The peripheral nervous system
The peripheral nervous system extends beyond the brain and spinal cord, and is split into two parts:
1. The autonomic nervous system
This controls involuntary muscles and internal organs to keep the body working as it should, via the sympathetic and parasympathetic nervous systems:
- The sympathetic nervous system prepares the body for action, for instance by causing breathing and heart rate to speed up and pupils to dilate, which is sometimes referred to as the fight or flight response and is fuelled by the hormone adrenaline
- The parasympathetic nervous system looks after the functions that happen when the body is at rest, for example the digestion of food.
2. The somatic nervous system
This coordinates voluntary movement via skeletal muscles.