Biomedical Engineering Reference
In-Depth Information
100
Full model
2 compartments
3 compartments
4 compartments
100
10
10
0.2
0.4
0.8
1.6
0.2
0.4
0.8
1.6
Injected current /
m
A cm
-2
Injected current /
m
A cm
-2
Figure 10.1
Comparison of the firing rate and first-spike latency of the reduced mitral cell models
with the original Bhalla-Bower model. (A) Firing frequency. (B) Time from current
onset to first action potential. From [10] with permission.
were made to convert the model from turtle to rat (see [23]). The model granule cell
responses agreed qualitatively with experimental recordings. The model Golgi cell
was developed just for the network model. In this case, a single-compartment model
was dictated by the lack of morphological reconstructions. Because of insufficient
voltage clamp data the Golgi cell model used the same ion channels as the granule
cell. Ion channel peak conductances were then tuned to give qualitative agreement
with current clamp recordings.
10.3
Synapses
A complete model of synaptic transmission would incorporate calcium release fol-
lowing action potential invasion of the pre-synaptic terminal, vesicle transport dock-
ing, release and recycling, neurotransmitter diffusion and removal from the synaptic
cleft, binding of neurotransmitter, conformational changes of ion channel proteins,
and entry of ions through open channels. A minimal model of synaptic transmis-
sion would consist of a pre-synaptic impulse triggering a step change in membrane
potential in the post-synaptic compartment. An appropriate level of description for
network models is likely to lie between these two extremes. Two common simplifi-
cations of the pre-synaptic mechanism are (i) an AP triggers, after a certain delay, a
square pulse of neurotransmitter at the post-synaptic mechanism; the post-synaptic
current is then affected by the pulse amplitude and duration; (ii) more drastically, a
presynaptic AP triggers a stereotyped post-synaptic response and details of neuro-
transmitter release/diffusion are ignored completely. An excellent discussion of the
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