cardiac AP 2 Flashcards
what are cardiac pacemakers for
to set rhythm of contraction
where is SA node located
right atrial wall
close to superior vena cava
how is SAN different to other muscle cells
smaller
contain fewer myofibrils
fewer intercarlated discs
is SA node the only pacemaker
no
but it is the dominant one
how many AP per minute can SAN generate
100
SAN generate AP subject to regulation by
autonomic nervous system
circulating hormones
healthy adult HR ranges from
60- 100 bpm
what does calcium influx cause in SAN
rapid upstroke
*diff from muscle cells na+ cause rapid upstroke
what happens when SAN repolarize
ca2+ chanel inactivation
k+ chanel activation
AP threshold of SAN between
-40 to -55mV
why SA node peak AP not as steep as cardiac myocytes
lack of stable mb potential
fewer K(ir) channels present thus less negative than in vent. cardiomyocytes
how many phases SAN have
3
phase 4,0,3
how does sodium influx occur in SAN
thru funny channels or HCN channels
when are f type channels active
only when mb potential more negative than -50mV
when does f type channels favour na+ entry
at a negative V(m)
-inward depolarising Na+
