Synapses and neurotransmitters 2 Flashcards
What is the criteria for a neurotransmitter?
Present in synaptic vesicles
Released in response to stimulation
Act on the post synaptic neuron
What does blocking the neurotransmitter prevent?
Synaptic transmission
What are 3 classes of neurotransmitter?
Amino acids
Amines
Peptides
What do peptide releasing hormones also sometimes release?
A small molecule transmitter called a ‘co-transmitter’
What can amino acids and amine neurotransmitters bind to?
Ligand gated ion channels
G protein coupled receptors
What can peptide neurotransmitters bind to?
G protein coupled receptors
Where are amino acids and amine neurotransmitters stored?
In synaptic vesicles
Where are peptide neurotransmitters stored?
Secretory granules
What is a ionotropic receptor?
Ligand gated ion channels that directly depolarise or hyperpolarise the postsynaptic cell
What is a metabotropic receptor?
G protein coupled receptor which can produce second messengers and cause biochemical changes throughout the cell
Is glutamate an excitatory or inhibitory neurotransmitter?
An excitatory
Where is Glutamate found?
In CNS, in all neurons
How is glutamate action terminated?
Selective reuptake into presynaptic terminals and glia
What are the 3 ionotropic receptors glutamate can act on?
AMPA
NMDA
Kainate
What does glutamate binding to AMPA receptors trigger?
Na+ and K+ currents, resulting in an EPSP
What do NMDA receptors often co exist with?
AMPA receptors
When do NMDA receptors open?
When the cell is already depolarised
- due to voltage dependent Mg2+ block
What ion is NMDA permeable to ?
Ca2+ ions
What is a coincidence factor?
A neuron that is activated right after a previous activation
What is the mechanism for a metabotropic glutamate receptors?
Activates G proteins which triggers a downstream signalling cascade
What is the consequence of mGluRs?
Allow glutamate to be inhibitory once G proteins are activated
Glutamic acid + Glutamic acid decarboxylase -> ?
Glutamate
How is GABA action terminated?
Selective uptake into presynaptic terminals and glia
What is the most common inhibitory transmitter in CNS?
GABA
What will GABA produce if the membrane potential is above chloride’s Nernst potential?
IPSPs via GABA A receptors
What would occur in the event of too little GABA inhibition?
Seizures
What would occur in the even of too much GABA inhibition?
Come or loss of consiousness
What are the downstream effects of GABA + GABA receptor?
Chloride channels open
Membrane potential gets closer to chloride Nernst potential
What is an allosteric drug?
A drug which has no effect without binding
Name 4 allosteric drugs which modulate GABA A receptors
Ethanol
Benzodiazepine
Barbiturates
Neurosteroids
Describe the function of GABA B receptor.
Open K+ channels
Close Ca2+ channels
Trigger other second messengers (cAMP)
Function of glycine?
Inhibits neurons via glycine gated chloride channels
Binds NDMA to glutamate receptors
Describe dendritic integration
Neurons receive inhibitory or excitatory signals on dendrites ->
EPSP is produced and propagates along the dendrite and arrive at the soma ->
Axon initial segment initiates the ap ->
The ap is actively regenerated and sent down the axon
When wont GABA A produce a IPSP?
If Vm is near the chloride Nernst potential
If GABA A receptors cant produce an IPSP, how do they act?
Via shunting inhibition
What is shunting inhibition?
Opening chloride conductance which decreases the membrane and the current is able to leak out
Describe presynaptic inhibition
Action potential arrives at the presynaptic terminal ->
At the same time, an ap arrives at presynaptic terminal of GABAergic neuron. GABA released onto neuron activates GABA B receptors which inactivated calcium channels ->
Less calcium binding means less neurotransmitter released ->
Causes a reduced effect on the postsynaptic neuron
What is the purpose of inhibition?
Organisation of neurons
If AMPA receptors are permeable to both Na+ and K+, why does activating them cause depolarisation?
Na+ flow into the cell whereas only a few K+ leave the neuron, causing an overall depolarisation.
What would happen if GABA open GABA A receptors and the membrane potential is below chloride’s Nernst potential?
The membrane would depolarisation
- Net outflow of chloride ions
