Pre-synaptic Function Flashcards
Outline synaptic vesicles
-balls of lipid membrane
-contain a multitude of membrane bound proteins for:
-filling vesicle with neurotransmitter
-docking at presynaptic membrane
-release of neurotrnamsitter
How do neurotransmitters get into vesicles
-transported by proton ‘antiporters’
-an ATPase creates a proton gradient between the inside and the outside of the vesicle
-transporters use this gradient to drive the movement of neurotransmitters into vesicles by coupling the translocation of neurotransmitters
How are neurotransmitters released
Action potentials trigger CA entry into presynaptic terminals, triggering release of neurotransmitters into cleft
Different subtypes of channels- N & P/Q
How is vesicle fusion with the presynaptic membrane mediated
SNARE proteins bring the vesicle closer to the membrane until they fuse with the membrane
-calcium dependent process
Outline the axon initial segment
Action potentials are initiated
Marks the boundary between a neurons somatodendritic and atonal compartments
Contains a very high density of voltage-gated Na channels to enable action potential generation
Where are synapses located
Boutons terminal (end of axons)
En passant boutons (intermediate positions on axons)
What is the probability of release
Probability ranges from 0-1
Not the same at all synapses
-at a single bouton, release probability is not fixed but is dynamic and changed by physiological factors
A high probability means a strong synapse
How can probability be altered
-changing the extracellular Ca concentration
-applying blockers of presynaptic Ca channels
-activating presynaptic receptors that alter Ca channel activity
Outline short term synaptic plasticity
Short lived changes in the strength of synaptic transmission that reflect the prior experience/ activity of the synapse
Dynamic changes in release probability, underpin most forms of short term synaptic plasticity
What do changes in amplitude in synaptic responses mean
A change in the release probability
Low P- exhibit ‘paired pulse facilitation’
High P- exhibit ‘paired pulse depression’
What is the ready releasable pool
Pool of vesicles in the presynaptic terminal released into the synaptic cleft when an actio potential is triggered
Why do we get PPF
few vesicles released, elevated Ca in presynaptic terminal, second stimulus is arriving before previous Ca is cleared away, causing more vesicles being released in the second response
Why do we get PPD
Many vesicles released in first trigger, fewer vesicles remaining for second trigger, less neurotransmitter release and therefore lower amplitude of synaptic response
