Anatomical terms of neuroanatomy

This article describes anatomical terminology that is used to describe the central and peripheral nervous systems - including the brain, brainstem, spinal cord, and nerves.

Anatomical terminology in neuroanatomy

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 from Latin and Greek, and like other areas of anatomy are generally standardised based on internationally accepted lexicons such as Terminologia Anatomica.

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

Location

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 straight CNS, 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, see anatomical terms of location.

For many purposes of anatomical description, positions and directions are relative to the standard anatomical planes and axes. Such reference to the anatomical planes and axes is called the stereotactic 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, particularly:

  • Rostral and caudal: In animals with linear nervous systems, 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 humans 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 and diencephalon (the midbrain-diencephalic junction). Thus, the terminology changes at either side of the midbrain-diencephalic 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 midbrain-diencephalic junction the term rostral is synonymous with superior and caudal is synonymous with inferior.[1]
  • Dorsal and ventral: In animals with linear nervous systems, the term dorsal (from the Latin dorsum, meaning "back") is synonymous with superior and the term ventral (from the Latin venter, meaning "belly") is synonymous with inferior. In humans, however the terminology differs on either side of the midbrain-diencephalic 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 midbrain-diencephalic junction the term dorsal is synonymous with posterior and ventral is synonymous with anterior.[1]
  • Contralateral and ipsilateral referring to a corresponding position on the opposite left or right side (the sagittal plane) and on the same side (ipsilateral) respectively.

Planes and axes

Human brain anatomical axes alterations
The anatomical axes of orientation of the human brain are at odds with the anatomical axes of the human body in the standard anatomical position.
Red axis shows how the head bent forward as the back pointed upwards:
c: Caudal
r: Rostral
Yellow axes show the conventions for naming directions in the brain itself:
c: Caudal (though not tail direction),
d: Dorsal
r: Rostral (effectively unchanged)
v: Ventral (though not belly direction)
Human brain anatomical planes letter annotations
Anatomical axes, planes and localisations in the human brain. Three axes:
  • d: Axial, Superior-inferior or Dorsoventral axis (yellow)
  • l: Left-right, or Lateral axis (cyan, blue-green)
  • m: Medial, Antero-posterior or Rostral-to-caudal axis (magenta)
Three major planes:
  • A: Axial (blue), containing the lateral axis and also the Medial axis
  • C: Coronal plane (green), containing the axial axis and the lateral axis
  • S: Sagittal plane (red), containing the axial axis and the medial axis
Also:
  • e: The eye at the anterior end of the brain
  • P: A Parasagittal plane (yellow) through one eye; parasagittal planes comprise the class of planes parallel to (and therefore lateral to) the sagittal plane.

Standard anatomical planes and anatomical axes are used to describe structures in animals. In humans and most other primates the axis of the central nervous system is not straight, but bent. This means that there are certain major differences that reflect the distortion of the brains of the Hominidae. For example, to describe the human brain, "rostral" still means "towards the face", or at any rate, the interior of the cranial cavity just behind the face. However, in the brain "caudal" means not "towards the tail", but "towards the back of the cranial cavity". Alternative terms for this rostro-caudal axis of the brain include medial or antero-posterior axis.

"Dorsal" means "in the direction away from the spinal cord i.e. in the direction of the roof of the cranial cavity". "Ventral" means downwards towards floor of the cranial cavity and thence to the body. They lie on the superior-inferior or Dorsoventral axis. The third axis passes through the ears, and is called the left-right, or lateral axis.

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, the plane that is horizontal and parallel to the axial plane of the body in the standard 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 both ears, and contains the lateral and dorsoventral axes.
  • Sagittal, a vertical plane that passes from between the nostrils, and between the cerebral hemispheres, dividing the brain into left and right halves. It contains the dorsoventral and medial axes of the brain. A parasagittal 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 is a fibre originating at the present point. For example, a striatal afferent is an afferent originating at the striatum.

An efferent 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. Note that that is the opposite of the direction in which the nerve fibre conducts signals.

Route

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

A chiasm (from Greek, meaning 'a crossing') is used to describe an X-shaped crossing of nerve fibres between the cerebral hemispheres. The major example in the human brain is the Optic chiasm. The main difference between such a chiasm and a decussation is that not all nerve fibres entering the chiasm cross over.

A commissure is a group of nerve fibres crossing the sagittal plane mainly parallel to the lateral axis and therefore without forming a cross-shape. For example, nerve fibre tracts that cross between the two cerebral hemispheres, are the anterior commissure, posterior commissure, corpus callosum, hippocampal commissure, and habenular commissure. The spinal cord contains a commissure as well: the anterior white commissure.

A decussation is where nerve fibers cross from one side of the brain to the other.

Gray690

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

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

Brain

Sulci Gyri Fundi in section of Human brain
Image of the human brain showing sulci, gyri, and fundi shown in a Coronal section.

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

A gyrus is an outward folding of the brain, for example the precentral gyrus. A sulcus is an inward fold, or valley in the brain's surface - for example the central 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

A fissure is used to describe:

  1. A deep groove produced by opercularisation. An example is the Sylvian Fissure.
  2. A deep groove produced by the differentiation of the telencephalic vesicles. An example is the Medial longitudinal fissure, also known as the interhemispheric fissure.

Imaging

MRI
Magnetic Resonance Imaging.

References

  1. ^ a b Hal., Blumenfeld, (2010). Neuroanatomy through clinical cases (2nd ed.). Sunderland, Mass.: Sinauer Associates. ISBN 9780878930586. OCLC 473478856.
Anterior vagal trunk

The anterior vagal trunk is a branch of the vagus nerve which contributes to the esophageal plexus. It consists primarily of fibers from the left vagus, but also contains a few fibers from the right vagus nerve.

Cavum Vergae

The cavum Vergae is a posterior extension of the cavum septi pellucidi, an anomaly that is found in a small percentage of human brains. It was first described by Andrea Verga.

Celiac branches of vagus nerve

The celiac (or coeliac) branches of vagus nerve are small branches which provide parasympathetic innervation to the celiac plexus.

Dentatothalamic tract

The dentatothalamic tract (or dentatorubrothalamic tract) is a tract which connects the dentate nucleus and the thalamus while sending collaterals to the red nucleus.The term "dentatorubrothalamocortical" is sometimes used to emphasize termination in the cerebral cortex.

Fascia dentata

The fascia dentata is the earliest stage of the hippocampal circuit. Its primary input is the perforant path from the superficial layers of entorhinal cortex. Its principal neurons are tiny granule cells which give rise to unmyelinated axons called the mossy fibers which project to the hilus and CA3. The fascia dentata of the rat contains approximately 1,000,000 granule cells. It receives feedback connections from mossy cells in the hilus at distant levels in the septal and temporal directions. The fascia dentata and the hilus together make up the dentate gyrus. As with all regions of the hippocampus, the dentate gyrus also receives GABAergic and cholinergic input from the medial septum and the diagonal band of Broca.

Free nerve ending

A free nerve ending (FNE) or bare nerve ending, is an unspecialized, afferent nerve fiber sending its signal to a sensory neuron. Afferent in this case means bringing information from the body's periphery toward the brain. They function as cutaneous nociceptors and are essentially used by vertebrates to detect pain.

Ganglion cell

A ganglion cell is a cell found in a ganglion. The term is also sometimes used to refer specifically to:

retinal ganglion cell (RGC) found in the ganglion cell layer of the retina

cells that reside in the adrenal medulla, where they are involved in the sympathetic nervous system's release of epinephrine and norepinephrine into the blood stream

cells of the sympathetic ganglia

cells of the parasympathetic ganglia

cells of the spiral ganglia

Globose nucleus

The globose nucleus is one of the deep cerebellar nuclei. It is located medial to the emboliform nucleus and lateral to the fastigial nucleus. This nucleus contains primarily large and small multipolar neurons.

The globose nucleus and emboliform nucleus are occasionally referred to collectively as the interposed nucleus.

Interpeduncular fossa

The interpeduncular fossa is a somewhat rhomboid-shaped area of the base of the brain, limited in front by the optic chiasma, behind by the antero-superior surface of the pons, antero-laterally by the converging optic tracts, and postero-laterally by the diverging cerebral peduncles.

The floor of interpeduncular fossa, from behind forward, are the posterior perforated substance, corpora mamillaria, tuber cinereum, infundibulum, and Pituitary Gland.

Contents of interpeduncular fossa include oculomotor nerve, and circle of willis.

Lemniscus (anatomy)

A lemniscus (Greek for ribbon or band) is a bundle of secondary sensory fibres in the brainstem. The medial lemniscus and lateral lemniscus terminate in specific relay nuclei of the diencephalon. The trigeminal lemniscus is sometimes considered as the cephalic part of the medial lemniscus.

Myelencephalon

The myelencephalon or afterbrain is the most posterior region of the embryonic hindbrain, from which the medulla oblongata develops.

Pars tuberalis

The pars tuberalis is part of the anterior lobe of the pituitary gland, and wraps the pituitary stalk in a highly vascularized sheath.

Parvocellular cell

Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus. "Parvus" is Latin for "small", and the name "parvocellular" refers to the small size of the cell compared to the larger magnocellular cells. Phylogenetically, parvocellular neurons are more modern than magnocellular ones.

Pontine cistern

The pontine cistern, also cisterna pontis and cisterna pontocerebellaris is a notable subarachnoid cistern on the ventral aspect of the pons.

It contains the basilar artery, and is continuous behind with the subarachnoid space of the spinal cord, and with the cisterna magna, and in front of the pons with the interpeduncular cistern.

Pontine nuclei

The pontine nuclei (or griseum pontis) are the nuclei of the pons involved in motor activity. The pontine nuclei are located in the ventral pons. Corticopontine fibres carry information from the primary motor cortex to the ipsilateral pontine nucleus in the ventral pons, and the pontocerebellar projection then carries that information to the contralateral cerebellum via the middle cerebellar peduncle. Extension of these nuclei in the medulla oblongata are named arcuate nucleus (medulla) which has the same function.

They therefore allow modification of actions in the light of their outcome, or error correction, and are hence important in learning motor skills.

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.

Prevertebral plexus

A prevertebral plexus is a nerve plexus which branches from a prevertebral ganglion.

Suprapineal recess

The suprapineal recess is an anatomical structure in the ventricular system of the brain.

It is located in the posterior part of the third ventricle, overlying the cerebral aqueduct.

In severe cases of hydrocephalus with increased pressure, this structure can dilate causing mass effect on the midbrain resulting in Parinaud's Syndrome with bilateral inward and downward deviation of the eyes.

Vestibulocerebellar tract

The vestibulocerebellar tract is a tract in the pontine tegmentum which connects the vestibular nerve and the cerebellar cortex. It terminates in the Archicerebellum.

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