Sympathetic and Parasympathetic Nerves

Parasympathetic nerves controls your body's systems when you are resting/digesting food.

Organ and Stimulation effect:

• Intercostal muscles: the parasympathetic nerves slow down the breathing rate, so would increase the time between the muscle contractions
• Heart: the nerves slow down the heart rate, and decrease the hearts stroke volume (volume of blood that is ejected from the left ventricle)
• Gut: stimulates the contractions of the muscles in the gut wall, (also known as peristalsis) moving food through the digestive system.

The parasympathetic nervous system also stops the release of adrenaline.

An example of a parasympathetic nerve is the vagus nerve that decreases the heart rate.

Think of the sympathetic nevrous system as being sympathetic to your plight. These nerves prepare your body and its systems for action. Sympathetic nerves are for the fight or flight response.

Organ and Stimulation effect:

• Intercostal muscles: the sympathetic nerves increase the breathing rate, so will increase the frequency of muscle contraction.
• the heart rate and stroke volume will be increased, allowing an increase in oxygen being supplied to muscles.
• inhibits peristalsis.

The sympathetic nerves will release adrenaline, for a longer term effect. Adrenaline will cause dilation of arterioles supplying skeletal muscles, and constriction of arterioles going to the digestive system and any other non-essential organs; maximising blood flow to the muscles you are about to move.