Unit 1

Biological Bases of Behavior: the one-page sheet

1.1 Interaction of Heredity and Environment

Behavior and mental processes come from heredity and environment working together. Twin, family and adoption studies estimate heritability, the share of variation in a trait within a group that is linked to genetic differences; it does not describe individuals or explain differences between groups. The evolutionary perspective explains shared human traits by natural selection, and its misuse in eugenics shows why claims about heredity must be read carefully.

Nature and nurture interact: heredity sets tendencies, and the environment shapes how they develop. Behavior comes from both, never one alone.
Heritability is the share of variation in a trait, within one group and environment, linked to genetic differences. It says nothing about one person, or about differences between groups.
Twin studies compare identical twins (all genes shared) with fraternal twins (about half); adoption studies compare a child with biological and adoptive parents; family studies track a trait across relatives.
Evolutionary psychology explains shared human traits by natural selection. Its misuse to rank people led to eugenics and forced sterilization.

relatives who share more genes tend to be more alike on many traits the same inheritance can lead to different outcomes in different environments researchers can estimate heritability: how much of the variation in a group is linked to genetic differences

nature and nurture: The question of how heredity (nature) and environment and experience (nurture) contribute to behavior and mental processes. Psychologists now study how the two interact rather than which one wins.
heredity: The passing of traits and tendencies from biological parents to their children.
heritability: The proportion of the variation in a trait, within a particular group and environment, that is linked to genetic differences. It does not apply to one person and can change when the environment changes.
evolutionary psychology: The study of how behavior and mental processes may have been shaped by natural selection because they helped our ancestors survive and reproduce.
natural selection: The process by which inherited traits that help an organism survive and reproduce are passed on more often, becoming more common over generations.
eugenics: A discredited movement, begun in the late 1800s, that tried to "improve" humanity by controlling who could have children; it led to forced sterilization and, in Nazi Germany, mass murder.
twin study: A study that compares how alike identical twins (who share all their genes) and fraternal twins (who share about half) are on a trait, to estimate genetic influence.
adoption study: A study that compares adopted children with their biological parents (shared genes) and their adoptive parents (shared environment).
family study: A study of how often a trait appears among relatives of different closeness, to see whether it runs in families.

1.2 Overview of the Nervous System

The nervous system is made of neurons organized into two parts. The central nervous system, the brain and spinal cord, takes in information and decides. The peripheral nervous system links it to the body: its somatic division moves skeletal muscles on purpose, and its autonomic division runs the organs automatically, with the sympathetic division arousing the body for action and the parasympathetic division calming it again.

The central nervous system (CNS) is the brain and spinal cord. The peripheral nervous system (PNS) is every nerve linking the CNS to the rest of the body.
The PNS has two parts: the somatic nervous system (voluntary movement of skeletal muscles, plus sensations from the body) and the autonomic nervous system (automatic control of the heart, lungs, glands and gut).
The autonomic system has two divisions that work in balance: the sympathetic nervous system arouses; the parasympathetic nervous system calms.
The neuron, or nerve cell, is the basic unit that carries information through every part of the system.

it sends commands out through the peripheral nervous system you move on purpose: catching, kicking, typing the heart speeds, pupils widen and digestion slows: the body is ready to act the heart slows and digestion resumes: the body calms and saves energy

nervous system: The body’s communication network of neurons, made of the central nervous system and the peripheral nervous system.
central nervous system: The brain and spinal cord, which take in information, make decisions and send out commands.
spinal cord: The column of nerve tissue inside the backbone that carries messages between the brain and the body; part of the central nervous system.
peripheral nervous system: All the nerves outside the brain and spinal cord, linking the central nervous system to the body; made of the somatic and autonomic nervous systems.
somatic nervous system: The part of the peripheral nervous system that controls voluntary movement of the skeletal muscles and carries sensations from the body.
autonomic nervous system: The part of the peripheral nervous system that controls automatic functions such as heart rate, breathing, digestion and glands; made of the sympathetic and parasympathetic divisions.
sympathetic nervous system: The division of the autonomic nervous system that arouses the body for action: it speeds the heart, widens the pupils, slows digestion and increases sweating.
parasympathetic nervous system: The division of the autonomic nervous system that calms the body and conserves energy: it slows the heart and lets digestion resume.
neuron: A nerve cell: the basic cell of the nervous system, specialized to receive and send information.

1.3 The Neuron and Neural Firing

A neuron collects messages on its dendrites, and if its charge passes threshold it fires an all-or-none action potential down its axon, sped by myelin. At the terminals it releases neurotransmitters that cross the synapse, bind to receptors and excite or inhibit the next neuron, until reuptake ends the message. Hormones carry slower messages in the blood. Drugs act as agonists, antagonists or reuptake inhibitors, and repeated use brings tolerance and withdrawal.

A neuron fires an action potential only when its charge passes threshold. Every action potential is the same size (all-or-none); a stronger stimulus means more frequent firing and more neurons firing.
After firing, a neuron has a brief refractory period when it cannot fire again.
Know the job of each listed neurotransmitter: dopamine (movement, reward), serotonin (mood, sleep, appetite), norepinephrine (alertness), glutamate (main excitatory), GABA (main inhibitory), endorphins (pain relief), substance P (pain signals), acetylcholine (muscles, learning).
Hormones travel in the blood and act more slowly and for longer: adrenaline, leptin (full), ghrelin (hungry), melatonin (sleep timing), oxytocin (bonding). The pituitary gland directs other glands.
Drugs work at the synapse: an agonist mimics or boosts a neurotransmitter, an antagonist blocks it, a reuptake inhibitor keeps it in the gap longer. Repeated use brings tolerance, and stopping brings withdrawal.

the neuron depolarizes toward threshold a full action potential fires and races down the axon (all-or-none); myelin makes it faster vesicles release neurotransmitter into the synapse that neuron is pushed toward firing (excitatory) or away from it (inhibitory) the message ends; drugs that block reuptake make it last longer

glial cell: A cell in the nervous system that supports neurons rather than carrying messages: glial cells hold neurons in place, supply nutrients, make myelin and clean up waste.
dendrite: A branching fiber of a neuron that receives messages from other neurons and carries them toward the cell body.
cell body: The part of a neuron (also called the soma) that holds the nucleus and keeps the cell alive; it sums up the messages arriving from the dendrites.
axon: The long fiber that carries a neuron's action potential away from the cell body toward the axon terminals.
myelin sheath: A fatty layer, made by glial cells, wrapped in segments around many axons. It insulates the axon and makes action potentials travel much faster. Damage to it causes multiple sclerosis.
axon terminal: A knob at the end of a branch of the axon, where vesicles release neurotransmitter into the synapse.
sensory neuron: A neuron that carries messages from the body's sensory receptors toward the spinal cord and brain (also called an afferent neuron).
motor neuron: A neuron that carries commands from the brain and spinal cord out to muscles and glands (also called an efferent neuron).
interneuron: A neuron inside the brain or spinal cord that passes messages between other neurons, such as between sensory and motor neurons in a reflex.
reflex arc: The quick pathway of a simple reflex: a sensory neuron carries the message to the spinal cord, an interneuron passes it on, and a motor neuron moves the muscle, before the brain is involved.
resting potential: The charge across a neuron's membrane when it is not firing, about -70 millivolts: the inside is negative compared with the outside.
threshold (neural): The level of charge, about -55 millivolts, that a neuron must reach to fire an action potential.
depolarization: A rise in the charge inside a neuron toward zero and beyond, as positive ions flow in; reaching threshold triggers an action potential.
action potential: A brief electrical signal that travels down a neuron's axon when the neuron fires: the inside charge jumps from about -70 to about +40 millivolts and back.
all-or-none principle: The rule that a neuron either fires a full action potential or does not fire at all; every action potential is the same size, whatever the stimulus.
refractory period: A brief time just after an action potential when a neuron cannot fire again, so signals travel one way and in separate pulses.
synapse: The junction where the axon terminal of one neuron meets another neuron, including the tiny synaptic gap the neurotransmitter crosses.
neurotransmitter: A chemical messenger released from an axon terminal into the synapse that binds to receptor sites on the next neuron.
reuptake: The return of leftover neurotransmitter from the synapse into the sending neuron, which ends the message.
excitatory neurotransmitter: A neurotransmitter that makes the receiving neuron more likely to fire, by depolarizing it; glutamate is the main one.
inhibitory neurotransmitter: A neurotransmitter that makes the receiving neuron less likely to fire; GABA is the main one.
dopamine: A neurotransmitter involved in movement, motivation and reward. Loss of dopamine neurons causes the movement problems of Parkinson's disease.
serotonin: A neurotransmitter involved in mood, sleep and appetite.
norepinephrine: A neurotransmitter that raises alertness and arousal.
glutamate: The brain's main excitatory neurotransmitter, important in learning; too much can overexcite neurons.
GABA: Gamma-aminobutyric acid, the brain's main inhibitory neurotransmitter: it calms neural activity. Alcohol and some anti-seizure drugs boost its effect.
endorphins: Neurotransmitters that act as the body's natural painkillers and can lift mood, for example during hard exercise.
substance P: A neurotransmitter that carries pain signals in the spinal cord and brain.
acetylcholine: A neurotransmitter that makes muscles contract and plays a role in learning and attention.
endocrine system: The body's slower chemical communication system: glands that release hormones into the blood.
hormone: A chemical messenger made by a gland and carried in the blood to targets elsewhere in the body; slower and longer-lasting than a neurotransmitter.
pituitary gland: A pea-sized gland at the base of the brain that releases hormones controlling growth and directing other endocrine glands.
adrenaline: A hormone (also called epinephrine) released by the adrenal glands in an emergency; it speeds the heart and breathing and prepares the body for action.
leptin: A hormone released by fat cells that signals the brain that the body has enough stored energy, reducing appetite.
ghrelin: A hormone released by an empty stomach that signals hunger.
melatonin: A hormone released in darkness that helps time sleep; levels rise in the evening and fall in the morning.
oxytocin: A hormone released during childbirth, nursing and close physical contact, linked to bonding between people.
psychoactive drug: A chemical that changes perception, mood or behavior by acting on the nervous system, usually at the synapse.
agonist: A drug that mimics a neurotransmitter or increases its effect, for example by binding to and activating its receptors.
antagonist: A drug that blocks a neurotransmitter's effect, for example by occupying its receptors without activating them.
reuptake inhibitor: A drug that blocks reuptake, so the neurotransmitter stays in the synapse longer and keeps acting on the receiving neuron.
stimulant: A drug that speeds up the nervous system, raising alertness and heart rate; examples are caffeine, nicotine, cocaine and amphetamines.
depressant: A drug that slows the nervous system, reducing alertness and reaction speed; alcohol is the most common.
hallucinogen: A drug that distorts perception and can cause sensory images without real input; LSD and psilocybin are examples.
opioid: A drug, such as morphine, heroin or fentanyl, that mimics endorphins: it relieves pain, slows breathing and is highly addictive.
tolerance (drugs): The need for a larger dose of a drug to get the same effect after repeated use, as the brain adapts to it.
withdrawal: The unpleasant physical and psychological symptoms that follow stopping a drug the body has adapted to.
multiple sclerosis: A disease in which the immune system damages myelin in the brain and spinal cord, slowing or blocking signals and causing weakness, numbness and vision problems.
myasthenia gravis: A disease in which the immune system attacks acetylcholine receptors where nerves meet muscles, so muscles weaken quickly with use.

1.4 The Brain

The brainstem keeps you alive and alert, the cerebellum smooths movement, and the limbic structures handle relay, drives, memory and fear. The cortex has four lobes, each with its own jobs, including the motor and somatosensory strips and the two language areas. Each hemisphere controls the opposite side of the body, and the corpus callosum links them. We know this from damage cases, lesions, EEG and fMRI, and the brain can rewire through neuroplasticity.

The brainstem keeps you alive: the medulla runs breathing and heart rate, and the reticular activating system controls arousal. The cerebellum coordinates balance and smooth movement.
Four lobes of the cerebral cortex: frontal (planning, judgment; the motor cortex; Broca's area for producing speech), parietal (touch, in the somatosensory cortex), occipital (vision), temporal (hearing; Wernicke's area for understanding speech).
Limbic structures: the thalamus relays senses, the hypothalamus keeps homeostasis and directs the pituitary, the hippocampus forms new memories, the amygdala handles fear.
Each hemisphere controls the opposite side of the body. The corpus callosum links them; split-brain cases show that language is mostly in the left hemisphere in most people.
Tools: case studies of damage, lesions in animal research, EEG (when, from the scalp) and fMRI (where, from blood flow). The brain rewires through neuroplasticity.

the thalamus relays them to the right areas of the cortex (smell is the exception) association areas combine the pieces into meaning the motor cortex sends commands to the opposite side of the body, and the cerebellum makes the movement smooth patterns of loss (lesions, strokes, split-brain surgery) reveal what each region does

brain: The organ inside the skull that, with the spinal cord, makes up the central nervous system; it controls the body and produces thought, emotion and behavior.
brainstem: The oldest part of the brain, joining the spinal cord to the rest of the brain; it controls automatic survival functions and contains the medulla and the reticular activating system.
medulla: The base of the brainstem, which controls heart rate and breathing.
reticular activating system: A network of neurons running through the brainstem that controls arousal: waking, sleeping, alertness and attention to the surroundings.
reward center: A set of structures deep in the brain, including the nucleus accumbens, where dopamine signals produce pleasure and drive motivation toward rewards such as food and, in addiction, drugs.
cerebellum: The "little brain" at the back, under the cerebrum, that coordinates balance and smooth, timed movement and helps with some kinds of learning.
cerebral cortex: The thin, wrinkled outer layer of the brain's two hemispheres, where sensing, planning, language and thinking take place.
cerebral hemisphere: One of the two halves of the cerebrum, left and right, joined by the corpus callosum.
frontal lobe: The lobe at the front of each hemisphere, involved in planning, judgment, decision making and movement; it contains the motor cortex and Broca's area.
prefrontal cortex: The front part of the frontal lobe, involved in planning, judgment, impulse control and personality.
motor cortex: A strip at the back of the frontal lobe that sends commands for voluntary movement to muscles on the opposite side of the body.
parietal lobe: The lobe at the top and upper back of each hemisphere that processes touch and body position and helps with spatial reasoning.
somatosensory cortex: A strip at the front of the parietal lobe, just behind the motor cortex, that registers touch, temperature and pain from the opposite side of the body.
occipital lobe: The lobe at the back of each hemisphere that processes visual information.
temporal lobe: The lobe on the side of each hemisphere, below the lateral fissure, that processes hearing and contains Wernicke's area.
association areas: Areas of the cortex not tied to one sense or movement that combine information for higher thinking such as learning, remembering, judging and speaking.
limbic system: A group of structures deep in the brain, below the cortex, involved in emotion, drives and memory, including the hippocampus and amygdala.
thalamus: The brain's sensory relay station: it routes signals from every sense except smell to the right areas of the cortex.
hypothalamus: A small structure below the thalamus that keeps homeostasis by regulating hunger, thirst, body temperature and sex drive, and directs the pituitary gland.
homeostasis: The body's tendency to keep a steady internal state, such as body temperature and blood sugar, by correcting changes.
hippocampus: A curved structure deep in each temporal lobe that is needed to form new memories of facts and events.
amygdala: Two almond-shaped clusters deep in the temporal lobes involved in fear and other emotional reactions to threats.
corpus callosum: The thick band of axons that connects the left and right hemispheres and lets them share information.
contralateral organization: The crossed wiring of the brain: each hemisphere receives sensations from, and controls movement on, the opposite side of the body.
hemispheric specialization: The tendency of each hemisphere to be more involved in certain tasks, such as language mostly on the left in most people; the two still work together.
split-brain: A condition in which the corpus callosum has been cut, usually to treat severe epilepsy, so the two hemispheres cannot share information directly.
Broca's area: An area in the lower left frontal lobe in most people that helps produce speech; damage makes speech slow and effortful.
Wernicke's area: An area in the upper back of the left temporal lobe in most people that helps understand language; damage leaves speech fluent but hard to understand.
aphasia: Loss of the ability to produce or understand language after brain damage, such as Broca's aphasia (slow, effortful speech) or Wernicke's aphasia (fluent speech with little meaning).
neuroplasticity: The brain's ability to change by forming new connections and reorganizing after learning or damage; it is greatest in childhood.
electroencephalogram: Electroencephalogram: a recording of the brain's electrical activity from electrodes on the scalp; it shows when activity changes, millisecond by millisecond, but not precisely where.
functional magnetic resonance imaging: Functional magnetic resonance imaging: a scan that tracks blood oxygen changes to show which brain areas are more active during a task; good for where, slower for when.
lesion: Damaged or destroyed brain tissue, from injury or disease, or made on purpose in animal research to learn what a region does.

1.5 Sleep

Consciousness shifts across a roughly 24-hour circadian rhythm. Each night the brain cycles about every 90 minutes through N1, N2 and deep N3, then REM, with N3 early and longer REM periods toward morning. Sleep restores the body and helps consolidate memories; activation-synthesis and consolidation theories explain dreams. When the cycle fails, the result can be insomnia, narcolepsy, sleep apnea, sleepwalking or REM sleep behavior disorder.

Your circadian rhythm is a roughly 24-hour clock set by light; melatonin rises at night. Teens' clocks naturally shift later.
Sleep cycles about every 90 minutes: N1 (light, falling sensations), N2 (most of the night), N3 (deep, slow delta waves, mostly early), then REM (active brain, darting eyes, limp muscles, vivid dreams), longer toward morning.
Why sleep: restoration (the body and brain recover and repair) and consolidation (new memories are stabilized). Dreams: activation-synthesis (the cortex makes a story from random brainstem signals) or consolidation (dreams reflect memory processing).
Disorders: insomnia (trouble falling or staying asleep), narcolepsy (sudden sleep, quick REM), sleep apnea (breathing stops), somnambulism (sleepwalking, in N3), REM sleep behavior disorder (acting out dreams).

you feel sleepy and enter N1, light sleep with drifting thoughts and hypnagogic sensations brain waves slow into large delta waves and the body does restorative work the brain becomes active, the eyes dart, the major muscles go limp and vivid dreams are common N3 shrinks and REM periods lengthen toward morning sleep disorders (insomnia, narcolepsy, sleep apnea, sleepwalking, REM sleep behavior disorder) and poorer memory and mood follow

consciousness: Awareness of yourself and your surroundings; it shifts across states such as alert waking, drowsiness, sleep and dreaming.
sleep: A regular, reversible state of reduced awareness and responsiveness, organized in cycles of NREM and REM stages, that the body and brain need for health, memory and mood.
circadian rhythm: The body's internal clock, a cycle of about 24 hours that times alertness, body temperature and sleep; daylight resets it each day, and melatonin rises in the dark.
NREM sleep: Non-rapid eye movement sleep, stages N1 (light), N2 (most of the night) and N3 (deep, slow delta waves); vivid dreams are less common than in REM.
REM sleep: Rapid eye movement sleep: the brain is nearly as active as when awake, the eyes dart, the major muscles are almost paralyzed and vivid dreams are common. REM periods lengthen toward morning.
hypnagogic sensations: Sensations at the edge of sleep, in N1, such as a feeling of falling, a sudden jerk, flashes of images or hearing one's name.
dream: A sequence of images, feelings and thoughts during sleep; most vivid and story-like in REM.
activation-synthesis theory: The theory that dreams begin as random neural activity from the brainstem during REM, which the cortex weaves into a story.
consolidation theory: The view that sleep, and the dreams in it, help process and store the day's experiences, stabilizing new memories.
restoration theory: The view that we sleep to restore and repair the body and brain, for example by repairing tissue and, possibly, clearing waste that builds up during waking.
insomnia: A sleep disorder of persistent trouble falling asleep or staying asleep, with tiredness or other problems during the day.
narcolepsy: A sleep disorder of sudden, uncontrollable attacks of sleep during the day, often entering REM within minutes; strong emotion can trigger a sudden loss of muscle tone.
REM sleep behavior disorder: REM sleep behavior disorder: the muscle paralysis of REM fails, so the sleeper acts out dreams, sometimes violently. It is most common in older men.
sleep apnea: A sleep disorder in which breathing repeatedly stops during sleep, briefly waking the person to breathe; loud snoring and daytime sleepiness are common.
somnambulism: Sleepwalking: walking or doing other actions while in deep N3 sleep, usually early in the night, with no memory of it later; more common in children.

1.6 Sensation

Sensation is detecting energy and transducing it into neural signals. Thresholds, Weber's law and signal detection describe what we notice, and adaptation and interaction change it. Rods and cones see; trichromatic and opponent-process theories explain color. Hair cells in the cochlea hear; place, frequency and volley theories explain pitch, and hearing loss is conduction or sensorineural. Smell, taste, touch, pain, balance and body position complete the senses.

Sensation starts with transduction. The absolute threshold is the faintest stimulus detected half the time; the just-noticeable difference grows with the stimulus (Weber's law: a constant proportion). Signal detection theory adds expectations and stakes.
Vision: rods (dim light, no color, around the edge) and cones (color, detail, packed in the fovea). Color: trichromatic theory (three cone types) and opponent-process theory (paired processes; afterimages).
Hearing: hair cells in the cochlea. Place theory explains high pitches, frequency theory low ones, the volley principle in between. Conduction deafness: outer or middle ear. Sensorineural deafness: cochlea or auditory nerve.
Chemical senses: olfaction and gustation (sweet, salty, sour, bitter, umami, and oleogustus for fat). Pain: gate control theory, phantom limbs. Body: vestibular sense (balance) and kinesthesis (position).

receptor cells transduce it into neural signals it is detected at or above the absolute threshold; a change is noticed only above the just-noticeable difference (Weber's law) sensory adaptation lowers the response the brain codes color, pitch, taste and pain, explained by trichromatic and opponent-process, place and frequency, and gate control theories

sensation: The process by which sense organs detect energy from the world (light, sound, chemicals, pressure) and send it to the brain as neural signals.
transduction: The conversion of one form of energy, such as light or sound waves, into neural signals by sensory receptor cells.
absolute threshold: The smallest amount of a stimulus a person can detect half of the time.
just-noticeable difference: The just-noticeable difference (difference threshold): the smallest change in a stimulus a person can detect half of the time.
Weber's law: The principle that the just-noticeable difference is a constant proportion of the original stimulus, so a bigger stimulus needs a bigger change to be noticed.
signal detection theory: The theory that whether a faint stimulus is detected depends on both its strength and the person's state, expectations and the costs of a miss or a false alarm.
sensory adaptation: A drop in sensitivity to a stimulus that stays the same, such as no longer smelling a room after a few minutes.
sensory interaction: One sense affecting another, such as smell shaping the flavor of food.
synesthesia: A condition in which stimulating one sense also triggers another, such as seeing colors when hearing music or reading numbers.
vision: The sense of sight: the eye focuses light on the retina, where rods and cones transduce it into neural signals sent to the occipital lobe.
retina: The light-sensitive layer at the back of the eye that contains the rods and cones.
rods: Receptors in the retina that work in dim light and detect black, white and gray but not color; most are outside the fovea.
cones: Receptors in the retina that detect color and fine detail and need bright light; they are packed in the fovea.
fovea: A small pit at the center of the retina, packed with cones, where vision is sharpest.
optic nerve: The bundle of axons that carries visual signals from the retina to the brain.
blind spot: The point where the optic nerve leaves the eye; it has no rods or cones, so light falling there is not detected.
trichromatic theory: The theory that color vision depends on three types of cones, most sensitive to red, green or blue light, whose combined signals code every color.
opponent-process theory: The theory that color is coded by paired, opposing processes (red-green, blue-yellow, black-white), which explains afterimages in the opposite color.
afterimage: An image that stays after the stimulus is gone; after staring at a color, its opposite color appears.
color vision deficiency: Trouble telling some colors apart because one type of cone is missing or works poorly; red-green deficiency is most common and is inherited, mostly in males.
prosopagnosia: Face blindness: being unable to recognize familiar faces even though vision is otherwise normal.
blindsight: Responding to visual stimuli a person reports not seeing, after damage to the visual cortex.
hearing: The sense of sound (audition): sound waves are funneled to the eardrum and middle-ear bones and transduced by hair cells in the cochlea.
cochlea: The snail-shaped, fluid-filled tube in the inner ear whose hair cells turn vibrations into neural signals.
place theory: The theory that we hear different pitches because different places along the cochlea vibrate most; it best explains high pitches.
frequency theory: The theory that the rate at which auditory neurons fire matches the frequency of the sound wave; it best explains low pitches.
volley principle: The volley principle: groups of auditory neurons take turns firing so that together they match a sound's frequency, extending frequency theory to middle pitches.
conduction deafness: Hearing loss from damage to the parts that conduct sound to the cochlea: the ear canal, eardrum or middle-ear bones.
sensorineural deafness: Hearing loss from damage to the hair cells of the cochlea or to the auditory nerve, often from loud noise or aging; it is usually permanent.
olfaction: The sense of smell: receptors high in the nose detect airborne chemicals. Unlike the other senses, its signals do not pass through the thalamus first.
gustation: The sense of taste: taste buds detect sweet, salty, sour, bitter, umami and probably fat.
umami: The savory taste, detected by receptors for glutamate, found in broth, soy sauce, tomatoes and aged cheese.
oleogustus: The proposed basic taste of fat, distinct from its texture.
supertaster: A person with many more taste buds than average who tastes some flavors, especially bitter ones, much more intensely.
gate control theory: The theory that the spinal cord has a neural "gate" that can block pain signals or let them through to the brain; rubbing a hurt spot or distraction can partly close it.
phantom limb: Sensations, including pain, felt in a limb that has been amputated, showing that the brain produces the experience of pain.
vestibular sense: The sense of balance and head movement, from fluid-filled canals and sacs in the inner ear.
kinesthesis: The sense of the position and movement of body parts, from receptors in muscles, tendons and joints.