Control of heart rate

Question 1

What is heart rate primarily determined by?

Answer 1

Autonomic influences on the SA node

Question 2

What division of the autonomic nervous system is the heart innervated by?

Answer 2

Both

Question 3

What is tachycardia and bradycardia?

Answer 3

Tachycardia- Increased activity in the sympathetic nerves to the heart increases HR
Bradycardia- Increased activity in the parasympathetic nerves to the heart decreases HR

Question 4

The two divisions of the autonomic NS affect heart rate by changing the slope of the pacemaker potential. What are these changes in rate called?

Answer 4

Chronotropic effect

Question 5

What is the pacemaker potential?

Answer 5

The slow depolarization of the membrane potential to the threshold potential
Once the threshold is reached, an AP is released

Question 6

What does the parasympathetic nervous system (vagus nerve in this case) release?

Answer 6

Acetylcholine (ACh; muscarinic receptors)

Question 7

What does the sympathetic nervous system release?

Answer 7

Noradrenaline (aka norepinephrine in USA; Beta1 adrenergic receptors)

Question 8

How does the parasympathetic NS decrease HR? 2 effects

Answer 8

1) Hyperpolarization of the SA node membrane potential (takes longer to reach threshold)
2) Decreases the rate of spontaneous depolarisation (Slope of pacemkaer potential is slower)

Question 9

What affect does ACh have on K+ permeability?

Answer 9

Ach increases K+ permeability by slowing the closure of K+ channels

Question 10

Parasympathetic stimulation decreases the AV nodes excitability which leads to what?

Answer 10

Prolongs transmission of impulses to the ventricles

Question 11

PNS shortens the plateau phase of the AP in atrial contractile cells which leads to what?

Answer 11

Weakening atrial contraction

Question 12

With the effect of the PNS of HR, what is the effect of the time between atrial and ventricular contraction?

Answer 12

The time increases

Question 13

SNS speeds up the HR through the effect on pacemaker tissue (tachycardia). What is the main effect of this?

Answer 13

To speed up depolarisation, so threshold is reached more rapidly

Question 14

In SNS, sympathetic stimulation of the AV node reduces AV nodal delay by doing what?

Answer 14

Increasing conduction velocity

Question 15

What effect does the SNS have on the AP?

Answer 15

Speeds up the spread of the AP

Question 16

What does it mean by the increased contractile strength of the atrial and ventricular contractile cells?

Answer 16

Heart beats more forcefully and squeezes out more blood

Question 17

When is the hormone adrenaline released?

Answer 17

In response to the sympathetic nervous system

Question 18

Differentiate chronotropic and inotopic action

Answer 18

C- Increase heart rate

I- Increase force of myocardial contraction