referring to the CNS or peripheral nerves as central synapses
are known to exhibit a great deal more variety than peripheral.
The CNS is more my stuff so from now on that's what I'm referrin to.
Where to start? Except from microcurcuits (i.e. dendrodendritic
synapses)the vesicle is transported to the presynaptic axon
terminal, as you wrote. Vesicles themselves exhibit variety in
synaptic position, size, mesh-frame and size.
For example vesicles secreting peptides are generally 80-130nm in
diameter wheras amino acid transmitters are stored in 25-60nm vesicles.
After releasing its contents vesicle membrane is retrogradely
transported up the axon for recycling or disposal. This
"produce and recycle" mechanism could constitute some sort of
vesicle distribution preference. That is, were vesicle production
to be turnover dependent the distribution of vesicles at different
axonal boutons would be affected by that bouton's location on the
As is known, specific sets of axons of one cell interface on a specific
region of the target cell. i.e. synapse contact can be axo-axonic,
axo-somatic or axo-dendritic.
This locational specificity of the pre-synapse to post-synapse interface
allows not only for multiple contact points (think of the large surface
area of the axon, soma and dendrite together and the number of relatively
small axons that can contact it, think 3-D) but also for a variety of
effects after transmitter release.
So with cells having so many inputs it's unlikely that a single synapse
would be capable of firing a cell above AP threshold. Some of the
inputs would be capable of exciting or inhibiting, producing a small
or large effect.
For example a specialized cell in the brain might receive strong
inhibition by multiple synapses at the somal surface,
and weak excitation by multiple synapses at the axon hillock.
Vesicle distribution depends on what it's releasing, where it's
releasing it and where it's come from!
A bit long winded, but I got there,