Excitable cells 13: synaptic physiology Flashcards
Purpose of chemical synapses?
Information transfer between cells
- Excitation
- Inhibition
- Modulation
Amplification of signals
Integration of multiple inputs
Plasticity - learning and memory
What is the main feature that determines whether a neurotransmitter has excitatory or inhibitory effects?
The ions associated with the receptor targeted by the neurotransmitter -> causes changes in membrane permeability -> membrane potential
Transmitter opens channels permeable to:
- Na+ or Ca2+ -> ion influx -> excitatory
- K+ -> Ion efflux -> inhibitory
- Cl- -> Ion influx -> inhibitory
Are chloride channels always inhibitory?
if ECl < Vm
- > net influx of Cl-
- > hyperpolarisation
if ECl > Vm
- > net efflux of Cl-
- > depolarisation
Young neurons have higher cytosol conc. of Cl- ions
and higher ECl (-40mV)
-> Cl- in younger neurons excitatory
3 important families of ligand-gates ion channels
- examples
Cys-loop receptors
- Nicotinic acetylcholine
- Glycine
- GABA
- 5HT3
Ionotropic glutamate receptors
- NMDA
- AMPA
- KAINATE
P2X receptors
- P2X1 - P2X7
Which cyc-loop receptors are inhibitory/excitatory? Main structural/chemical difference between these receptors?
Nicotinic acetylcholine + 5HT3 -> Excitatory
- Extracellular domain negative, intracellular negative
- attracts positive ions, repel negative
Glycine + GABA -> Inhibitory
- Extracellular domain positive, intracellular positive
- attract negative ions, repel positive
Why might a mutant Glycine receptor be inhibitory?
Important +charged amino-acid residue domains deleted, or substituted to AAs of opposite polarity
(Positive to negative)
e.g. threonine to valine
- Mutant receptor cation selective
what are EPSPs and how are they caused? Difference to AP?
Excitatory post synaptic potentials
- caused usually by Na+ influx through ligand gated CATION channels
- action potentials caused by Na+ influx through voltage gated Na+ channels
