In this article, we will be learning about the peripheral nervous system which is everything outside of the brain and spinal cord. The peripheral nervous system further divides into the somatic and autonomic peripheral nervous systems. The somatic nervous system is composed of sensory and motor nerves. Sensory nerves deliver information to the brain to process while motor nerves deliver the interpreted messages to the muscles of the body. When the muscles are excited, they will contract.

The autonomic system controls the automatic functions of the body, hence the name. The autonomic system divides again into the parasympathetic and sympathetic divisions. All organs are innervated by parasympathetic and sympathetic fibers. They are always both at work, but one or the other is more dominant at a given time. Whenever a person is under stress, the sympathetic nerves activate your “fight or flight” response. Think about what would happen if you encounter a lion. Your heart would beat faster, which makes your blood pressure shoot up. Your pupils would dilate so you could see better. The blood vessels to your skeletal muscles, heart, and brain would also dilate (increase in diameter) so that you could prepare to run and make a quick decision. Your airway would expand to let in more air to your lungs. The parasympathetic effects are the opposite of the sympathetic effects. When you are relaxed, the parasympathetic nerves return your body to homeostasis and help you “rest and digest.” Specifically, you begin to salivate, your gut starts to move food down, and your mucus production also increases.