Lesson 16: Topic 12 - Cardiac Conductance and SA Node Flashcards
what is the SA node?
a bundle of cells that is kind of like a muscle/nerve that has a membrane potential that changes based on ions in and out of the cell
- all it does is initiate the action potentials and sends depolarization through the intercalated disc gap junctions throughout the atria
true or false: we say SA contraction.
false, we say SA node depolarization
is the heart self exitatory?
yes, it is an intrinsic heart beat
- does not need nervous information from the brain or nervous system. if we pull it out of the body, it will still beat because we do not need the nerves to innervate it
what is the pacemaker potential?
the beginning of a depolarization/pacemaker potential in the SA node which generates a wave of depolarization in the muscle tissue
is there more potassium inside or outside of the cell?
inside
is there more sodium inside or outside of the cell?
outside
its the movement of what in and out of the cell that generates the action potential for the SA node?
sodium, potassium and calcium
what is membrane potential?
essentially the charge inside the cell compared to outside the cell
- described in millivolts (mV)
what is the membrane potential where the action potential happens?
-40mV
(threshold potential is from -60 to -40)
at what membrane potential does the SA node depolarize?
-60 mV
what does an action potential in the SA node generate?
a wave of depolarization
what determines an action potential in the SA node?
a pacemaker potential
what determines action potential frequency (heart rate)?
how quickly the pacemaker potential rises
if the pacemaker potential slope is steeper, what happens?
increases the action potential frequency
the rate at which action potentials in the SA node occur is entirely dependent on?
the pacemaker potential
what are the three steps in generating action potential in the SA node?
- progressive decrease in K+ permeability (K+ channels close) - potassium cannot leave the cell to drop the potential (positive charge so it increases the potential)
- increase in Na+ permeability (opening of F-type Na+ channels to enter the cell) - its a positive charge so it increases the potential and then it closes before step 3
- increase in Ca2+ permeability (opening of T-type Ca2+ channels) (brings it to the threshold potential by bringing calcium in and then closes once threshold potential is reached)
what does “F-type” mean? what does it do?
- funny type channel
- allows for a slow influx of sodium into the channel to continue to rise the membrane potential
what does “T-type” mean? what does it do?
- transit type calcium channel
- open for not long
- open to allow for some calcium to pump in at a relatively slow rate
why do we not want a fast change in membrane potential?
it will give us a really high heart rate
what opens once threshold potential is reached?
L-type Ca2+ channels to generate that action potential
what does “L-type” stand for? what does it do?
- long-type
- it allows for a calcium influx (faster rate that T-type) (where action potential occurs)
what happens at the peak of the action potential?
calcium channels close and potassium channels open to allow potassium to rush out the cell and drop the membrane potential
what determines the rate of action potential generation?
slope of pacemaker potential
the main source of change in the membrane potential is determined by?
the calcium
without any extrinsic information to the SA node, what would be our AP/minute?
100 action potentials per minute without ANY external input
does the AV node also have a “pacemaker potential” ?
yes, its just much slower than the SA node
- also has its own intrinsic action potential rate but its paced by the SA node in a normal healthy heart
- about 25-40 APs/min
without the SA node, what would happen?
the atria would not be in the rhythm with the ventricles because the ventricles would beat on their own. however, the ventricles need to be paced
what is a pacemaker device?
- there is a pulse generator and it is implanted into the cardiac tissue (in between the atrium and then another at the bottom of the bundle branches)
- it acts as an SA node and AV node
can a permanent pacemaker limit you?
yes because if its set at 80BPM, you need a higher rate if you want to exercise
