Topic 9.8 Control of heart rate in mammals

Question 1

States the name and location of the two nodes involved in heart rate contraction

Answer 1

Sinoatrial node (SAN): within the wall of the right atrium.

Atrioventricular node (AVN): near lower end of right atrium in the wall that separates the 2 atria.

Question 2

Describe how heartbeats coordinated

Answer 2

1. SAN initiates wave of depolarisation (WOD).
2. WOD spreads across both atria = atrial systole.
3. Layer of fibrous, non-conducting tissue delays inpulse while ventricles fill and valves close.
4. AVN conveys WOD down septum via Bundle of His, which branches into purkinje fibres along ventricles.
5. Causes ventricles to contract from apex upwards.

Question 3

What is the autonomic system?

Answer 3

System that controls involuntry actions if glands and muscles.

2 subdivisions: sympathetic and parasympathetic.

Question 4

Name the receptors involved in changeing heart rate and state their location

Answer 4

Baroreceptors (detect changes in blood pressure): carotid body.

Chemoreceptors (detect changes in pH e.g. due to increase in CO₂ concentration): carotid body and aortic body

Additionally thermoreceptors and proprioreceptors in the muscles.

Question 4

Name the receptors involved in changeing heart rate and state their location

Answer 4

Baroreceptors (detect changes in blood pressure): carotid body.

Chemoreceptors (detect changes in pH e.g. due to increase in CO₂ concentration): carotid body and aortic body

Additionally thermoreceptors and proprioreceptors in the muscles.

Question 5

How does the body respond to an increase in blood preasure?

Answer 5

1. Baroreceptors send more impulses to cardioinhibitory centre in the medulla oblongata.
2. More impulses to SAN down vagus nerve via parasympathetic nervous system.
3. Stimulates release of acetylcholine, which decreases heart rate.

Question 6

How does the body respond to a decrease in blood preassure?

Answer 6

1. Baroreceptors send more impulses to cardioaccelaratory centre in the medulla oblongata.
2. More impulses to SAN via sympathetic nervous system.
3. Stimulates release of noradrenaline, which increases heart rate and strength of contraction.

Question 7

How does the body respond to an increase in CO₂ concentration?

Answer 7

1. Chemoreceptors detect pH decrease and send more impulses to cardioaccelartaory centre of the medulla oblongata.
2. More impulses to SAN via sympathetic nervous system.
3. Heart rate increases, so rate of blood flow to lungs increases = rate of gas exchange and ventilation rate increase.

Question 8

What effects does adrenaline have on heart rate?

Answer 8

Stress or shock can cause the CNS to stimulate the adrenal medulla:
* Increased frequency of nerve impulses in a branch of the sympathetic autonomic nervous system
* Results in the release of adrenaline, a hormone, which then circulates in the blood
* Adrenaline affect target cells in the cardiac centre and in the SAN
* Causes increased HR to prepare the body for increased activity