<s>
Postsynaptic	B-Algorithm
potentials	I-Algorithm
are	O
changes	O
in	O
the	O
membrane	O
potential	O
of	O
the	O
postsynaptic	O
terminal	O
of	O
a	O
chemical	O
synapse	B-Application
.	O
</s>
<s>
Postsynaptic	B-Algorithm
potentials	I-Algorithm
are	O
graded	B-Algorithm
potentials	I-Algorithm
,	O
and	O
should	O
not	O
be	O
confused	O
with	O
action	B-Algorithm
potentials	I-Algorithm
although	O
their	O
function	O
is	O
to	O
initiate	O
or	O
inhibit	O
action	B-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
They	O
are	O
caused	O
by	O
the	O
presynaptic	O
neuron	O
releasing	O
neurotransmitters	O
from	O
the	O
terminal	O
bouton	O
at	O
the	O
end	O
of	O
an	O
axon	B-Algorithm
into	O
the	O
synaptic	O
cleft	O
.	O
</s>
<s>
This	O
is	O
an	O
excitatory	O
postsynaptic	B-Algorithm
potential	I-Algorithm
(	O
EPSP	O
)	O
,	O
as	O
it	O
brings	O
the	O
neuron	O
's	O
potential	O
closer	O
to	O
its	O
firing	O
threshold	O
(	O
about	O
−55mV	O
)	O
.	O
</s>
<s>
This	O
is	O
an	O
inhibitory	O
postsynaptic	B-Algorithm
potential	I-Algorithm
(	O
IPSP	O
)	O
,	O
as	O
it	O
changes	O
the	O
charge	O
across	O
the	O
membrane	O
to	O
be	O
further	O
from	O
the	O
firing	O
threshold	O
.	O
</s>
<s>
EPSPs	O
and	O
IPSPs	O
are	O
transient	O
changes	O
in	O
the	O
membrane	O
potential	O
,	O
and	O
EPSPs	O
resulting	O
from	O
transmitter	O
release	O
at	O
a	O
single	O
synapse	B-Application
are	O
generally	O
far	O
too	O
small	O
to	O
trigger	O
a	O
spike	B-Algorithm
in	O
the	O
postsynaptic	O
neuron	O
.	O
</s>
<s>
However	O
,	O
a	O
neuron	O
may	O
receive	O
synaptic	O
inputs	O
from	O
hundreds	O
,	O
if	O
not	O
thousands	O
,	O
of	O
other	O
neurons	O
,	O
with	O
varying	O
amounts	O
of	O
simultaneous	O
input	O
,	O
so	O
the	O
combined	O
activity	O
of	O
afferent	O
neurons	O
can	O
cause	O
large	O
fluctuations	O
in	O
membrane	O
potential	O
or	O
subthreshold	B-Algorithm
membrane	I-Algorithm
potential	I-Algorithm
oscillations	I-Algorithm
.	O
</s>
<s>
If	O
the	O
postsynaptic	O
cell	O
is	O
sufficiently	O
depolarized	O
,	O
an	O
action	B-Algorithm
potential	I-Algorithm
will	O
occur	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
low-threshold	B-Algorithm
spikes	I-Algorithm
depolarizations	O
by	O
the	O
T-type	O
calcium	O
channel	O
occur	O
at	O
low	O
,	O
negative	O
,	O
membrane	O
depolarizations	O
resulting	O
in	O
the	O
neuron	O
reaching	O
the	O
threshold	O
.	O
</s>
<s>
Action	B-Algorithm
potentials	I-Algorithm
are	O
not	O
graded	O
;	O
they	O
are	O
all-or-none	O
responses	O
.	O
</s>
<s>
Postsynaptic	B-Algorithm
potentials	I-Algorithm
begin	O
to	O
be	O
terminated	O
when	O
the	O
neurotransmitter	O
detaches	O
from	O
its	O
receptor	O
.	O
</s>
<s>
Postsynaptic	B-Algorithm
potentials	I-Algorithm
are	O
subject	O
to	O
summation	O
,	O
spatially	O
and/or	O
temporally	O
.	O
</s>
<s>
Spatial	O
summation	O
:	O
If	O
a	O
cell	O
is	O
receiving	O
input	O
at	O
two	O
synapses	B-Application
that	O
are	O
near	O
each	O
other	O
,	O
their	O
postsynaptic	B-Algorithm
potentials	I-Algorithm
add	O
together	O
.	O
</s>
<s>
If	O
the	O
cell	O
is	O
receiving	O
two	O
excitatory	O
postsynaptic	B-Algorithm
potentials	I-Algorithm
,	O
they	O
combine	O
so	O
that	O
the	O
membrane	O
potential	O
is	O
depolarized	O
by	O
the	O
sum	O
of	O
the	O
two	O
changes	O
.	O
</s>
<s>
If	O
the	O
cell	O
is	O
receiving	O
both	O
inhibitory	O
and	O
excitatory	O
postsynaptic	B-Algorithm
potentials	I-Algorithm
,	O
they	O
can	O
cancel	O
out	O
,	O
or	O
one	O
can	O
be	O
stronger	O
than	O
the	O
other	O
,	O
and	O
the	O
membrane	O
potential	O
will	O
change	O
by	O
the	O
difference	O
between	O
them	O
.	O
</s>
<s>
Temporal	O
summation	O
:	O
When	O
a	O
cell	O
receives	O
inputs	O
that	O
are	O
close	O
together	O
in	O
time	O
,	O
they	O
are	O
also	O
added	O
together	O
,	O
even	O
if	O
from	O
the	O
same	O
synapse	B-Application
.	O
</s>
<s>
Thus	O
,	O
if	O
a	O
neuron	O
receives	O
an	O
excitatory	O
postsynaptic	B-Algorithm
potential	I-Algorithm
,	O
and	O
then	O
the	O
presynaptic	O
neuron	O
fires	O
again	O
,	O
creating	O
another	O
EPSP	O
,	O
then	O
the	O
membrane	O
of	O
the	O
postsynaptic	O
cell	O
is	O
depolarized	O
by	O
the	O
total	O
of	O
the	O
EPSPs	O
.	O
</s>
