Control of heart rate

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)

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)

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

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

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.

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

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.

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.

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.