AP PSYCHOLOGY UNIT 1 BIOLOGICAL BASES OF BEHAVIOR 2026
Unit 1: Biological Basis of Behavior (1.1 – 1.6 + Unit 0 extras)
Unit 0: Research Methods
Longitudinal Study: Same group over time; shows developmental changes; expensive.
Cross-Sectional Study: Compares different groups at one point; cheaper; no individual tracking.
1.1 Interactions of Heredity & Environment
Epigenetics: Environment can turn genes on/off without changing DNA sequence.
Biological Psychology: Links biology (brain, hormones, nervous system) & behavior.
Evolutionary Psychology: Traits/behaviors survive if they help reproduction/survival.
Twin Studies: Compare identical vs. fraternal twins to separate genetic vs. environmental effects.
1.2 Overview of the Nervous System
CNS: Brain + spinal cord; main control center.
PNS: Connects CNS to body.
Somatic NS: Voluntary movement.
Autonomic NS: Involuntary functions:
Sympathetic: “Fight-or-flight” → ↑ heart rate, ↓ digestion.
Parasympathetic: “Rest-and-digest” → calms body.
1.3A Neural Communication & Endocrine System
Neuron Structure & Function
Dendrites: Receive messages from other neurons.
Soma (Cell Body): Processes signals; contains nucleus.
Axon: Sends impulses away from cell body.
Myelin Sheath: Insulates axon; speeds signals; made of glial cells.
Nodes of Ranvier: Gaps in myelin → faster signal transmission.
Axon Terminals: Release neurotransmitters into synapse.
Synapse: Gap where neurotransmitters cross to next neuron.
Neurotransmitters: Chemical messengers (ACh, Dopamine, Serotonin, Norepinephrine, GABA, Glutamate, Endorphins).
Types of Neurons:
Sensory (Afferent): Carry info to CNS.
Motor (Efferent): Carry info from CNS to muscles/glands.
Interneurons: Connect sensory & motor neurons in CNS.
Neural Firing Process: Resting potential → action potential → refractory period → all-or-none principle.
Endocrine System: Pituitary (master), adrenal (stress), thyroid (metabolism); slower than nervous system but long-lasting effects.
1.3B Substance Use Disorders & Psychoactive Drugs
Key Terms: Psychoactive drugs, substance use disorder, tolerance, withdrawal, addiction.
Drug Type | Example | Effects | Risks/Withdrawal |
|---|---|---|---|
Stimulants | Nicotine | Energy, alertness, dopamine | Cravings, heart disease |
Depressants | Alcohol | Relaxation, slowed CNS | Memory loss, liver damage |
Hallucinogens | LSD | Altered perception, hallucinations | Flashbacks, panic attacks |
Opioids | Heroin | Pain relief, euphoria | Addiction, respiratory failure |
1.4A Brain: Neuroplasticity & Tools of Discovery
Neuroplasticity: Brain reorganizes after damage/learning.
Lesions: Tissue destruction → function loss.
Brain Tools:
Tool | Measures | Structure/Function | Pros | Cons |
|---|---|---|---|---|
EEG | Electrical activity | Function | Great timing | Poor spatial detail |
CT | X-rays | Structure | Quick, cheap | Radiation |
MRI | Magnetic fields | Structure | High detail, no radiation | Expensive |
fMRI | Blood flow/oxygen | Structure + function | Real-time activity | Slower than EEG |
PET | Glucose metabolism | Function | Shows active regions | Less detail, radiation |
MEG | Magnetic fields | Function | Timing + location precision | Rare, expensive |
1.4B Brain Regions & Structures (In Depth)
Hindbrain
Medulla: Heartbeat, breathing.
Pons: Sleep, arousal, movement coordination.
Reticular Formation: Alertness, attention.
Cerebellum: Balance, coordination, procedural memory.
Limbic System
Hippocampus: Memory formation.
Hypothalamus: Homeostasis, hunger, thirst, sexual behavior; controls pituitary.
Thalamus: Sensory relay (except smell).
Amygdala: Fear, aggression, emotional memory.
Pituitary Gland: Master endocrine gland.
Cerebral Cortex & Lobes
Frontal Lobe: Planning, judgment, voluntary movement, Broca’s area.
Parietal Lobe: Sensory info, spatial reasoning.
Occipital Lobe: Vision.
Temporal Lobe: Hearing, Wernicke’s area, memory.
Language Areas
Broca’s Area: Speech production.
Wernicke’s Area: Speech comprehension.
Corpus Callosum
Connects hemispheres; allows communication; split-brain research shows independent hemisphere function.
Brain Lateralization: Left vs. Right Hemispheres
Hemisphere | Main Functions |
|---|---|
Left | Language, speech, writing, math, logic; controls right side of body |
Right | Spatial skills, facial recognition, music, art, emotion; controls left side |
1.5 Sleep & Sleep Disorders
Sleep Stages & Brain Waves
Stage | Brain Waves | Key Features |
|---|---|---|
NREM-1 | Theta | Light sleep, hypnagogic sensations (falling/floating) |
NREM-2 | Theta + spindles + K-complex | Deeper sleep, body temp drops, heart rate slows |
NREM-3 | Delta | Deep sleep, growth hormone release, body repairs |
REM | Beta | Vivid dreams, paradoxical sleep (active brain, paralyzed body), memory consolidation |
Cycle: NREM-1 → NREM-2 → NREM-3 → NREM-2 → REM → repeat (~90 min).
Theories on Sleep: Protection, restoration, memory consolidation, creativity/problem-solving.
Sleep Disorders
Insomnia: Trouble falling/staying asleep; causes fatigue, memory problems.
Narcolepsy: Sudden sleep attacks; may enter REM instantly; cataplexy possible.
Sleep Apnea: Breathing stops during sleep → awakenings; causes loud snoring, daytime sleepiness.
Somnambulism (Sleepwalking): Occurs in NREM-3; walking/talking while asleep.
Other Terms:
Circadian rhythm → 24-hour biological clock.
Melatonin → hormone signaling sleep onset.
Sleep deprivation → memory issues, immune suppression, irritability.
1.6 Sensation & Perception (In Depth)
Basic Concepts
Sensation, perception, bottom-up/top-down processing, transduction, absolute threshold, signal detection, difference threshold (JND), Weber-Fechner Law, sensory adaptation, synesthesia.
Vision
Eye Structures: Cornea, iris, pupil, lens, retina (rods, cones, bipolar, ganglion), fovea, optic nerve.
Processing: Feature detectors, parallel processing.
Color Vision Theories: Trichromatic (cones = R,G,B), Opponent-Process (red-green, blue-yellow, black-white).
Color Blindness: Dichromacy = 2 cone types; Monochromacy = 1 or none.
Vision Problems: Myopia (nearsighted), Hyperopia (farsighted), Presbyopia (aging lens).
Ear Structures:
Outer: Pinna, auditory canal
Middle: Eardrum, ossicles (hammer, anvil, stirrup)
Inner: Cochlea, basilar membrane, semicircular canals, auditory nerve
Sound Processing: Amplitude = loudness; Frequency = pitch.
Pitch Theories: Place theory (high), Frequency theory (low).
Hearing Loss: Conduction (mechanical), Sensorineural (nerve damage).
Other Senses
Touch: Pressure, warmth, cold, pain; nociceptors; Gate-Control Theory; sensory adaptation.
Taste (Gustation): 5 tastes: sweet, sour, salty, bitter, umami; taste buds & receptor cells.
Smell (Olfaction): Chemical sense; olfactory bulb → brain; linked to memory/emotion.
Vestibular Sense: Balance; semicircular canals detect head movement.
Kinesthetic Sense: Awareness of body position & movement; receptors in muscles, joints, tendons.
Sensory Interaction: Senses influence each other (e.g., smell + taste = flavor).