<s>
The	O
Purkinje	B-Algorithm
fibers	I-Algorithm
(	O
;	O
often	O
incorrectly	O
;	O
Purkinje	O
tissue	O
or	O
subendocardial	B-Algorithm
branches	I-Algorithm
)	O
are	O
located	O
in	O
the	O
inner	O
ventricular	O
walls	O
of	O
the	O
heart	O
,	O
just	O
beneath	O
the	O
endocardium	O
in	O
a	O
space	O
called	O
the	O
subendocardium	O
.	O
</s>
<s>
The	O
Purkinje	B-Algorithm
fibers	I-Algorithm
are	O
specialized	O
conducting	O
fibers	O
composed	O
of	O
electrically	O
excitable	O
cells	O
.	O
</s>
<s>
They	O
conduct	O
cardiac	B-Algorithm
action	I-Algorithm
potentials	I-Algorithm
more	O
quickly	O
and	O
efficiently	O
than	O
any	O
of	O
the	O
other	O
cells	O
in	O
the	O
heart	O
's	O
electrical	B-Algorithm
conduction	I-Algorithm
system	I-Algorithm
.	O
</s>
<s>
Purkinje	B-Algorithm
fibers	I-Algorithm
allow	O
the	O
heart	O
's	O
conduction	B-Algorithm
system	I-Algorithm
to	O
create	O
synchronized	B-Algorithm
contractions	I-Algorithm
of	O
its	O
ventricles	O
,	O
and	O
are	O
essential	O
for	O
maintaining	O
a	O
consistent	O
heart	B-Algorithm
rhythm	I-Algorithm
.	O
</s>
<s>
Purkinje	B-Algorithm
fibers	I-Algorithm
are	O
a	O
unique	O
cardiac	O
end-organ	O
.	O
</s>
<s>
The	O
electrical	O
origin	O
of	O
atrial	O
Purkinje	B-Algorithm
fibers	I-Algorithm
arrives	O
from	O
the	O
sinoatrial	O
node	O
.	O
</s>
<s>
Given	O
no	O
aberrant	O
channels	O
,	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
are	O
distinctly	O
shielded	O
from	O
each	O
other	O
by	O
collagen	O
or	O
the	O
cardiac	O
skeleton	O
.	O
</s>
<s>
The	O
Purkinje	B-Algorithm
fibers	I-Algorithm
are	O
further	O
specialized	O
to	O
rapidly	O
conduct	O
impulses	O
(	O
having	O
numerous	O
fast	O
voltage-gated	O
sodium	O
channels	O
and	O
mitochondria	O
,	O
and	O
fewer	O
myofibrils	O
,	O
than	O
the	O
surrounding	O
muscle	O
tissue	O
)	O
.	O
</s>
<s>
Purkinje	B-Algorithm
fibers	I-Algorithm
take	O
up	O
stain	O
differently	O
from	O
the	O
surrounding	O
muscle	O
cells	O
because	O
of	O
having	O
relatively	O
fewer	O
myofibrils	O
than	O
other	O
cardiac	O
cells	O
.	O
</s>
<s>
The	O
presence	O
of	O
glycogen	O
around	O
the	O
nucleus	O
causes	O
Purkinje	B-Algorithm
fibers	I-Algorithm
to	O
appear	O
,	O
on	O
a	O
slide	O
,	O
lighter	O
and	O
larger	O
than	O
their	O
neighbors	O
,	O
being	O
arranged	O
along	O
the	O
longitudinal	O
direction	O
(	O
parallel	O
to	O
the	O
cardiac	O
vector	O
)	O
.	O
</s>
<s>
The	O
Purkinje	B-Algorithm
fibers	I-Algorithm
do	O
not	O
have	O
any	O
known	O
role	O
in	O
setting	O
heart	O
rate	O
unless	O
the	O
SA	O
node	O
is	O
compromised	O
(	O
when	O
they	O
can	O
act	O
as	O
pacemaker	B-Algorithm
cells	O
)	O
.	O
</s>
<s>
During	O
the	O
ventricular	O
contraction	O
portion	O
of	O
the	O
cardiac	O
cycle	O
,	O
the	O
Purkinje	B-Algorithm
fibers	I-Algorithm
carry	O
the	O
contraction	O
impulse	O
from	O
both	O
the	O
left	O
and	O
right	O
bundle	O
branch	O
to	O
the	O
myocardium	O
of	O
the	O
ventricles	O
.	O
</s>
<s>
Purkinje	B-Algorithm
fibers	I-Algorithm
also	O
have	O
the	O
ability	O
of	O
firing	O
at	O
a	O
rate	O
of	O
20	O
–	O
40	O
beats	O
per	O
minute	O
if	O
upstream	O
conduction	B-Algorithm
or	O
pacemaking	O
ability	O
is	O
compromised	O
.	O
</s>
<s>
In	O
short	O
,	O
they	O
generate	O
action	B-Algorithm
potentials	I-Algorithm
,	O
but	O
at	O
a	O
slower	O
rate	O
than	O
the	O
sinoatrial	O
node	O
.	O
</s>
<s>
When	O
a	O
Purkinje	B-Algorithm
fiber	I-Algorithm
does	O
fire	O
,	O
it	O
is	O
called	O
a	O
premature	B-Error_Name
ventricular	I-Error_Name
contraction	I-Error_Name
or	O
PVC	O
,	O
or	O
in	O
other	O
situations	O
can	O
be	O
a	O
ventricular	O
escape	O
.	O
</s>
<s>
Purkinje	B-Algorithm
fibers	I-Algorithm
are	O
named	O
after	O
the	O
Czech	O
scientist	O
Jan	O
Evangelista	O
Purkyně	O
,	O
who	O
discovered	O
them	O
in	O
1839	O
.	O
</s>
