Needle
Electrodes
166
Biomedical Signal and Image Processing
In the preceding relation, G
Max
+
K
is the maximum (peak) conductance, and the time
function n(t) is calculated by the following experimentally designed differential
equation:
dn ( )
t
−V + 10
−V m
= 0 0
. 1
m
(1 − n t
( )) − 0 125
. e 80 n( t) )
(8.18)
dt
⎛ −V +10 ⎞
⎜
m
⎝ e 10 −1 ⎟
⎠
The Hodgkin–Huxley model, described earlier, is known to provide one of the most
reliable estimations of the electric activities of the cell. The exact set of parameters
and constants depend on the exact cell to be modeled. This model is heavily used in
modeling of the electric activities of single neurons as well as the communications
among biological neural networks.
Knowing the mechanism of action potentials both on qualitative and quantitative
levels, now we are ready to discuss how these electric activities are captured using
electrodes.
8.5 ELECTRIC DATA ACQUISITION
Action potentials can be measured with the help of conductors called electrodes.
Such electrodes can be placed in contact with the cell membrane, inside the cell, or
even at the surface of the organ that envelops the sources of action potentials. All
biological media have an ample supply of ions throughout the entire tissue to conduct the currents resulting from electric potentials anywhere in the tissue. Electrodes
measure the potential of every point in the tissue against a ground electrode or even
a conveniently chosen reference point on the body itself.
In experimental as well as research setups, the cellular potential is often measured
by a microelectrode such as popular needle electrodes. In such cases, the relative
electric potential of the inside of the cell with respect to the outside can be measured
as negative values at first (during the rest period) but then flip to a positive values
during depolarization. In a clinical setting, due to the cost as well as the intensive
nature of such electrode, this type of measurements is rarely used. A typical needle
electrode is shown in Figure 8.6.
FIGURE 8.6 Needle electrode.
Electrodes
166
Biomedical Signal and Image Processing
In the preceding relation, G
Max
+
K
is the maximum (peak) conductance, and the time
function n(t) is calculated by the following experimentally designed differential
equation:
dn ( )
t
−V + 10
−V m
= 0 0
. 1
m
(1 − n t
( )) − 0 125
. e 80 n( t) )
(8.18)
dt
⎛ −V +10 ⎞
⎜
m
⎝ e 10 −1 ⎟
⎠
The Hodgkin–Huxley model, described earlier, is known to provide one of the most
reliable estimations of the electric activities of the cell. The exact set of parameters
and constants depend on the exact cell to be modeled. This model is heavily used in
modeling of the electric activities of single neurons as well as the communications
among biological neural networks.
Knowing the mechanism of action potentials both on qualitative and quantitative
levels, now we are ready to discuss how these electric activities are captured using
electrodes.
8.5 ELECTRIC DATA ACQUISITION
Action potentials can be measured with the help of conductors called electrodes.
Such electrodes can be placed in contact with the cell membrane, inside the cell, or
even at the surface of the organ that envelops the sources of action potentials. All
biological media have an ample supply of ions throughout the entire tissue to conduct the currents resulting from electric potentials anywhere in the tissue. Electrodes
measure the potential of every point in the tissue against a ground electrode or even
a conveniently chosen reference point on the body itself.
In experimental as well as research setups, the cellular potential is often measured
by a microelectrode such as popular needle electrodes. In such cases, the relative
electric potential of the inside of the cell with respect to the outside can be measured
as negative values at first (during the rest period) but then flip to a positive values
during depolarization. In a clinical setting, due to the cost as well as the intensive
nature of such electrode, this type of measurements is rarely used. A typical needle
electrode is shown in Figure 8.6.
FIGURE 8.6 Needle electrode.