AP Psychology 1.1–1.3: Heredity, Nervous System & Neurotransmitters

1.1 Heredity

The genetic transfer of traits and characteristics from biological parents to offspring. Example: Eye color, blood type, and height potential are determined by the genes passed down from your biological parents.

1.1 Eugenics

A discredited, unethical movement that aimed to "improve" the genetic quality of the human population through selective breeding or forced sterilization. Example: In the early 20th century, policies were enacted to sterilize individuals with intellectual disabilities to prevent them from passing on their genes.

1.1 Evolutionary Psychology

The study of how natural selection and evolutionary principles explain human behavior, mental processes, and psychological adaptations. Example: Explaining our preference for high-calorie fatty foods as an evolutionary survival mechanism from when food was scarce.

1.1 Natural Selection

The evolutionary process where traits that increase an organism's chances of survival and reproduction are more likely to be passed on to future generations. Example: Early humans who possessed a fear of dangerous predators were more likely to survive, reproduce, and pass on that trait.

1.1 Nature and Nurture

The debate and interaction concerning the relative contributions of genetic inheritance (nature) and environmental factors (nurture) in human development. Example: A child may inherit a genetic predisposition for musical talent (nature), but will only become a skilled pianist if they receive lessons and practice time (nurture).

1.1 Behavior Genetics

The scientific study of the relative power and limits of genetic and environmental influences on behavior and traits. Example: Researchers studying whether a tendency toward high anxiety is caused primarily by specific genes or by stressful childhood environments.

1.1 Twin Studies

Research comparing identical twins (100% shared genes) and fraternal twins (50% shared genes) to isolate the influences of heredity versus environment. Example: Finding that identical twins raised in separate households still share remarkably similar personality traits suggests a strong genetic component to personality.

1.2 Nervous System

The body's primary electrochemical communication network, consisting of all nerve cells in the central and peripheral systems. Example: When you touch a hot stove, your nervous system rapidly sends sensory signals to your brain and motor signals to pull your hand away.

1.2 Central Nervous System (CNS)

The body's master control center, consisting exclusively of the brain and the spinal cord. Example: The brain interprets the meaning of spoken words and formulates a reply, while the spinal cord routes signals down toward the vocal cords.

1.2 Peripheral Nervous System (PNS)

The sensory and motor neurons that connect the Central Nervous System to the rest of the body (muscles, organs, and glands). Example: Nerves running from your spine down to your toes that allow you to feel the floor and wiggle your toes.

1.2 Somatic Nervous System

A subdivision of the PNS that controls voluntary movements of skeletal muscles and transmits sensory info to the CNS. Example: Consciously deciding to reach out your arm and pick up a water bottle.

1.2 Autonomic Nervous System

A subdivision of the PNS that regulates involuntary, automatic internal bodily functions like heartbeat, digestion, and breathing. Example: Your stomach digesting food or your heart pumping faster while running without you consciously thinking about it.

1.2 Sympathetic Nervous System

The division of the autonomic nervous system that arouses the body and mobilizes energy during stress ("fight or flight"). Example: Your heart rate spikes, pupils dilate, and breathing quickens when you suddenly hear a loud crash in the dark.

1.2 Parasympathetic Nervous System

The division of the autonomic nervous system that calms the body and conserves energy after a stressful event ("rest and digest"). Example: Your heart rate slows down and your breathing normalizes after discovering the loud noise was just a fallen book.

1.3 Neuron

A specialized cell that serves as the basic building block of the nervous system, receiving, processing, and transmitting electrochemical information. Example: A single nerve cell firing an electrical impulse along its axon to communicate with a neighboring nerve cell.

1.3 Glial Cells

Non-neuronal cells in the nervous system that support, nourish, insulate (via myelin), and protect neurons. Example: Schwann cells and oligodendrocytes producing myelin sheaths to speed up electrical conduction along neurons.

1.3 Spinal Cord

A thick bundle of nerve fibers running through the spine that connects the brain to the peripheral nervous system and handles simple reflexes. Example: Signals traveling up the spinal cord to tell the brain you tripped, while automatically catching your balance.

1.3 Reflex Arc

A direct, simple neural pathway that controls an involuntary response, bypassing the brain for speed by processing through the spinal cord. Example: Pulling your hand off a sharp pin instantly before your brain actually perceives the pain sensation.

1.3 Sensory Neurons (Afferent)

Neurons that carry incoming information from sensory receptors (eyes, skin, ears) toward the brain and spinal cord. Example: Sensory neurons in your fingertip sending signals to your brain when you touch soft velvet.

1.3 Motor Neurons (Efferent)

Neurons that carry outgoing information from the brain and spinal cord to muscles and glands to trigger movement. Example: Motor neurons signaling your leg muscles to contract so you can step forward.

1.3 Interneurons

Neurons located exclusively within the brain and spinal cord that process information internally between sensory inputs and motor outputs. Example: Neurons in your spinal cord taking a signal from a sensory neuron and immediately passing it to a motor neuron during a reflex.

1.3 All-or-None Response

The principle that a neuron fires completely at full strength or does not fire at all; increasing stimulus strength will not increase impulse speed or size. Example: Pressing a light switch—flipping it harder does not make the bulb turn on brighter or faster; it simply turns on.

1.3 Depolarization

The sudden change in electrical charge across a neuron's membrane when sodium ions rush inside, making the interior less negative and triggering an action potential. Example: Positive sodium ions rushing into an axon, causing the internal charge to flip from -70mV to +40mV.

1.3 Resting Potential

The baseline, polarized state of an inactive neuron, where the inside of the cell has a negative charge (-70mV) relative to the outside. Example: A neuron sitting ready to fire, holding a negative charge internally like a charged battery waiting to be used.

1.3 Refractory Period

A brief resting pause after a neuron has fired during which it resets its electrical charge and cannot fire another action potential. Example: Immediately after pulling a toilet handle, you cannot flush it again until the tank re-fills with water.

1.3 Threshold

The minimum level of stimulation required to trigger a neural impulse/action potential (typically around -55mV). Example: Gently brushing against a single hair may not trigger a nerve impulse, but pushing harder crosses the threshold and fires the neuron.

1.3 Reuptake

The reabsorption of excess neurotransmitters by the sending axon terminal after they have transmitted a signal across the synaptic gap. Example: A neuron re-absorbing leftover serotonin from the synapse to recycle it for future use.

1.3 Multiple Sclerosis (MS)

A chronic disease in which the immune system attacks and degrades the myelin sheath surrounding axons, slowing or blocking neural signals. Example: A patient experiencing muscle weakness, numbness, and loss of coordination because signal transmission along motor nerves is disrupted.

1.3 Myasthenia Gravis

An autoimmune disorder where antibodies block or destroy acetylcholine receptors at the neuromuscular junction, leading to muscle weakness. Example: A person experiencing drooping eyelids and difficulty chewing due to impaired muscle contraction signals.

1.3 Excitatory

A signal or neurotransmitter that increases the likelihood that a receiving neuron will cross threshold and fire an action potential. Example: Glutamate binding to a postsynaptic neuron, pushing its electrical charge closer to the firing threshold.

1.3 Inhibitory

A signal or neurotransmitter that decreases the likelihood that a receiving neuron will fire an action potential. Example: GABA binding to a postsynaptic neuron, hyperpolarizing it and making it stay at rest.

1.3 Action Potential

A brief electrical impulse (spike) that travels down the axon of a neuron when it is stimulated past its threshold. Example: The wave of positive charge rushing down a sensory nerve fiber from your hand to your spine.

1.3 Neurotransmitters

Chemical messengers that cross the synaptic gap between neurons to bind to receptor sites on receiving cells. Example: Dopamine traveling across a synapse to bind to receptor proteins on an adjacent cell.

1.3 Acetylcholine (ACh)

A key neurotransmitter responsible for enabling muscle action, learning, and memory (depleted in Alzheimer's disease). Example: ACh released at neuromuscular junctions allows your biceps muscle to contract when lifting a weight.

1.3 Dopamine

A neurotransmitter associated with movement, learning, attention, and the brain's pleasure/reward system (linked to Parkinson's and schizophrenia). Example: Feeling a surge of satisfaction after winning a game, reinforcing the desire to play again.

1.3 Serotonin

A neurotransmitter that regulates mood, hunger, sleep, and arousal (undersupply is strongly linked to clinical depression). Example: Having balanced levels of serotonin helps maintain emotional stability and healthy sleep cycles.

1.3 Norepinephrine

A neurotransmitter and hormone involved in controlling alertness, physical arousal, and the body's response to stress. Example: Increasing your mental alertness and heart rate during an unexpected high-stress exam.

1.3 GABA (Gamma-Aminobutyric Acid)

The major inhibitory neurotransmitter in the brain that calms neural activity and reduces anxiety. Example: Taking an anti-anxiety medication that boosts GABA activity to stop racing, panicked thoughts.

1.3 Glutamate

The primary excitatory neurotransmitter in the central nervous system, critical for memory formation and learning. Example: Brain pathways releasing glutamate while you study new vocabulary cards to strengthen synaptic connections.

1.3 Endorphins

Natural, opiate-like neurotransmitters linked to pain control, stress reduction, and feelings of pleasure. Example: The diminished perception of pain and feeling of euphoria experienced during a "runner's high."

1.3 Substance P

A neurotransmitter involved in sending pain signals from the peripheral nervous system to the central nervous system. Example: When you stub your toe, damaged tissue triggers the release of Substance P to send pain messages to your brain.

1.3 Endocrine System

The body's "slow" chemical communication network, consisting of glands that secrete hormones directly into the bloodstream. Example: The thyroid gland secreting hormones that regulate metabolism throughout the body over hours and days.

1.3 Hormones

Chemical messengers synthesized by endocrine glands that travel through the bloodstream to affect distant tissues and organs. Example: Insulin released by the pancreas traveling through blood to instruct cells to absorb sugar.

1.3 Adrenaline (Epinephrine)

An endocrine hormone secreted by the adrenal glands during stress that increases heart rate, blood pressure, and energy supply. Example: A sudden surge of adrenaline giving you a burst of energy to dodge an oncoming car.

1.3 Leptin

A hormone produced by fat cells that signals satiety (fullness) to the brain to suppress appetite. Example: High leptin levels tell your hypothalamus that you have eaten enough food and can stop eating dinner.

1.3 Ghrelin

A hunger-arousing hormone secreted primarily by an empty stomach to signal the brain that it is time to eat. Example: A growling stomach before lunchtime releasing ghrelin to make you feel hungry.

1.3 Melatonin

A hormone produced by the pineal gland that regulates sleep-wake cycles (circadian rhythms) in response to darkness. Example: Your brain producing increased melatonin in the evening as lights dim, making you feel sleepy.

1.3 Oxytocin

A hormone and neurotransmitter involved in social bonding, trust, maternal behavior, and romantic affection. Example: Oxytocin released during hugging or physical affection, promoting feelings of trust and closeness.

1.3 Agonists

Chemical substances (like drugs or toxins) that mimic or enhance the action of a neurotransmitter by binding to its receptor sites. Example: Morphine acting as an endorphin agonist to mimic natural pain relief in the brain.

1.3 Antagonists

Chemical substances that block or inhibit the normal action or release of a specific neurotransmitter. Example: Curare poison blocking acetylcholine receptors, paralyzing muscles because ACh cannot bind.

1.3 Reuptake Inhibitors

Drugs that block the reabsorption of neurotransmitters by the sending neuron, leaving more in the synapse to bind to receptors. Example: SSRIs (Selective Serotonin Reuptake Inhibitors) keeping serotonin in the synapse longer to elevate mood in depressed patients.

1.3 Psychoactive Drugs

Chemical substances that alter brain function, resulting in temporary changes in perception, mood, consciousness, or behavior. Example: Drinking a cup of coffee to change your mental state from drowsy to alert.

1.3 Stimulants

Drugs (e.g., caffeine, cocaine, amphetamines) that excite neural activity and speed up body functions and central nervous system processing. Example: Cocaine blocking dopamine reuptake, causing a rapid spike in energy, confidence, and heart rate.

1.3 Depressants

Drugs (e.g., alcohol, barbiturates) that reduce neural activity and slow down central nervous system and bodily functions. Example: Consuming alcohol slowing down reaction times, impairing speech, and disrupting balance.

1.3 Hallucinogens

Psychedelic drugs (e.g., LSD, marijuana/THC) that distort perceptions and evoke sensory images in the absence of real sensory input. Example: Smoking marijuana leading to altered time perception, heightened sensory experiences, or vivid visual distortions.

1.3 Opioids

Drugs derived from or mimicking opium (e.g., heroin, morphine) that depress neural activity, temporarily lessening pain and anxiety. Example: Heroin binding to endorphin receptor sites to flood the user's brain with intense euphoria and pain relief.

1.3 Tolerance

The diminishing effect with regular use of the same dose of a drug, requiring the user to take larger doses to achieve the initial effect. Example: A daily coffee drinker needing three cups of coffee to feel the alertness they used to get from just one cup.

1.3 Addiction/Dependence

Compulsive craving and use of a substance (or behavior) despite harmful consequences, often accompanied by physical or psychological reliance. Example: Continuing to use nicotine even after developing severe health problems and wanting to quit.

1.3 Withdrawal Symptoms

The painful physical and psychological distress or discomfort that follows discontinuing the use of an addictive drug. Example: Experiencing severe headaches, irritability, and shaking after suddenly stopping heavy daily caffeine or alcohol consumption.