Control of Heart Rate

To understand how heart rate is controlled, it is important to understand how the cardiac cycle is controlled in the first place.

Control of the Cardiac Cycle:

1) The sinoatrial node (SAN) is a group of cells found in right atrium of the heart, that acts as a pacemaker.

2) A wave of electrical activity spreads out from the SAN, across the atria causing them to contract simultaneously.

3) The atriventricular septum prevents the wave crossing to the ventricles (this allows the atria to complete their contraction and completely empy of blood).

4) The wave passes to the atrioventricular node (AVN), which lies between the atria.

5) After a short delay, the AVN passes on the wave along specialised fibres called the Bundle of His.

6) When the wave of electrical activity is released from the fibres, the ventricles can contract.

• the control of heart rate involves the brain and autonomic nervous system

The Autonomic Nervous System:

- means self-governing

- controls the involuntary activities of internal muscles and glands

- two divisions:

1) Sympathetic Nervous System

- stimulates effectors so speeds up activity

- helps us to cope with stressful situations (i.e. by heightening awareness and preparation for activity).

2) Parasympathetic Nervous System

- inhibits effectors so slows down activity

- controls activity under normal resting conditions

- focussed on conserving energy and replenishing the body's reserves

* the two systems are antagonistic because they oppose one another

• the average heart rate of a typical adult is 70 beats per minute

- this has to be altered to meet the varying demand for oxygen

The Medulla Oblongata:

- the region of…