1. Control of heart rate

2. Heart rate Cardiac muscle – myogenic
If removed from body – still beats
Lots of different cells – coordination and regulation needed
Nervous (electrical impulses) and Hormonal (chemical)

3. Regulation of heart beat
Cardiac cycle started by the pacemaker or Sinoatrial Node (these cells don’t contract)
SAN / pacemaker (1) – right atrium
Impulse spread to Atrioventricular Node (AVN) (2) then to rest of heart via the Bundle of His (3) and Purkinje fibres (4 and 5)

5. Heart rate is controlled by:
Hormones:
Adrenaline
Noradrenaline
Nerves:
Parasympathetic nervous system
Sympathetic nervous system

6. Hormonal Control of heartbeat
Sympathetic nervous system – increases
Stress: noradrenaline released by sympathetic nerves and the cardiac nerve.
Adrenal gland secretes adrenaline and noradrenaline.
Increase the force and rate of heart contraction, increasing cardiac output.
More blood pumped to the muscles

7. Nervous control of heartbeat
Sympathetic and parasympathetic – antagonistic (work against each other)
Sympathetic stimulation via cardiac nerve is the predominant influence.
The effector bringing about the response is the heart muscle.

8. Controls conditions under stress or activity
Sympathetic
Stimulates effectors
Controls conditions under stress or activity
Speeds us up (fight or flight)
Parasympathetic
Inhibits effectors
Controls actions under resting conditions
Slows down activity
Conserves energy

10. Medulla oblongata Area of the brain that controls the heart rate.
Two parts:
1. A centre linked to sinoatrial node that increases heartrate via the sympathetic nervous system.
2. A centre linked to the sinoatrial node that decreases heart rate via the parasympathetic nervous system.

11. Receptors
Pressure changes in the blood – pressure receptors in wall of aorta and carotid artery send messages via SNS if blood pressure low and through PSNS when blood pressure high.
Chemical changes in the blood – low O2 means increased CO2 and reduced pH. Detected by chemoreceptors in wall of aorta and carotid artery. Heart rate increases via SYS. Removal of CO2 increases pH, and heart rate reduced via PSNS.

12. and finally………
What would be the effect of severing the nerves from the medulla to the SAN?
Explain how high blood pressure in the aorta causes the heart to slow down.
Draw a poster to explain how heart rate is controlled.