What does the heritability of a trait estimate?	The proportion of variation in a trait across a population that can be attributed to genetic differences. It describes groups, not how much of one person's trait is genetic.
Why do researchers compare identical and fraternal twins?	Identical (monozygotic) twins share nearly all their genes and fraternal (dizygotic) twins share about half, so greater similarity between identical twins on a trait points to a genetic influence.
What can adoption studies reveal about behavior?	By comparing adopted children with their biological and adoptive parents, they help separate genetic influences (shared with biological parents) from environmental ones (shared with adoptive parents).
How does the evolutionary perspective explain behavior?	As the product of natural selection: behaviors that helped ancestors survive and reproduce were more likely to be passed on (e.g., a preference for sweet, calorie-rich food).
How does endocrine system communication differ from neural communication?	The endocrine system sends hormones through the bloodstream, which is slower than neural signaling but produces longer-lasting, more widespread effects.
Why is the pituitary gland called the master gland?	Under the direction of the hypothalamus, it releases hormones (such as growth hormone) that regulate the other endocrine glands.
What do the adrenal glands release during stress?	Epinephrine (adrenaline) and norepinephrine, which raise heart rate, blood pressure and blood sugar for fight or flight. They also release the stress hormone cortisol.
Which hormone is linked to social bonding, childbirth and breastfeeding?	Oxytocin, released by the pituitary gland.
Which hormone does the pineal gland secrete, and what does it regulate?	Melatonin, which rises in darkness and helps regulate the sleep-wake cycle.
How do ghrelin and leptin differ in their effect on hunger?	Ghrelin, secreted by an empty stomach, signals hunger. Leptin, secreted by fat cells, signals fullness and reduces appetite.
What is an agonist?	A drug or chemical that mimics a neurotransmitter or increases its effect at the receptor (e.g., morphine mimics endorphins).
What is an antagonist?	A drug or chemical that blocks a neurotransmitter from activating its receptor (e.g., curare blocks acetylcholine receptors and causes paralysis).
What does a reuptake inhibitor do at the synapse?	It stops the sending neuron from reabsorbing a neurotransmitter, so more stays in the synapse for longer (e.g., SSRIs and serotonin).
How do depressants affect the nervous system?	They slow neural activity and body functions (e.g., alcohol, barbiturates, benzodiazepines), often by enhancing the inhibitory effect of GABA.
How do stimulants affect the nervous system?	They speed up neural activity and arousal (e.g., caffeine, nicotine, cocaine, methamphetamine), many by increasing dopamine and norepinephrine activity.
What are hallucinogens?	Drugs that distort perception and evoke sensory images without sensory input (e.g., LSD and psilocybin).
How do opioids reduce pain?	They act as agonists at the brain's endorphin receptors, depressing neural activity and dulling pain (e.g., morphine, heroin, fentanyl).
What is drug tolerance?	The need for larger and larger doses to get the same effect, as the brain adapts to the drug's presence.
What is withdrawal?	The discomfort and distress that follow stopping an addictive drug, often the opposite of the drug's effects (e.g., fatigue and low mood after stopping a stimulant).
What is a circadian rhythm?	The body's roughly 24-hour biological clock that regulates sleep, alertness and temperature. Light resets it through the suprachiasmatic nucleus of the hypothalamus.
What brain waves mark NREM-3 sleep?	Large, slow delta waves. NREM-3 is the deepest stage, the hardest to wake from, and when most growth hormone is released.
What happens in the body during REM sleep?	The eyes dart, the brain is as active as when awake, vivid dreams occur and voluntary muscles are nearly paralyzed, which is why REM is called paradoxical sleep.
How does activation-synthesis theory explain dreams?	Dreams are the brain's attempt to make sense of random neural activity that the brainstem generates during REM sleep (Hobson and McCarley).
How does consolidation theory explain the function of sleep and dreams?	Sleep, including dreaming, helps the brain sort, strengthen and store the day's memories.
What is narcolepsy?	A sleep disorder with sudden, uncontrollable attacks of sleepiness, sometimes dropping the person straight into REM sleep.