<s>
End	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
(	O
EPPs	O
)	O
are	O
the	O
voltages	O
which	O
cause	O
depolarization	O
of	O
skeletal	O
muscle	O
fibers	O
caused	O
by	O
neurotransmitters	O
binding	O
to	O
the	O
postsynaptic	O
membrane	O
in	O
the	O
neuromuscular	O
junction	O
.	O
</s>
<s>
When	O
an	O
action	B-Algorithm
potential	I-Algorithm
reaches	O
the	O
axon	O
terminal	O
of	O
a	O
motor	O
neuron	O
,	O
vesicles	O
carrying	O
neurotransmitters	O
(	O
mostly	O
acetylcholine	O
)	O
are	O
exocytosed	O
and	O
the	O
contents	O
are	O
released	O
into	O
the	O
neuromuscular	O
junction	O
.	O
</s>
<s>
In	O
the	O
absence	O
of	O
an	O
action	B-Algorithm
potential	I-Algorithm
,	O
acetylcholine	O
vesicles	O
spontaneously	O
leak	O
into	O
the	O
neuromuscular	O
junction	O
and	O
cause	O
very	O
small	O
depolarizations	O
in	O
the	O
postsynaptic	O
membrane	O
.	O
</s>
<s>
This	O
small	O
response	O
(	O
~	O
0.4mV	O
)	O
is	O
called	O
a	O
miniature	O
end	B-Algorithm
plate	I-Algorithm
potential	I-Algorithm
(	O
MEPP	O
)	O
and	O
is	O
generated	O
by	O
one	O
acetylcholine-containing	O
vesicle	O
.	O
</s>
<s>
In	O
order	O
for	O
a	O
muscle	O
to	O
contract	O
,	O
an	O
action	B-Algorithm
potential	I-Algorithm
is	O
first	O
propagated	O
down	O
a	O
nerve	O
until	O
it	O
reaches	O
the	O
axon	O
terminal	O
of	O
the	O
motor	O
neuron	O
.	O
</s>
<s>
The	O
motor	O
neuron	O
then	O
innervates	O
the	O
muscle	O
fibers	O
to	O
contraction	O
by	O
causing	O
an	O
action	B-Algorithm
potential	I-Algorithm
on	O
the	O
postsynaptic	O
membrane	O
of	O
the	O
neuromuscular	O
junction	O
.	O
</s>
<s>
End	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
are	O
produced	O
almost	O
entirely	O
by	O
the	O
neurotransmitter	O
acetylcholine	O
in	O
skeletal	O
muscle	O
.	O
</s>
<s>
There	O
are	O
two	O
types	O
of	O
ion	O
channels	O
involved	O
in	O
the	O
neuromuscular	O
junction	O
and	O
end	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
:	O
voltage-gated	O
ion	O
channel	O
and	O
ligand-gated	O
ion	O
channel	O
.	O
</s>
<s>
When	O
an	O
action	B-Algorithm
potential	I-Algorithm
propagates	O
down	O
a	O
nerve	O
and	O
reaches	O
the	O
axon	O
terminal	O
of	O
the	O
motor	O
neuron	O
,	O
the	O
change	O
in	O
membrane	O
voltage	O
causes	O
the	O
calcium	O
voltage	O
gated	O
ion	O
channels	O
to	O
open	O
allowing	O
for	O
an	O
influx	O
of	O
calcium	O
ions	O
.	O
</s>
<s>
These	O
receptors	O
are	O
slow	O
and	O
therefore	O
are	O
unable	O
to	O
measure	O
a	O
miniature	O
end	B-Algorithm
plate	I-Algorithm
potential	I-Algorithm
(	O
MEPP	O
)	O
.	O
</s>
<s>
When	O
an	O
action	B-Algorithm
potential	I-Algorithm
propagates	O
down	O
the	O
motor	O
neuron	O
axon	O
and	O
arrives	O
at	O
the	O
axon	O
terminal	O
,	O
it	O
causes	O
a	O
depolarization	O
of	O
the	O
axon	O
terminal	O
and	O
opens	O
calcium	O
channels	O
.	O
</s>
<s>
The	O
vesicles	O
release	O
their	O
entire	O
quantity	O
of	O
acetylcholine	O
and	O
this	O
causes	O
miniature	O
end	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
(	O
MEPPs	O
)	O
to	O
occur	O
which	O
are	O
less	O
than	O
1mV	O
in	O
amplitude	O
and	O
not	O
enough	O
to	O
reach	O
threshold	O
.	O
</s>
<s>
Miniature	O
end	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
are	O
the	O
small	O
(	O
~	O
0.4mV	O
)	O
depolarizations	O
of	O
the	O
postsynaptic	O
terminal	O
caused	O
by	O
the	O
release	O
of	O
a	O
single	O
vesicle	O
into	O
the	O
synaptic	O
cleft	O
.	O
</s>
<s>
These	O
small	O
depolarizations	O
are	O
not	O
enough	O
to	O
reach	O
threshold	O
and	O
so	O
an	O
action	B-Algorithm
potential	I-Algorithm
in	O
the	O
postsynaptic	O
membrane	O
does	O
not	O
occur	O
.	O
</s>
<s>
During	O
experimentation	O
with	O
MEPPs	O
,	O
it	O
was	O
noticed	O
that	O
often	O
spontaneous	O
action	B-Algorithm
potentials	I-Algorithm
would	O
occur	O
,	O
called	O
end	O
plate	O
spikes	B-Algorithm
in	O
normal	O
striated	O
muscle	O
without	O
any	O
stimulus	O
.	O
</s>
<s>
It	O
was	O
believed	O
that	O
these	O
end	O
plate	O
spikes	B-Algorithm
occurred	O
as	O
a	O
result	O
of	O
injury	O
or	O
irritation	O
of	O
the	O
muscles	O
fibers	O
due	O
to	O
the	O
electrodes	O
.	O
</s>
<s>
Recent	O
experiments	O
have	O
shown	O
that	O
these	O
end	O
plate	O
spikes	B-Algorithm
are	O
actually	O
caused	O
by	O
muscle	O
spindles	O
and	O
have	O
two	O
distinct	O
patterns	O
:	O
small	O
and	O
large	O
.	O
</s>
<s>
Small	O
end	O
plate	O
spikes	B-Algorithm
have	O
a	O
negative	O
onset	O
without	O
signal	O
propagation	O
and	O
large	O
end	O
plate	O
spikes	B-Algorithm
resemble	O
motor	O
unit	O
potentials	O
(	O
MUPs	O
)	O
.	O
</s>
<s>
When	O
an	O
action	B-Algorithm
potential	I-Algorithm
causes	O
the	O
release	O
of	O
many	O
acetylcholine	O
vesicles	O
,	O
acetylcholine	O
diffuses	O
across	O
the	O
neuromuscular	O
junction	O
and	O
binds	O
to	O
ligand-gated	O
nicotinic	O
receptors	O
(	O
non-selective	O
cation	O
channels	O
)	O
on	O
the	O
muscle	O
fiber	O
.	O
</s>
<s>
The	O
small	O
depolarization	O
associated	O
with	O
the	O
release	O
of	O
acetylcholine	O
from	O
an	O
individual	O
synaptic	O
vesicle	O
is	O
called	O
a	O
miniature	O
end-plate	B-Algorithm
potential	I-Algorithm
(	O
MEPP	O
)	O
,	O
and	O
has	O
a	O
magnitude	O
of	O
about	O
+	O
0.4mV	O
.	O
</s>
<s>
MEPPs	O
are	O
additive	O
,	O
eventually	O
increasing	O
the	O
end-plate	B-Algorithm
potential	I-Algorithm
(	O
EPPs	O
)	O
from	O
about	O
-100mV	O
up	O
to	O
the	O
threshold	O
potential	O
of	O
-60mV	O
,	O
at	O
which	O
level	O
the	O
voltage-gated	O
ion	O
channels	O
in	O
the	O
postsynaptic	O
membrane	O
open	O
,	O
allowing	O
a	O
sudden	O
flow	O
of	O
sodium	O
ions	O
from	O
the	O
synapse	O
and	O
a	O
sharp	O
spike	B-Algorithm
in	O
depolarization	O
.	O
</s>
<s>
This	O
depolarization	O
voltage	O
spike	B-Algorithm
triggers	O
an	O
action	B-Algorithm
potential	I-Algorithm
which	O
propagates	O
down	O
the	O
postsynaptic	O
membrane	O
leading	O
to	O
muscle	O
contraction	O
.	O
</s>
<s>
It	O
is	O
important	O
to	O
note	O
that	O
EPPs	O
are	O
not	O
action	B-Algorithm
potentials	I-Algorithm
,	O
but	O
that	O
they	O
trigger	O
action	B-Algorithm
potentials	I-Algorithm
.	O
</s>
<s>
Once	O
the	O
membrane	O
potential	O
reaches	O
threshold	O
,	O
an	O
action	B-Algorithm
potential	I-Algorithm
occurs	O
and	O
causes	O
a	O
sharp	O
spike	B-Algorithm
in	O
membrane	O
polarity	O
.	O
</s>
<s>
There	O
are	O
five	O
phases	O
of	O
an	O
action	B-Algorithm
potential	I-Algorithm
:	O
threshold	O
,	O
depolarization	O
,	O
peak	O
,	O
repolarization	O
,	O
and	O
hyperpolarization	O
.	O
</s>
<s>
It	O
gradually	O
returns	O
to	O
resting	O
potential	O
and	O
is	O
ready	O
for	O
another	O
action	B-Algorithm
potential	I-Algorithm
to	O
occur	O
.	O
</s>
<s>
During	O
the	O
action	B-Algorithm
potential	I-Algorithm
before	O
the	O
hyperpolarization	O
phase	O
,	O
the	O
membrane	O
is	O
unresponsive	O
to	O
any	O
stimulation	O
.	O
</s>
<s>
This	O
inability	O
to	O
induce	O
another	O
action	B-Algorithm
potential	I-Algorithm
is	O
known	O
as	O
the	O
absolute	O
refractory	O
period	O
.	O
</s>
<s>
During	O
the	O
hyperpolarization	O
period	O
,	O
the	O
membrane	O
is	O
again	O
responsive	O
to	O
stimulations	O
but	O
it	O
requires	O
a	O
much	O
higher	O
input	O
to	O
induce	O
an	O
action	B-Algorithm
potential	I-Algorithm
.	O
</s>
<s>
Once	O
the	O
action	B-Algorithm
potential	I-Algorithm
has	O
finished	O
in	O
the	O
neuromuscular	O
junction	O
,	O
the	O
used	O
acetylcholine	O
is	O
cleared	O
out	O
of	O
the	O
synaptic	O
cleft	O
by	O
the	O
enzyme	O
acetylcholinesterase	O
.	O
</s>
<s>
Several	O
diseases	O
and	O
problems	O
can	O
be	O
caused	O
by	O
the	O
inability	O
of	O
enzymes	O
to	O
clear	O
away	O
the	O
neurotransmitters	O
from	O
the	O
synaptic	O
cleft	O
leading	O
to	O
continued	O
action	B-Algorithm
potential	I-Algorithm
propagation	O
.	O
</s>
<s>
Current	O
research	O
is	O
attempting	O
to	O
learn	O
more	O
about	O
end	B-Algorithm
plate	I-Algorithm
potentials	I-Algorithm
and	O
their	O
effect	O
on	O
muscle	O
activity	O
.	O
</s>
<s>
Many	O
current	O
diseases	O
involve	O
disrupted	O
end	B-Algorithm
plate	I-Algorithm
potential	I-Algorithm
activity	O
.	O
</s>
<s>
It	O
was	O
found	O
that	O
a	O
combination	O
of	O
the	O
jitter	O
and	O
blocking	O
rate	O
of	O
the	O
acetylcholine	O
receptors	O
caused	O
a	O
reduced	O
end-plate	B-Algorithm
potential	I-Algorithm
similar	O
to	O
what	O
is	O
seen	O
in	O
cases	O
of	O
myasthenia	O
gravis	O
.	O
</s>
<s>
Tetrodotoxin	O
is	O
a	O
poison	O
found	O
in	O
the	O
certain	O
poisonous	O
fishes	O
such	O
as	O
pufferfish	O
and	O
triggerfish	O
which	O
blocks	O
the	O
sodium	O
ion	O
channels	O
and	O
prevents	O
an	O
action	B-Algorithm
potential	I-Algorithm
on	O
the	O
postsynaptic	O
membrane	O
.	O
</s>
