Guide
to
Electrophysiological
Recording
cell,
it
provides
the
voltage
‐
clamp
circuit
with
an
accurate
measure
of
V
m
provided
that
there
is
no
net
current
flow.
Under
normal
conditions
however,
there
is
current
flowing
across
the
membrane
and
this
current
not
only
produces
a
voltage
drop
across
the
membrane
but
also
across
any
resistance
that
is
in
series
with
the
membrane
and
the
system
ground.
These
extraneous
resistances
can
be
lumped
together
as
“series
resistance”
(R
s
).
The
voltage
drop
across
R
s
is
called
the
series
resistance
error
or
bath
error
potential.
The
voltage
drop
across
R
s
causes
the
bath
potential
to
deviate
from
the
zero
current
potential
by
an
amount
directly
proportional
to
the
current
flowing.
Thus,
for
example,
if
you
have
a
series
resistance
of
2
k
Ω
and
a
5
μ
A
peak
current
occurs
during
a
voltage
step,
then
the
peak
membrane
voltage
error
is
10
mV.
For
a
detailed
discussion
of
this
type
of
series
resistance
and
the
methods
used
to
minimize
it,
see
Bath
Error
Potentials
on
page
65.
Selection
of
the
Membrane
Voltage
Recording
Headstage
(CHANNEL
1)
Usually
you
will
use
a
low
‐
noise
type
headstage
for
the
voltage
‐
recording
microelectrode,
as
this
allows
for
some
capacitance
compensation
to
be
applied
if
necessary
while
taking
advantage
of
the
very
low
‐
noise
voltage
recording
characteristics
of
these
headstages.
The
headstages
are
designed
to
be
compact
and
robust
so
that
they
can
be
mounted
on
the
micromanipulator
as
close
as
possible
to
the
recording
point.
This
strategy
greatly
reduces
the
input
capacitance.
For
this
reason,
the
electrode
holders
are
designed
to
plug
directly
into
the
headstage
input.
It
is
recommended
that
you
use
the
simplest
configuration
and
add
more
complex
features
as
the
need
arises.
In
this
case
all
that
is
required
are
two
headstages,
one
for
voltage
(CHANNEL
1)
and
the
other
for
current
passing
(CHANNEL
2).
The
bath
ground
electrode
is
plugged
into
the
ground
jack
on
the
CHANNEL
1
headstage.
101
