Anomalous: irregular, abnormal. (Oxford)

Apex: the tip or summit of an “organ.” (OxfordMed) Adjective - ‘apical.’

Aqueduct: a canal containing fluid. (OxfordMed)

Arbor: a tree-like structure. (OxfordMed)

Archein: editor’s note - German word meaning 'beginning,'  'original,' or 'primitive.'  For example, ‘archicortex.'

Area: also referred to as “region.”

Basal: of, pertaining to, situated at, or forming, a base. (Oxford) Relating to or located at the lowest portion of a structure. (NCIt) Example - "basal ganglia."

Blood Brain Barrier: a network of “blood vessels” with closely spaced cells that makes it difficult for potentially “toxic” substances to penetrate the blood vessel walls and enter the brain. (GHR) Barrier between the brain and “blood.” Cells and “molecules” in the bloodstream, which freely pass into tissue elsewhere in the body, are unable to cross into brain tissue. The brain’s isolation behind the blood-brain barrier deprives it of access to the vital “immune system” that fights infection and disease. (Instead “microglia” perform this function.) (Fields, 42) The blood-brain barrier lets some substances, such as "water," "oxygen," "carbon dioxide," and general "anesthetics," pass into the brain. It also keeps out "bacteria" and other substances, such as many anticancer drugs. (NCIt) Created by tight-fitting "endothelial cells" that surround blood vessels. (Chudler, 51)

Brain: an Anglo-Saxon word for the tissue that is found within the “skull.” (Kolb, 5) The part of “central nervous system” that is contained within the skull. Arises from the “neural tube.” (MeSH) Consists of three main parts: the “forebrain,” the “midbrain,” and the “hindbrain.” (Koch, 16) An organ composed of “gray” and “white matter” containing billions of neurons that is the center for intelligence and reasoning. It is protected by the bony cranium. (NCI) Editor’s note - see “ways to divide the brain” for more examples of brain divisions.

Cauda: a tail-like structure. (OxfordMed) Constituting or relating to a tail; situated near the tail. (NCIt) For example - "cauda equina."

Cavity: a hollow enclosed area. (OxfordMed) A hollow area or hole. It may describe a body cavity (such as the space within the abdomen) or a hole in a tooth caused by decay. (NCIt)

Cerebellum: connected to the “midbrain,” “pons,” and “medulla” of the “brainstem.” Similar to the the “cerebrum,” contains an outer rim of gray matter (the ‘cerebellar cortex’), an inner core of white matter nerve fibers, and deep cerebellar nuclei located within the white matter. (Patestas, 77-78) A key structure in the central nervous system. Contains nearly half the neurons in the brain. Also contains a pair of (brain) maps. (Blakeslee, 24) Involved in "motor" function and “memory.” (Fields, 313) Pivotal in motor coordination skills as well as non-motor behavioral functions, such as “learning.” (Fisch, 2) Some recent studies have associated it with cognitive functions, such as learning and “attention.” One of the few mammalian brain structures where adult “neurogenesis” has been confirmed. (3D Brain) Controls the fine coordination of movements and is also involved in balance, gait, and posture. When the “motor cortex” sends a “signal” to the muscles via the spinal cord, a copy of that signal gets sent to the cerebellum. The cerebellum also receives “sensory” feedback from muscle and joint “receptors” throughout the body.  Able to detect any ‘mismatches’ that may occur between the ‘intended’ action and the ‘actual action,’ and can insert appropriate ‘corrections’ into the outgoing motor signal, (referred to as a) “servo-control loop.” (Ramachandran, 18) Associated functions include coordination of voluntary movement, motor-learning, balance, reflex memory, posture, timing, and sequence learning. Associated disorders include “autism,” “schizophrenia,” and “dyslexia.” Associations with damage include loss of fine coordination, “tremor,” inability to walk, dizziness, and slurred speech. (3D Brain) Modulates the output of the “corticospinal” and other descending motor systems. Significant inputs from the brainstem and spinal cord. Major inputs from motor cortex. (Blumenfeld, 34)

Cerebellar Hemispheres: (left and right) sides of the cerebellum. (Kolb, 5)

Dentate Nucleus: part of the pathway between the motor cortex and the ‘cerebellar cortex.’ Receives inputs from the cerebellar cortex and sends outputs to the “thalamus” where they are relayed on to the motor cortex. (Fisch, 268-269)

Cerebral: meaning of, or relating to the brain, intellect, or "cerebrum." Appealing to the intellect rather than to the “emotions.” (Oxford)

Cerebrum: what most people think of when they think about ‘the brain.’ (Great Brain, 45) A key structure in the central nervous system. The larger, anterior part of the brain. (Oxford) The “telencephalon.” Composed of the cerebral hemispheres, the “basal ganglia,” the “ventricular system,” and other brain systems. (Patestas, 69) Also referred to as ‘main brain.’

Cervical: of, or relating to, the neck. (OxfordMed) Relating to the neck, or to the neck of any organ or structure. ‘Cervical lymph nodes’ are located in the neck; ‘cervical cancer’ refers to ‘cancer of the cervix,’ which is the lower, narrow end (the "neck") of the “uterus.” (NCIt)

Cinereus: editor’s note - Latin word meaning 'ashen hued.' For example 'fasciola cinerea.'

Cingulum: editor’s note - Latin word meaning ‘girdle’ or ‘belt.’ For example, "cingulate cortex."

Cleft: a split or indentation in something. (NCIt)

Collateral: accessory or secondary. Also, a branch (e.g. of a nerve fiber) that is at right angles to the main part. (OxfordMed) Situated or running side by side; accompaniment to something else. (NCIt)

Column: an arrangement of objects one under another in a line. (NCIt)

Commissure: a bundle of nerve fibers crossing from one side to the other side of the brain or spinal cord. (NCIt) A bundle of nerve fibers that crosses the midline of the central nervous system often connecting similar structures on each side. Also, any tissue connecting two similar structures.  (OxfordMed)

Concavity: the concave surface or side of an arch, hemisphere, etc. The quality, or condition of, being concave. (Oxford)

Contexere: editor’s note - Latin word meaning ‘weave together.’ For example, "context effect."

Contralateral: opposite-sided. (Blumenfeld, 32) On or affecting the opposite side of the body. (OxfordMed) Having to do with the opposite side of the body. (NCIt)

Corpus Callosum: a large C-shaped band of white matter.  (Blumenfeld, 25) A large “myelinated”  “fiber”  “tract” that forms an anatomical and functional connection between the right and left cerebral hemispheres. (Patestas, 69) Band of fibers that connect the two halves of the brain. When this band is cut, the two sides can no longer communicate. (Ramachandran, 10) A mass of 200 million axons... In certain cases of intractable epileptic “seizures,” part or all of these pathways between the hemispheres are surgically cut as a last resort to prevent aberrant electrical activity from spreading from one hemisphere to the other and thereby causing convulsions. The resulting ‘split-brain’ patients appear no different from how they were before the operation. (Koch, 288-289)

Splenium: the thickest part of the corpus callosum, rounded and protruding backwards over the “thalami,” the “pineal gland,” and the midbrain. (OxfordMed)

Cortex: the periphery of a structure. (Patestas, 4) The outer part of an organ, situated immediately beneath its outer membrane. (OxfordMed) Adjective - 'cortical.' Editor’s note - many authors use this term when referring to the “cerebral cortex.”

Allocortex: meaning ‘other’ cortex. Ancient forms of cortex, which do not have six distinct layers. In fish and amphibians, the “archicortex,”  “paleocortex,” and “corticoid areas” form the major portion of the cerebral hemispheres. Only in mammals does the (cerebral cortex) predominate. (Blumenfeld, 823) Found in the "hippocampal formation." (Patestas, 346) Also referred to as ‘heterogenetic cortex.’

Archicortex: meaning ‘first or original’ cortex. The archicortex has only three layers. Found in the “hippocampal formation.” (Blumenfeld, 823) The hippocampal archicortex consists of three layers: the “molecular,” the “pyramidal,” and the “polymorphic" layers. (Patestas, 347) (They are also) the three layers of the “dentate gyrus,” moving inward from the “pia,” as the molecular layer, granule cell layer, and polymorphic layer. (Blumenfeld, 830) Also referred to as ‘archipallium.’

Archicortex Molecular Layer: the deepest layer of the hippocampal archicortex. Merges with the molecular layers of the dentate gyrus and the “neocortex.” Consists of dendritic ‘trees’ and axon terminals. The axon terminals belong to granule cells whose cell bodies reside in the granule cell layer of the dentate gyrus. (Patestas, 347) 

Archicortex Polymorphic Layer: hippocampus and subiculum layer. (Blumenfeld, 830-831)

Archicortex Pyramidal Layer: the middle, most prominent, layer of the hippocampal archicortex. Consists of “pyramidal neurons.” It merges with the internal pyramidal layer of the neocortex. (Patestas, 347-348)

Corticoid Areas: simple-structured cortex-like regions that overlie or merge with subcortical nuclei such as the “amygdala,” and the "septal region." Corticoid areas do not contain consistent layers and are considered the most rudimentary form of cortex. (Blumenfeld, 823)

Laminar Position: the layer of “cortex” in which the cell body of a neuron is found. The laminar position is an important determinant of the cell’s morphology, input, output, and functional role. (Koch, 339)

Mesocortex: meaning ‘middle’ cortex. Found in the “limbic lobe” and (in the) anterior inferior “insula.” (Blumenfeld, 823) A transitional cortex between the allocortex and neocortex. Has three to six cell layers. (Patestas, 399) Editor's note - some authors classify portions of the mesocortex as "paleocortex." Also referred to as ‘transitional cortex’ and ‘juxtallocortex.’

Neocortex: editor's note - many authors used this term interchangeably with "cerebral cortex.”

Paleocortex: meaning ‘old’ cortex. Found in the “olfactory” area. (Blumenfeld, 823) Found in the “parahippocampal gyrus.” Has three to five cell layers. (Patestas, 399) Also referred to as ‘paleopallium’ and ‘periallocortex.’

Crus: an elongated “process” or part of a structure. (OxfordMed)

Decussation: a point at which two or more structures of the body cross to the opposite side. The term is used particularly for the point at which nerve fibers cross over in the “central nervous system.” (OxfordMed) (For example), at the “optic decussation” the fibers from the medial part of each retina cross to project to the other side of the brain while the lateral retinal fibers continue on the same side. As a result each half of the brain receives information about the contralateral visual field from both eyes. (MeSH) Adjective - ‘decussate.’

Dentate: editor’s note - Latin word meaning 'tooth-shaped.' For example, "dentate gyrus."

Dys: a prefix with Greek origin used to form nouns and adjectives with the sense bad, difficult, unfavorable, abnormal, and impaired. (Oxford) For example, “dyslexia,”  “dysplasia,” and “dystonia.”

Emovere: editor’s note - Latin word meaning 'to disturb.'  For example, "emotion."

Encephalon: editor’s note - Greek word for the brain meaning ‘in the head.’ For example, "diencephalon." 

Endo: prefix meaning internal, inner, inside. (Oxford) For example, “endoderm,” and “endoplasmic reticulum.”

Explicit: distinctively expressing all that is meant; leaving nothing merely implied or suggested; unambiguous; clear. (Oxford)

Fasciola: editor’s note - Latin word meaning 'band.' For example, 'fasciola cinerea.’

Focal: of or pertaining to a focus; collected or situated at a focus. Of a disease occurring at a discrete foci; localized. (Oxford) A central point or locus, especially of an infection. (NCIt)

Foramen: an opening or hole, particularly in a bone. (OxfordMed) Plural - ‘foramina.’ For example, "foramen magnum."

Fusiform: adjective meaning spindle-shaped; tapering at both ends. (OxfordMed) For example, "fusiform gyrus."

Ganglia: a collection of neurons in the “peripheral nervous system." (Patestas, 28) A cluster of nervous tissue principally composed of neuronal cell bodies external to the central nervous system. (NCIt) Simple invertebrates are attractive for neuroscience research because each ganglion usually consists of between 500 and 1500 neurons, much smaller numbers than those found in more complex animals. (The Brain-Eric Kandel, 29) Singular - ‘ganglion.’

Gray Matter: the nerve tissue composed of nerve cell bodies, unmyelinated nerve fibers and supportive tissue found in the brain and spinal cord. It is differentiated from the white matter by color of the tissues and the presence of more myelinated nerve cells in the white matter. (NCIt) More brown than gray. Gets its darker hue from the tight packing of many “neuron cell bodies.” (Damasio, 309) Includes all the neuron (cell bodies) and short local non-myelinated pathways. (Goldberg, 40) Also found in large clusters of cells located deep within the cerebral hemispheres and brainstem including the “basal ganglia,” thalamus, and “cranial nerve” nuclei. (Blumenfeld, 21) Also referred to as ‘grey matter.’

Layered Gray Matter: found in the cerebral cortex and in the cerebellar cortex. (Damasio, 309)

Nonlayered Gray Matter: made of nuclei (found in the) basal ganglia, the amygdala, the thalamus, the “hypothalamus,” and the brain stem. (Damasio, 309)

Hemi: prefix denoting the right or left half of the body. (Oxford Med) For example, “cerebral hemispheres.”

Heterotypic: adjective meaning unequal. (Blumenfeld, 881)

Hyper: prefix meaning over, beyond, above. (Oxford) For example, “hyperopia,” and “hyperkinetic movement disorder.”

Hypo: prefix meaning under or below. (Oxford) For example, “hypothalamus.”

Intrinsic: belonging to a thing, or by its very nature; inherent, essential, natural. (Oxford)

Ipsilateral: same-sided. (Blumenfeld, 32) On the same side of the body as another structure or a given point. (NCIt)

Limbus: editor’s note - Latin word meaning ‘border,’  ‘edge,’ or ‘fringe.’ For example, 'limbic system.'

Lobe(s): a major division of an “organ” or part of an organ, especially one having a rounded form and often separated from other lobes or “fissures” or bands of connective “tissue.” For example, the brain, the liver, and the lung are divided into lobes. (OxfordMed). The four main sections of the cerebral cortex, each separated by deep folds, and each with a left and a right half. (Blakeslee, 10) Have distinct domains of functioning, although in practice there is a great deal of interaction between them. (Ramachandran, 19) Adjective - ‘lobular.’ Editor's note - some authors include the “limbic lobe” as a fifth cerebral cortex lobe.

Lobule: a subdivision of a part or organ that can be distinguished from the whole by boundaries that are visible with or without a microscope. (OxfordMed) For example “right parietal lobule” and “right temporal lobule.”

Median: (in anatomy) situated in or denoting the ‘median plane,’ which divides the body into right and left halves. (OxfordMed)

Meso: editor’s note - German word meaning 'middle' or 'intermediate.' For example, “mesocortex” and “mesoderm.”

Metencephalon: editor’s note - Greek word for the brain area which includes the pons and the cerebellum.

Modality: a form of “sensation,” such as smell, hearing, tasting, or detecting temperature. Differences in modality are not due to differences in the structure of the nerves concerned, but to differences in the working of the "sensory receptors” and the areas of the brain that receive the "message." (OxfordMed)

Modular: grouped in modules as in organization, or movement or action between modules, as in a modular process. In neuroscience, the organization of the brain is not modular, but highly interactive and distributed. (Goldberg, 105)

Module: a cluster of highly individualized neurons devoted to a specific function. For example, there are at least thirty discrete modules devoted to vision. (CampbellVA, 159) A self-contained component (unit or item) that is used in combination with other components. (NCIt)

Neo: editor’s note - German word meaning 'new.' For example, "neostriatum."

Neural: of, pertaining to, or resembling a nerve, or the nervous system. (Oxford) Having to do with nerves or the nervous system, including the brain and the spinal cord. (NCIt)

Neurofilaments: the major “cytoskeletal” element in nerve axons and dendrites. (MeSH)

Nuclei: large clusters of cells. (Blumenfeld, 21) A collection of neurons within the central nervous system. (Patestas, 28) Neural clusters. For example, those found on the floor of the pons. (RamachandranTTB, 18) Aggregations of nerve cell bodies embedded deep within the cerebrum or in the spinal cord. (Patestas, 399) Plural - ‘nuclei.’ Editor's note - not to be confused with a “cell nucleus.”

Opercula: editor’s note - Latin word meaning ‘lids.’  For example, "operculi."

Ovoid: adjective meaning egg-shaped; oval with one end more pointed than the other. (Oxford)

Palaios: editor’s note - Greek word meaning ‘old.’ For example, "paleocortex."

Parietal: belonging to, or connected with, the wall of the body or the lining of a body cavity. (Oxford)

Pathway: a set or series of interactions, often forming a network, which biologists have found useful to group together for organizational, historic, biophysical, or other reasons. (NCIt)

Peduncle: a narrow process or stalklike structure, serving as a support or a connection. For example, the ‘middle cerebellar peduncle’ connects the pons and cerebrum. (OxfordMed)

Perisynaptic: surrounding the synapse. (Fields, 32)

Pes: editor’s note - Latin word for 'foot.' For example, “pes hippocampus.”

Plexus: a network of nerves or blood vessels. (OxfordMed)

Pole: the extremity of the axis of the body, an organ, or a cell. (OxfordMed)

Process: a thin prominence or protuberance. (OxfordMed) Editor's note - often used to describe neuron “axons” and “dendrites.”

Ramification: a subdivision of a complex structure analogous to the branches of a tree. (Oxford) To form branches, subdivisions, or offshoots; spread out as branches or ramifications. (Oxford) Verb - 'ramify.'

Ramus: a branch. (OxfordMed) Plural - ‘rami.’

Region: an area or portion of something with more or less definite boundaries designed or specified according to some established biological, administrative, economic, demographic, etc. criteria. (NCIt)

Reticulum: editor’s note - Latin word meaning ‘little net.’ For example, "reticular formation.”

Skull: the bones that form the head. (NCIt) The skeleton of the head including the bones of the face and the bones enclosing the brain. (MeSH) Also referred to as ‘cranium.”

Spatial: of or relating to space; subject to or governed by the conditions of space, frequently as opposed to those of time. Of a faculty or sense; perceiving space or extension. (Oxford)

Superficial: situated at or close to a surface. (OxfordMed)

Supra: prefix denoting above; over. (OxfordMed, 709) For example, “supramarginal gyrus.”

Syn: prefix meaning together, similarly, alike. (Oxford) For example, “synapse.”

Telencephalon: Greek word for the anterior subdivision of the “embryonic” forebrain or the corresponding part of the adult forebrain that includes the cerebrum and associated structures. (MeSH)

Temporal: of, pertaining to, or situated in the temples of the head. (Oxford)

White Matter: a mass of millions of tightly bundled communication lines connecting neurons between distant points in the brain. (Fields, 18) Long myelinated pathways. (Goldberg2, 27) More tan than white. Gets its lighter appearance from the insulating (“mylelin sheaths”) of the axons that emanate from the cell bodies located in the gray matter. (Damasio, 309) In the spinal cord, white matter pathways lie on the outside, while the gray matter is in the inside. (Blumenfeld, 21)