AP® Psychology · Unit 1 · Topic 1.2
The Peripheral Nervous System
The peripheral nervous system is every nerve outside the brain and spinal cord, and it splits into the somatic division, which carries voluntary commands to skeletal muscles, and the autonomic division, which runs involuntary functions like heart rate and digestion.
The nervous system has two main branches: the central nervous system, which is the brain and spinal cord, and the peripheral nervous system, which is every nerve that fans out from the spinal cord to the rest of the body. The peripheral nervous system is the messenger service. It carries commands out to muscles and glands, and carries sensory information back in. That messenger service splits into two divisions based on what kind of job it's doing. The somatic division handles skeletal muscle, the kind you move on purpose, so it carries the signal when you decide to lift your arm or type a sentence. The autonomic division handles the organs you never have to think about, like your heart, lungs, and gut, so it keeps your heart beating and your stomach digesting without asking for your input.
The autonomic division itself splits again, into sympathetic and parasympathetic. Sympathetic nerves gear the body up for action, the fight-or-flight response: faster heartbeat, dilated pupils, slowed digestion. Parasympathetic nerves do the opposite, calming the body back down after the threat passes, often called rest-and-digest. So the full tree runs: nervous system, down to central and peripheral, peripheral splits into somatic and autonomic, autonomic splits into sympathetic and parasympathetic.
This branching explains why damage can be so selective. Somatic and autonomic nerves are physically separate pathways, so an injury to one leaves the other untouched in that same body part. This sets up the next topic nicely, the neuron itself, since every one of these divisions is really just a specialized set of neurons sending electrical and chemical signals along these separate routes.
Key terms
- Peripheral nervous system
- All the nerves outside the brain and spinal cord that connect the central nervous system to the rest of the body.
- Somatic division
- The branch of the peripheral nervous system that carries voluntary commands to skeletal muscles.
- Autonomic division
- The branch of the peripheral nervous system that controls involuntary functions like heart rate and digestion.
- Sympathetic nervous system
- The autonomic subdivision that activates the fight-or-flight response, speeding heart rate and alertness.
- Parasympathetic nervous system
- The autonomic subdivision that calms the body down, supporting rest and digestion after arousal.
Watch it explained
- How it worksHow does the peripheral nervous system branch into the somatic and autonomic divisions?
- How it worksWalk me through the whole nervous system tree from central all the way down to sympathetic.
- Going furtherWhat changes about a voluntary movement when the somatic nerves to that muscle are cut?
Check yourself
End of topic.