This is a glossary of terms, concepts, and structures relevant to the study of the nervous system.
A Acetylcholine A neurotransmitter involved in muscle activation, attention, arousal, and memory. It acts at both nicotinic and muscarinic receptors throughout the central and peripheral nervous systems.
Achromatopsia Loss of color vision as a result of damage to extrastriate visual cortex.
Action Potential A rapid electrical signal that travels down the axon of a neuron.
Activation The time-dependent opening of ion channels in response to a stimulus, typically membrane depolarization.
Adaptation The phenomenon of sensory receptor adjustment to different levels of stimulation; critical for allowing sensory systems to operate over a wide dynamic range.
Adenylyl cyclase Membrane-bound enzyme that can be activated by G-proteins to catalyze the synthesis of cyclic AMP from ATP.
Adrenal cortex The outer region of the adrenal gland, responsible for producing steroid hormones such as cortisol and aldosterone, which regulate metabolism and stress responses.
Adrenal medulla The central part of the adrenal gland that, under visceral motor stimulation, secretes epinephrine and norepinephrine into the bloodstream.
Adrenaline See epinephrine.
Afferent nerve fiber An axon that conducts action potentials from the periphery toward the central nervous system.
Agnosia The inability to name objects, typically resulting from brain damage in the occipital or temporal lobes.
Agonist A chemical that binds to and activates a receptor, mimicking the action of a natural neurotransmitter.
Akinesia A loss or impairment of voluntary movement, often associated with Parkinson's disease and basal ganglia dysfunction.
Allodynia A condition in which normally non-painful stimuli are perceived as painful, often due to nerve damage or sensitization.
Alpha wave A type of brainwave oscillation in the frequency range of 8–13 Hz, commonly associated with relaxed, wakeful states and measured using electroencephalography (EEG).
Alzheimer's disease A progressive neurodegenerative disorder characterized by memory loss, cognitive decline, and the presence of amyloid plaques and neurofibrillary tangles in the brain.
Amygdala A brain structure involved in emotion, particularly fear, aggression, and emotional memory formation. It is part of the limbic system.
Anencephaly A severe congenital condition in which a major portion of the brain, skull, and scalp is missing due to failed closure of the neural tube.
Anhedonia The inability to experience pleasure, commonly associated with depression and certain neurological disorders.
Anterograde amnesia A form of memory loss in which new memories cannot be formed following brain injury or trauma; often associated with damage to the hippocampus.
Anterior cingulate cortex A region of the cingulate cortex implicated in functions such as emotion regulation, cognitive control, error detection, and decision-making.
Aphasia A language disorder resulting from brain damage, most often in the left hemisphere, that affects the production or comprehension of speech and writing.
Apoptosis A form of programmed cell death involved in development and disease. In the nervous system, apoptosis shapes neural circuits and removes damaged neurons.
Arachnoid mater The middle of the three layers of the meninges that surround the brain and spinal cord, located between the dura mater and the pia mater.
Arousal A physiological and psychological state of alertness and readiness, regulated by the reticular activating system and neurotransmitters such as norepinephrine and dopamine.
Astrocyte A star-shaped glial cell in the central nervous system involved in maintaining the blood–brain barrier, regulating neurotransmitter levels, and supporting neuronal function.
Ataxia A neurological symptom characterized by a lack of coordination and balance, typically caused by damage to the cerebellum or its connections.
Auditory cortex A part of the temporal lobe responsible for processing auditory information, including pitch, volume, and sound localization.
Autonomic nervous system A division of the peripheral nervous system that controls involuntary physiological processes, including heart rate, digestion, and respiration. It is divided into the sympathetic and parasympathetic systems.
Axon A long, slender projection of a neuron that conducts action potentials away from the cell body to synaptic terminals, where neurotransmitters are released.
Axon hillock The cone-shaped region of a neuron’s soma where the axon originates and action potentials are typically initiated.
B Babinski sign A reflex where the big toe extends upward and the other toes fan out when the sole of the foot is stimulated. Present in infants, but indicative of damage to the corticospinal tract in adults.
Barrel cortex A region of the somatosensory cortex in rodents that contains clusters of neurons corresponding to individual whiskers, used as a model for studying sensory processing and plasticity.
Baroreceptor A sensory nerve ending in blood vessels that detects changes in blood pressure and relays information to the brainstem for autonomic regulation.
Basal ganglia A group of subcortical nuclei involved in motor control, procedural learning, routine behaviors or "habits", and cognition. Dysfunction is associated with Parkinson’s disease, Huntington’s disease, and other movement disorders.
Behavioral neuroscience A subfield of neuroscience that explores how the brain affects behavior, often using techniques from biology, psychology, and physiology.
Beta wave A type of brain wave oscillation in the frequency range of approximately 13–30 Hz, typically associated with active concentration, alertness, and cognitive engagement.
Bilateral In neuroscience, refers to structures or functions that involve both sides of the brain or body. For example, bilateral activation may occur in both hemispheres during a cognitive task.
Binocular rivalry A phenomenon that occurs when two different images are presented to each eye, and perception alternates between them. It is used to study visual awareness and consciousness.
Bipolar cell A type of amacrine cell that transmits signals from photoreceptors (rods and cones) to ganglion cells in the eye, playing a key role in visual processing.
Bipolar disorder A mood disorder characterized by alternating episodes of depression and mania, associated with dysregulation in neurotransmitter systems and structural brain changes.
Blood–brain barrier (BBB) A selective barrier formed by endothelial cells lining brain capillaries that restricts the passage of substances from the bloodstream into the central nervous system, protecting the brain from pathogens and toxins.
Bouton Also known as an axon terminal or synaptic bouton, this is the swollen end of an axon where neurotransmitters are released into the synaptic cleft.
Brain The central organ of the nervous system, responsible for processing sensory information, regulating bodily functions, and enabling thought, emotion, memory, and consciousness.
Brain-derived neurotrophic factor (BDNF) A protein that supports the survival of existing neurons and encourages the growth and differentiation of new neurons and synapses. It is crucial for long-term memory and synaptic plasticity.
Brain plasticity Also called neuroplasticity, this refers to the brain’s ability to reorganize and adapt by forming new neural connections throughout life, especially after injury or in response to learning and experience.
Brainstem The posterior part of the brain that connects the cerebrum with the spinal cord. It includes the midbrain, pons, and medulla oblongata and regulates essential functions such as breathing, heart rate, and sleep.
Brain ventricles A set of interconnected cavities within the brain that produce and circulate cerebrospinal fluid (CSF). Includes the lateral, third, and fourth ventricles.
Brain waves Patterns of electrical activity in the brain, typically detected by electroencephalography (EEG). Brain waves are categorized by frequency, such as alpha, beta, delta, and theta waves.
Brain-computer interface (BCI) A technology that enables direct communication between the brain and an external device, often used in research, prosthetics, and communication aids for individuals with disabilities.
Bradykinesia Slowness of movement, often a symptom of Parkinson’s disease and other disorders involving the basal ganglia.
Broca's area A region in the frontal lobe, typically in the left hemisphere, associated with the production of speech. Damage can result in Broca's aphasia, characterized by impaired speech fluency.
Broca's aphasia A language disorder caused by damage to Broca's area, resulting in slow, laborious speech with relatively preserved comprehension.
Brodmann areas Regions of the cerebral cortex defined by Korbinian Brodmann based on cytoarchitecture. These areas are still widely used to describe functional brain localization (e.g., Brodmann area 17 = primary visual cortex).
Burst firing A pattern of rapid spikes from a neuron followed by a period of quiescence. It plays a role in sensory encoding and signal amplification in various brain circuits.
C Calcium channel A type of ion channel located on the cell membrane that allows the selective entry of calcium ions (Ca²⁺) into the neuron, playing a crucial role in neurotransmitter release, gene expression, and synaptic plasticity.
Capsaicin A compound found in chili peppers that activates TRPV1 receptors on sensory neurons, leading to the sensation of heat or burning. It is used in research and in topical analgesics for chronic pain.
Caudate nucleus A C-shaped structure located in the basal ganglia, involved in motor control, learning, memory, and reward processing. It works closely with the putamen and globus pallidus.
Central nervous system (CNS) Consists of the brain and spinal cord, responsible for processing and coordinating sensory data and motor commands.
Cerebellum A brain structure located at the back of the skull that plays a central role in motor coordination, balance, posture, and some cognitive functions such as attention and language.
Cerebral cortex The outermost layer of the cerebrum, composed of gray matter. It is involved in higher-order brain functions such as sensory perception, language, decision-making, and voluntary motor control.
Cerebral hemisphere One of the two halves of the cerebrum, divided into left and right hemispheres. Each hemisphere specializes in different functions but communicates via the corpus callosum.
Cerebrospinal fluid (CSF) A clear fluid found in the brain and spinal cord that cushions neural tissue, removes waste, and provides nutrients. It circulates through the ventricular system and subarachnoid space.
Chemoreceptor A sensory receptor that responds to chemical stimuli, such as taste molecules or blood oxygen levels. Located in tissues including the tongue, nasal cavity, and blood vessels.
Cholinergic Refers to cells or systems that use acetylcholine as a neurotransmitter. Cholinergic neurons are involved in memory, attention, and muscle activation.
Choroid plexus A network of cells located in the ventricles of the brain that produces cerebrospinal fluid and contributes to the maintenance of the blood–CSF barrier.
Chromatolysis A cellular response to neuronal injury, characterized by swelling of the cell body and dispersal of Nissl substance, indicating a disruption in protein synthesis.
Cingulate cortex A part of the limbic system located on the medial side of the cerebral hemispheres. It is involved in emotion formation, pain perception, decision-making, and cognitive control.
Cognition