• The diversity of the receptor conductance depending on the dimeric
composition
• The biophysical properties of the PSD
2.2 Extrasynaptic factors of the EPSP variability
By looking just outside the restricted synaptic space, several other factors can
influence the EPSP formation. In short we can say that, according to Eqs. (1) and
(2), any factor which can influence the membrane potential in the proximity of the
synapse can play a role in shaping the EPSP. The first important structure that we
found outside of the synaptic space is the neck of the spine. It is the communication
way between the synapse and the dendrite, and its electrical resistance determines
the amount of information passed to the cell (dendrite). The value of the neck
resistance is, then, crucial for the flow of information among different areas of the
dendrites and the soma. Spine morphology is variable, and consequently its bioelectric properties [62, 67, 68, 70] and the presence of voltage-gated channels can
further influence its ability to transfer the synaptic information [70]. According to
some authors, the neck diameter and resistance are modulated also during a single
synaptic event [62, 63, 67]. Modulation of the neck resistance produces, as a consequence, a modulation of the EPSP transmitted to the soma. However, the neck does
not only carry the synaptic information to the dendrite. It acts also in the opposite
direction by carrying the information on the state of dendrite to the PSD. In other
words, the PSD is kept informed of the information arriving from other synapses
located in the proximity. Dendritic activity, in fact, producing a difference of
potential between the dendrite and the head of the spine, produces a net current,
the direction of which depends on the difference of potential between the two
structures. The current arriving from the dendrite is essentially amplified by the
high input impedance of the PSD influencing strongly the total EPSP and the
Figure 3.
Simulation of EPSP during dendritic activity produced by different firing frequencies of excitatory and
inhibitory synapses. Depending on the firing frequencies of the other synapses located in the proximity, the
membrane voltage under the spine has different amplitude and types of oscillation. The phase and the level of
oscillation at the moment of the EPSP start, modulate the amplitude its amplitude and time course. In these
simulations the EPSP occurred always at 600 ms. The black line is the time course of the membrane potential if
no dendritic activity is present, and hence it is constant at the resting level (À65 mV).
99
Information Processing and Synaptic Transmission
DOI: http://dx.doi.org/10.5772/intechopen.88405
composition
• The biophysical properties of the PSD
2.2 Extrasynaptic factors of the EPSP variability
By looking just outside the restricted synaptic space, several other factors can
influence the EPSP formation. In short we can say that, according to Eqs. (1) and
(2), any factor which can influence the membrane potential in the proximity of the
synapse can play a role in shaping the EPSP. The first important structure that we
found outside of the synaptic space is the neck of the spine. It is the communication
way between the synapse and the dendrite, and its electrical resistance determines
the amount of information passed to the cell (dendrite). The value of the neck
resistance is, then, crucial for the flow of information among different areas of the
dendrites and the soma. Spine morphology is variable, and consequently its bioelectric properties [62, 67, 68, 70] and the presence of voltage-gated channels can
further influence its ability to transfer the synaptic information [70]. According to
some authors, the neck diameter and resistance are modulated also during a single
synaptic event [62, 63, 67]. Modulation of the neck resistance produces, as a consequence, a modulation of the EPSP transmitted to the soma. However, the neck does
not only carry the synaptic information to the dendrite. It acts also in the opposite
direction by carrying the information on the state of dendrite to the PSD. In other
words, the PSD is kept informed of the information arriving from other synapses
located in the proximity. Dendritic activity, in fact, producing a difference of
potential between the dendrite and the head of the spine, produces a net current,
the direction of which depends on the difference of potential between the two
structures. The current arriving from the dendrite is essentially amplified by the
high input impedance of the PSD influencing strongly the total EPSP and the
Figure 3.
Simulation of EPSP during dendritic activity produced by different firing frequencies of excitatory and
inhibitory synapses. Depending on the firing frequencies of the other synapses located in the proximity, the
membrane voltage under the spine has different amplitude and types of oscillation. The phase and the level of
oscillation at the moment of the EPSP start, modulate the amplitude its amplitude and time course. In these
simulations the EPSP occurred always at 600 ms. The black line is the time course of the membrane potential if
no dendritic activity is present, and hence it is constant at the resting level (À65 mV).
99
Information Processing and Synaptic Transmission
DOI: http://dx.doi.org/10.5772/intechopen.88405