The Heart and Circulatory System
The regular heart beat and pulse is produced by contractions of the
heart muscle during the cardiac cycle. These contractions are caused
by an electrical stimulus called the cardiac impulse. This natural
pacemaker of the heart, called the Sinoatrial node, is located in the
The electrical impulse leaves the Sinoatrial node and travels to the
right and left Atria, causing them to contract together. After
contraction, there is a period of insensitivity to stimulation which
allows the Ventricles to fill with blood. The impulse now at the
Atrioventricular node moves to the Bundle of His then divides into ...view middle of the document...
pressure is high, the rate of heart beat is lowered by impulses which
slow heart rate, from the cardiovascular centre via the vagus nerve.
When blood pressure is low, the rate of heart beat is increased. The
rate of heart beat is also influenced by impulses from the higher
centres of the brain.
Another factor that affects heart rate is Adrenaline. Adrenaline is a
hormone produced by the adrenal gland and secreted in tiny amounts
when you are afraid. It raises your heart rate immediately, preparing
you to run or fight. Adrenaline also improves the strength of the
contractions of the heart. Caffeine, sugar and other substances can
also affect heart rate.
Mechanisms of control of heart rate - nervous etc
Regulatory impulses come from the cardiovascular centre in the medulla
of the hind brain via two nerves:
The Sympathetic Nerve - part of the Sympathetic nervous system, helps
prepare the body for "fight or flight" and create conditions in the
tissues for physical activity. It is stimulated by strong emotions
such as anger and excitement and will therefore speed up heart rate,
increase the activity of sweat glands, adrenal glands, and decrease