Biomedical Engineering Reference
In-Depth Information
Figure 4. Modes of synaptic integration. A: traditional mechanism based on spatiotemporal summation
of EPSPs and exclusive axonal firing. B: Proposed mechanism based on firing of spikes in dendritic
substations that sum up in the axon. C: Multiplexed language. Both mechanisms may co-exist. Also
burst firing and isolated spikes.
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C
A
out
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to maintain much better the temporal structure
of selected inputs.
Although we advocate for this novel form of
synaptic integration, it certainly does not exclude
the functionality of the traditional mechanism
based on spatiotemporal summation of inputs.
As a matter of fact, the two may operate as a
multiplexed language in the axon (Figure 4).
It is very common that irregularly firing cells
display isolated action potentials mixed up with
occasional burst-like firing. The dendritic origin
of the later has been proven in some cell types.
The mixed patterns should not present any con-
ceptual handicap. Although there is a single axon
stemming out of the soma, most bifurcate one or
several times and/or give off collaterals that con-
tact different cell types in different brain nuclei.
Even if a mixed message gets to different target
cells, the specialized postsynaptic machinery of
each one may be variably tuned to decode the
incoming message and extract the interesting
parts of it, so that only listen to either the bursts
or the isolated action potentials. Thus, what might
be considered input noise in some circuits, may
actually be positive messages in others, all in just
one delivery.
FUTURE RESEARCH DIRECTIONS
Through the chapter we tried to highlight the
importance of getting reliable experimental data
to feed the biophysical models. Small changes in
some parameters that physiologists may not deem
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