Control of heart rate (A-level only) Flashcards
Stages involved in 1 heart beat:
Sinoatrial node (SAN)
Contraction of the atria
Atrioventricular node (AVN)
Contraction of the ventricles
Sinoatrial node (SAN)
The SAN is located in the wall of the right atrium.
The SAN acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals.
Contraction of the atria
The electrical waves from the SAN cause the right and left atria to contract together.
This forces blood in the right atrium into the right ventricle and blood in the left atrium into the left ventricle.
Atrioventricular node (AVN)
The waves of electrical activity cannot pass from the atria to the ventricles due to a collection of non-conducting tissue.
This creates a delay to ensure the atria are empty before the ventricles begin to contract.
The electrical activity passes through the AVN to the bundle of His.
The bundle of His is a collection of conducting tissue that transmits the electrical activity to the apex (bottom) of the heart and around the ventricle walls along fibres called the Purkyne fibres.
Contraction of the ventricles
As the waves of electrical activity pass along the Purkyne fibres, the ventricles contract together.
Blood is forced out of the ventricles and out of the heart.
2 main receptors in controlling heart rate:
Chemoreceptors
Baroreceptors
Chemoreceptors
Sensitive to changes in CO2 concentration.
If CO2 concentration is high, heart rate increases.
Found in the aortic body, in the wall of the aorta.
Found in the carotid body, in the wall of the carotid artery in the neck.
Baroreceptors
Sensitive to changes in blood pressure.
If blood pressure increases, heart rate decreases.
Found in the walls of various arteries but particularly in the carotid sinus (in the wall of the carotid artery).
Medulla oblongata
When stimulated, chemoreceptors and baroreceptors send a signal to a region in the brain called the medulla oblongata.
The region in the medulla which modifies heart rate is the cardiovascular centre.
The cardiovascular centre has two regions:
Cardio-inhibitory centre.
Cardio-acceleratory centre.
Nervous impulses are sent from these centres along the autonomic nervous system to the sinoatrial node (SAN).
Responses to high blood pressure
Detected by baroreceptors.
Impulses are sent from the medulla along parasympathetic neurones to the sinoatrial node (SAN.)
Acetylcholine is released (a neurotransmitter).
Heart rate slows down and blood pressure decreases.
Responses to low blood pressure
Detected by baroreceptors.
Impulses are sent from the medulla along sympathetic neurones to the SAN.
Noradrenaline is released (a neurotransmitter).
Heart rate rises and blood pressure increases.
Responses to Low CO2/High O2
Detected by chemoreceptors.
Impulses are sent from the medulla along parasympathetic neurones to the SAN.
Acetylcholine is released (a neurotransmitter).
Heart rate slows down and CO2 levels increase/O2 levels decrease.
Responses to low O2/high CO2
Detected by chemoreceptors.
Impulses are sent from the medulla along sympathetic neurones to the SAN.
Noradrenaline is released (a neurotransmitter).
Heart rate rises and O2 levels increase/CO2 levels decrease.
