Biological Bases of Behavior
Nature and nurture, the nervous and endocrine systems, neurons and neurotransmitters, brain structures, sleep, and how the senses turn energy into experience.
Developing Understanding
Unit 1 builds the biological foundation for the rest of the course. Behavior and mental processes emerge from an interacting nervous system and endocrine system, so the unit moves from broad questions about genes and environment down to the level of a single neuron, back out to major brain structures, and finally to how sensory systems detect and transmit information about the world.
What you need to know for Unit 1
These groupings follow the order terms are introduced in the course. Be ready to explain and apply each one, not just define it.
Genetics and Evolutionary Perspectives
Behavior arises from the interaction of genes and environment, not one or the other. Heritability describes how much variation in a trait within a group is linked to genetic differences, and evolutionary psychology asks how natural selection may have shaped recurring behavioral tendencies.
Organization of the Nervous System
The central nervous system (brain and spinal cord) and peripheral nervous system work together. The peripheral system splits into the somatic system (voluntary movement and sensation) and the autonomic system, which further divides into sympathetic (arousal) and parasympathetic (calming) branches.
Neurons and Neural Communication
A neuron receives signals through dendrites, fires an all-or-none action potential down its axon once threshold is reached, and communicates across the synaptic gap using neurotransmitters. Agonists mimic or boost a neurotransmitter's effect; antagonists block it.
Neurotransmitters and the Endocrine System
Specific neurotransmitters are linked to specific functions — dopamine with reward and movement, serotonin with mood, acetylcholine with muscles and memory, GABA and glutamate as the brain's main inhibitory and excitatory chemicals. The endocrine system, directed largely by the hypothalamus and pituitary gland, communicates more slowly through hormones.
The Brain: Structures and Function
The brainstem (medulla, pons, reticular formation) handles automatic survival functions and arousal. The cerebellum manages balance and motor learning. Limbic structures — the thalamus, hippocampus, and amygdala — route sensory information and support memory and emotion. The cerebral cortex, divided into frontal, parietal, occipital, and temporal lobes, supports higher-order thought, movement, sensation, and language, including Broca's and Wernicke's areas.
Sleep and States of Consciousness
The circadian rhythm is the body's roughly 24-hour internal clock. Sleep cycles between REM sleep, marked by vivid dreaming and high brain activity, and the progressively deeper stages of NREM sleep.
Sensation and Perception
Sensory transduction converts physical energy into neural signals. Detection depends on absolute and difference thresholds, Weber's Law, and signal detection theory, while sensory adaptation explains why constant stimuli fade from awareness. Rods and cones support vision in different conditions, and place and frequency theory explain how pitch is coded.
Unit 1 Vocabulary
All 59 terms for this unit, grouped to match the key concepts above. Prefer flashcards? Use the flashcard tool filtered to Unit 1.
Genetics and Evolutionary Perspectives
Nature-Nurture Interaction
Behavior reflects interacting genetic and environmental influences rather than a simple either-or cause.
Heritability
A population statistic estimating how much variation in a trait, within a particular group and environment, is associated with genetic differences.
Evolutionary Psychology
An approach that considers how natural selection may have shaped behavioral and mental tendencies.
Organization of the Nervous System
Central Nervous System
The brain and spinal cord.
Peripheral Nervous System
All nerves outside the brain and spinal cord that connect the CNS with the rest of the body.
Somatic Nervous System
The peripheral division involved in voluntary skeletal-muscle control and sensory information.
Autonomic Nervous System
The peripheral division regulating glands and internal organs.
Sympathetic Nervous System
The autonomic division that mobilizes the body for action or stress.
Parasympathetic Nervous System
The autonomic division that calms the body and conserves energy.
Neurons and Neural Communication
Neuron
A specialized cell that receives, processes, and transmits information.
Dendrite
A branching neuron structure that typically receives incoming signals.
Axon
The neuron fiber that carries an electrical signal away from the cell body.
Myelin Sheath
A fatty covering that speeds neural transmission along many axons.
Action Potential
A brief all-or-none electrical impulse traveling down an axon after threshold is reached.
Refractory Period
A brief period after neural firing when another action potential is difficult or impossible.
Synapse
The junction where one neuron communicates with another cell.
Neurotransmitter
A chemical messenger released by neurons into a synapse.
Agonist
A substance that increases or mimics a neurotransmitter's effect.
Antagonist
A substance that blocks or reduces a neurotransmitter's effect.
Neurotransmitters and the Endocrine System
Dopamine
A neurotransmitter involved in movement, motivation, reward learning, and other functions.
Serotonin
A neurotransmitter involved in mood, sleep, appetite, and other functions.
Acetylcholine
A neurotransmitter important in muscle action, attention, and memory.
Gaba
A major inhibitory neurotransmitter in the brain.
Glutamate
A major excitatory neurotransmitter involved in learning and memory.
Endorphins
Naturally produced opioid-like chemicals involved in pain reduction and pleasure.
Endocrine System
Glands that secrete hormones into the bloodstream.
Hypothalamus
A forebrain region involved in homeostasis, motivation, endocrine control, and links between nervous and endocrine systems.
Pituitary Gland
An endocrine gland controlled largely by the hypothalamus that influences several other glands.
The Brain: Structures and Function
Medulla
A brainstem structure involved in vital automatic functions such as breathing and heart rate.
Pons
A brainstem region involved in sleep, arousal, movement, and communication among brain areas.
Reticular Formation
A brainstem network important for arousal and alertness.
Cerebellum
A hindbrain structure important for balance, coordination, motor learning, and some cognitive functions.
Thalamus
A forebrain relay station for most sensory information headed to the cortex.
Hippocampus
A limbic structure crucial for forming new explicit memories.
Amygdala
A limbic structure involved in emotional processing, especially threat and emotional learning.
Cerebral Cortex
The brain's outer layer involved in complex perception, thought, language, and voluntary action.
Frontal Lobe
A cortical lobe involved in planning, decision making, speech production, and voluntary movement.
Parietal Lobe
A cortical lobe involved in touch and body-position processing and spatial attention.
Occipital Lobe
The cortical lobe that contains primary visual processing areas.
Temporal Lobe
A cortical lobe involved in hearing, language, object recognition, and aspects of memory.
Motor Cortex
A frontal-lobe region involved in controlling voluntary movement.
Somatosensory Cortex
A parietal-lobe region processing touch and body sensations.
Broca'S Area
A left-frontal region important for speech production in most people.
Wernicke'S Area
A left-temporal region important for language comprehension in most people.
Corpus Callosum
The large fiber bundle connecting the two cerebral hemispheres.
Neuroplasticity
The nervous system's ability to change in response to experience, learning, or injury.
Sleep and States of Consciousness
Circadian Rhythm
An approximately 24-hour biological cycle regulating sleep-wake patterns and other functions.
Rem Sleep
A recurring sleep stage with rapid eye movements, vivid dreaming, and high brain activity.
Nrem Sleep
Non-rapid-eye-movement sleep, including progressively deeper stages.
Sensation and Perception
Sensory Transduction
Conversion of physical stimulus energy into neural signals.
Absolute Threshold
The minimum stimulation detected about half the time under specified conditions.
Difference Threshold
The smallest detectable difference between two stimuli about half the time.
Weber'S Law
The principle that a noticeable difference is often a constant proportion of the original stimulus.
Signal Detection Theory
A framework explaining detection as influenced by signal strength, experience, expectations, motivation, and alertness.
Sensory Adaptation
Decreased sensitivity to a constant, unchanging stimulus.
Rods
Retinal receptors especially useful for dim light and peripheral vision.
Cones
Retinal receptors concentrated near the fovea that support color and fine detail.
Place Theory
The idea that pitch is coded partly by the location of maximal vibration along the cochlea.
Frequency Theory
The idea that pitch is coded partly by the rate of neural firing matching sound frequency.
AP-Style Practice Questions
Try these multiple-choice questions drawn from the Unit 1 question bank. Click "Show Answer" to check your work and read the explanation. Want more? Build a full set on the Practice Exam page.
Which psychological concept is best described as: Removing a desirable consequence to decrease a behavior.
- A. Reinforcement for the first response after unpredictable time intervals.
- B. Removing a desirable consequence to decrease a behavior.
- C. Responding similarly to stimuli that resemble the conditioned stimulus.
- D. Learning by watching others and the consequences they experience.
Which psychological concept is best described as: Marked, persistent fear of a specific object or situation that is disproportionate to actual danger.
- A. Marked, persistent fear of a specific object or situation that is disproportionate to actual danger.
- B. Psychotherapy delivered to multiple clients together.
- C. Change associated with expectations about treatment rather than its specific active ingredient.
- D. A disorder involving obsessions, compulsions, or both that cause significant distress or impairment.
Which psychological concept is best described as: A tendency for biological systems to maintain stable internal conditions.
- A. A perspective emphasizing interaction among cognition, behavior, and social situations.
- B. A perspective emphasizing growth, personal meaning, free will, and self-concept.
- C. Increased liking for a stimulus after repeated exposure.
- D. A tendency for biological systems to maintain stable internal conditions.
Which psychological concept is best described as: The ability to perceive the world in three dimensions and judge distance.
- A. The Gestalt tendency to group nearby items together.
- B. Judging category membership by similarity to a prototype, sometimes ignoring base rates.
- C. A value from -1 to +1 describing the direction and strength of a linear relationship.
- D. The ability to perceive the world in three dimensions and judge distance.
Which psychological concept is best described as: Belief in one's ability to succeed at a particular task or situation.
- A. Belief in one's ability to succeed at a particular task or situation.
- B. Attitude change based on careful consideration of arguments and evidence.
- C. Reduced individual effort when working in a group on a shared task.
- D. The principle that optimal arousal varies with task difficulty, with very high arousal often harming complex performance.
Which psychological concept is best described as: Changing existing schemas or creating new ones to fit new information.
- A. Changing existing schemas or creating new ones to fit new information.
- B. Biologically programmed growth processes that unfold with development.
- C. A parenting style combining warmth and responsiveness with clear, consistent expectations.
- D. A design that follows the same people over an extended period.
Which psychological concept is best described as: A person's developing sense of self, values, roles, and commitments.
- A. Reinforcement for the first response after unpredictable time intervals.
- B. A person's developing sense of self, values, roles, and commitments.
- C. Reinforcing successive approximations toward a target behavior.
- D. An attachment pattern involving caregiver use as a secure base and effective comfort upon reunion.
Which psychological concept is best described as: Explicit memory for personally experienced events.
- A. Explicit memory for personally experienced events.
- B. Remembering information but misremembering or forgetting where it came from.
- C. Getting information into memory.
- D. Memory expressed without conscious recollection, such as skills or conditioned associations.
Which psychological concept is best described as: A substance that blocks or reduces a neurotransmitter's effect.
- A. A substance that blocks or reduces a neurotransmitter's effect.
- B. A brainstem network important for arousal and alertness.
- C. Glands that secrete hormones into the bloodstream.
- D. A forebrain region involved in homeostasis, motivation, endocrine control, and links between nervous and endocrine systems.
Which psychological concept is best described as: Reduced attempts to escape or change aversive conditions after repeated experiences of uncontrollability.
- A. An enduring emotional bond between an infant or child and a caregiver.
- B. Understanding that other people can have thoughts, beliefs, and perspectives different from one's own.
- C. Learning that occurs without obvious reinforcement and may appear later when useful.
- D. Reduced attempts to escape or change aversive conditions after repeated experiences of uncontrollability.
How to Study This Unit
Connect Structure to Function
For every brain structure or neurotransmitter, be ready to say what it does, not just its name. Exam questions almost always describe a function or scenario and ask you to identify the structure.
Don't Mix Up the Divisions
Sympathetic vs. parasympathetic, and CNS vs. PNS, are common mix-ups. Practice sorting examples into the correct branch until it's automatic.
Use Real Scenarios
Picture an actual moment — jumping at a loud noise, feeling calm after a meal — and identify which system or structure is driving it.