Cardiac Conduction and Mechanics Flashcards
how fast a signal moves through the heart
velocity of conduction
velocity of conduction dependent on 3 things:
- muscle cell diameter
- # of gap junctions
- increase slope of phase 0 of nodal myocyte action potentials
beats per minute
heart rate
conduction system of the heart composed of ______
specialized cardiac myocytes
conduction signal gets conveyed to ventricles through ______
AV node
conduction speed through bundle branches and purkinge fibers
fast
conduction speed through AV node
slow
what happens if SA node can’t set the heart rate
other pacemaker regions will step up, it will just be much slower
only conductive bridge between the atria and ventricles
AV node
injury to AV node that causes slow conduction; ventricular rate and atrial rate still same
1st degree heart block
injury to AV node that causes intermittent failure of conduction to ventricles; ventricular rate<atrial
2nd degree heart block
complete loss of AV node conduction; atria and ventricles beat independently of each other
3rd degree heart block
when a 3rd degree heart block happens, where do ventricles get conduction from
AV bundle (next in line to AV node)
what happens when AV bundle is injured
ventricles get conduction from bundle branches/purkinge fibers that is scary slow (bradycardia)
the more you fill the heart, the more _____ it will contract
forcefully (Starling Mechanism)
load the heart is working against
arterial pressure (aortic pressure)
how much blood did the ventricles fill up with before heart contracts
preload
depends on arterial pressure decreasing
afterload
what happens when heart overstretches (this normally doesn’t happen)
lose capacity to generate force
autonomic regulation of heart that controls blood pressure
baroreceptors
role of afferents from the heart
go from carotid sinus and aorta to brainstem and give message of whether bp is too high or low
role of parasympathetic efferents
go to SA and AV node and decrease HR and conduction speed
role of sympathetic efferents
go to SA and AV node, and myocardium and increase HR and speed of conduction and contractility
main steps of how parasympathetics decrease HR
- Ach binds to Gi couple receptor on SA node
- reduces cAMP
- decreases HCN (less Na+ leaking)
- K+ opens
overall effect of parasympathetics on heart
decrease pacemaker rate of SA/AV nodes
main steps of how sympathetics increase HR
- NE binds B1 (Gs coupled receptor)
- increases cAMP
- increases HCN (more Na+ leak)
overall effect of sympathetics on heart
increased pacemaker rate of SA and AV node and increased contractility (whole curve shifts up)
relative force that can be generated at any given muscle length
contractility
how sympathetics cause an increase in contractility
- NE binds B1 receptors on ventricular myocytes
- increase cAMP and PKA
- increase Ca2+ (L-type)
increasing contractility of heart increases what
stroke volume (how much blood is pumped per 1 beat)
sympathetic stimulation increases speed of what two things
contraction and relaxation
what reduces the duration of action potential plateau by inhibiting PLB and increasing sequestration of Ca2+
NE binding to B1 and increasing cAMP and PKA (phosphorylation of PLB)
a reduced duration of action potential plateau shortens systole and allows for what
better diastolic filling at higher HR’s
chronotropy
rate
inotropy
contractility
lusitropy
relaxation rate
dromotropy
conduction velocity
