Cardiac Conduction and Mechanics

Question 1

how fast a signal moves through the heart

Answer 1

velocity of conduction

Question 2

velocity of conduction dependent on 3 things:

Answer 2

1. muscle cell diameter
2. # of gap junctions
3. increase slope of phase 0 of nodal myocyte action potentials

Question 3

beats per minute

Answer 3

heart rate

Question 4

conduction system of the heart composed of ______

Answer 4

specialized cardiac myocytes

Question 5

conduction signal gets conveyed to ventricles through ______

Answer 5

AV node

Question 5

conduction speed through bundle branches and purkinge fibers

Answer 5

fast

Question 6

conduction speed through AV node

Answer 6

slow

Question 7

what happens if SA node can’t set the heart rate

Answer 7

other pacemaker regions will step up, it will just be much slower

Question 8

only conductive bridge between the atria and ventricles

Answer 8

AV node

Question 9

injury to AV node that causes slow conduction; ventricular rate and atrial rate still same

Answer 9

1st degree heart block

Question 10

injury to AV node that causes intermittent failure of conduction to ventricles; ventricular rate<atrial

Answer 10

2nd degree heart block

Question 11

complete loss of AV node conduction; atria and ventricles beat independently of each other

Answer 11

3rd degree heart block

Question 12

when a 3rd degree heart block happens, where do ventricles get conduction from

Answer 12

AV bundle (next in line to AV node)

Question 13

what happens when AV bundle is injured

Answer 13

ventricles get conduction from bundle branches/purkinge fibers that is scary slow (bradycardia)

Question 14

the more you fill the heart, the more _____ it will contract

Answer 14

forcefully (Starling Mechanism)

Question 15

load the heart is working against

Answer 15

arterial pressure (aortic pressure)

Question 16

how much blood did the ventricles fill up with before heart contracts

Answer 16

preload

Question 17

depends on arterial pressure decreasing

Answer 17

afterload

Question 18

what happens when heart overstretches (this normally doesn’t happen)

Answer 18

lose capacity to generate force

Question 19

autonomic regulation of heart that controls blood pressure

Answer 19

baroreceptors

Question 20

role of afferents from the heart

Answer 20

go from carotid sinus and aorta to brainstem and give message of whether bp is too high or low

Question 21

role of parasympathetic efferents

Answer 21

go to SA and AV node and decrease HR and conduction speed

Question 22

role of sympathetic efferents

Answer 22

go to SA and AV node, and myocardium and increase HR and speed of conduction and contractility

Question 23

main steps of how parasympathetics decrease HR

Answer 23

1. Ach binds to Gi couple receptor on SA node
2. reduces cAMP
3. decreases HCN (less Na+ leaking)
4. K+ opens

Question 24

overall effect of parasympathetics on heart

Answer 24

decrease pacemaker rate of SA/AV nodes

Question 25

main steps of how sympathetics increase HR

Answer 25

1. NE binds B1 (Gs coupled receptor) 2. increases cAMP 3. increases HCN (more Na+ leak)

Question 26

overall effect of sympathetics on heart

Answer 26

increased pacemaker rate of SA and AV node and increased contractility (whole curve shifts up)

Question 27

relative force that can be generated at any given muscle length

Answer 27

contractility

Question 28

how sympathetics cause an increase in contractility

Answer 28

1. NE binds B1 receptors on ventricular myocytes 2. increase cAMP and PKA 3. increase Ca2+ (L-type)

Question 29

increasing contractility of heart increases what

Answer 29

stroke volume (how much blood is pumped per 1 beat)

Question 30

sympathetic stimulation increases speed of what two things

Answer 30

contraction and relaxation

Question 31

what reduces the duration of action potential plateau by inhibiting PLB and increasing sequestration of Ca2+

Answer 31

NE binding to B1 and increasing cAMP and PKA (phosphorylation of PLB)

Question 32

a reduced duration of action potential plateau shortens systole and allows for what

Answer 32

better diastolic filling at higher HR's

Question 33

chronotropy

Answer 33

rate

Question 34

inotropy

Answer 34

contractility

Question 35

lusitropy

Answer 35

relaxation rate

Question 36

dromotropy

Answer 36

conduction velocity