore inhibitory
what does a K channel antagonist do
closes K channel, retains K in the cell, favours positive rmp and is therefore excitatory
neurotransmitter: events at the synapse
1) action potential depolarises axon terminal
2) depolarization opens voltage gated Ca2+ channels and Ca2+ enters
3) Calcium entry triggers exocytosis of synaptic vesicles
4) Neurotransmitters travel across synaptic cleft and bind to receptors on the postsynaptic cell
5) Neurotransmitter binding initiates a response in the postsynaptic cell
neurotransmission: Inactivation of neurotransmitters
1) neurotransmitters can be returned to axon terminals for reuse or transported into glial cells
2) Enzymes inactivate neurotransmitters
3) Neurotransmitters can diffuse out of the synaptic cleft
what is an astrocyte
a type of glial cell that provides support and protection to neurons in the central nervous system
function of an astrocyte in the reuptake of neurotransmitters
help regulate the concentration of neurotransmitters in the synaptic cleft by taking up neurotransmitters such as glutamate.
how do the astrocytes take up the glutamate
there are glutamate transporters on the astrocyte and this is important for the termination of glutamates synaptic action.
Post-synaptic action of a NT, there are 2 modes of action, what are they
neurotransmitters act directly or indirectly on ion channels.
how does direct gating happen
Ionotropic receptors. The receptor is an integral component of the molecule that forms the channel it controls.
how does indirect gating happen
Mediated by activation of Metabotropic receptors. Receptor and the channel it controls are distinct.
what are the two major families of ligand gated channels.
Ionotropic glutamate receptors
Nicotinic acetylcholine receptors
why could glutamate have a inhibitory response despite being a major excitatory neurotransmitter
its response at metabotropic glutamate receptors
which receptor controls a channel permeable to Na+, Ca2+ and K+
NMDA
what are the non- NMDA ionotropic receptors and how quickly do they elicit a response
AMPA and Kainate
mediate fast excitatory synaptic transmission in the CNS
how quickly does NMDA elicit a response
NMDA contributes a slow component to the excitatory synaptic potential.
what does NMDA have a high permeability to
Ca2+ hence thought to promote neurotoxicity
metabotropic glutamate receptors dont have an integral ion channel, how do they exert their effect
by activation of a second messenger cascade
what is the main inhibitory neurotransmitter
GABA
what are the two receptors GABA acts on
Ionotropic GABAa receptor that operates a Cl- channel
GABAb a metabotropic receptors, often activates a potassium channel
how do benzodiazepines work
positive allosteric modulator of GABAa receptor so enhance Cl entry, decreasing the rmp, enhancing inhibition in presence of GABA
how do barbiturates work
positive allosteric modulator of GABAa, enhances Cl- entry, lowering rmp, enhancing inhibition in presence of GABA
how does Baclofen work
agonist of GABAb receptor, enhances K current increasing inhibition
what type of neurotransmitter is glycine and how does it act
inhibitory
acts on glycine ionotropic receptor that gates Cl- channel. released by interneurones in spinal cord to inhibit antagonist muscles motoneurones.
ionotropic gating of ions is what
rapid
metabotropic gating is what
slower
slow actions of metabotrobic receptors are not sufficient to trigger an action potential rather they what
they have a modulatory synaptic action
how do metabotropic modulate synaptic action
acting on channels in the presynaptic terminal to modulate transmitter release
modulating transmitter-gated channels to regulate the size of the post synaptic potential
modulate the resting and voltage-gated ion channels in the neuronal soma to alter e.g. resting Em and AP firing pattern
cholinergic synaptic transmission in autonomic ganglia display both what
direct and indirect transmitter actions
what is fast excitatory post synaptic potential (EPSP) due to
the activation of nicotinic (ionotropic) Ach receptors. Channels conduct Na+ and K+
what does slow EPSP follow
it follows the activation of muscarinic (G protein coupled) Ach receptors. Ach closes a K+ channel (M-type)
EPSP meaning
(Excitatory postsynaptic potential)
Depolarizing change in rmp caused by the actions of excitatory neurotransmission. Multiple ESPSs or very large ESPSs can cause rmp to cross threshold and result in an action potential
IPSP meaning
(Inhibitory postsynaptic potential)
negative change in rmp caused by release of an inhibitory neurotransmitter. Inhibits crossing of the threshold and inhibits AP.
Graded potential meaning
a change in the rmp caused by an EPSP or IPSP, such a change is caused by (inhibitory or excitatory) neurotransmitter release and is not of a magnitude large enough to cross threshold in an AP
If a graded potential does not go beyond the threshold at the trigger zone, what happens
an action potential will not be generated
what is an interneurone
a locally-acting neurone, typically releases GABA ad so brings about an IPSP and inhibition, function is locally processing of information
