control of the heart rate

Question 1

stages of slowing the heart

Answer 1

1. chemoreceptors in the carotid arteries detect high levels of O2, low CO2 and low acidity
2. baroreceptors detect high Bp
3. receptors send nerve impulses to the medulla oblongata
4. medulla oblongata sends nerve impulses along the PARAsympathetic nerve
5. parasympathetic nerve secretes neurotransmitters which signal the SAN to slow the heart

Question 2

describe how the SAN controls the heart rate:

Answer 2

1. SAN initiates the heartbeat
2. it sends electrical impulses across the atria
3. stimulating the atria to contract
4. insulating tissue prevents the electrical impulse from reaching the ventricles
5. the AVN delays the electrical impulse, so the atria can contract and empty BEFORE the ventricles contract
6. the AVN sends electrical impulse down the Bundle of His and along the Purkinje fibres
7. the ventricles contract from the base upwards

Question 3

during atrial systole:

Answer 3

> the atria are contracting
the ventricles are relaxed
the AV valves are open
the SL valves are closed

Question 4

during ventricular systole

Answer 4

> the atria are relaxed
the ventricles are contracting
the AV valves are closed
the SL valves are open

Question 5

during diastole

Answer 5

> the atria are relaxed and passively filling
the ventricles are relaxed
the AV valves are open
the SL valves are closed