AP Psychology Unit 1: Biological Bases of Behavior Study Guide

Unit 1 of AP Psychology is where the course earns its reputation for being harder than students expect. It front-loads biology vocabulary before you have a behavioral story to attach it to. The fix is to stop treating the unit as a list of parts and start treating it as a chain: a cell receives input, generates a signal, releases a chemical, joins a circuit, and the circuit produces behavior.

Step 1: The neuron is an input-output device

A neuron has three functional regions worth knowing cold. Dendrites collect incoming signals. The cell body adds them up. The axon carries the outgoing signal to the terminals, wrapped in a fatty myelin sheath that speeds the trip.

The signal itself is the action potential: an all-or-nothing electrical event. All-or-nothing means intensity is not coded by a bigger spike; it is coded by how often the neuron fires. That distinction is a favorite exam question.

Step 2: Neurons talk chemically

Neurons never touch. At the synapse, the electrical signal triggers the release of neurotransmitters into a gap, where they bind to receptors on the next cell. Leftover chemicals are taken back up — the process most antidepressants target.

Learn each neurotransmitter by its behavioral job, not its spelling:

Neurotransmitter	Behavioral job	A memorable case
Dopamine	Reward, motivation, movement	Loss of dopamine neurons is central to Parkinson's disease
Serotonin	Mood, sleep, appetite	Targeted by SSRI antidepressants
Acetylcholine	Muscle movement, memory	Depleted in Alzheimer's disease
GABA	Main inhibitory signal	Enhanced by anti-anxiety medication
Glutamate	Main excitatory signal	Excess is linked to seizures
Endorphins	Pain relief, euphoria	The "runner's high"

Step 3: The nervous system is a set of nested boxes

The central nervous system is the brain and spinal cord. Everything else is the peripheral nervous system, which splits into the somatic system (voluntary muscles) and the autonomic system (automatic organs). The autonomic system splits once more: sympathetic for arousal and parasympathetic for calming down.

Draw those nested boxes once by hand. On exam day you will reconstruct them in under a minute, and every question about "which system is active during a stress response" becomes a lookup instead of a guess.

Step 4: Brain structures, sorted by what they do

Rather than memorizing a diagram, sort structures by function.

• Survival and regulation: medulla (heartbeat, breathing), pons, reticular formation (arousal), hypothalamus (hunger, thirst, temperature, hormones).
• Movement and coordination: cerebellum, basal ganglia.
• Emotion and memory: amygdala (fear and threat detection), hippocampus (forming new explicit memories).
• Thinking and planning: the four cortical lobes — frontal (planning, judgment, motor cortex), parietal (touch, spatial), temporal (hearing, language comprehension), occipital (vision).

Step 5: Connect biology to behavior

Free-response questions rarely ask for a definition alone. They ask you to apply a structure to a scenario. Practice the sentence form: "Because [structure] is responsible for [function], damage to it would cause [specific behavioral change]."

Try it three times right now with the amygdala, the hippocampus, and the frontal lobe. If you can produce those three sentences without notes, you understand Unit 1 better than a student who has re-read the chapter twice.

A one-page review plan

1. Sketch the neuron and label six parts from memory.
2. Write the six neurotransmitters and one behavior each.
3. Draw the nervous system boxes.
4. Group ten brain structures by the four functions above.
5. Write three "damage to X would cause Y" sentences.

That is the whole unit compressed into five active-recall passes — far more effective than another highlighter session.