Control of Heart Rate

Question 1

what is the heart innverated by

Answer 1

the heart is innervated by both divisions of the autonomic nervous system and contraction is not required

Question 2

What is bradycardia and tachycardia

Answer 2

Increased activity in the sympathetic nerves to the heart increases HR - tachycardia
Increased activity in the parasympathetic nerves to the heart decreases HR - bradycardia

Question 3

what do tachycardia and bradycardia

Answer 3

Tachycardia and bradycardia affect heart rate by changing slope of the pacemaker potential changes in the rate are the chronotropic effect

Question 4

what neurotransmitters does parasymapethic and symapethic nervous sytem

Answer 4

parasympathetic nervous system releases ACh while the sympathetic nervous system releases noradrenaline

Question 5

What are ACH and NorAd coupled to

Answer 5

ACH is coupled to an inhibitory G protein that reduces activity of the cAMP pathway
NorAd is coupled to a stimulatory G protein that accelerates the cAMP pathway

Question 6

Parasympathetic NS decreases heart rate through 2 effects on pacemaker tissue

Answer 6

Parasympathetic NS decreases heart rate through 2 effects on pacemaker tissue
Hyperpolarisation of the SA node membrane (takes longer to reach threshold)
Decreases the rate of spontaneous depolarisation
ACH increases K permeability by G proteins coupled inwardly rectifying potassium channels

Question 7

Other effects of parasympathetic stimulation on heart activity

Answer 7

Parasympathetic stimulation decreases the AV node excitability which prolongs the transmission of impulses to the ventricles.
Shortens the plateau phase of the AP in atrial contractile cells, weakening atrial contraction.
Parasympathetic stimulation has little effect on ventricular contraction
decrease in HR, the time between atrial and ventricular contraction is increased and atrial contraction is weaker

Question 8

effects of sympathetic stimulation on the SA node

Answer 8

Sympathetic NS speeds up heart rate through its effect on pacemaker tissue
main effect is to speed up depolarisation so threshold is reached more rapidly - NorAd augments If and T type channel activity

Question 9

Other effects of sympathetic stimulation of heart activity

Answer 9

Sympathetic stimulation of the AV node reduces AVnodal delay by increasing conduction velocity.
Speeds up spread of the AP throughout the specialised conduction pathway.
Increased contractile strength of the atrial and ventricular contractile cells (heart beats more force fully and squeezes out more blood)
Increased Ca2+permeability through prolonged opening of L-type Ca2+channels.*Speeds up relaxation

Question 10

Sympathetic stimulation of the heart is to improve its effectiveness as a pump

Answer 10

increase heart rate
decreasing the delay between atrial and ventricular contraction
Decreasing conduction time through the heart
increasing the force of contraction and speeding up the relaxation process so that more time is available for filling

Question 11

what is antagonist

Answer 11

Parasymapethic and sympathetic effects on heart rate are antagonistic

Question 12

what is heart rate determined by te balance of what

Answer 12

Heart rate is determined by the balance of the SA node (vagus) and stimulation (sympathetic nerves)

Question 13

Heart rate can be altered by what

Answer 13

Heart rate can be altered by shifting the balance of autonomic nervous stimulation.
HR is increased by simultaneously increasing sympathetic and decreasing parasympathetic activity
Conversely, HR is decreased by simultaneously increasing parasympathetic. and decreasing sympathetic. activity
The activity of the autonomic nervous system is co-ordinated by the cardiovascular control centre, located in the brain stem

Question 14

What is the primary mena by which HR is rgualted

Answer 14

autonomic innervation is the primary means by which HR is regualted