physiology Flashcards
which phase of the pacemakers action potential sets the heart rate?
phase 4
list the pacemakers from fastest to slowest firing rate
1) Sinoatrial node
2) Atrioventricular node
3) bundle of his
4) Purkinje fibers
if the AV node takes over and becomes the pacemaker of the heart, it is called
ectopic pacemaker, or ectopic focus.
list the myocardial tissues with conduction velocity from fastest to slowest
1) His-Purkinje
2) Ventricles/Atria
3) slowest: Atrioventricular nodes
why does the AV node have low conduction velocity?
it causes a delay to ensure that the ventricles don’t activate too early and won’t pump w/o blood
what is the distinction between the absolute and effective refractory periods?
that absolute means absolutely no stimulus is large enough to generate
another action potential; effective means that a conducted action
potential cannot be generated (i.e., there is not enough inward current to
conduct to the next site).
at which refractory period can an AP be spread to neighboring cells?
at Relative refractory period.
during the ………… period, the cell is more excitable than normal during this
period. meaning that just a slight influx of Na+ can induce a and AP
supranormal period, which follows the relative
refractory period.
the parasympathetic NS has contractility effect on which part of the heart?
it has decreased contractility effect on atria ONLY (no effect on ventricles)
what is chronotropic effects.?
Autonomic NS Effects on Heart Rate; production of rythm
Positive chronotropic effects increases in heart rate by………………..?
stimulation of the sympathetic nervous system.
–>Norepinephrine, released from sympathetic nerve fibers, activates β1
receptors in the SA node, producing an increase in If (funny channels for release of NAa+), which increases the rate of phase 4 depolarization.
by the release of what substance does the threshold potential decrease, meaning that not much depolarization is needed to reach threshold?
Ca+
Negative chronotropic effects decreases in heart rate by………….
Acetylcholine (ACh), released from parasympathetic nerve fibers, activates muscarinic (M2) receptors in the SA node.
the parasympathetic nervous system decreases heart rate through
three effects on the SA node:
1)slowing the rate of phase 4 depolarization,
2) hyperpolarizing the maximum diastolic potential so that more inward
current is required to reach threshold potential, and
3) increasing the threshold potential.
Increases in conduction velocity are called positive …………………….,
and decreases in conduction velocity are called negative …………….
dromotropic effects
