Nordgren Week 1 Flashcards
used to coordinate and appropriately time the contractile activity
electrical stimulus
develop tension in, as well as shorten and relax the muscle cells
mechanical activity
How do cardiac muscle APs differ from skeletal APs and promote synchronous rhythmic excitation of the heart?
- self-generating 2. conducted directly from cell to cell 3. long duration (long refractory period)
What prevents summation and tetanus in cardiac muscle that you see in skeletal muscle?
long duration and long refractory period
what creates an electrical potential?
separation of electrical charges across a membrane
What changes the electrical potential of a cell membrane?
flow of current through the cell membrane
When is transmembrane voltage stable?
when there is no net current
What are the two interstitial fluid ions?
Na and Ca
What is the intracellular fluid ion?
K
What is the potassium equilibrium potential?
-90mV
electrical charge is very soluble or insoluble in lipids?
insoluble and so must pass through lipid bilayer via transmembrane protein structures
Name 3 transmembrane protein structures
ion channels, ion exchangers, ion pumps
What are the three states of ion channels?
open, closed, inactivated
what does it mean when said ‘high permeability to sodium’
many of the Na ion channels are open
What responds quickly to membrane depolarization QUICKLY by opening?
activation gates
What responds to membrane depolarization SLOWLY by closing; limits the time a channel can remain open, despite continued stimulation; NOT in all channels?
inactivation gates
What type of cardiac muscle has action potentials similar to those of neurons and skeletal muscle?
myocardial contractile cells
What type of cardiac muscle generates action potentials spontaneously due to unstable membrane potential?
myocardial autorhythmic or pacemaker cells
What type of cardiac cell has a rapid depolarization with large overshoot (+mV), rapid reversal of overshoot, long plateau, re, repolarization to a stable, high (-mV) resting membrane potential?
Contractile cells
What type of cardiac cell has slower initial depolarization, lower amplitude overshoot, shorter and less stable plateau, repolarization to unstable slowly depolarizing ‘resting’ membrane potential
Pacemaker cells
What is the main differences in AP between the contractile and the pacemaker cells in phase 0?
contractile cells: mediated by Na
pacemaker cells: Ca
What is the main differences in AP between the contractile and the pacemaker cells in phase 1 and 2?
absent in pacemaker cells
What is the main differences in AP between the contractile and the pacemaker cells in phase 3?
none
What is the main differences in AP between the contractile and the pacemaker cells in phase 4?
resting versus pacemaker potential
specialized adherens junction structure that connects ends of two adjacent cells
intercalated disks
Name 3 types of adhering junctions that make up intercalated discs
- fascia adherens 2. macula adherens (aka desmosomes) 3. gap junctions
anchoring sites for actin, connect to the closest sarcomere
fascia adherens
join cells together by binding intermediate filaments
macula adherens (aka desmosomes)
channels formed of proteins called connexin permit passage of ions between cells, thus allowing the spread of action potentials
gap junctions
What ensures the transmission of force from one muscle cell to the next?
firm mechanical attachments: fascia adherens and macula adherens (desmosomes)
What facilitates the transmission of electrical impulse from cell to cell?
low-resistance electrical connections: channels formed of proteins called connexin in structures called gap junctions
What largely determines the speed at which action potentials travel between cells?
the number of gap junctions in the intercalated discs; more=faster
Which has more gap junctions: AV node or the SA node and atrial myocardium?
AV node has fewer gap junctions
What is the rate of action potential conduction of the SA node, atrial tissue?
1 m/sec
What is the rate of action potential conduction of the AV node?
0.05 m/sec
What is the rate of action potential conduction of the ventricular tissue?
0.3-0.5 m/sec
What is the rate of action potential conduction of bundle of His, Purkinje?
4 m/sec
What does an electrocardiogram measure?
record of how the voltage between two points on the body surface changes with time as a result of the electrical events of the cardiac cycle
Where do fibers from the sympathetic nervous system and parasympathetic nervous system terminate to increase or decrease the automaticity of pacemaker cell firing from the intrinsic level?
cells in SA node
What is released by the cardiac parasympathetic fibers via vagus nerves?
acetylcholine
How does acetylcholine affect the permeability of resting membrane K?
increases permeability
How does acetylcholine affect diastolic funny current through HCN channels?
decreases diastolic
Net effect of parasympathetic nervous system
slow heart rate via prolonging time to depolarization, slows rate of spontaneous depolarization and causes initial hyperpolarization of resting membrane potential
Net effect of sympathetic cardiac fibers? how?
speeds heart rate via release of norepinephrine to increase diastolic inward currents through HCN channels
Define preload
the passive/resting tension placed on cardiac muscle cells before contraction (a function of the volume and pressure at the end of diastole)
What 4 things increase the preload?
hypervolemia, regurgitation of cardiac valves and heart failure
Define afterload
the active tension placed on cardiac muscle cells during contraction (a function of the resistance the left ventricle must overcome to circulate blood)
What 2 things increase afterload?
hypertension and vasoconstriction
What does active tension depend on?
active tension developed during isometric contraction depends on the muscle length at which contraction occurs (which is linked to the resting tension)
What type of contraction has the same load but the length changes?
isotonic contraction
What influences the amount of tension the muscle can develop and the amount of shortening the muscle can achieve?
ionotrope
a positive ionotrope that increases afterloaded shortening; increases isometric tension
norepinephrine
What do the length-tension relationships of cardiac muscle fibers in the ventricular wall determine?
the volume and pressure tensions in the chamber
What leads to an increase in the length of the cardiac muscle cells?
an increase in ventricular volume causes an increase in ventricular circumference and therefore an increase in ventricular circumference
What leads to an increase in intraventricular pressure?
an increase in tension (at any volume) of individual cells in the wall
as ventricular volume decreases what happens to total force?
lesser total force is needed by the muscle cells in the ventricular walls to produce any given intraventricular pressure
what does the TOTAL ventricular wall tension (T) depend on?
intraventricular pressure (P) and the internal ventricular radius (r); T=Pxr
