Unit 1 Vocab: Biological Bases of Behavior

Nature and Nurture

This refers to the debate about whether human traits and behaviors are shaped more by genetics and biology (nature) or by environment and experiences (nurture).

• Nature includes things like heredity and brain chemistry.

• Nurture includes parenting, culture, and life experiences.

Genetic Predisposition

A tendency for certain traits to be inherited, including physical and mental conditions and disorders.

Evolutionary Perspective

This approach in psychology explains behavior and mental processes as adaptations that helped our ancestors survive and reproduce. Traits like fear, attraction, and parenting instincts are seen as results of natural selection over time.

Eugenics

A now-discredited belief that society could improve its genetic makeup by encouraging reproduction among people with “desirable” traits and discouraging it among those with “undesirable” traits. It led to harmful policies like forced sterilization and is considered scientifically flawed and ethically wrong.

Twin studies

A research method that compares identical and fraternal twins to see how much traits are influenced by genes versus environment. If identical twins are more alike than fraternal twins, it suggests a genetic influence.

Central Nervous System (CNS)

The entire complex of neurons, axons, and supporting tissue that constitute the brain and spinal cord. The CNS is primarily involved in mental activities and in coordinating and integrating incoming sensory messages and outgoing motor messages.

Peripheral Nervous System (PNS)

The part of the nervous system outside the brain and spinal cord. It carries messages to and from the central nervous system using sensory (afferent) and motor (efferent) nerves.

Somatic Nervous System (SNS)

The part of the nervous system comprising the sensory and motor neurons that innervate the sense organs and the skeletal muscles, as opposed to the autonomic nervous system.

Autonomic Nervous System (ANS)

The part of the nervous system that controls involuntary body functions like heart rate, digestion, and breathing. It includes the sympathetic and parasympathetic systems and works automatically without conscious effort.

Sympathetic vs. Parasympathetic nervous system

These are the two parts of the autonomic nervous system. The sympathetic system activates the body for stress or danger (fight-or-flight), increasing heart rate and slowing digestion. The parasympathetic system calms the body down (rest-and-digest), slowing heart rate and boosting digestion.

Glial cell

A type of cell in the nervous system that supports and protects neurons. Glial cells help with things like providing nutrients, cleaning up waste, and insulating neurons to help signals travel efficiently.

Neurons 

The basic cell of the nervous system that sends and receives messages. It has dendrites to receive signals, an axon to send them, and communicates with other cells at synapses.

Reflex arc

A simple neural circuit that controls automatic responses. It involves a sensory neuron sending a signal to the spinal cord, which then quickly sends a message through a motor neuron to a muscle or gland to react.

Sensory neurons

A neuron that receives information from the environment, via specialized receptor cells, and transmits this information—in the form of nerve impulses—through synapses with other neurons to the central nervous system.

Motor neurons

A neuron that sends signals from the nervous system to muscles, causing them to contract. It’s the final link between the brain and body movement.

Interneurons

any neuron that is neither sensory nor motor but connects other neurons within the central nervous system. Also called connector neuron.

Neural transmission

The process of sending signals between neurons or from neurons to muscles or glands. It usually happens chemically through neurotransmitters at synapses, but can also be electrical.

All-or-nothing principle

A neuron either fires completely or not at all—there’s no partial firing. Once the threshold is reached, the action potential happens with full strength

Action potential

A brief electrical signal that travels down a neuron’s axon. It shifts the cell’s charge from about –70 mV (resting) to +30 mV (active), then quickly returns to –70 mV after a slight dip below it. This process allows neurons to send messages rapidly.

Depolarization

The electrical shift that kickstarts a neuron’s firing. Normally, the inside of a neuron is about –70 mV compared to the outside, meaning it’s negatively charged. When stimulated, sodium ions (Na⁺) flood in, making the inside less negative—if it reaches about –55 mV (the threshold), this triggers an action potential.

Refractory period

A period of inactivity after a neuron or muscle cell has undergone excitation.

Resting potential

The electrical charge across a neuron’s membrane when it’s not firing. It typically sits between –50 to –100 mV, with more negative ions inside the cell than outside, keeping the neuron ready to respond.

Reuptake

The process where neurotransmitters released into the synapse are taken back up by the neuron that sent them. Transporter proteins on the presynaptic membrane handle this recycling, helping regulate signal strength and duration.

Firing threshold

The minimum level of stimulation needed for a neuron to fire an action potential. Typically around –55 mV, this is the point where depolarization becomes strong enough to trigger the electrical signal that travels down the axon. If the threshold isn’t reached, the neuron won’t fire—this follows the all-or-nothing principle.

Multiple sclerosis (MS)

A chronic disease of the central nervous system where the immune system attacks the myelin sheath that insulates nerve fibers, disrupting communication between the brain and body. Symptoms often begin with vision problems and can progress to fatigue, muscle weakness, numbness, coordination issues, and cognitive difficulties.

Myasthenia gravis

A progressive autoimmune disorder where the body attacks acetylcholine receptors, disrupting communication between nerves and muscles. It causes muscle weakness and fatigue, especially in the face and neck, often worsening with activity like eating or speaking. Over time, it can affect muscles throughout the body.

Neurotransmitters (excitatory or inhibitory)

Neurotransmitters are chemical messengers that transmit signals across synapses between neurons.

• Excitatory neurotransmitters increase the likelihood that the receiving neuron will fire an action potential. They depolarize the membrane, bringing it closer to the firing threshold. Examples include glutamate and norepinephrine.

• Inhibitory neurotransmitters decrease the likelihood of firing by hyperpolarizing the membrane, making it more negative and farther from threshold. Examples include GABA and serotonin (depending on receptor type).

Dopamine

A neurotransmitter involved in movement, motivation, reward, and emotional regulation. It’s synthesized from the amino acid tyrosine, which is converted to L-dopa and then to dopamine. Low dopamine levels are linked to motor disorders like Parkinson’s disease, while imbalances in other brain regions are associated with mental health conditions such as schizophrenia.

Serotonin

A neurotransmitter that helps regulate mood, sleep, appetite, sexual behavior, and pain perception. It’s made from the amino acid tryptophan and can be converted into melatonin in the pineal gland. Low serotonin levels are linked to depression, anxiety, and sleep disorders, and many antidepressants work by boosting serotonin activity.

Norepinephrine

A neurotransmitter and hormone that plays a key role in alertness, arousal, and the fight-or-flight response. In the brain, it helps regulate attention, mood, and stress. It’s synthesized from dopamine and acts as an excitatory signal, increasing heart rate, blood pressure, and energy in response to stress. Imbalances are linked to conditions like depression, anxiety, and ADHD.

Glutamate

The brain’s primary excitatory neurotransmitter, glutamate plays a central role in learning, memory, and neural activation. It increases the likelihood that neurons will fire by depolarizing the postsynaptic membrane. While essential for normal brain function, excessive glutamate activity can lead to excitotoxicity—overstimulation that damages or kills neurons—implicated in conditions like stroke, epilepsy, and neurodegenerative diseases.

GABA

The brain’s main inhibitory neurotransmitter, GABA reduces neuronal excitability by making it harder for neurons to fire. It hyperpolarizes the postsynaptic membrane—moving it farther from the firing threshold—helping regulate anxiety, sleep, and muscle tone. Many anti-anxiety and sleep medications enhance GABA’s effects to calm neural activity.

Endorphins

Natural painkillers produced by the brain and nervous system. These neurotransmitters bind to opioid receptors, reducing pain and boosting pleasure. They’re released during activities like exercise, laughter, eating, and even stress—helping improve mood and promote a sense of well-being. Often called the body’s “feel-good” chemicals.

Substance P

A neuropeptide involved in transmitting pain signals from the body to the brain. It’s released by neurons in response to injury or stress and binds to receptors that heighten pain perception. Beyond pain, Substance P also plays roles in inflammation, mood regulation, and stress responses. Elevated levels are linked to chronic pain conditions and emotional disorders like anxiety and depression.

Acetylcholine

A key “movement” neurotransmitter that’s mostly excitatory but can also be inhibitory, depending on the receptor type. In the central nervous system, it supports learning and memory and is linked to Alzheimer’s disease. In the peripheral nervous system, it drives muscle contraction—skeletal, cardiac, and smooth—and disruptions in its signaling are associated with movement disorders like myasthenia gravis.

Hormones

A chemical messenger released into the bloodstream by glands or organs to regulate activity in distant tissues. Hormones control vital processes like growth, metabolism, mood, and reproduction.

Adrenaline (Epinephrine)

A fast-acting hormone and neurotransmitter released during stress or danger, triggering the body’s fight-or-flight response. It increases heart rate, expands airways, boosts blood flow to muscles, and sharpens alertness. Produced by the adrenal glands, adrenaline prepares the body for quick action and is also used medically to treat severe allergic reactions and cardiac arrest.

Leptin

A hormone-like protein released by fat cells that signals the brain about the body’s energy stores. When leptin binds to receptors in the hypothalamus, it helps suppress appetite and regulate food intake. Higher leptin levels generally indicate more stored fat, contributing to long-term energy balance.

Ghrelin

A hunger-stimulating peptide released by the stomach. It binds to receptors in the hypothalamus and anterior pituitary, triggering appetite and promoting the release of growth hormone. Ghrelin levels rise before meals and fall afterward, helping regulate eating behavior and energy balance.

Melatonin

A sleep-regulating hormone made by the pineal gland from serotonin. It helps control the body’s circadian rhythm—your internal clock—and is linked to sleep onset, seasonal biological changes, and possibly puberty.

Oxytocin

A hormone and neuropeptide known for its role in social bonding, trust, and emotional connection. It’s released during childbirth and breastfeeding to promote maternal behaviors, and also during moments of intimacy, touch, and cooperation. Sometimes called the “love hormone,” oxytocin influences attachment, reduces stress, and enhances feelings of empathy and closeness.

Agonist vs. antagonist

a substance that simultaneously binds to multiple receptors, mimicking the action of the body’s natural neurotransmitter at one type of receptor and inhibiting that action at another, different type of receptor.

Reuptake inhibitors

A substance that blocks the reabsorption of neurotransmitters by the neuron that released them, increasing their availability in the synaptic cleft. This enhances signaling between neurons.

Brain stem

The part of the brain that connects the cerebrum with the spinal cord. It includes the midbrain, pons, and medulla oblongata and is involved in the autonomic control of visceral activity, such as salivation, respiration, heartbeat, digestion, and other so called vegetative functions.

Medulla

The lowest part of the hindbrain, located just above the spinal cord. It serves as a vital relay station, transmitting nerve signals between the spinal cord and higher brain regions. The medulla houses autonomic centers that regulate essential functions like breathing, heart rate, and blood pressure—making it critical for survival.

Reticular activating system

A network within the reticular formation that plays a key role in regulating arousal, alertness, and the sleep–wake cycle. It filters incoming sensory information and helps determine what stimuli are important enough to reach conscious awareness. The RAS is essential for maintaining wakefulness and attention, and its disruption can lead to fatigue or altered states of consciousness.

Reward center

A term used to describe brain regions—especially within the hypothalamus and limbic system—that, when electrically stimulated, can evoke sensations of pleasure. These areas are often identified through intracranial self-stimulation studies, where animals repeatedly activate electrodes in specific brain sites. While such stimulation suggests a role in reward and pleasure, the concept of a singular “pleasure center” remains unproven, as responses vary with stimulation intensity, duration, and individual differences.

Cerebellum

A hindbrain structure located above the brainstem, connected via cerebellar peduncles. Often called the “little brain,” it fine-tunes motor activity by coordinating smooth, precisely timed movements and maintaining balance. It predicts body position during motion and is essential for motor learning and conditioning, especially in tasks requiring rapid, ballistic movements.

Cerebral cortex

The outer layer of the brain’s cerebral hemispheres, made up of gray matter, responsible for higher-order functions like thinking, planning, language, and perception. It’s divided into lobes (frontal, parietal, occipital, temporal), each with specialized roles. The cortex processes sensory input and coordinates voluntary motor activity, making it essential for conscious experience and complex behavior.

Hemispheres

The two symmetrical halves of the brain—left and right—that make up the cerebrum or cerebellum.

Limbic system

A network of brain structures—including the hippocampus, amygdala, thalamus, and parts of the cerebral cortex—that regulates emotion, memory, and motivation. It also influences autonomic functions like heart rate and digestion. The limbic system plays a key role in forming emotional responses and storing long-term memories.

Thalamus

A brain structure located in the center of the forebrain that acts as a relay station for sensory and motor signals traveling to and from the cerebral cortex. It processes information from the body and directs it to appropriate areas of the brain, playing a key role in sensation, attention, and consciousness.

Hypothalamus

A small but crucial brain structure located below the thalamus that regulates autonomic functions like hunger, thirst, body temperature, and sexual behavior. It helps maintain homeostasis by responding to internal and external stimuli and also plays a role in sleep and emotional activity. The hypothalamus links the nervous system to the endocrine system via the pituitary gland.

Pituitary gland

A pea-sized gland at the base of the brain, connected to the hypothalamus, known as the “master gland” of the endocrine system. It has two parts: the anterior lobe, which releases hormones that regulate other glands (like growth hormone and thyroid-stimulating hormone), and the posterior lobe, which releases oxytocin and vasopressin. It plays a central role in controlling growth, reproduction, and metabolism.

Amygdala

An almond-shaped structure in the temporal lobe, part of the limbic system, involved in processing emotions like fear and aggression. It plays a key role in threat detection, emotional memory, and fear learning. The amygdala helps coordinate autonomic responses to emotional stimuli and is essential for survival-related behaviors.

Hippocampus

A seahorse-shaped brain structure located in the temporal lobe, part of the limbic system, crucial for forming and storing declarative memories (facts and events) and learning. It helps convert short-term memories into long-term ones and is especially active during spatial navigation and memory consolidation. Damage to the hippocampus can impair the ability to form new memories.

Corpus callosum

A thick band of nerve fibers that connects the left and right cerebral hemispheres, allowing communication between them. It coordinates motor, sensory, and cognitive information across both sides of the brain and is essential for integrated brain function.

Lobes of the cortex

The cerebral cortex is divided into four main lobes, each with specialized functions.

Occipital lobes

The rearmost lobes of the cerebral cortex, primarily responsible for visual processing. They receive and interpret information from the eyes, allowing us to recognize shapes, colors, motion, and spatial orientation. Damage to the occipital lobes can lead to visual impairments or difficulties in visual perception.

Frontal lobes

The front part of the cerebral cortex, responsible for higher-level cognitive functions like decision-making, planning, reasoning, and impulse control. They also manage voluntary movement (via the motor cortex) and speech production (Broca’s area). The frontal lobes are essential for personality expression and executive functioning.

Parietal lobes

Located at the top and rear of the cerebral cortex, the parietal lobes process sensory information related to touch, temperature, pain, and body position. They help us perceive spatial relationships and coordinate movements in response to our environment. The somatosensory cortex, housed here, maps sensations from different parts of the body.

Split Brain Research

Studies of patients who have had their corpus callosum surgically severed—usually to treat severe epilepsy—revealing how the two hemispheres of the brain function independently. These experiments, notably by Roger Sperry and Michael Gazzaniga, showed that the left hemisphere typically handles language and logic, while the right processes spatial and visual information. Split-brain research highlights lateralization of brain function and how each hemisphere controls the opposite side of the body.

Right/Left hemispheres

The left hemisphere is typically dominant for language, logic, and analytical thinking, while the right hemisphere specializes in spatial abilities, facial recognition, creativity, and emotional processing. Though they have distinct functions, the hemispheres communicate through the corpus callosum to coordinate behavior and cognition across both sides of the body.

Broca’s area

A region in the left frontal lobe, typically in the left hemisphere, responsible for speech production and language expression. Damage to Broca’s area can result in Broca’s aphasia, characterized by difficulty speaking fluently while comprehension remains intact. Named after Paul Broca, who discovered its role in language in the 1860s.

Wernicke’s area

A region in the left temporal lobe, specifically in the superior temporal gyrus, responsible for language comprehension. Damage to this area can result in Wernicke’s aphasia, where individuals speak fluently but struggle to understand language and produce meaningful speech. Discovered by Karl Wernicke in 1874, it plays a key role in interpreting spoken and written language.

Aphasia

An acquired language disorder caused by brain damage, typically in the left hemisphere, that impairs communication. It can affect speaking, understanding, reading, or writing. Expressive aphasia (e.g., Broca’s aphasia) involves difficulty producing language, while receptive aphasia (e.g., Wernicke’s aphasia) affects comprehension. Aphasia may be classified as fluent (speech is smooth but lacks meaning) or nonfluent (speech is effortful and fragmented), depending on the location and nature of the brain injury. Common causes include stroke, trauma, or neurodegenerative diseases.

Test with split brain patients

A research method used to study individuals whose corpus callosum has been severed, preventing communication between the brain’s hemispheres. In classic tests, visual stimuli are presented to one visual field at a time:

• Left visual field → right hemisphere: patient can draw or recognize the object but cannot name it.

• Right visual field → left hemisphere: patient can verbally identify the object.

Contralateral organization

A principle of brain function where each hemisphere of the brain controls the opposite side of the body. For example, the left hemisphere governs movement and sensation on the right side, while the right hemisphere controls the left side. This organization is key to understanding motor control, sensory processing, and effects of brain injuries.

Plasticity

Also called neuroplasticity, this refers to the brain’s ability to change and adapt as a result of experience. It includes the formation of new neural connections, strengthening or weakening of existing ones, and even structural changes in response to learning, injury, or environmental demands. Plasticity is especially active during childhood but continues throughout life, supporting recovery from brain damage and the acquisition of new skills.

EEG

A noninvasive method used to measure electrical activity in the brain by placing electrodes on the scalp. EEG detects brain waves and is commonly used to study sleep stages, brain disorders (like epilepsy), and cognitive states. It provides high temporal resolution, meaning it can track rapid changes in brain activity, but offers limited spatial detail about where activity occurs.

fMRI

Functional magnetic resonance imaging (fMRI) is used to study intelligence by identifying which brain regions are active during specific cognitive tasks. It provides precise, real-time data on brain activity, helping researchers pinpoint where and when information processing occurs. These measures reveal how different areas of the brain contribute to problem-solving, reasoning, and other components of intelligence.

Case studies

In-depth studies of one person or group to explore unique psychological phenomena. Rich detail, but limited generalizability.

Lesioning procedure

A technique in neuroscience where specific areas of the brain are intentionally damaged or removed to study their function. Often used in animal research, lesioning helps identify which brain regions are responsible for behaviors, emotions, or cognitive processes. It can also occur naturally through injury or disease.