SYNAPSES AND THE ROLE OF NEUROTRANSMITTERS Flashcards
What are the two types of synapses?
Electrical (gap junction)
Chemical
Give 5 features of an electrical synapse
- Fast
- Bi-directional
- Glial - glial or glial - neurone transmission
- Communication between neurones in the CNS rare
- Direct transfer of ionic current
Explain a chemical synapse
- Nt released from presynaptic membrane
- NT diffuse across synaptic cleft
- NT binds to receptors on post synaptic membrane
Explain the two ways signals are terminated in a chemical synapse
- NT reuptake - goes back to Pre synaptic terminal and is taken up by vesicles
- Enzymatic breakdown of NT
Explain the NMJ
- Stimulus causes depolarisation
- Depolarisation results in V.G Na+ channels opening and Na+ entering cell
- Depolarisation causes voltage-gated Ca2+ ion channels to open
- Influx of Ca2+ into the cell
- Triggers exocytosis
- Vesicles containing NT fuse with PSM
- NT released and diffuses across synaptic cleft
- Binds to receptors on muscle cell membrane - depolarises membrane
- Rapid termination of signal
Name the major excitatory NT in the nervous system and the major inhibitory NT
- Excitatory = Glutamate
- Inhibitory = GABA
Explain the IONOTROPIC receptor signalling mechanism
- Receptor operated/ Ligand gated channels
- Neurotransmitter binds to a channel
- Channel undergoes a conformational change
- Change results in channel opening and NT being released
Explain the METABOTROPIC receptor signalling mechanism
- G protein-coupled receptor
- NT binds to extracellular receptor
- Conformational change
- Intracellular G protein activated
- Activates effector systems
- Has indirect effects e.g channels opening and closing, stimulating or inhibiting enzymes
Example of an ionotropic receptor
Nicotinic acetylcholine receptor
What is the effect when an inotropic receptor is activated?
If it is excitatory then there is a small excitatory postsynaptic potential
If it is inhibitory then there is a small inhibitory postsynaptic potential
2 example of a metabotropic receptor
Muscharinic acetylcholine receptor
GABA
2 example of a metabotropic receptor
Muscharinic acetylcholine receptor
GABA
Definition of spatial summation
Postsynaptic potentials are produced at multiple different synapses. The potentials are then summed together. If they exceed the threshold for an action potential then Na+ voltage-gated ion channels will open for depolarisation
Definition of temporal summation
Temporal looks at the frequency of action potentials fired and sums multiple post-synaptic potentials from the same synapse if they occur in rapid succession
