Unit 1: Cardiac Physiology- Pt.2 Flashcards
(Pick) the Atrial and Ventricular heart muscles are squamous/striated elongated grouped into irregular/regular anatamosing columns with 1-2/over 3 centrally located nuclei.
striated elongated
irregular
1-2 nuclei
What are the specialized excitatory and conductive muscle fibers? Do they contract strong or weakly? Are there many for few fibrils?
SA node, AV node, Purkinge fibers
contract weakly
few fibrils
Cardiac muscle has a syncytial nature. What is syncytium and how does it occur?
= many acting as one
Due to presence of intercalated discs
- low resistance pathways connecting cardiac cells end to end
- presence of gap junctions
What is the duration of an action potential in cardiac muscle?
from .2-.3 sec
What are the three channels found in cardiac muscle?
- fast Na+ channels
- slow Ca++/Na+ channels
- K+ channels
What is the permeability changes of cardiac muscle, as in when they increase?
Na+
Ca++
K+
Na + sharp increase at onset of depolarization
Ca++ increased during plateau
K+ increased during the resting polarized state
Describe the membrane permeability changes for Na+ during an action potential in cardiac tissue.
increase at onset of depolarization, decrease during repolarization (same with Ca++)
Describe the membrane permeability changes for Ca++ during an action potential in cardiac tissue.
increase at onset of depolarization, decrease during repolarization (same as Na+)
Describe the membrane permeability changes for K+ during an action potential in cardiac tissue.
decreases at onset of depolarization, increases during repolarization
During depolarization of typical cardiac muscle, what types of channels open? (fast/slow)
both fast Na+ channels and slow Ca++/Na+ channels open
During depolarization, what channels are operational for specialized excitatory cells like the SA node? What does that do to the depolarization time?
only slow Ca++/Na+ channels are, therefore increasing depolarization time
What does Tetradotoxin do?
blocks fast Na+ channels, therefore changing a fast response into a slow response
Passive ion movement across a cell takes into consideration what 3 things?
- concentration gradient (high to low)
- electrical gradient (opposite charge attract, like charge repel)
- membrane permeability (dependent on ion channels (open or closed)
What is the Nernst equilibrium potential?
it is what an ion will seek to meet if its ion channel is open; it is why a cell repolarizes to a certain voltage b/c finds that balance where are NEP
How is the concentration gradient favoring ion movement in one direction offset?
by the electrical gradient (+ or -)
During the resting membrane potential (Er) in cardiac muscle, which channels are open and which are closed?
fast Na+ and slow Ca++/Na+ channels are closed
ONLY K+ channels are open, therefore K+ ions are free to move and when reach their Nerst equilibrium potential, a stable Er is maintained
The ________ is energy dependent and pumps ____ Na+ out and ___ K+ into cardiac cells.
Na+/K+ ATPase (pump); 3 Na+ out; 2 K+ in
When the Na+/K+ ATPase pump is in action, what is occuring when it comes to the charge of the cell?
there is a net loss of one + charge form the interior each cycle, helping the interior of the cell remain negative
What drug will bind to the Na+/K+ ATPase pump and inhibit it? What other pump does that effect?
Digitalis
is tied to Ca++ exchange protein and therefore will inhibit that pump and will increase Ca++ which will increase contraction strength
What is the Ca++ exchange protein? What is it “tied” to?
it is in cardiac cell membrane and exchanges Ca++ from the interior in return for Na+ that is allowed to enter the cell
- fxn of this exchange protein is tied to the Na+/K+ pump
When does the Absolute Refractory Period occur? And how is re-stimulation impacted?
occurs during the plateau (before Relative RP); unable to re-stimulate cardiac cell, no matter how strong the stimulus
When does the Relative Refractory Period occur? And how is re-stimulation impacted?
occurs during repolarization (after Absolute RP); requires a supra-normal stimulus have an effect
T/F. In a Slow response cardiac muscle cell the Relataive Refractory Period is shortened and the refractory period is about 25% shorter.
False–the Relative Refractory period is PROLONGED, and the refractory period is about 25% LONGER
What purpose does the prolonged refractory period in a Slow response cardiac muscle cell serve in an AV node and bundle?
it serves to protect the ventricles from supra-ventricular arrhythmias
(so if atrium is abnormal, like in A-fib, ventricles will be protected)