Control of heart rate

Question 1

What does it mean when the cardiac muscle is myogenic?

Answer 1

It contracts on its own accord but the rate of contraction is controlled by wave of electrical activity

Question 2

Where is the SAN, AVN, purkyne fibres + bundle of his?

Answer 2

SAN- located in right atrium known as pacemaker
AVN- located near the border of the right + left ventricle within the atria still
Purkyne fibres- in walls of ventricles
Bundle of His- runs through the septum

Question 3

Control of heart rate

Answer 3

-SAN releases a wave of depolarisation across the atria causing it to contract
-AVN releases another wave of depolarisation when the first wave reaches it. Non-conductive layer between atria and ventricles prevents wave of depolarisation travelling down to ventricles
-Bundle of His can conduct wave of depolarisation down septum + purkyne fibres in walls of ventricles
-Apex + walls of ventricles contract. There’s a short delay before this happens whilst AVN transmits second wave of depolarisation
-This allows enough time for atria to pump all blood into ventricles. Finally cells repolarise + cardiac muscle relaxes

Question 4

How is heart rate controlled by the brain?

Answer 4

The medulla oblongata in the brain controls heart rate via autonomic nervous system
2 parts:
-centre linked to SAN that increases heart rate via sympathetic nervous system
-another that decreases heart rate via the parasympathetic nervous system

Question 5

What causes heart rate to change?

Answer 5

-heart rate changes in response to pH and pressure
-these are detected by chemoreceptors and pressure receptors in the aorta + carotid artery

Question 6

Response to high blood pressure

Answer 6

-If blood pressure is too high this can cause damage to the walls of the arteries + mechanisms must be put in place to reduce blood pressure
-This results in more impulses via the parasympathetic nervous system to decrease heart rate

Question 7

Response to low blood pressure

Answer 7

• If blood pressure is too low, there may be insufficient supply of oxygenated blood to the respiring cells + removal of waste
• This results in more impulses via the sympathetic nervous system to increase heart rate

Question 8

Response to pH

Answer 8

-pH of blood will decrease during times of high respiratory rate due to production of CO2 or lactic acid
-excess acid must be removed from blood rapidly to prevent enzymes denaturing + this is done by increasing heart rate (more impulses via sympathetic nervous system to SAN) so CO2 can diffuse into the alveoli more rapidly