Neuroscience/Nootropics Glossary & List of Acronyms
We created this list of commonly used terms in Neuroscience, Nootropics, and even a little Pharmacology. If you think there some terms that are important to cover (that we missed), please feel free to add below to the comments. We will try to update the list as we feel necessary.
Acetylcholine: Neurotransmitter found at the neuromuscular junction, within the autonomic nervous system, and the basal forebrain. Acetylcholine neurotransmission at the neuromuscular junction is essential for skeletal muscle activation. In the brain, acetylcholine is believed to play a key role in memory. Acetylcholine is chemically related to choline (choline is a precursor of acetylcholine); neurons that use acetylcholine as a neurotransmitter are referred to as cholinergic neurons. Acetylcholine acts at two main types of acetylcholine receptors, namely muscarinic and nicotinic receptors. Support for this concept comes from the fact that acetylcholine neurons die preferentially in Alzheimer’s disease and drugs that increase acetylcholine neurotransmission can improve memory and cognition in the disease.
Acetylcholinesterase: Enzyme that metabolizes or breaks down acetylcholine molecules in the synaptic cleft. This enzyme is important for controlling neurochemical communication between acetylcholine-containing neurons. The highest concentration of acetylcholinesterase enzymes in the body is at neuromuscular junctions, between nerves and muscles. Acetylcholinesterase is also found within certain synapses within the brain.
Action potential: Electrical activity that travels down a neuron’s axon, causing the release of neurotransmitter from the cell. An action potential is caused by the rapid depolarization of a neuron. A neuron receives a constant barrage of individual neurochemical inputs, each input making it slightly more or less likely to fire an action potential. Once these inputs reach a critical point, the neuron “fires” (aka undergoes an action potential).
ADHD: Attention deficit-hyperactivity disorder. While it is grouped into one disorder, ADHD has two core symptom constellations: inattention and impulsivity/hyperactivity. Individuals with ADHD usually exhibit symptoms in both areas, but one set of symptoms usually predominates. Symptoms of inattentive ADHD include the inability to focus and maintain attention, difficulty organizing activities, and slowed cognitive processing. Individuals in the impulsive/hyperactive ADHD group are characterized by restlessness, excessive talking, excessive movement, and impulsiveness.
Adrenaline/Epinephrine: A catecholamine hormone or neurotransmitter. Epinephrine is produced by the adrenal gland and by neurons within the sympathetic nervous system. Epinephrine in the bloodstream acts to increase cardiac output (heart rate, blood pressure), dilate airways, and raise blood glucose levels. Exogenous epinephrine may be administered to support blood pressure in people with acute cardiovascular problems (e.g. cardiac arrest, cardiopulmonary failure) or to treat anaphylaxis.
Afferent: A nerve that travels toward the brain or central nervous system. A sensory neuron is a typical example of an efferent.
Agonist: A molecule that binds to a receptor, causing a biological response. An agonist may be a substance that the body produces and releases to act on a receptor, or it can be a molecule introduced into the body (e.g. a drug) to create the same or similar biological effect. An agonist may be a small molecule, peptide, hormone, or antibody, among others.
Allergen: An allergen is a substance that induces a hypersensitivity reaction in vulnerable individuals. In resistant individuals, that same substance causes no effect. An allergen causes an immediate, Type I hypersensitivity reaction, which is commonly known as an allergic reaction.
Angiogenesis: The process by which the body makes new blood vessels from existing blood vessels. Angiogenesis is the normal response to growing tissue. For example, as people produce more fat or muscle, angiogenesis creates blood vessels to supply that new tissue. The same process takes place in growing tumors, which is why angiogenesis inhibitors are an intriguing potential treatment for certain forms of cancer. Angiogenesis may also occur in damaged/injured tissue and tissue that chronically lacks oxygen (i.e. hypoxic tissue).
Anhedonia: The inability to enjoy pleasurable activities. Anhedonia is a symptom of several psychiatric disorders including major depressive disorder, schizophrenia, and Parkinson’s disease, among others.
Antagonist: A molecule that blocks the effects of an agonist. In its simplest form, an antagonist binds to a receptor and blocks the ability of the agonist to stimulate a biological response.
Amino acids: Individual building blocks of peptides and proteins. An amino acid contains a carboxylic acid and an amine connected by a carbon atom. That central carbon atom contains a functional group that distinguishes it from other amino acids. Humans use 20 different amino acids in different capacities throughout the body, nine of which cannot be made by the body and must be obtained from the diet (i.e. essential amino acid). Amino acids may form larger proteins such as enzymes and heme molecules, or they may act as neurotransmitters or hormones, among other purposes.
Amygdala: Almond shaped brain region (one in each temporal lobe) that plays a role in decision-making and emotional processing. The amygdala participates in pain processing, reward, anger/rage, fear and anxiety.
Amyloid-beta protein: A protein that clumps together to form beta amyloid plaques, which are found in high concentrations in the brains of people with Alzheimer’s disease. Beta-amyloid plaques can interfere with nerve cell signaling and can induce inflammatory actions. As such, they are believed to play a role in the development and progression of Alzheimer’s disease.
ASD: Autism Spectrum Disorder. A group of related developmental disorders that vary in severity. ASD now applies to various conditions that formerly had individual names including pervasive developmental disorder, autism, Asperger syndrome, and childhood disintegration syndrome. Individuals with autism spectrum disorder may have difficulty communicating and interacting with others, intellectual impairment, a narrowed range of behaviors, activities, or interests, and repetitive or stereotyped movements—all of which may lead to impaired function.
Autonomic nervous system: Division of the peripheral nervous system that is outside of conscious control. The autonomic nervous system drives vegetative functions such as heart rate, respiration, and pupil dilation, among others. The autonomic nervous system is further divided into the parasympathetic and sympathetic nervous systems. These systems generally work antagonistically on various organs (i.e. one causes the opposite effect of the other). Lastly, the enteric nervous system is found along the gastrointestinal tract, which produces gastric motility and aids in digestion.
Axon: Relatively long portion of a neuron capable of firing an action potential to transmit electrochemical information to other cells. An axon is covered by a myelin sheath that helps insulate it and promotes electrical signal propagation down the length of the cell. Once in axon fires an action potential, neurotransmitters are released from the end of the axon at synaptic boutons.
Basal ganglia: A collection of brain regions connected through complex circuitry of excitatory and inhibitory pathways. The basal ganglia participates in motivation, working memory, and decision-making behaviors. Damage to certain parts of the basal ganglia causes a range of movement disorders, from hypokinetic (Parkinson’s disease; substantia nigra pars compacta) to hyperkinetic (Huntington’s disease; stratum) disorders.
BDNF: Brain-derived neurotrophic factor. BDNF is a protein that supports the survival of neurons, facilitates the growth and differentiation of new neurons, and helps to form synaptic connections between neurons. BDNF also participates in long-term memory formation.
Bioavailability: A pharmacological term that describes the amount of drug that reaches the systemic circulation after administration. The term is most important for oral medications and describes the amount of drug that is absorbed by the gastrointestinal tract, travels through the portal circulation, and emerges from the liver in its original state (after first pass metabolism). The bioavailability of the drug can have profound implications on the potency of that drug. A drug with low bioavailability means that only a relatively small fraction reaches the bloodstream to cause a desired effect.
Biomarker: A detectable and often quantifiable indicator of a biological process. For example, the presence of certain cardiac enzymes (e.g. troponins) in the blood is a biomarker for heart attack. Biomarkers may be used to diagnose disease and to track the effectiveness of treatment.
Blood Brain Barrier (BBB): A physical barrier around capillaries in the brain that prevents most substances from diffusing from the bloodstream into the brain. Hydrophilic (water-loving) molecules are generally restricted from entering the brain by the blood brain barrier. On the other hand, smaller hydrophobic (water-hating)/fat-soluble substances may be able to cross the blood brain barrier. Molecules that are important for brain function, such as glucose, are actively transported across the blood brain barrier through transporter proteins. Any drug intended to act in the brain must be able to cross the blood brain barrier.
Brainstem: Collection of neurons and nerve fibers at the base of the brain and at the top of the spinal cord including the midbrain, the pons, and the medulla oblongata. The brainstem maintains consciousness, regulates the sleep/wake cycle, and 10 of the 12 cranial nerves originate in the brainstem.
Catecholamine: An organic molecule that contains a catechol group and a single amine group. In neuroscience, important catecholamines are epinephrine, norepinephrine, and dopamine.
Central nervous system: The brain and spinal cord, the optic nerve, the olfactory nerves, and the retina. The central nervous system is so named as to distinguish it from the peripheral nervous system. Most regions of the central nervous system are protected by the blood brain barrier, while the peripheral nervous system is not.
Cerebellum: The second-largest brain structure after the cerebrum. It is located below the rear of the cerebrum and behind the pons/brainstem. While the cerebrum is directly responsible for movement, the cerebellum improves coordination and the precision of movements. The cerebellum is important for fine motor movements, equilibrium, and maintaining posture. The cerebellum also participates in motor learning.
Cerebral cortex: Outer portion of the cerebrum that contains the cell bodies of neurons in the brain (gray matter). The thickness of a person’s cerebral cortex roughly correlates with their intelligence quotient (IQ). As the cortex thins due to aging or neurodegenerative diseases, a person’s cognitive capacity diminishes.
Cerebrospinal fluid (CSF): The clear liquid that surrounds the brain and spinal cord and fills brain ventricles, cushioning the brain against head trauma. Cerebrospinal fluid is produced by the choroid plexus and circulates around the brain and spinal cord. A sample of cerebrospinal fluid is obtained during a spinal tap (a.k.a. lumbar puncture) and abnormalities detected in the sample can help diagnose various infections and neurological diseases.
Cerebrum: The largest part of the brain. It contains the cortex and subcortical structures. The cerebrum specifically does not include the cerebellum or the brainstem. The cerebrum is responsible for executive function, sensory processing, language, learning and memory formation, and voluntary movement. The cerebrum is separated into two hemispheres, which are connected by the corpus callosum.
Cognition: A term that broadly applies to the mental processes of thinking, learning, and memory. Cognition generally applies to higher mental function, rather than autonomic and automatic processes. For example, actively acquiring new knowledge is a form of cognition, but emotional reactions to events or processes that drive heart rate and breathing rate are not.
Corpus callosum: The main connection between the right and left hemispheres of the brain. The corpus callosum is comprised of nerve fibers that transmit information between cerebral hemispheres.
Cortisol: Steroid hormone produced by the adrenal glands in response to stressors such as infection, sleep deprivation, or trauma. Normal levels of cortisol are important for maintaining glucose levels and blood pressure. Chronically elevated levels of cortisol, on the other hand, can suppress the immune system, increase body weight, and interfere with cognition, among other effects.
CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats. A molecular biological technology that allows researchers to target and edit DNA at precise locations within a genome. Researchers can permanently modify genes with CRISPR (aka CRISPR-Cas9) meaning they can be passed to new cells or, when used on sperm or ovum, they can be passed to offspring. CRISPR and related technologies are among the most advanced and powerful tools available for gene editing.
CTE: Chronic Traumatic Encephalopathy. Degenerative brain disease found most commonly in individuals who sustain repeated trauma to the brain, such as combat military personnel and contact sport athletes. CTE may lead to cognitive impairment, personality changes, depression, suicidality, and parkinsonism (signs and symptoms of Parkinson’s disease). Individuals with CTE often have accumulations (clumps) of tau protein in various regions in their brains. The amount of tau protein correlates with the severity of the clinical symptoms.
CT/CAT: Computed tomography/Computed axial tomography. A device that uses x-rays to create a series of detailed images of the body (slices). A computer is used to stack and reconstruct the slices providing a two-dimensional (and in some cases three-dimensional) representation of internal anatomy. A CT scan is ideal for diagnosing and monitoring soft tissue diseases.
Dendrites: Branch-like structures extending from the cell body of a neuron that collect chemical information from other neurons. Dendrites constantly receive input from other neurons in the form of neurotransmitters that bind to cell membrane receptors. Tof neurotransmitters that bind to cell membrane receptors. The input dendrites receive makes it more or less likely that the neuron will fire an action potential. Thus, strengthening or weakening the strength of communications at dendrites can influence the function of the neuron.
DNA: Deoxyribonucleic acid. Nucleic acid sequence that forms a double helix orientation within chromosomes. DNA contains four base pairs: adenine, cytosine, guanine, and thymine. Arrangements of DNA into genes and chromosomes make up most of the genetic information that is passed from parents to offspring.
Dominant (as in gene): See Recessive
Dopamine: A catecholamine neurotransmitter. Dopamine is produced in many neuron groups in the brain, though it is found in particularly high concentrations in the substantia nigra and in the ventral tegmental area. The role dopamine plays depends on its location. For example, dopamine in the mesolimbic pathway creates a sensation of motivation, desire, and reward. Abnormal stimulation in this region may also lead to addiction or hallucinations. On the other hand, dopamine in the nigrostriatal pathway participates in motor control.
Efferent: A nerve that travels away from the brain or central nervous system. A lower motor neuron is a typical example of an efferent.
ECT: Electroconvulsive therapy. Therapeutic intervention by which electrical stimulation is applied to the brain to induce seizure activity within brain tissue. ECT is used to treat bipolar disorder and severe major depressive disorder, usually in cases that do not sufficiently respond to drug or other therapies. In modern ECT, patients are anesthetized during the procedure and do not experience whole body convulsions. While ECT has negative historical connotations, it can be remarkably effective in individuals for whom other treatments have failed.
EEG: Electroencephalography. Device that measures electrical activity within the brain. Numerous EEG electrodes are attached to the scalp each corresponding to a certain brain region. The electrodes detect neural electrical activity, which is recorded and available for analysis. EEG is useful for diagnosing seizure disorders such as epilepsy, tracking sleep stages and diagnosing sleep disorders, among other applications.
Eicosanoid: A substance that participates in signaling over short distances (aka local hormone). The three major eicosanoids are prostaglandins, thromboxanes, and leukotrienes, which are produced from a precursor, arachidonic acid. Most eicosanoids act to constrict blood vessels, constrict lung airways, aggregate platelets, and signal white blood cells. In essence, eicosanoids participate in inflammatory and allergic processes.
Endogenous: Originating naturally within the body. For example, the body produces and releases endogenous opioids that stimulate opioid receptors. Conversely, drugs such as morphine and heroin are exogenous opioids, meaning they are introduced into the body from the outside world.
Endorphins: Natural (endogenous) neuropeptide hormones are released in response to pain or vigorous aerobic exercise and bind to/act on opioid receptors. Like exogenous opioids, endorphins block pain signals and pain processing, which reduces the perception of pain. Endogenous endorphins can create a mild euphoria, just as exogenous opioids can.
Enzyme: A protein that metabolizes other molecules. An enzyme holds molecules in a favorable orientation within a binding pocket so that chemical reactions can take place. The enzyme generally does not change during the process; instead, it acts as a catalyst for the reaction. Many drugs target enzymes to block their effect and cause a certain outcomes within cells.
Epigenetics: Processes that change the activity of genes without altering the DNA sequence of the gene itself. Epigenetic changes may increase, decrease, or stop the transcription of genes, which can have profound consequences for the cell and the entire organism. Because epigenetic changes take place without changing the DNA sequence, epigenetic manipulation may be a way to alter a gene’s output without changing the gene itself, and without passing that change to offspring.
Executive Function: Executive function includes higher-level cognitive abilities including abstract thinking, complex task planning, emotional inhibition, impulse control, and problem solving. Executive function is required to plan and initiate complex tasks, rather than more mundane or automatic behaviors. For example, creating a grocery list requires executive function because one must consider what objects are needed and how they will be used for future meals. On the other hand, grabbing a box off the grocery store shelf does not require executive function because it is a more mundane cognitive task.
Exogenous: Coming from outside of the body. In exogenous substance is any substance that has been introduced to the body through one or more routes of administration. The term is particularly important for describing substances that the body can produce, but that can also be administered. For example, the body makes (endogenous) insulin, but people can receive exogenous insulin injections.
Epinephrine: See Adrenaline
First-pass metabolism: Degradation of an orally consumed substance by the intestines and liver. First pass metabolism is responsible for the difference between the amount of drug orally consumed and the amount that reaches the systemic circulation. With the exception of the anus, drugs that are absorbed through the intestine first enter the hepatic circulation and reach the liver where they are metabolized (first-pass metabolism) before entering the bloodstream. First-pass metabolism is a major factor is a drug’s bioavailability.
Frontal Lobe: Front section of the cerebrum lying behind the forehead and extending back to the ears. The frontal lobe controls executive functioning, abstract thinking, decision-making, speech formation, and voluntary movements. A person’s personality mostly resides in the frontal lobe; damage to the frontal lobe can result in marked changes to personality causing anger, aggressive behavior, and social isolation.
Gamma-aminobutyric acid (GABA): The main inhibitory neurotransmitter in the central nervous system. GABA acting on GABA receptors on pre-and postsynaptic neurons hyperpolarizes neurons and makes them less likely to fire action potentials. Drugs that increase GABA activity such as benzodiazepines tend to reduce seizure potential (by reducing neuronal activity) and decrease anxiety.
Gene: A stretch of deoxyribonucleic acid (DNA) within a larger chromosome that gives rise to one or more specific traits. A gene is a blueprint from which a peptide/protein is made. Approximately 20,000 genes are passed to children within 23 chromosomes each from the mother and father; each child receives two copies of a gene, one gene from the mother and one gene from the father.
Gene Mapping: The process of determining the location of genes within and across chromosomes. For example, the huntingtin gene, which is associated with Huntington’s disease, has been mapped to the p arm (short arm) of chromosome 4. More specifically, it is at position 16.3 and spans between base pairs 3,074,510 to 3,243,960 in humans. Gene mapping was the process used to determine the human genome and genomes of other species.
Genome: The entire collection of genetic material within an organism, including coded and non-coded regions. Coded regions are referred to as genes while non-coded regions occur in between genes on chromosome. The genome includes nuclear DNA and mitochondrial DNA. While every person’s specific DNA sequence (individual genome) is unique, humans share a common genome (the human genome). An individual’s genome is more than 99% similar to any other human’s genome.
Glial cell/Glia: Cells that provide support, insulation, protection, and nutrition to neurons. Certain forms of glia also destroy pathogens and help remodel neuronal connections after injury. The main types of glia are astrocytes, oligodendrocytes, Schwann cells, ependymal cells, radial cells, and microglia.
Glutamate: The most abundant excitatory neurotransmitter in the central nervous system. Glutamate participates in excitatory neurotransmission in most neurons in the brain. Excessive glutamate neurotransmission may lead to excitotoxicity, which destroys neurons through excessive stimulation.
Glycine: Glycine is an inhibitory neurotransmitter found in the brain and the spinal cord. Glycine is also required along with glutamate to stimulate NMDA receptors, which is a major excitatory system in the brain. Thus, glycine has inhibitory and excitatory actions in the central nervous system.
Gray Matter: Along with white matter, gray matter is a way of describing the gross appearance of brain. Gray matter corresponds to the cell bodies of neurons (as opposed to the white matter, which are the axons of neurons). Gray matter generally exists at the outside edges of the brain and interior portions of the spinal cord.
Half-Life: In pharmacology, a half-life is the time in which it takes a drug to decrease in concentration by 50%. A half-life of a drug usually refers to the time it takes to decrease its peak concentration by 50%. (Two half-lives would be the time it would take the drug to go its original concentration to 25%; half then half again). A drug with a short half-life must be taken more frequently to obtain a continuous effect. A once-a-day drug usually has a half-life of around 24 hours.
Hippocampus: Structure within the medial temporal lobe of the brain and major component of the limbic system. The hippocampus participates in the consolidation of short-term memory into long-term memory, and participates in spatial memory. Damage to the hippocampus results in short-term memory loss, spatial memory loss, and disorientation. The hippocampus exhibits a phenomenon called long-term potentiation, which is considered a neural substrate for memory formation.
Histamine: In neuroscience, histamine primarily acts as a neuron modulator. Histamine receptor stimulation results in changes in acetylcholine, dopamine, norepinephrine, and serotonin release, and the release of certain peptides. Histamine is also a particularly potent modulator in the hypothalamus, and affects pain processing.
Homeostasis: The mechanisms by which a cell or organism maintains an equilibrium or balance with its environment. For example, when the pH of the blood becomes too acidic, homeostatic mechanisms in the lungs and kidneys work to raise the blood’s pH. Homeostasis is a way of protecting the cell or organism from damage or death when exposed to a change in environmental conditions.
Hormone: A substance that is released by a gland to create a biological effect at another location in the body. For example, thyroid hormone is released by the thyroid gland in the neck to affect the metabolic activity of cells throughout the body. Hormone levels in the blood are tightly regulated under normal circumstances; abnormally high or low levels of hormones in the blood may cause a constellation of signs and symptoms.
Hypothalamus: Component of the limbic system located under the thalamus. It contains a number of nuclei with specific functions. The hypothalamus releases hormones and neuropeptides that act on the pituitary gland and/or other glands and tissues throughout the body. Once stimulated, the pituitary gland, in turn, releases hormones into the bloodstream. For example, the hypothalamus secretes thyrotropin-releasing hormone that acts on the anterior pituitary to release thyroid-stimulating hormone, which in turn stimulates the thyroid gland to release thyroid hormone.
Ionotropic receptor: Ligand-gated ion channel. Ionotropic receptor stimulation results in the opening of a transmembrane ion channel which allows ions to pass through, changing the electrical potential of the cell. Classic (“fast”) neurotransmission usually involves inotropic receptors.
Limbic system: A collection of brain structures including the amygdala, basal ganglia, cingulate gyrus, hippocampus, hypothalamus, and thalamus. The limbic system is responsible for integrating higher order functions (executive function, task planning) with lower order brain functions (emotional pain processing, emotional memory processing).
LLLT: Low-level laser therapy. A form of phototherapy in which low power laser light is applied to the treatment area to produce a biological effect. Importantly, LLLT uses laser light energies far below those in other medical laser applications such as ablation. LLLT does not cut, vaporize, or even significantly heat the treatment area. In neuroscience, LLLT has been used for rehabilitation for stroke, traumatic brain injury, and neuromuscular disorders.
Locus Coeruleus: Brainstem nucleus that houses the brain’s densest concentration of norepinephrine-containing neurons. The locus coeruleus participates in arousal, attention, and memory, and it may also participate in normal and abnormal expressions of mood, alertness, and anxiety.
LTP: Long term potentiation. A persistent (long-term) increase in the strength of synaptic communication induced by high-frequency electrical stimulation. LTP is believed to be the anatomic/cellular basis for learning and memory formation. LTP may be impaired in certain dementias, particularly Alzheimer’s disease.
Melatonin: A hormone produced by the pineal gland that conveys information to other brain regions about the light/dark cycle (circadian rhythm). Melatonin levels increase in the evening and decrease in the morning. Exogenous melatonin (i.e., melatonin in a pill form) or drugs that mimic the effect of melatonin may be useful as a sleep aids.
Meta-analysis: A form of scientific inquiry in which multiple clinical studies are combined and statistically analyzed. The main potential benefit of meta-analysis is that it can increase the number of study subjects beyond that of any one trial. Thus, the treatment effect size calculated from a meta-analysis is likely to be more accurate than the treatment effect of any one clinical trial.
Metabotropic receptor: A membrane receptor that, when stimulated, activates a second messenger system. Unlike inotropic receptors, metabotropic receptor stimulation does not generally change the resting potential of the neuron immediately. Instead, it stimulates a cascade of intracellular events. This may lead to a delayed change in electrical potential of the neuron.
Motor Cortex: A band of cortical neurons at the rear of the frontal lobe that participates in planning and initiation of bodily movement. The motor cortex can be divided into the primary motor cortex, the supplementary motor area, and the premotor cortex. Regions of the cerebral motor cortex correspond to the skeletal muscles they control (homunculus).
MRI: Magnetic resonance imaging. A medical device that uses a powerful magnet to create images of a person’s internal anatomy (no radiation is used including x-rays). An MRI takes a series of images called “slices” through the body that can be stacked and reconstructed to provide a 2D/3D image of the body. An MRI can provide the highest resolution of any imaging study, and is an extremely powerful tool in neurology and neuropsychiatry.
Myelin: The fatty substance that organizes itself into a myelin sheath, which surrounds an axon to help insulate it during an action potential. Myelin can be found in oligodendrocytes in the central nervous system and Schwann cells in the peripheral nervous system. In demyelinating disorders such as multiple sclerosis, patients lose the myelin sheath around some neurons. This causes affected neurons to lose the ability to fire properly, causing dysfunction.
N-methyl-D-aspartate receptor (NMDA receptor): A receptor that responds to the most abundant excitatory neurotransmitter in the brain, glutamate. The N-methyl-D-aspartate (NMDA) receptor is a channel located in the plasma membrane of certain neurons. When the NDMA receptor is stimulated, the channel opens and allows ions (sodium, calcium, and potassium) to flow through, which increases the likelihood the cell will fire an action potential. Excessive stimulation at the NMDA receptor causes a process called excitotoxicity, which can be lethal to neurons. As such, NMDA receptor antagonists may act as neuroprotective agents against excitotoxicity.
Neuron: A nerve cell. A nerve cell collects electrical and/or chemical input and, once conditions are met, can fire an action potential along its axon. The action potential causes the release of neurotransmitters into the synaptic cleft, which can then act on adjacent neurons. The human brain has about 100 billion neurons arranged in an astonishingly complex network.
Neurogenesis: The process by which new neurons (nerve cells) are created. The majority of neurons in the central nervous system are created prior to birth and during early development; however, neurogenesis can occur in adult brain to a limited degree.
Neuroplasticity/Plasticity: The process by which neurons, particularly in the brain, create and reorganize connections between cells to adapt to injury, environmental changes, or novel situations. Neuroplasticity explains how a person with brain injury can regain the ability to walk, as healthy regions of the brain adapt to take over the responsibilities of the injured region. Neuroplasticity also encompasses the changes that take place in the brain during learning and memory formation.
Neuroprotective: An activity, drug, or treatment that prevents neurons from dying. Unlike most cells in the body, neurons do not regenerate once they die (under most circumstances). Therefore, nerve cell death in neurodegenerative diseases such as Alzheimer’s disease causes irreversible symptoms. Neuroprotective agents help fortify or shield neurons from being destroyed.
Neurotrophin/neurotrophic factor: A small molecule, usually a peptide, that contributes to the growth, differentiation, and survival of nerve cells. Neurotrophic factors are important for the growth and development of new neurons and the development and maturation of existing neurons. Examples of neurotrophic factors include brain derived neurotrophic factor (BDNF), nerve growth factor (NGF), and glial cell line–derived neurotrophic factor (GDNF), among others.
Nootropic: An agent that improves cognitive function in healthy individuals. In this context, cognitive function includes executive function, memory, alertness, and/or attention. Conversely, drugs intended to improve cognition in people with dementia or mild cognitive impairment are not strictly considered nootropics, though the term may be used in that context.
Noradrenaline/Norepinephrine: A catecholamine hormone or neurotransmitter. Norepinephrine is produced by three separate structures in the body, the adrenal gland, sympathetic nervous system ganglia, and locus coeruleus neurons in the brain. Norepinephrine acting in the systemic circulation or within the sympathetic nervous system increases heart rate and blood pressure, among other functions. In the brain, norepinephrine neurotransmission increases alertness, speed of action, and vigilance.
Occipital Lobe: Lower part of the cerebrum located at the back of the skull under the parietal lobe, behind the temporal lobe, and on top of the cerebellum. The occipital lobe is primarily involved in receiving and processing visual information. The occipital lobe compiles information from the visual pathways to create an integrated image from light that enters the eyes. The occipital lobe determines the visual attributes of vision including color, distance, and size, not only using this information to create vision but also to form visual memories.
Olfactory: Involving the sense of smell. In humans, the olfactory system includes the nose and internal nasal structures, the olfactory epithelium, olfactory bulbs, olfactory neurons, and the olfactory cortex. Molecules stimulate sensory receptors within the olfactory system, which are perceived as odors by the brain.
Opiate: Opiate is an outdated term that refers to opioids, which are molecules that stimulate opioid receptors. Opioids can provide profound pain relief, but they can also cause euphoria, constipation, and depress the drive to breathe. Chronic use of these substances may lead to dependence and withdrawal symptoms. Endogenous opioids are opioids produced by the body, while exogenous opioids are drugs such as morphine, heroin, and methadone.
Opioid Receptors (mu, delta, kappa): Receptors to which endogenous or exogenous opioids bind to produce physiological and behavioral effects. The major types of opioid receptors are mu, delta, and kappa opioid receptors. Some opioids are selective for one of these receptors while other opioids stimulate two or all three. Opioid receptor stimulation can block pain symptom signals, which provides analgesia. Mu receptor stimulation may also lead to physical dependence, respiratory depression, and euphoria. Kappa receptor stimulation may cause depression, hallucinations, sedation, and reduce the likelihood of having a seizure. Lastly, delta receptor stimulation may increase the risk of having a seizure and contribute to physical dependence (i.e. addiction).
Parietal Lobe: Top part of the cerebrum lying between the ears and the back of the skull. The parietal lobe is important for integrating sensory information influencing how we perceive information from the outside world. The parietal lobe is responsible for processing language, visual information, tactile stimulation, and visuospatial reasoning.
Partial agonist: A ligand that binds to a receptor and creates a submaximal (less than maximum) response. By contrast, an agonist produces a maximal response. A partial agonist stimulates the target receptor to minimal degree, but also blocks a full agonist from binding to the same receptor. In this way, a partial agonist can also be thought of as a partial antagonist that produces some agonist effect at a receptor.
Peptide (Oxytocin for example): A polymer (chain) of 2 to 50 unbranched amino acids. Some peptides, such as the nine amino acid-long peptide, oxytocin, act as hormones, neuropeptides, or both. These peptides are released by one type of cell and act on another type of cell to create a biological effect.
Peripheral nervous system: The nerves and ganglia that occur outside of the brain and spinal cord. With the exception of the optic nerves and olfactory nerves, the cranial nerves are also part of the peripheral nervous system. The peripheral nervous system is sometimes subdivided into the somatic nervous system and the autonomic nervous system. However, if it is unspecified, the peripheral nervous system indicates the somatic nervous system, which controls skeletal muscles and receives most sensory information.
Pharmacodynamics: Concept in pharmacology that describes the physiological effect(s) of a drug at receptors across various drug concentrations. The core product of a pharmacodynamics study is a dose-response curve. While pharmacokinetics describes what the body does to a drug, pharmacodynamics describes what a drug does to the body.
Pharmacokinetics: Concept in pharmacology that describes the absorption, distribution, metabolism, and excretion of substances, such as drugs or toxins. Pharmacokinetics describes the timing of and manner by which a drug enters the bloodstream, crosses into various tissues, is broken down, and is removed from the body.
Pituitary gland: Gland at the base of the brain under the hypothalamus. The pituitary gland is divided into anterior and posterior sections. The anterior pituitary gland produces growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone, and prolactin. The posterior pituitary produces oxytocin, vasopressin, and antidiuretic hormone. The hypothalamus stimulates the pituitary gland to release these hormones under certain circumstances.
Pineal gland: Small gland responsible for producing and secreting melatonin. The pineal gland is located at the rear of the thalamus below the rear portion of the corpus callosum.
Placebo: A substance or procedure that is not intended to cause a physiological effect. A placebo is usually created to match the active treatment in every way, except that it contains no active ingredient (e.g., sugar pill, saline injection, etc.). The effects of an active ingredient are compared to those of a placebo to assess and quantify a biological effect of the active ingredient.
PET: Positron emission tomography. A small amount of radioactive substance called a radiotracer is injected into the patient’s body (or swallowed or inhaled), which is then detected by the PET device. The radiotracer collects in areas of interest and shows up as “hot” spots on the scan. One form of PET that is commonly used in neuroscience, neurology, and psychiatry uses 18-fluorodeoxyglucose (FDG) as the tracer. FDG levels increase on the PET scan in areas of increased glucose uptake, which is believed to correspond with increased neuronal activity.
Postsynaptic: Referring to the cell that is affected by neurotransmitter released by the presynaptic neuron. The postsynaptic neuron is usually the site of a high concentration of ion channels that respond to neurotransmitter.
PTSD: Posttraumatic stress disorder. Psychiatric disorder that results from one or more psychological traumas resulting in long-term cognitive, emotional, physical, and behavioral consequences. Individuals with PTSD often have recurrent and unavoidable memories of the event and/or flashbacks. PTSD sufferers usually try to avoid things that are associated with the traumatic event and are socially withdrawn. PTSD also causes an exaggerated startle response, hypervigilance, reckless or self-destructive behavior, irritability, impaired concentration, and impaired sleep.
- The process by which a substance that possesses a minor inherent effect increases the effect or potency of another substance. In potentiation, the pharmacological effect of two drugs is greater than the sum of the individual effect of each drug.
- The short-term or long-term increase in the strength of nerve impulses and connections between neurons. Long-term potentiation is believed to be the cellular basis for some types of memory formation.
Precursor: A molecule that can form another molecule of interest through a chemical reaction. For example, L-dopa is a precursor of dopamine, which is itself a precursor of norepinephrine. A precursor may or may not be biologically active.
Prefrontal cortex: The frontmost portion of the brain. The prefrontal cortex is responsible for complex task planning, decision-making, and appropriate social inhibition. Moreover, the prefrontal cortex is believed to generate a substantial portion of a person’s personality. The prefrontal cortex is critical for executive function and attention.
Presynaptic: Referring to the cell that releases neurotransmitter into the synaptic cleft. A presynaptic neuron receives input from several neurons, eventually leading to an action potential, which causes the release of neurotransmitter from the presynaptic cell into the synaptic cleft. Most neurotransmitter reuptake occurs in the presynaptic neuron.
Primary auditory cortex (A1): Relatively small cortical region lying within the temporal lobe just above the ears. The primary auditory cortex, also referred to as A1, is principally responsible for processing sound information including volume and pitch. Neurons in the primary auditory cortex are arranged by the pitch they recognize. The primary auditory cortex sends processed sound information to other cortical areas for further processing.
Primary motor cortex: Strip of cortex that extends across both sides of the head, and is the topmost part of the brain (rearmost part of the frontal lobe). The primary motor cortex is the principal initiator of voluntary, skeletal muscle movements. The primary motor cortex receives input from other motor areas including the supplementary motor area and premotor cortex to produce planned, complex movements.
Primary somatosensory cortex (S1): Top part of the brain, located above the ears, and behind the primary motor cortex. The primary somatosensory cortex is responsible for receiving and integrating tactile information (i.e. sense of touch). The primary somatosensory cortex, also referred to as S1, perceives vibration, light touch, and proprioception (i.e. the position of one’s own body), and may also perceive and process pain, deep touch, and temperature information.
Primary visual cortex (V1): Rearmost part of the brain, located at the back of the skull. The primary visual cortex, also referred to as V1, receives visual information from the eyes, optic nerves, optic tracts, and optic radiations. The primary visual cortex is responsible for perceiving color, motion, position, spatial relationships, and recognizing shapes. The primary visual cortex generates a cohesive, integrated perception of the visual world.
Prodrug: A substance that is chemically altered to become an active drug. A prodrug may be inactive or less active than the drug it becomes. For example, codeine has no effect on pain, but P450 enzymes in the liver convert codeine into the powerful opioid analgesic, morphine. A prodrug may be administered instead of the active drug because it is more efficiently absorbed by the gut, metabolized more slowly, or more readily crosses the blood brain barrier than the active drug.
Receptor: A protein molecule to which certain chemicals bind, causing a biological effect. The structure of the receptor protein is such that only certain molecules can bind to it to cause the effect. Receptors may be found on a cell membrane, on intracellular membranes, or within the nucleus of a cell (i.e. nuclear receptors).
Recessive (as in gene): See Dominant.
Reuptake: During synaptic transmission, neurotransmitter is released from the presynaptic cell. One of the ways the neurotransmitter is removed from the synaptic cleft is by reuptake. Relatively large proteins called reuptake transporters on the presynaptic neuron actively move neurotransmitter from the synaptic cleft into the neuron. This helps to replenish neurotransmitter in the presynaptic cell and end synaptic transmission after an action potential.
RNA: Ribonucleic acid. Nucleic acid sequence containing four types of base pairs: adenine, guanine, cytosine, and uracil. Different forms of RNA have different functions within cells including messenger RNA, transfer RNA, ribosomal RNA, small nuclear RNA, microRNA, and small interfering RNA, among others.
ROA (Route of administration): The manner in which a substance, usually a drug or toxin, enters the body. Routes of administration include oral, subcutaneous, intramuscular, sublingual (under the tongue), parental (injected into a blood vessel), intraosseous, rectal, transdermal (i.e. patch, topical), inhalation, endotracheal, intranasal, and intrathecal (into the cerebral spinal fluid).
Serotonin: A monoamine neurotransmitter (aka 5-hydroxytryptamine). Serotonin in the brain is involved in mood, appetite, and sleep regulation. The primary source of serotonin in the brain is the raphe nuclei in the brainstem. Certain antidepressants (e.g. selective serotonin reuptake inhibitors) act by increasing serotonin neurotransmission.
Steroids (for example estrogen, testosterone): Organic compound with four rings and attached functional groups. Estrogen and testosterone are examples of sex steroids, which act as hormones to drive sexual development and differentiation. Sex steroids are produced almost exclusively in the ovaries or testes, respectively.
Stroke: An interruption in arterial blood flow to brain tissue, starving the brain of glucose and oxygen. If blood flow is not restored, brain cells will die. More than 80% of strokes are ischemic strokes. In ischemic stroke, a blood clot blocks one of the arteries that supply the brain. The other type of stroke is a hemorrhagic stroke, a condition in which a blood vessel bursts. Ischemic strokes may be treated with “clotbusting” drugs, while hemorrhagic strokes may be treated with neurosurgical interventions.
Synapse: Anatomical area where two neurons interact with one another. At a synapse, a (presynaptic) neuron releases chemicals called neurotransmitters into the synaptic cleft, the space between two neurons. Neurotransmitters diffuse across the synaptic cleft and interact with receptors of the adjacent (postsynaptic) neuron. The neurotransmitter makes it more or less likely that the adjacent neuron will fire an action potential, depending on whether it is an excitatory or inhibitory neuron, respectively.
Synaptic bouton/button: Bulbous area at the end of a neuron’s axon that releases neurotransmitter after an action potential. The synaptic bouton is the main site of neurotransmitter synthesis, storage, release, and reuptake. Neurotransmitter reuptake transporters are generally located in the synaptic bouton. The synaptic bouton makes up the presynaptic area of the synapse.
Synaptic vesicles: Spherical intracellular vesicles that contain high concentrations of neurotransmitter. Synaptic vesicles release neurotransmitter into the synaptic cleft after an action potential.
Temporal Lobe: Lower part of the brain that sits deep to the ears, extending from the temples back to the occipital cortex. The temporal lobe is responsible for processing auditory input and recognizing language. The temporal lobe also includes the hippocampus. Thus, the temporal lobe is important for long-term memory formation.
Thalamus: Brain structure that rests in the center of the brain below the corpus callosum that serves as a relay center of sensory information between the sensory organs and sensory cortices. All senses (except olfactory sensation) pass through the thalamus.
tDCS: Transcranial direct current stimulation. Neuromodulation technique in which scalp electrodes deliver a constant, low intensity electrical current to a cortical region. tDCS does not directly cause neurons to fire, as would occur with electroconvulsive therapy, but it does affect spontaneous neuronal firing. While, tDCS is considered an experimental treatment, researchers have used it to treat severe major depressive disorder.
TMS: Trancranial magnetic stimulation. A technology that can be used for diagnosis or treatment of neurological and psychiatric conditions. The TMS device generates a powerful magnetic field that is applied to the outside of the skull, which affects brain tissue under the skull. TMS can be used to assess the extent of damage/dysfunction in people with stroke, multiple sclerosis, upper motor neuron disease, among others. TMS may be used to treat severe depression, but may be used to treat addiction, PTSD, and other mental health disorders in the future.
TBI: Traumatic brain injury. A severe injury or accumulation of smaller, less severe injuries to the head (e.g. concussions) that result in neurological dysfunction. TBI encompasses a wide range of symptoms and deficits among the people who suffer these injuries. The symptoms of mild TBI may be transient and resolve, while severe TBI can lead to substantial, permanent brain dysfunction.
USP: United States Pharmacopoeia. Nonprofit organization that publishes a national formulary of drug ingredients and products. USP establishes reference standards for drugs, medicinal foods, dietary supplements, herbal medicines, and excipients. The USP also tests manufacturers’ products for purity and concentration, allowing consumers to objectively evaluate these products.
White matter: Areas or bundles of myelinated axons that appear white in contrast to cell bodies, which appear gray (i.e. gray matter). White matter makes up the interior portions of the cerebrum and cerebellum, and the outer portions of the spinal cord.