ANS control of heart

Question 1

contractility

Answer 1

• alters tension development independent of fiber length
• increase in velocity of fiber shortening
• increase in pressure development

Question 2

contractility is mediated by what ion

Answer 2

calcium

Question 3

during sympathetic stimulation, what happens to contractility of heart

Answer 3

rates of pressure development and dissipation are increased (max pressure is higher; and pressure increases more quickly)

Question 4

under normal circumstances, a single AP provides sufficient free cytoplasmic CA2+ to activate how many crossbridges

Answer 4

1/2 of them

*providing additional cytoplasmic CA2+ will result in additional force production

Question 5

tension development in cardiac muscle is dependent on what ion concentration

Answer 5

calcium

Question 6

function of digitalis and digoxin

Answer 6

• inhibits Na+K+ ATPase and therefore reverses the Na+/Ca2+ exchanger so that there is a higher intracellular Ca2+
• result: enhanves force of contraction (contractility)

Question 7

parasympathetics have what response on contractility

Answer 7

a negative inotropic effect

Question 8

catecholamines have what effect on contractility

Answer 8

a positive inotropic effect

Question 9

how does heart rate affect inotropy

Answer 9

increases inotropy in a stepwise fashion (the “treppe” effect, Bowditch effect)

*inability of Na+/K+ ATPase to keep up with the influx of Na+, leading to accumulation of Ca2+ via the Na+/Ca2+ exchanger

Question 10

parasympathetic nervous system innervates what parts of the heart

Answer 10

PNS (vagus nerve) primarily innervates SA and AV nodes

Question 11

Sympathetic nervous system innervates what portions of the heart

Answer 11

• SA and AV nodes
• atrium
• ventricles

Question 12

chronotropicity

Answer 12

heart rate

Question 13

dromotropicity

Answer 13

conduction

Question 14

SNS stimulation does what to heart

Answer 14

increases

1. HR
2. conduction
3. contractility

*via adrenergic receptor subtype

Question 15

PNS stimulation does what to the heart

Answer 15

decreases

• HR
• conduction
• contractility (minor)

*via muscarinic receptor subtype

Question 16

PNS has what affect on SA node

Answer 16

• decreases rate of SA node depolarization
• increases permeability of SA node to K+
• hyperpolarizes SA node
• decreases inward movement of Na+ and Ca2+

Question 17

SNS has what effect on SA node

Answer 17

• increases the rate of SA node depolarization
• increases inward movement of Na+ and Ca2+

Question 18

in SA node slow action potential, when does Ca2+ T-type channel close, and Ca2+ L-type channel open

Answer 18

L-type Ca2+ current is not until threshold is reached

Question 19

what is the maximum diastolic potential for SA slow action potential

Answer 19

-65mV

Question 20

what is PNS effect on AV node

Answer 20

Ach decreases AV nodal conduction velocity (M2)

• increased permeability of AV node to K+
• slows AV node delay
• increases PR interval

Question 21

What is SNS effect on nodal conduction

Answer 21

• increases T-type Ca2+ current
• decreases P-R interval

Question 22

How does SNS enhance contractility

Answer 22

increased inward Ca2+ through L-type channels

Question 23

In SNS innervation, contractility of the heart is increased; however, ventricular relaxation is also increased; What is this due to

Answer 23

relaxation increased due to stimulation of SERCA pump activity