lecture 4 - claudia racca Flashcards
what are the two types of receptors
ionotropic and metabotropic
what are receptors distinguished by
the NT that they bind to
what are the types of receptors that bind to ACh
muscarinic and nicotinic
what are the types of receptors that bind to glutamate
NMDA
non-NMDA (AMPA and kainate)
what are the types of the receptors that bind to GABA
GABAa
GABAb
etc
what is the main excitatory NT
glutamate
are glutamate receptors (AMPA, NMDA and kainate) ionotropic or metabotropic
ionotropic receptors
How does the NMDA receptor function
At resting membrane potential (~65mV) the receptor is blocked by Mg2+ molecule in the pore.
when the membrane depolarises the Mg2+ moves out of the pore.
The NMDA receptor also requires glycine as well as glutamate to open.
Then calcium and sodium can move in and potassium out.
examples of ionotropic receptors
- ACh nicotinic
- Glutamate (AMPA, NMDA and kainate)
- GABAa
- Glycine receptor
examples of metabotropic receptors
- ACh muscarinic
- Glutamate metabotropic
- GABAb
- 5HT receptor
- Dopamine receptor
- NE receptor
what is an autoreceptor
receptors on the presynaptic membrane
what do autoreceptors do
regulate neurotransmitter synthesis and release
excitatory receptors cause
depolarisation of the post synaptic membrane by sodium moving across the membrane
inhibitory receptors cause
hyperpolarisation of the post synaptic membrane by chloride ions moving across the membrane
how do metabotropic receptors work
they are G protein coupled
how many membrane spanning domains do metabotropic receptors have
7
G protein can also be inhibitory or excitatory
Gs - stimulates effector protein
Gi - inhibits effector protein
two metabotropic effector systems
shortcut (GABAb, mACh)
2nd messenger cascade (NE)
G protein shortcut pathway
ACh binds to the muscarinic receptor and activates the G protein and the alpha subunit which is bound to GTP phosphorylates the potassium channel which will then open.
G protein 2nd messenger cascade pathway
activation of the G protein causes phosphorylation of an enzyme and this causes a signalling cascade
takes longer but creates a stronger response (more channels open)
a single neuron receives thousand of synapses and the inputs may be…
excitatory and inhibitory
these inputs interact to produce a…
synaptic potential
if above threshold the cell will fire an action potential
what are the different types of synapses
axodendritic
axosomatic
axoaxonic
EPSP spatial summation
multiple excitatory synapses coming in to the same dendrite at the same time
causes a large increase in membrane potential
EPSP temporal summation
one synapse on a dendrite but there are multiple APs coming in from the same axon within 1-15ms of each other
the individual EPSEs generated at the same synapse add together.
whether or not an EPSE contributes to the generation of an AP depends on
- number of coactive synapses
- distance of the synapse from the spike initiation zone in the axon
- properties of dendritic membrane
- nature of the synapses (excitatory vs inhibitory)
current is injected into the dendrite and the depolarisation is recorded. as this current spreads down the dendrite, much of it dissipates across the membrane. therefore the depolarisation (EPSP) measured at a distance from the site of current injection is…
smaller than that measured at the site of injection
voltage gated channels are present on dendrites and can…
amplify small EPSPs
inhibitory synapse causes the depolarising current from the excitatory synapse to leak out before it reaches the soma. this is called…
shunting
the effect of NE binding to NE beta receptors
- NE binding to beta receptors activated G protein
- G protein activates the enzyme adenylyl cyclase
- adenylyl cyclase converts ATP –> cAMP
- cAMP activated a protein kinase
- kinase phosphorylates a potassium channel in the dendrite
- phosphorylation causes potassium channel to close
- closure of potassium channels insulates the dendrite, excitable signals spread to soma more easily
