Overview of the
Nervous System
Explore how your body's electrical communication network coordinates every thought, sensation, and action through billions of interconnected neurons.
AP Psychology
What Is the Nervous System?
The nervous system is your body's primary communication network. It uses electrochemical signals to transmit information at incredible speeds, allowing you to think, feel, move, and respond to your environment.
Two Major Divisions
Central Nervous System (CNS)
The brain and spinal cord: the command center that processes and integrates all incoming information.
Peripheral Nervous System (PNS)
All nerves outside the brain and spinal cord: the communication lines connecting the CNS to the rest of the body.
The Neuron: Building Block
How Neurons Communicate
1
Resting potential: The neuron is at about \( -70 \, \text{mV} \), waiting for a signal (more negative ions inside).
2
Action potential: If stimulation exceeds the threshold, an electrical impulse fires down the axon in an all-or-nothing response.
3
Synapse: The impulse reaches the terminal buttons and triggers the release of neurotransmitters into the synaptic gap.
4
Reception: Neurotransmitters bind to receptors on the next neuron's dendrites, continuing or inhibiting the signal.
Nervous System Hierarchy
Somatic vs Autonomic
| Somatic | Autonomic | |
|---|---|---|
| Control | Voluntary | Involuntary |
| Targets | Skeletal muscles | Organs, glands, smooth muscle |
| Example | Raising your hand | Heart rate speeding up |
| Key Feature | Conscious awareness | Operates "behind the scenes" |
Sympathetic vs Parasympathetic
Sympathetic
Arouses the body for action. Increases heart rate, dilates pupils, inhibits digestion, releases glucose for energy.
Parasympathetic
Calms the body down. Slows heart rate, constricts pupils, stimulates digestion, conserves energy.
Key Neurotransmitters
Serotonin
Regulates mood, sleep, and appetite. Low levels linked to depression.
Dopamine
Drives reward, motivation, and movement. Linked to addiction and Parkinson's disease.
Acetylcholine
Enables muscle action, learning, and memory. Deterioration linked to Alzheimer's.
GABA
Major inhibitory neurotransmitter. Calms neural activity. Low levels linked to anxiety.
The Synaptic Gap
Three Types of Neurons
Sensory (Afferent)
Carry signals from sense organs to the CNS. They bring information in.
Motor (Efferent)
Carry signals from the CNS to muscles and glands. They send commands out.
Interneurons
Connect sensory and motor neurons within the CNS. They process and integrate information.
The Reflex Arc in Action
Nervous System + Endocrine System
| Nervous System | Endocrine System | |
|---|---|---|
| Speed | Fast (milliseconds) | Slow (seconds to hours) |
| Signal Type | Electrochemical impulses | Hormones via bloodstream |
| Duration | Brief, precise | Long-lasting, widespread |
| Target | Specific neurons/muscles | Multiple organs at once |
How to Identify Components
1
Is it voluntary or involuntary? Voluntary = somatic. Involuntary = autonomic.
2
Is the body aroused or calmed? Aroused = sympathetic. Calmed = parasympathetic.
3
Where is information going? Toward the brain = sensory (afferent). Away from brain = motor (efferent).
4
Is it fast or slow? Fast and specific = nervous system. Slow and widespread = endocrine system.
Example: A Bear in the Woods
You are hiking and suddenly see a bear. Your heart races, your pupils dilate, and your muscles tense. Let's trace the nervous system response:
1
Eyes (sensory receptors) detect the bear and send signals via sensory neurons to the brain.
2
The brain (CNS) interprets the danger via interneurons.
3
The sympathetic division activates: heart rate increases, adrenaline surges, digestion halts.
4
Motor neurons signal your legs to run (somatic, voluntary response).
Example: After the Danger Passes
You realize the "bear" is just a large dog. The threat is gone. What happens next?
Parasympathetic Activates
Heart rate slows, breathing deepens, digestion resumes, pupils constrict.
Homeostasis Restored
The body returns to its baseline state. Energy conservation mode activates.
Common Mistakes
✕ Confusing CNS with PNS
The brain and spinal cord are CNS. All other nerves are PNS. Don't mix them up.
✕ Mixing Up Sympathetic
Sympathetic = arousal (fight/flight), not "sympathy." Parasympathetic = calm (rest/digest).
✕ Afferent vs Efferent
Afferent = arriving at brain (sensory). Efferent = exiting brain (motor). Use the mnemonic!
Complete Summary
| Component | Function | Key Detail |
|---|---|---|
| CNS | Processes information | Brain + Spinal Cord |
| PNS | Transmits signals | All other nerves |
| Somatic | Voluntary movement | Skeletal muscles |
| Autonomic | Involuntary control | Organs and glands |
| Sympathetic | Fight or flight | Arouses the body |
| Parasympathetic | Rest and digest | Calms the body |
Question 1 of 5
Which division of the nervous system consists of the brain and spinal cord?
The Central Nervous System (CNS) is composed exclusively of the brain and spinal cord. The PNS includes all nerves outside these structures. Somatic and autonomic are subdivisions of the PNS.
Question 2 of 5
When you touch a hot pan and your hand jerks away before you feel pain, this is because:
In a reflex arc, the spinal cord (not the brain) processes the signal and sends a motor response. The brain is notified after the hand has already moved, which is why you feel pain a moment later.
Question 3 of 5
A student's heart races before giving a speech. Which division of the autonomic nervous system is most responsible?
The sympathetic nervous system activates the body's "fight or flight" response, increasing heart rate, blood pressure, and alertness. The parasympathetic system would slow the heart rate after the stressor passes.
Question 4 of 5
Which neurotransmitter is most closely associated with voluntary muscle movement and has been linked to Alzheimer's disease?
Acetylcholine plays a critical role in muscle contraction, learning, and memory. Its deterioration is strongly linked to Alzheimer's disease. Dopamine is linked to Parkinson's; serotonin to depression; GABA to anxiety.
Question 5 of 5
Sensory neurons are also called afferent neurons because they:
Afferent means "arriving": sensory neurons carry information toward the CNS. Efferent means "exiting": motor neurons carry signals away from the CNS to muscles and glands.