AP Psychology · Unit 1
AP Psychology Unit 1: Biological Bases of Behavior Terms
Biological Bases of Behavior is the unit that explains the hardware. Once you can picture a signal moving down an axon and across a synapse, half the vocabulary explains itself.
Read each definition with its example attached. Biology terms stick far better when they're tied to something you can actually picture happening in a body.
Study tip
Draw one neuron from memory and label six parts. If you can do that without looking, most of this unit's vocabulary is already in place.
22 terms, defined
Neuron
The basic cell of the nervous system, built to receive, carry, and pass along signals.
Example: The cell that fires when you touch something hot, before you have consciously decided anything.
Dendrite
The branching ends of a neuron that receive incoming messages from other neurons.
Example: The 'inbox' side of the cell, collecting signals from dozens of neighbors at once.
Axon
The long fiber that carries the neuron's signal away from the cell body toward other cells.
Example: A single axon running from your spinal cord all the way down to a muscle in your toe.
Myelin sheath
The fatty insulation wrapped around many axons that speeds up signal transmission.
Example: The reason a reflex arrives in milliseconds rather than crawling along the nerve.
Action potential
The brief electrical charge that travels down an axon once the neuron reaches its firing threshold.
Example: The all-or-nothing spike that either happens fully or does not happen at all.
Synapse
The tiny gap between two neurons where chemical messages cross.
Example: The space a neurotransmitter floats across after it is released from the sending neuron.
Neurotransmitter
A chemical messenger released at the synapse that influences whether the next neuron fires.
Example: Serotonin, dopamine, and GABA all doing very different jobs in the same gap.
Dopamine
A neurotransmitter involved in reward, motivation, movement, and learning what to repeat.
Example: The surge that makes you want to check your phone again after one interesting notification.
Serotonin
A neurotransmitter involved in mood, sleep, appetite, and arousal.
Example: Frequently discussed in research on depression and commonly targeted by SSRI medications.
Acetylcholine
A neurotransmitter involved in muscle movement, learning, and memory.
Example: Blocking it at the muscle produces paralysis; losing it in the brain is linked to memory loss.
Central nervous system
The brain and the spinal cord — the body's processing center.
Example: The spinal cord handling a knee-jerk reflex before the brain is even informed.
Peripheral nervous system
All the nerves outside the brain and spinal cord that connect it to the rest of the body.
Example: The nerves carrying the message from your fingertip to your spinal cord.
Sympathetic nervous system
The branch that mobilizes the body for action — the 'fight or flight' response.
Example: Heart pounding and palms sweating the second you realize you're being called on.
Parasympathetic nervous system
The branch that calms the body back down and conserves energy — 'rest and digest.'
Example: The slow settling you feel a few minutes after a near-miss in traffic.
Hypothalamus
A small brain structure regulating hunger, thirst, body temperature, and hormone release.
Example: The reason you start feeling cold and hungry at the same time on a long study night.
Hippocampus
A brain structure central to forming new explicit, long-term memories.
Example: Damage here can leave old memories intact while making new ones impossible to form.
Amygdala
A structure involved in processing fear, threat, and other strong emotional reactions.
Example: The jolt you feel before you consciously identify the shape in the dark as a coat.
Cerebral cortex
The wrinkled outer layer of the brain responsible for higher-order thinking and processing.
Example: Where the language you're reading right now is being interpreted.
Plasticity
The brain's ability to reorganize and form new connections in response to experience or injury.
Example: Nearby regions gradually taking over some functions after a stroke.
Circadian rhythm
The roughly 24-hour biological cycle that governs sleep, alertness, and body temperature.
Example: The mid-afternoon slump that arrives on schedule whether or not you slept well.
REM sleep
The sleep stage marked by rapid eye movement, vivid dreaming, and near-paralyzed muscles.
Example: Waking mid-dream and being briefly unable to move.
Absolute threshold
The minimum stimulation needed to detect a stimulus half the time.
Example: The quietest volume at which you can still just barely hear a tone.
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