3: Pacemaker

Question 1

Where are slow type action potential cells found

Answer 1

SA and AV nodes

Question 2

What node dictates heart rate

Answer 2

SA

Question 3

Slow type

Phase 4

Answer 3

Increasing funny Na conductance
Fast type Na channels inactive
Decrease K+ conductance
Max neg. potential dependent on Na and K interaction

Question 4

Slow type

Phase 0

Answer 4

Ca channels open at -55mV
-causes slow rising AP
Funny Na close

Question 5

Slow type

Phase 3

Answer 5

Slow depolarization
Dec Ca conductance
Inc K+ conductance

Question 6

Is refractory period longer or shorter in slow type cells

Answer 6

Longer

Question 7

What are fast type AP dependent on

Answer 7

Extracellular Na

Question 8

What are slow type AP dependent on

Answer 8

Extracellular Ca

Question 9

What does depolarization of SA node trigger

Answer 9

Atrial tissue depolarization-gap junctions

Question 10

What area of the heart does the SA node activate

Answer 10

Atrium

Question 11

What area of the heart does the AV node activate

Answer 11

Ventricles

Question 12

Characteristics of AV node

Answer 12

slower discharge rate
Delay to allow sufficient ventricular filling
Long refractory period

Question 13

What does the bundle of His become

Answer 13

Separates into right and left bundle branches

Question 14

Features of Purkinje fibers

Answer 14

Largest diameter fibers in the heart
Long duration plateau phase
Protect ventricles from premature atrial contractions

Question 15

Heart rate without AV

Answer 15

Slower

Determined by SA node

Question 16

Heart rate without AV or SA nodes

Answer 16

Too slow to support life

Determined by Purkinje fibers

Question 17

First regions to be excited

Answer 17

Interventricular septum

Papillary muscles

Question 18

Is the right or left myocardium activated first by Purkinje fibers

Answer 18

Right, thinner wall

Question 19

What happens after myocardial depolarization

Answer 19

muscle contraction and then relaxation