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This article describesanatomical terminology that is used to describe thecentral andperipheral nervous systems - including thebrain,brainstem,spinal cord, andnerves.

Neuroanatomy, 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 fromLatin andGreek, and like other areas of anatomy are generally standardised based on internationally accepted lexicons such asTerminologia Anatomica.

To help with consistency, humans and other species are assumed when described to be instandard anatomical position, with the body standing erect and facing observer, arms at sides, palms forward.

Anatomical terms of location depend on the location and species that is being described.

To understand the terms used for anatomical localisation, consider an animal with a straightCNS, such as a fish or lizard. In such animals the terms "rostral", "caudal", "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, seeanatomical terms of location.

For many purposes of anatomical description, positions and directions are relative to the standardanatomical planes andaxes. Such reference to the anatomical planes and axes is called thestereotactic approach.

Standard terms used throughout anatomy includeanterior / 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, andproximal / distal for structures close to and far away from a set point.

Some terms are used more commonly inneuroanatomy, particularly:

• Rostralandcaudal: In animals with linearnervous systems, the termrostral (from the Latinrostrum, meaning "beak") is synonymous withanterior and the termcaudal (from the Latincauda, meaning "tail") is synonymous withposterior. Due tohumans having an upright posture, however, our nervous system is considered to bend about 90°. This is considered to occur at the junction of themidbrain anddiencephalon (themidbrain-diencephalic junction). Thus, the terminology changes at either side of themidbrain-diencephalic junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems;rostral is synonymous withanterior andcaudal is synonymous with posterior. Inferior to themidbrain-diencephalic junction the termrostral is synonymous withsuperior andcaudal is synonymous withinferior.^[1]
• Dorsalandventral: In animals with linearnervous systems, the termdorsal (from theLatin dorsum, meaning "back") is synonymous withsuperior and the termventral (from theLatin venter, meaning "belly") is synonymous withinferior. In humans, however, the terminology differs on either side of themidbrain-diencephalic junction. Superior to the junction, the terminology is the same as in animals with linear nervous systems;dorsal is synonymous withsuperior andventral is synonymous withinferior. However, inferior to themidbrain-diencephalic junction the termdorsal is synonymous withposterior andventral is synonymous withanterior.^[1]
• Contralateral andipsilateral referring to a corresponding position on the opposite left or right side (thesagittal plane) and on the same side (ipsilateral) respectively.

Standardanatomical planes andanatomical axes are used to describe structures in animals. In humans and many otherprimates 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 thehuman brain, "rostral" still means "towards the beak or snout (Latinrostrum)", or at any rate, the interior of thecranial cavity just behind the face. "Caudal" means "towards the tail (Latincauda"), but not "towards the back of the cranial cavity", which is "posterior" (behind, in ordinary motion). Therostro-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, theoccipital 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 theforebrain, 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 thestandard anatomical position. 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 thecerebral 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. Aparasagittal plane is any plane parallel to the sagittal plane.

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

Anafferent nerve fiber is a fibre originating at the present point. For example, a striatal afferent is an afferent originating at thestriatum.

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

Specific terms are also used to describe the route of a nerve or nerve fibre:

Achiasm (from Greek Chi) is used to describe different types of crossings of or withinperipheral nerve fibres between the cerebral hemispheres. The major example in the human brain is theOptic chiasm.

Adecussation (from Latin decussis 'ten', written as a capitalX) refers to nerve fibers that cross thesagittal plane from one side of thecentral nervous system to the other, and connectdifferent brain regions. There are two kinds:

• Type 1 crosses the sagittal plane in thesame brain region or spinal segment where the cell body is located. Examples areMauthner cells infish andamphibians.
• Type 2 crosses the sagittal plane in adifferent brain region. Example:pyramidal decussations.

The first type is known also forinvertebrates, whereas the second type only occurs invertebrates. The second type is thought to be due to anaxial twist, such that each hemisphere of the forebrain represents predominantly thecontralateral side of the body.

Acommissure 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 theanterior commissure,posterior commissure,corpus callosum,hippocampal commissure, andhabenular commissure. The spinal cord contains a commissure as well: theanterior white commissure.

Aganglion can also have the form of crossing nerves, but a ganglion always containssynapses betweenneurons as well as theircell bodies. The other kinds of nerve crossings never contain synapses of cell bodies of neurons.

Thedifference between achiasm and adecussation is that the first refers to peripheral nerves whereas the latter refers to crossings inside central nervous system. Acommissure connects the same brain region of each side whereas adecussation connects different brain regions.

• 
  The brainstem from the front, showing adecussation of the superior pedicle and lemniscus, where nerve fibres from one side cross over to the next
• 
  Theoptic chiasm in the human brain, showing pathways conveying information from the visual field of each eye to the contralateral visual cortex

Specific terms are used to represent thegross anatomy of the brain:

Agyrus is an outward folding of the brain, for example theprecentral gyrus. Asulcus is an inward fold, or valley in the brain's surface - for example thecentral sulcus. 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

Afissure is used to describe:

1. A deep groove produced byopercularisation. An example is theSylvian Fissure.
2. A deep groove produced by the differentiation of the telencephalic vesicles. An example is thelongitudinal fissure, also known as theinterhemispheric fissure.

Look upfundus in Wiktionary, the free dictionary.

Specific acronyms are used to represent imaging. Some common acronyms include MRI (Magnetic Resonance Imaging) and CT (Computed tomography).

• Anatomical terms of muscle
• Anatomical terms of motion

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