Neurotransmitters and Receptors Flashcards
How quickly do neurotransmitters act and why?
Act very quickly by producing fast EPSPs and IPSPs
How fast are the EPSPs and IPSPs produced by neurotransmitters?
Very fast - milliseconds
How quickly do neuromodulators act and what do they act through?
Act slowly through GPCRs
How fast are the EPSPs and IPSPs produced by neuromodulators?
Very slow that last for several hundred millseconds
What two groups can classical neurotransmitters be divided into?
- Excitatory transmitters
2. Inhibitory transmitters
What is an example of an excitatory neurotransmitter?
L-glutamate
What is an example of an inhibitory neurotransmitter?
GABA
What two groups can neuromodulators be divided into?
- Monoamines
2. Neuropeptides
What are three examples of monoamines?
Noradrenaline, dopamine and serotonin
What are two examples of neuropeptides?
Substance P and Enkephalin
What are the criteria that must be satisfied in order to classify something as a neurotransmitter?
- It must be synthesised in the presynaptic neuron
- It must be stored in the presynaptic neuron (high concentrations must be present in the axon terminal)
- It must be be released from the presynaptic terminal
- It must diffuse across the synaptic cleft
- It must have an action of the postynaptic membrane
- It must be inactivated
Where are neurotransmitters stored in the presynaptic membrane?
In vesicles
Where does neurotransmitter synthesis take place?
The the axon terminal/presynaptic element
What is the precursor for acetylcholine and what is the enzyme that converts it to Ach in the axon terminal?
Choline and acetic acid (acetyl coA) are converted to acetylcholine by choline acteyl transferase
Where are neuropeptides synthesised?
In the cell body
What is the precursor for neuropeptides and what happens to these?
They are large polypeptides broken into smaller molecules by enzymes
How are neuropeptides transmitted from the cell body to the axon?
Via anterograde axonal transport
Why are calcium ions important in neurotransmitter release?
Depolarisation of the presynaptic membrane means voltage gated calcium channels open - the calcium ions then enter and initiate transmitter release
How could you block transmitter release to test is a synapse is chemical?
Use magnesium ions instead of calcium ions
What does transmitter release is quantal mean?
It means when one transmitter packet is released one MEPP of a partcular amplitude is sensed at the postynaptic membrane, if two packets are released, the MEPP is twice the amplitude and so on so release is QUANTAL as transmitters are released in uniform packs
What is a MEPP?
A miniature endplate potential
What are the packets that make transmitter release quantal?
A vesicle per MEPP amplitude
Where are autoreceptors found?
On the presynaptic membrane
What do autoreceptors do?
They are activated when the transmitter is released and can influence the release of the transmitter by regulating synthesis
What are the two classes of receptor that neurotransmitters bind?
- Ionotropic receptors (ion channels)
2. Metabotropic (GPCRs)
What happens when a neurotransmitter binds an ionotropic receptor?
Ion channels open and ions pass through - the channel closes when the neurotransmitter leaves the receptor
What is an example of an ionotropic receptor on the postsynaptic membrane?
An acetylcholine nicotinic receptor
What do GPCRs do instead of open ion channels?
Use second messangers like cAMP which go on to do different things including opening the ion channels
How fast do GPCRs operate?
Slowly which is why neuromodulator action is slow
What is an example of a GPCR/metabotropic receptor?
Acetylcholine muscarinic receptor
What other things can second messagners do?
Produce cascades that go on have long-term effects like regulating gene transcription
What three ways lead to the inactivation of the neurotransmitter?
- Broken down by specific enzymes
- Specific uptake (reuptake) by neurons and glial cells
- Diffusion away from synaptic cleft
What is an enzyme that breaks down acetylcholine to inactivate it?
Acetylcholine esterase
