Block I: CV II Flashcards
the heart beat starts in [] and spreads to []
- specialized cardiac conduction cells (pacemaker)
2. all parts myocardium
what node is most vulnerable to injury, disease and inflammation and why is this?
the SA node
because it is located 1 mm beneath visceral pericardium
the SA node is heavily innervated by []
sympathetic and parasympathetic fibers
after the SA nodes, where to APs go?
AV nodes
what are the 3 atrial fibers that connect the SA node to the AV node
- anterior
- middle (tract of wenckebach)
- posterior (tract of thorel)
after the AV node where do APs go?
bundle of his
[] is a triangle shaped node that lies within the posterior border of interventricular septum
bundle of his
the two lower ends of the triangle of the bundle of his give rise to []
R and L bundle branches
describe depolarization
cells become transiently positive due to influx of Na and Ca ions
what leads to repolarization
return to more neative charge, pumping out of K +
describe the AP route of travel
- SA node
- 3 internodal pathways (anterior, middle, posterio)
- AV node
- bundle of his
- purkinje fibers
- ventricular myocardium
activation is AKA []
depolarization
deactivation is AKA []
repolarization
describe the refractory period
heart muscles cannot contract, ensures diastole and completes cardiac cycle
why is the AP delayed in the region of the AV node?
to permit ventricular filling by atrial contraction (atrial kick)
what ions are involved in muscle cell APs
- Cl-
- Na+
- Ca+
- K+
[] is the movement of ions in and out of a cell that creates voltage across the cell membrane
membrane potential
[] is an electrical charge difference
voltage
[] is the difference between resting membrane potential and decreased negative charge causes by depolarization
cardiac action potential
what is the resting membrane potential of myocardial fibers
-90 mV
[] is recorded extracellularly in summed electrical activity of all cardiac muscle fibers, and is a combined electrical record whose overall shape reflects electrical activity from cells of different regions of the heart
ECG
as Ih (hyperpolarization) increases membranes []
depolarize, noticed that cell is becoming to negative to positive ions will be drawn in
what are the two types of calcium channels
- T (transient)
2. L (long)
AP in pacemaker cells of the SA and AV nodes are primarily caused by what ion?
Ca++ (relatively no contribution from Na+ influx)
which is why CCBs are used to help with HTN
is there a sharp, rapid depolarizing spike before the plateau in pacemaker potentials
no
ACH [increases/decreases] nerve firing rates
decreases
cholinergic fibers release [] to [] HR and are a part of the [] nerve
- ACH
- DECREASE
- VAGUS
when cholinergic vagal fibers are stimulated, membrane becomes []
hyperpolarized, slope of prepotential is decreased
how does ACH slow down APs?
nodal tissues membrane permeability is increased for K+, which leaks out of cell and causes repolarization
-this occurs via M2 muscarinic receptors
also decreases cAMP, which slows Ca2+ channel openings and decreases firing rate
SLOWS depolarizing effect of Ih
sympathetic noradrenergic stimulation [increases/decreases] membrane potential of SA node
increases
what is the effect of sympathetic noradrenergic stimulation of SA node
increases membrane potential of SA node
-stimulation of sympathetic cardiac nerves SPEEDS up depolarizing effect of Ih
so that rate of spontanenous discharge increases
NE secreted by sympathetic nerve endings bind [] receptors to increase cAMP which []
- beta-1
2. increases L Ca2+ channels to increase Intracellular Ca and the rapidity of depolarization phase of the impulse
as temperature increases, discharge frequency []
increases
explains why tachycardia is assoc. with fever
[] is the sum of all cardiac action potentials
ECG
what does the P wave represent
Atrial depolarization and conduction through AV node
that does the PR interval represent
measure of time from the onset of atrial activation to the onset of ventricular activation
i.e. the time necessary to travel from the sinus node to the AV node to the his-purkinje system to ventricular myocardial cells
what does the QRS complex represent
sum of all ventricular muscle cells depolarization and repolarization
what does the T wave represent
ventricular repolarization
what does the QT interval represent
electrical systole of ventricle
-varies inversely with HR
what is the purpose of intercalated discs
specialized cell junction for the spread of AP
which muscles: heart or skeletal- produce more aTP
heart
which muscles: heart or skeletal have readier access to ions in the interstial space and why
heart due to transverse tubules
so it can work constantly ( skeletal muscle doesnt have to)
contraction happens with the [] shortens and adjacent [] lines move closer together
- sarcomere
2. Z lines
the width of the A band [remains unchanged, becomes narrower} during contraction
remains unchanged
the width of the I band [remains unchanged/becomes narrower] during contraction
becomes more narrow
overlap between thin and thick filaments [increases/decreases] during contraction
increases
describe the first stage of the cross bridge cycle
cross bridge formation
- ATP binds myosin head, ATP hydrolyzed to ADP to activate myosin heat
- hydrolyzed by inorganic phosphate - Ca2+ released from sarcoplasmic reticulum
- binds to troponin
- creates conformational change within tropomyosin
- myosin binding sites on actin made available to mind with myosin head (exposed)
what must happen to my myosin head before it can bind with myosin binding sites on the actin filament?
it must bind with ATP, that ATP must be hydrolyzed by an inorganic phosphate to ADP to activate the myosin head
-inorganic phosphate will be released
what must happen to the tropomyosin before it can bind myosin?
Ca2+ will be released from sarcoplasmic reticulum so that it can bind with troponin
binding troponin creates conformational change with tropomyosin
myosin binding sites are made available
what is the 2nd stage of the cross bridge cycle
power stroke
ADP released from myosin, myosin head pivots to slide thin myofilament closer to center of sarcomere
what is the 3rd stage of the cross bridge cycle
cross bridge detachment
ATP molecule binds myosin head
-bond between atcin and myosin weakens
what is the 4th phase of the cross bridge cycle
reactivation of myosin head
ATP hydrolzed to ADP by inorganic phosphate
myosin head reactivated and primed for binding with actin
what threshold causes funny Na+ channels to open on Pacemaker Cells
< 40 mV
causes a less, negative charge (depolarization)
what are two other names for depolarization in pacemaker cells
- pacemaker potential
2. pre-potential
once pacemaker potential is reached, Na+ channels close and [] channels open
what is the threshold?
Ca2+
- T-type: -50mV
- L-type: -40mV
causes further depolarization of cell, rising phase of curve
what happens at peak depolarization of pacemaker cells?
K+ channels open to allow K+ movement out of cells
Ca2+ channels close
voltage returns to -60mV
what is the resting potential of myocytes
-90mV (diff from pacemaker, -60mv)
what triggers myocyte depolarization
when they are stimulated by adjacent cells via IC disc (pacemaker autorhythmic and don’t need stimulation from other cells)
ions from adjacent cells cause membrane potential to reach [] in myocardial cells
-70mV
causes cell to reach threshold AP
what is the threshold AP for myocytes
-70mV (-40 for pacemaker)
once myocytes are at potential, what happens?
fast Na+ channels leak open for rapid influx Na+ which causes depolarization
once myocyte reaches [] Ca channels open
-40 mV (L-type) causes slow, steady influx of calcium into cell
when myocytes reah their peak, what happens?
Na+ channels close, while Ca2+ channels remain open.
causes PLATEAU PHASE
describe what is happening in the plateau phase are myocardial cells
Na+ channels close, while Ca2+ channels remain open. becomes slightly more negative but does hangs around depolarization for a while.
plateau phase distinct for myocardial cells (NOT pacemakers)
describe calcium induced calcium release
calcium from ion channels stimulate sarcoplasmic reticulum to release more calcium, to bind troponin and allow cross bridge cycle for contraction
when does muscle contraction occur in the myocyte?
halway through plateau phase, lasts until calcium channels close
what happens in myocytes when calcium channels close?
K efflux out of cell for repolarization
