Class lecture 1

Question 1

Specialized myocardium

Answer 1

unique electrical property (automaticity)

SA / AV node, Bundle of HIS, Purkinje

Question 2

Contractile myocardium

Answer 2

undergoes electrical stimulation/depolarization

atrium and ventricles

Question 3

resting membrane potential

Answer 3

electronegativity inside the cell
-90mV (determined by K+ efflux)

Question 4

How many Na+/K+ move in/out of the cell?

Answer 4

3 Na+ out, 2K+ in
-high Na+ conc outside of the cell
-high K+ conc inside of the cell

Question 5

2 ways to produce RMP

Answer 5

1. high Na+ conc. outside of the cell, high K+ inside of the cell
2. dependent on K+ efflux

Question 6

What is an action potential

Answer 6

stimulates the cell by electrical currents
-Na+ or Ca2+ (cations in general; could also be hormones)
-reduce electronegativity by adding cations to achieve depolarization

Question 7

Threshold potential

Action Potential

Answer 7

-70mV
Na+ channels open (briefly)

Question 8

Depolarization

Action Potential

Answer 8

occurs when Na+ concentration inside of the cell increases and depolarizes the membrane
-Na+ channels close after short period

0mV electroneutrality is reached

Question 9

Plateau

Action Potential

Answer 9

1. 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)

Question 10

Repolarization

Action Potential

Answer 10

occurs when K+ efflux continues
-re-establishes negativity

Question 11

Gap junctions

Answer 11

used to move the action potential from cell to cell
-each part of the membrane depolarizes the next to move across the entire membrane

Question 12

SA Node

Step 1

Action Potential

Answer 12

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

Question 13

Contractile Atrial Cell

Step 2

Action Potential

Answer 13

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

Question 14

AV Nodal Cell

Step 3

Action Potential

Answer 14

similar to SA node
-slow and less gap junctions
-less electronegative (less conduction bc less influx)

Ca2+ dependent depolarization

Question 15

Purkinje Fibers

Step 4

Action Potential

Answer 15

fast conduction with long plateau

Na+ dependent depolarization

Question 16

Sympathetic NS

Answer 16

increases HR
-circulating epinephrine
-cardiac nerve endings (N.E): B1 adrenergic receptors on all myocardium (SA / AV node, contractile myocardium, Bundle of HIS)

Question 17

Parasympathetic NS

Answer 17

decreases HR
-vagal stimulation (ACh)
-M2 muscarinic receptors (SA / AV node, atrial contractile myocardium, none on ventricular myocardium)

Question 18

SA node

Answer 18

automaticity focused
-increases HR = + chronotropic
-decreases HR = - chronotropic

Question 19

AV node

Answer 19

conductivity focused
-increased conductivity = + dromotropic
-decreased conductivity = - dromotropic

Question 20

Sympathetic NS on SA + AV Node

(stimulation)

Answer 20

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)

Question 21

Parasympathetic NS on SA + AV node

(inhibition)

Answer 21

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)

Question 22

Electromechanical coupling on contractile/myocardial cell

Answer 22

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