Glossary A–Z

The first neurotransmitter discovered; it triggers skeletal muscle contraction, runs the parasympathetic system and supports attention and memory in the brain.

An all-or-nothing reversal of the membrane voltage lasting about a millisecond, driven by sodium rushing in and potassium rushing out, that travels along the axon.

A cluster of nuclei deep in each temporal lobe that detects emotionally important events, drives fear responses and strengthens emotional memories.

A disorder of producing or understanding language, most often after a left-hemisphere stroke; Broca's and Wernicke's aphasias are classic types.

A glial cell that clears neurotransmitter and potassium, supplies energy, links neurons to blood vessels and helps form the blood-brain barrier.

The single long fibre that carries action potentials away from the cell body to the axon terminals, often insulated with myelin.

Interconnected structures including the striatum, globus pallidus, subthalamic nucleus and substantia nigra that gate movement and learn from reward.

Brain-derived neurotrophic factor, a neurotrophin that helps neurons survive and synapses change; levels rise with exercise.

Tight junctions between the cells lining brain capillaries that keep most large molecules, germs and many drugs out of the brain.

A system that records and decodes brain activity to control a computer, robotic arm or synthetic voice — used experimentally by people with paralysis.

The medulla, pons and midbrain, which control breathing, heart rate and arousal and carry all signals between brain and body.

Part of the left inferior frontal gyrus important for producing speech and grammar, named after Paul Broca, who described it in 1861.

The structure at the back of the brain that times and fine-tunes movement and balance and drives motor learning; it holds about 80% of the brain's neurons.

A 2–4 mm thick layer of grey matter, mostly six-layered, divided into lobes and areas for senses, movement, language and thought.

Clear fluid made by the choroid plexus that fills the ventricles and surrounds the brain and spinal cord, providing buoyancy and clearing waste.

Daily cycles of sleep, alertness, temperature and hormones set by the suprachiasmatic nucleus and reset by light.

A wiring diagram of a nervous system, from region-to-region pathways to every synapse between every neuron.

A thick band of about 200 million axons connecting the left and right cerebral hemispheres; cutting it produces the split-brain condition.

A developmental stage when a brain system is especially sensitive to specific input, as for binocular vision and language.

Electrodes placed in deep brain targets deliver electrical pulses to treat Parkinson's disease, tremor, dystonia, epilepsy and OCD.

Regions including the medial prefrontal and posterior cingulate cortex that are more active at rest and during self-related thought, memory and imagination.

Branched extensions of a neuron that receive synaptic inputs from other neurons, often covered in tiny dendritic spines.

A monoamine released by midbrain neurons that signals reward prediction errors and 'wanting'; its loss causes Parkinson's disease.

Electroencephalography measures the summed electrical activity of cortical neurons with millisecond timing, used in sleep, epilepsy and cognition research.

A neuropeptide that acts on opioid receptors to dampen pain and contribute to reward and stress responses.

The set of neurons and synaptic changes that store a particular memory; in mice, engram cells can be reactivated with light.

Inhibition, working memory and cognitive flexibility, supporting planning and self-control; they depend on the prefrontal cortex.

Functional MRI tracks the BOLD signal — changes in blood oxygenation that follow neural activity — with millimetre resolution over seconds.

Gamma-aminobutyric acid, the main 'brake' of the brain; alcohol, benzodiazepines and many anaesthetics boost its receptors.

Astrocytes, oligodendrocytes, Schwann cells, microglia and ependymal cells, which support, insulate, feed and defend neurons.

The amino acid used by most excitatory synapses; it drives learning through NMDA receptors but kills neurons in excess (excitotoxicity).

Tissue dominated by neuron cell bodies, dendrites and synapses, forming the cortex and deep nuclei; it looks grey compared with myelinated white matter.

Entorhinal cortex cells that fire at regularly spaced locations, forming a coordinate system for navigation; discovered by the Mosers in 2005.

A gyrus is a ridge on the folded cortex and a sulcus a groove; folding lets a large cortical sheet fit inside the skull.

Donald Hebb's 1949 rule that a connection strengthens when one neuron repeatedly helps fire another — a foundation of theories of learning.

A medial temporal lobe structure essential for forming new episodic and semantic memories and for spatial navigation.

A figure drawn in proportion to the cortical area devoted to each body part — with huge hands and lips — mapped by Wilder Penfield.

A small region regulating temperature, hunger, thirst, sleep, stress and hormones through the pituitary gland.

A neuron that links sensory and motor neurons or other neurons within the CNS; many cortical interneurons are inhibitory and use GABA.

Perception of heartbeat, breathing, hunger and other internal signals, processed in the insula and important for emotion.

Selective pores that open in response to voltage, chemicals, stretch or temperature, underlying every electrical signal in neurons.

LTP, discovered by Bliss and Lømo in 1973, is an activity-dependent increase in synaptic strength and a leading cellular model of memory.

Glial cells that patrol the brain, engulf debris and prune synapses; many Alzheimer's risk genes act in them.

The primary motor cortex on the precentral gyrus sends commands to muscles on the opposite side of the body, arranged as a body map.

Layers of membrane wrapped around axons by oligodendrocytes and Schwann cells, enabling fast saltatory conduction.

The production of neurons from progenitor cells — massive before birth and debated in the adult human hippocampus.

A cell specialised to receive, integrate and transmit electrical and chemical signals via dendrites, cell body and axon.

Changes in synapses, structure and maps in response to experience, learning and injury, continuing throughout life.

Molecules such as glutamate, GABA, dopamine and serotonin that neurons release to influence other cells.

An ion channel opening only with glutamate plus depolarisation, letting in calcium that triggers learning; blocked by ketamine.

Free nerve endings that respond to intense pressure, extreme temperature and chemicals from damaged tissue, starting the pain pathway.

Short unmyelinated stretches of axon packed with sodium channels, where the action potential is regenerated as it jumps along.

Also called norepinephrine; released by the locus coeruleus in the brain and by sympathetic nerves for fight-or-flight.

A glial cell in the brain and spinal cord that wraps segments of many axons in myelin.

Inserting light-sensitive opsins into specific neurons so they can be switched on or off by flashes of light in milliseconds.

Hippocampal neurons that fire when an animal is in a particular place, discovered by John O'Keefe in 1971.

The front part of the frontal lobe supporting working memory, planning, impulse control, decisions and social behaviour.

Information from muscle spindles, tendon organs and joints that tells the brain the position and movement of the limbs.

Proteins on cells that bind neurotransmitters or drugs — either ion channels (ionotropic) or G-protein-coupled (metabotropic).

A stereotyped response organised in the spinal cord or brainstem, such as the knee jerk or pulling away from heat.

Rapid eye movement sleep, with wake-like brain waves, vivid dreams and muscle paralysis, discovered in 1953.

The voltage across a resting neuron's membrane, set mainly by potassium leaking out and maintained by the sodium-potassium pump.

A learning signal carried by dopamine neurons: a burst for better-than-expected outcomes, a dip for worse.

The regeneration of the action potential only at nodes of Ranvier, making conduction much faster and more efficient.

A monoamine (5-HT) from the raphe nuclei with at least 14 receptor types; target of SSRIs and psychedelics.

A column of nervous tissue in the spine carrying signals and organising reflexes and walking rhythms, with 31 pairs of spinal nerves.

A presynaptic terminal, a narrow cleft and a postsynaptic membrane with receptors; named by Charles Sherrington in 1897.

The elimination of weak or inactive synapses during childhood and adolescence, partly carried out by microglia.

Paired structures relaying all senses except smell to the cortex and helping regulate attention, sleep and consciousness.

Cranial nerve X, linking the brainstem to the heart, lungs and gut and carrying most parasympathetic fibres.

Part of the left superior temporal gyrus important for language comprehension, described by Carl Wernicke in 1874.

Tissue made mostly of myelinated axons connecting brain regions; its fat-rich myelin gives it a pale colour.

A limited system (about four chunks) for keeping and manipulating information for seconds, relying on prefrontal and parietal cortex.