Central Synapses Flashcards
The synaptic terminals of exc. and inh. neurons can be distinguished by their…
Ultrastructure.
Type I synapses have what effect?
Excitatatory.
Type II synapses have what effect?
Inhibitory.
Type I synapse structure:
Round vesicles, electron dense regions on presynaptic (active zones) and postsynaptic (postsynaptic density) membranes. Postsynaptic density even larger. Gives asymmetric appearance.
Type II synapse structure:
Oval/flattened vesicles, less obvious pre and postsynaptic specialisations. More symmetric.
Where are excitatory synapses?
Mostly axodendritic, occuring mostly on dendritic spines.
Where are inhibitory synapses?
Dendritic shafts, the cell body, and axon initial segment.
How is fast excitatory transmission terminated?
Glu diffuses out of cleft, reuptake by astrocytes, convert to glutamine. Glutamine taken up by neurons.
Why does GABAa opening generally lead to hyperpolarisation?
Cl- equilibrium potential negative to RMP.
How is GABA removed from extracellular fluid?
GABA transporters (GATs).
How do benzodiazapines act on GABAa receptors?
Increase the total conduction of Cl- across the neuronal cell membrane when GABA is already bound to its receptor.
The decision of whether AP depends on spatial and temporal summation of excitatory and inhibitory inputs at the …
Axon initial segment.
How does reduction of cAMP lead to reduced excitability?
Less activation of protein kinase A (PKA), decreased ion channel phosphorylation, reduces their activity.
What presynaptic GluR acts as an autoreceptor?
mGluR2.
How does presynaptic mGluR2 exert its effect?
Inhibition of adenylyl cyclase, reduction of cAMP, suppressed Ca2+ channel activity, less Glu release.
mGluR2 acts as a negative feedback mechanism to…
Protect neurons from excitotoxicity.
How do presynaptic (metabotropic) GABAb receptors exert their autoreceptor effect?
Inhibition of adenylyl cyclase, reduced cAMP etc.
How do postsynaptic (metabotropic) GABAb receptors exert their effect?
Activate GIRKs, hyperpolarises.
Where are postsynaptic GABAb found?
On motor neurons in the spinal cord.
What drug highlights the role of postsynaptic GABAb receptors?
Baclofen, GABAb antagonist, used as muscle relaxant in spasticity treatment.
Why does signalling via metabotropic receptors take onger?
Trigger a second messenger response that requires multiple proteins to interact with each other in a sequential order.
Inhibitory mAChRs are coupled to what G protein? Postsynaptic reduction of cAMP.
Gi.
Where are M2 (Gi coupled) mAChRs? What do they do?
Found in heart, mediate bradycardia.
Where are M4 (Gi coupled) mAChRs? What do they do?
CNS, particularly striatum, regulate dopaminergic transmission, implicated in PD.
