This article describes

anatomical terminology Anatomical terminology is a form of scientific terminology used by anatomists, zoologists, and health professionals such as doctors. Anatomical terminology uses many unique terms, suffixes, and prefixes deriving from Ancient Greek and Latin ...

that is used to describe the central and peripheral nervous systems - including the brain,

brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is conti ...

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spin ...

, and

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the ...

Anatomical terminology in neuroanatomy

Neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, like other aspects of anatomy, uses specific terminology to describe anatomical structures. This terminology helps ensure that a structure is described accurately, with minimal ambiguity. Terms also help ensure that structures are described consistently, depending on their structure or function. Terms are often derived from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

and

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

, and like other areas of anatomy are generally standardised based on internationally accepted lexicons such as

Terminologia Anatomica ''Terminologia Anatomica'' is the international standard for human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology, a program of the International Federation of Associations of Anatomis ...

. To help with consistency, humans and other species are assumed when described to be in ''

standard anatomical position The standard anatomical position, or standard anatomical model, is the scientifically agreed upon reference position for anatomical location terms. Standard anatomical positions are used to standardise the position of appendages of animals with ...

'', with the body standing erect and facing observer, arms at sides, palms forward.

Location

Anatomical terms of location Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

depend on the location and species that is being described. To understand the terms used for anatomical localisation, consider an animal with a straight CNS, such as a fish or lizard. In such animals the terms "

rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale The rostral scale, or rostral, in snakes and other sc ...

", "

caudal Caudal may refer to: Anatomy * Caudal (anatomical term) (from Latin ''cauda''; tail), used to describe how close something is to the trailing end of an organism * Caudal artery, the portion of the dorsal aorta of a vertebrate that passes into the ...

", "ventral" and "dorsal" mean respectively towards the rostrum, towards the tail, towards the belly and towards the back. For a full discussion of those terms, see

anatomical terms of location Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

. For many purposes of anatomical description, positions and directions are relative to the standard

anatomical planes An anatomical plane is a hypothetical plane used to transect the body, in order to describe the location of structures or the direction of movements. In human and animal anatomy, three principal planes are used: * The sagittal plane or latera ...

and

axes Axes, plural of '' axe'' and of '' axis'', may refer to * ''Axes'' (album), a 2005 rock album by the British band Electrelane * a possibly still empty plot (graphics) A plot is a graphical technique for representing a data set, usually as a gra ...

. Such reference to the anatomical planes and axes is called the

stereotactic Stereotactic surgery is a minimally invasive form of surgical intervention that makes use of a three-dimensional coordinate system to locate small targets inside the body and to perform on them some action such as ablation, biopsy, lesion, inj ...

approach. Standard terms used throughout anatomy include '' anterior / posterior'' for the front and back of a structure, '' superior / inferior'' for above and below, '' medial / lateral'' for structures close to and away from the midline respectively, and '' proximal / distal'' for structures close to and far away from a set point. Some terms are used more commonly in

neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, particularly: * ''

Rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale The rostral scale, or rostral, in snakes and other sc ...

'' and ''caudal'': In animals with linear

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes t ...

s, the term ''rostral'' (from the Latin ''rostrum'', meaning "beak") is synonymous with ''anterior'' and the term ''caudal'' (from the Latin ''cauda'', meaning "tail") is synonymous with ''posterior''. Due to

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, an ...

s having an upright posture, however, their nervous system is considered to bend about 90°. This is considered to occur at the junction of the

midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "m ...

and

diencephalon The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in ol ...

(the

diencephalic The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in ol ...

junction). Thus, the terminology changes at either side of the

junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems; ''rostral'' is synonymous with ''anterior'' and ''caudal'' is synonymous with posterior. Inferior to the

junction the term ''rostral'' is synonymous with ''superior'' and ''caudal'' is synonymous with ''inferior''. * ''

Dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal co ...

'' and ''ventral'': In animals with linear

s, the term ''dorsal'' (from the

dorsum, meaning "back") is synonymous with ''superior'' and the term ''ventral'' (from the

venter, meaning "belly") is synonymous with ''inferior''. In humans, however, the terminology differs on either side of the

junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems; ''dorsal'' is synonymous with ''superior'' and ''ventral'' is synonymous with ''inferior''. However, inferior to the

junction the term ''dorsal'' is synonymous with ''posterior'' and ''ventral'' is synonymous with ''anterior''. * ''

Contralateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

ipsilateral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

'' referring to a corresponding position on the opposite left or right side (the

sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divi ...

) and on the same side (ipsilateral) respectively.

Planes and axes

Standard

anatomical plane An anatomical plane is a hypothetical plane used to transect the body, in order to describe the location of structures or the direction of movements. In human and animal anatomy, three principal planes are used: * The sagittal plane or latera ...

s and

anatomical axes Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

are used to describe structures in animals. In humans and many other

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians (monkeys and apes, the latter including hum ...

s the axis of the central nervous system is not straight, but bent to allow for forward vision when the body is vertical. This means that differences in terminology are needed to reflect the differences between the brains of primates and the brains of nearly all other vertebrates. For example, to describe the

human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the ...

, "rostral" still means "towards the beak or snout (Latin ''rostrum'')", or at any rate, the interior of the

cranial cavity The cranial cavity, also known as intracranial space, is the space within the skull that accommodates the brain. The skull minus the mandible is called the ''cranium''. The cavity is formed by eight cranial bones known as the neurocranium that i ...

just behind the face. "Caudal" means "towards the tail (Latin ''cauda''"), but not "towards the back of the cranial cavity", which is "posterior" (behind, in ordinary motion). The ''rostro-caudal'' axis of the human central nervous system (magenta in the diagram) makes a near 90° bend at the level of the midbrain and continues through the brain-stem and spinal cord. In human anatomy, the occipital lobes and the back of the head are posterior but not caudal to the frontal lobes and the face. "Superior" and "inferior" are adjectives from human anatomy, respectively meaning towards to top of the head or the soles of the feet when standing. The brain is superior to the spinal cord in people, but in quadrupeds the brain is anterior (forward in motion) to the spinal cord. "Dorsal" means "in the direction away from the ridge of the human back or its equivalent in other animals. In human neuroanatomy the word is somewhat distorted, becoming synonymous with "superior" in the forebrain. i.e. in the direction of the roof of the cranial cavity"cranial cavity and thence to the body. "Ventral" in the central nervous system also refers to the rostro-caudal axis, which changes within the head. These three axes of the human brain match the three planes within which they lie, even though the terms for the planes have not been changed from the terms for the bodily planes. The most commonly used reference planes are: *''Axial'' or "transverse" or "horizontal", the plane that is horizontal and parallel to the ground with the body standing in the

. It contains (and thus is defined by) the lateral and the medial axes of the brain. *''Coronal'', a vertical plane that passes through the coronal suture of the skull (or through both ears), or any plane parallel to this. There is no term "paracoronal" comparable to the commonly used "parasagittal". *''Sagittal'', a vertical plane that passes from between the nostrils, and between the cerebral hemispheres, dividing the brain into left and right halves. "Median plane" specifically defines the midline between left and right sides of the body. It contains the dorsoventral and medial axes of the brain. A ''

parasagittal The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and divid ...

'' plane is any plane parallel to the sagittal plane.

Nerves

Function

Specific terms are used for peripheral nerves that originate from, or arrive at, a specific point. An ''

afferent nerve fiber Afferent nerve fibers are the axons (nerve fibers) carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections ''arrive'' at a particular brain region. Efferent nerve fibers a ...

'' is a fibre originating at the present point. For example, a striatal afferent is an afferent originating at the

striatum The striatum, or corpus striatum (also called the striate nucleus), is a nucleus (a cluster of neurons) in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamate ...

. An ''

efferent nerve fiber Efferent nerve fibers refer to axonal projections that ''exit'' a particular region; as opposed to afferent projections that ''arrive'' at the region. These terms have a slightly different meaning in the context of the peripheral nervous syst ...

'' is one that arrives at the present point. For example, a cortical efferent is a fibre coming from elsewhere, and arriving to the cortex. Note that that is the opposite of the direction in which the nerve fibre conducts signals.

Nerve fibre crossings

Specific terms are also used to describe the route of a nerve or nerve fibre: A chiasm () is used to describe different types of crossings of or within

peripheral A peripheral or peripheral device is an auxiliary device used to put information into and get information out of a computer. The term ''peripheral device'' refers to all hardware components that are attached to a computer and are controlled by the ...

nerve fibres between the cerebral hemispheres. The major example in the human brain is the

Optic chiasm In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebra ...

. A

decussation Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

() refers to nerve fibers that cross the

from one side of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

to the other, and connect ''different'' brain regions. There are two kinds: * Type 1 crosses the sagittal plane in the ''same'' brain region or spinal segment where the cell body is located. Examples are Mauthner cells in

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

and

amphibian Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arborea ...

s. * Type 2 crosses the sagittal plane in a ''different'' brain region. Example: pyramidal decussations. The first type is known also for

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

, whereas the second type only occurs in

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

. The second type is thought to be due to an axial twist. A

commissure A commissure () is the location at which two objects abut or are joined. The term is used especially in the fields of anatomy and biology. * The most common usage of the term refers to the brain's commissures, of which there are five. Such a commi ...

is a bilateral connection of axons connecting the left and right side of the same brain region. For example, nerve fibre tracts that cross between the two cerebral hemispheres, are the

anterior commissure The anterior commissure (also known as the precommissure) is a white matter tract (a bundle of axons) connecting the two temporal lobes of the cerebral hemispheres across the midline, and placed in front of the columns of the fornix. In most exis ...

posterior commissure The posterior commissure (also known as the epithalamic commissure) is a rounded band of white fibers crossing the middle line on the dorsal aspect of the rostral end of the cerebral aqueduct. It is important in the bilateral pupillary light refl ...

corpus callosum The corpus callosum (Latin for "tough body"), also callosal commissure, is a wide, thick nerve tract, consisting of a flat bundle of commissural fibers, beneath the cerebral cortex in the brain. The corpus callosum is only found in placental ma ...

hippocampal commissure The fornix (from lat, fornix, lit=arch) is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus. The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon ...

, and

habenular commissure The habenular commissure, is a brain commissure (a band of nerve fibers) situated in front of the pineal gland that connects the habenular nuclei on both sides of the diencephalon. The habenular commissure is part of the habenular trigone (a small ...

. The spinal cord contains a commissure as well: the

anterior white commissure The anterior white commissure (ventral white commissure) is a bundle of nerve fibers which cross the midline of the spinal cord just anterior (in front of) to the gray commissure ( Rexed lamina X). A delta fibers (Aδ fibers) and C fibers car ...

. A

ganglion A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system there are both sympathe ...

can also have the form of crossing nerves, but a ganglion always contains

synapses In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

between

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

as well as their

cell bodies The soma (pl. ''somata'' or ''somas''), perikaryon (pl. ''perikarya''), neurocyton, or cell body is the bulbous, non-process portion of a neuron or other brain cell type, containing the cell nucleus. The word 'soma' comes from the Greek '' σῶμ ...

. The other kinds of nerve crossings never contain synapses of cell bodies of neurons. The difference between a ''chiasm'' and a ''decussation'' is that the first refers to peripheral nerves whereas the latter refers to crossings inside central nervous system. A ''commissure'' connects the same brain region of each side whereas a ''decussation'' connects different brain regions. Gray690.png, The brainstem from the front, showing a ''decussation'' of the superior pedicle and lemniscus, where nerve fibres from one side cross over to the next Optic processing human brain.jpg, The

optic chiasm In neuroanatomy, the optic chiasm, or optic chiasma (; , ), is the part of the brain where the optic nerves cross. It is located at the bottom of the brain immediately inferior to the hypothalamus. The optic chiasm is found in all vertebra ...

in the human brain, showing pathways conveying information from the visual field of each eye to the contralateral visual cortex

Brain

Specific terms are used to represent the

gross anatomy Gross anatomy is the study of anatomy at the visible or macroscopic level. The counterpart to gross anatomy is the field of histology, which studies microscopic anatomy. Gross anatomy of the human body or other animals seeks to understand the rela ...

of the brain: A ''

gyrus In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other ...

'' is an outward folding of the brain, for example the

precentral gyrus The precentral gyrus is a prominent gyrus on the surface of the posterior frontal lobe of the brain. It is the site of the primary motor cortex that in humans is cytoarchitecturally defined as Brodmann area 4. Structure The precentral gyrus li ...

. A '' sulcus'' is an inward fold, or valley in the brain's surface - for example the

central sulcus In neuroanatomy, the central sulcus (also central fissure, fissure of Rolando, or Rolandic fissure, after Luigi Rolando) is a sulcus, or groove, in the cerebral cortex in the brains of vertebrates. It is sometimes confused with the longitudinal ...

. Additional terms used to describe these may include: * '' Annectent gyrus'', for a small gyrus hidden in the depth of a sulcus * ''sulcal fundus'', for the bottom of a sulcus, an inward fold A ''

fissure A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes. Ground fissure A ...

'' is used to describe: # A deep groove produced by opercularisation. An example is the

Sylvian Fissure In neuroanatomy, the lateral sulcus (also called Sylvian fissure, after Franciscus Sylvius, or lateral fissure) is one of the most prominent features of the human brain. The lateral sulcus is a deep fissure in each hemisphere that separates the ...

. # A deep groove produced by the differentiation of the telencephalic vesicles. An example is the

longitudinal fissure The longitudinal fissure (or cerebral fissure, great longitudinal fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continu ...

, also known as the ''interhemispheric fissure''.

Imaging

Specific acronyms are used to represent imaging. Some common acronyms include MRI (

Magnetic Resonance Imaging Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves ...

) and CT ( Computed tomography).

References

{{Reflist

Human anatomy Neuroanatomy