AP® Psychology review sheet from Aim for Five (aimforfive.com/psych/units/1/1-2)
Unit 1 · Topic 1.2
1.2 Overview of the Nervous System
Your nervous system has two main parts: the central nervous system (brain and spinal cord), which makes decisions, and the peripheral nervous system, which carries messages between the central system and the rest of your body. The peripheral system splits into the somatic system for voluntary movement and the autonomic system for automatic functions, whose sympathetic branch arouses you and whose parasympathetic branch calms you.
Key terms
- central nervous system
- peripheral nervous system
- somatic nervous system
- autonomic nervous system
- sympathetic nervous system
- parasympathetic nervous system
The big picture
Think of your nervous system as an organization with headquarters and messengers. The central nervous system (CNS) is headquarters: your brain and your spinal cord. It takes in information, makes sense of it and decides how to respond. The spinal cord also carries messages between your brain and body and handles some simple reflexes on its own.
The peripheral nervous system (PNS) is the messengers: all the nerves outside the brain and spinal cord. It carries sensory information from your body into the CNS and carries commands from the CNS out to your muscles and organs.
| Division | What it includes | Main job |
|---|---|---|
| Central nervous system | Brain and spinal cord | Processes information and decides on responses |
| Peripheral nervous system | All nerves outside the brain and spinal cord | Relays messages between the CNS and the body |
| Somatic nervous system | Nerves to skeletal muscles and from sense receptors | Voluntary movement and sensory input |
| Autonomic nervous system | Nerves to organs and glands | Involuntary functions like heartbeat and digestion |
| Sympathetic nervous system | Part of the autonomic system | Arouses the body for action (fight or flight) |
| Parasympathetic nervous system | Part of the autonomic system | Calms the body and saves energy (rest and digest) |
Somatic versus autonomic
The somatic nervous system controls the skeletal muscles you move on purpose. When you raise your hand, type a text or kick a ball, your somatic system carries the command from your brain to those muscles. It also carries information from your senses, like touch on your skin, back to the CNS.
The autonomic nervous system runs things you don't consciously control: heart rate, breathing rate, digestion, sweating and pupil size. 'Autonomic' sounds like 'automatic,' which is a handy way to remember it.
Sympathetic versus parasympathetic
The autonomic system has two branches that usually work in opposite directions. The sympathetic nervous system prepares you to handle a threat or challenge. It speeds up your heart and breathing, dilates your pupils, sends blood to your muscles, releases stored energy, increases sweating and slows digestion. It also triggers the release of the hormone adrenaline, which keeps the arousal going.
The parasympathetic nervous system brings you back to baseline. It slows your heart and breathing, constricts your pupils and restarts digestion. Picture finishing a scary roller coaster: your sympathetic system was in charge during the drop, and your parasympathetic system takes over as you calm down on the walk to the next ride.
One way to remember them: sympathetic is for stress (both start with s), and parasympathetic is for peace (both start with p).
Why it matters in psychology
These divisions show up all over the course. The sympathetic response is the body side of emotion (4.7) and stress (5.1). Lie detector tests (polygraphs) measure sympathetic arousal like heart rate and sweating, which is why they can mistake nervousness for lying. Therapies such as biofeedback (5.5) teach people to lower their sympathetic arousal on purpose.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Identifying the active division
Maya is giving a speech in class. Her heart pounds, her mouth goes dry and her hands sweat. After she sits down, her breathing slows and she suddenly feels hungry. Which divisions of the nervous system explain each part of her experience?
Show the solutionHide the solution
- Step 1: During the speech, her heart rate rose, saliva decreased and she sweated. These are involuntary, so they belong to the autonomic nervous system.
- Step 2: They are signs of arousal, so they come from the sympathetic branch, which slows digestion (dry mouth) and prepares the body for action.
- Step 3: After the speech, her breathing slowed and digestion restarted (hunger). Those calming changes come from the parasympathetic branch.
- Step 4: Her walking to and from the front of the room is voluntary movement, which is controlled by the somatic nervous system.
Answer: Sympathetic (autonomic) during the speech, parasympathetic (autonomic) as she calms down, and somatic for her voluntary movements.
Common mistakes
- Thinking 'sympathetic' means kind or calming. In psychology, the sympathetic branch is the arousing one; the parasympathetic branch calms.
- Placing the spinal cord in the peripheral nervous system. It is part of the central nervous system.
- Saying the somatic system controls heartbeat or digestion. Those are autonomic; the somatic system handles voluntary skeletal muscle movement.
On the exam
- Multiple-choice questions often describe a body reaction and ask which division is active. Ask yourself: voluntary or involuntary? Aroused or calming?
- If a free-response question involves stress, emotion or fear, mentioning sympathetic arousal is often a strong, accurate link.
Connected topics
Videos
Check yourself
4 questions on 1.2 Overview of the Nervous System. Pick an answer to see if you got it, and why.
| Condition | Heart rate (beats per minute) | Saliva produced (mL in 5 minutes) | Pupil diameter (mm) |
|---|---|---|---|
| Resting baseline | 70 | 1.5 | 3.5 |
| Watching a frightening film clip | 92 | 0.6 | 5.0 |
| After 10 minutes of slow breathing | 66 | 1.7 | 3.3 |
Hypothetical means for 40 adult volunteers, each measured in all three conditions
The changes from the resting baseline to the frightening film clip are best explained by increased activity in the
Before the film, volunteers were asked to keep their heart rate and pupil size steady by willpower alone. Almost none could. This finding is most consistent with the fact that these changes are controlled by
After a diving accident, a swimmer has damage to his spinal cord in his upper back. Which part of the nervous system was injured?
A soccer player sees an open net and decides to kick the ball toward it. The nerves that carry the command from her spinal cord to the muscles in her leg belong to the
0 of 4 answered