The body’s automatic

control of the heart

The Autonomic Nervous system

Controls your body automatically (without you having to think about it)

Is made up of two parts:Sympathetic (which speeds things up)Parasympathetic (which slows things down)

If a scary monster jumps out at you, sympathetic nerves tell the SA node in your heat to increase heart rate (so you can FREAK OUT)

If the scary monster is actually friendly and wants to have a cup of tea with you, parasympathetic nerves tell your SA node to slow your heart rate down (so you can chill out)

Blood pressure control

It is important that blood pressure isn’t too high or too low. If it is too low then blood won’t travel well around your body. If it is too high it strains and weakens the walls of the blood vessels.

The sympathetic nervous system can increase blood pressure when needed by increasing heart rate AND by causing constriction of blood vessels

The parasympathetic nervous system can decrease blood pressure when needed by decreasing heat rate AND by dilating blood vessels.

Special receptors (called baroreceptors) in the walls of the carotid arteries detect high blood pressure

They send a signal to a part of the brain called the medulla oblongata, which is in charge of the autonomic nervous system, and tell it to stimulate the parasympathetic nervous system to decrease blood pressure

When blood pressure is low the baroreceptors shut off, so the medulla oblongata will stop stimulating the parasympathetic nervous system and instead stimulate the sympathetic nervous system to increase blood pressure

Chemicals that affect blood vessels

If there is a build up of harmful substances such as acids, lactic acid, and CO2 in the blood then the blood vessels will detect this and dilate (to help increase blood flow of these wastes away from tissues)

If that scary monster comes back your sympathetic nervous system will stimulate your body to produce the hormones epinephrine and norepinephrine

Both of these hormones increase heart rate, breathing rate and cause constriction of blood vessels (which is called the “fight or flight” reaction)