stimuli, both internal and external, are detected and lead to a response: Control of heart rate

Question 1

Describe how a heartbeat is initiated and coordinated

Answer 1

1. waves of electrical impulses are sent from the sinoatrial node and spread our across both atria, both atria contract
2. layer of non-conductive tissue prevents the waves crossing to the ventricles
3. waves passing through a second group of cells called the atrioventricular node, between the atria and ventricles
4. AVN delays while atria empty and ventricles fill
5. AVN conveys electrical waves between ventricles and along a series of specialised cells called ‘Bundle of His’
6. Bundle of His conducts the waves through the septum to the base of the ventricles where it spreads out into the Purkinje fibres
7. waves released cause the ventricles to contract from base upwards.

Question 2

what are baro/chemo receptors and where are they found?

Answer 2

baroreceptors detect pressure found in the walls of the ceratoid arteries and the aorta
chemoreceptors detect changes in pH located in the walls of the ceratoid arteries.

Question 3

how are baroreceptors used to increase heart rate?

Answer 3

baroreceptors located in the walls of the ceratoid arteries and aorta detect low pressure
sends more electrical impulses to medulla oblongata
medulla oblongata send more impulses to SAN via the sympathetic nervous system
SAN increases frequency of electrical impulses by secreting noradrenaline, so heart rate increases

Question 4

how are chemoreceptors used to increase heart rate?

Answer 4

chemoreceptors in the walls of the ceratoid arteries detect low blood pH
sends more electrical impulses to medulla oblongata
medulla oblongata sends more electrical impulses to SAN via the sympathetic nervous system
SAN increases the frequency of electrical impulses by secreting noradrenaline, so increases heart rate

Question 5

how are baroreceptors used to decrease heart rate?

Answer 5

baroreceptors in the walls of the ceratoid arteries and aorta detect high pressure
sends more electrical impulses to medulla oblongata
medulla oblongata sends more electrical impulses to the SAN down the parasympathetic nervous system
SAN reduces frequency of electrical impulses sent out by secreting acetylcholine
decreases impulses sent to AVN