Class lecture 1 Flashcards
Specialized myocardium
unique electrical property (automaticity)
SA / AV node, Bundle of HIS, Purkinje
Contractile myocardium
undergoes electrical stimulation/depolarization
atrium and ventricles
resting membrane potential
electronegativity inside the cell
-90mV (determined by K+ efflux)
How many Na+/K+ move in/out of the cell?
3 Na+ out, 2K+ in
-high Na+ conc outside of the cell
-high K+ conc inside of the cell
2 ways to produce RMP
- high Na+ conc. outside of the cell, high K+ inside of the cell
- dependent on K+ efflux
What is an action potential
stimulates the cell by electrical currents
-Na+ or Ca2+ (cations in general; could also be hormones)
-reduce electronegativity by adding cations to achieve depolarization
Threshold potential
Action Potential
-70mV
Na+ channels open (briefly)
Depolarization
Action Potential
occurs when Na+ concentration inside of the cell increases and depolarizes the membrane
-Na+ channels close after short period
0mV electroneutrality is reached
Plateau
Action Potential
- voltage gated K+ channels open gradually (K+ leaks out = slight electronegativity)
2.voltage gated Ca2+ channels open triggered by K+ channels (brief) - Ca2+ moves into the cell (losing K+ & no Ca2+ = re-establish polarity)
Repolarization
Action Potential
occurs when K+ efflux continues
-re-establishes negativity
Gap junctions
used to move the action potential from cell to cell
-each part of the membrane depolarizes the next to move across the entire membrane
SA Node
Step 1
Action Potential
specialized in automaticity
-spontaneous depolarization
-generation of RMP by leaky Na+ channels (slightly permeable)
-depolarization = -60mV to -45mV triggers Ca2+ channels to open
-voltage gated Na+ channels remain closed permanently
-repolarization = K+ leaks out
-Ca2+ channels create depolarization current through atrial cells (once repolarization of SA node occurs)
Ca2+ dependent depolarization
Contractile Atrial Cell
Step 2
Action Potential
SA node repolarization creates Ca2+ depolarization current; waits for impulse - no automaticity
-depolarization: Na+ channels open brifely and close
-plateau: K+ efflux and Ca2+ influx
-repolarization: K+ efflux only
Na+ dependent depolarization
AV Nodal Cell
Step 3
Action Potential
similar to SA node
-slow and less gap junctions
-less electronegative (less conduction bc less influx)
Ca2+ dependent depolarization
Purkinje Fibers
Step 4
Action Potential
fast conduction with long plateau
Na+ dependent depolarization
Sympathetic NS
increases HR
-circulating epinephrine
-cardiac nerve endings (N.E): B1 adrenergic receptors on all myocardium (SA / AV node, contractile myocardium, Bundle of HIS)
Parasympathetic NS
decreases HR
-vagal stimulation (ACh)
-M2 muscarinic receptors (SA / AV node, atrial contractile myocardium, none on ventricular myocardium)
SA node
automaticity focused
-increases HR = + chronotropic
-decreases HR = - chronotropic
AV node
conductivity focused
-increased conductivity = + dromotropic
-decreased conductivity = - dromotropic
Sympathetic NS on SA + AV Node
(stimulation)
increases automaticity on SA node
-B1 adrenergic receptors where N.E. binds
-G stimulating protein loses GDP and gains GTP (high energy)
-G stim protein + GTP activate Adenine cyclase, activating cyclic AMP + PKA
-phosphorylation of Ca2+ channels = Ca2+ enters the cells
-more negative RMP = easier action potential (increased Ca2+ conc. inside of the cell)
Parasympathetic NS on SA + AV node
(inhibition)
cholinergic = - chronotropic action (electrical activity)
-ACh activates M2 muscarinic receptors
-G inhibitory protein stimulated by ACh + M2 receptors
-moves towards adenine cyclase + inhibts cAMP + PKA
-reduces phosphorylation of Ca2+ channels (Ca2+ does not enter the cell)
-opens specific K+ channels for K+ efflux (high to low conc)
Electromechanical coupling on contractile/myocardial cell
increased Ca2+ loaded into the cell = + inotropic action (contractile activity)
-increase in Ca2+ conc during plateau phase stimulates SR
-SR releases high amount of intracellular stored Ca2+
-Ca2+ now available to actin and myosin
-Ca2+ binds to troponin + activates tropomyosin to pull away
-actin + myosin contract with each other
-Ca2+/Na+ exchanges move excess Ca2+ out + brings Na+ into the cell
-plateau phase ends (close Ca2+ channels)
-excess Ca2+ moves back into storage
-troponin and tropomyosin stop interacting = relaxation
