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| Anatomical terminology |
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Ananatomical plane is an imaginary flat surface (plane) that is used to transect the body, in order to describe the location of structures or the direction of movements. In anatomy, planes are mostly used to divide the body into sections.[1]
Inhuman anatomy three principal planes are used: thesagittal plane,coronal plane (frontal plane), andtransverse plane.[2] Sometimes themedian plane as a specific sagittal plane is included as a fourth plane.[1][3] In animals with a horizontal spine the coronal plane divides the body into dorsal (towards the backbone) and ventral (towards the belly) parts and is termed thedorsal plane.[4][5]
There could be any number of sagittal planes, sometimes calledparasagittal planes but they all run parallel to themedian plane.[1] The termcardinal refers to the one plane that divides the body into equal segments, with exactly one half of the body on either side of the cardinal plane. The termcardinal plane appears in some texts as theprincipal plane. The terms are interchangeable.[7]
In human anatomy, the anatomical planes are defined in reference to a body in thestandard anatomical position, the upright or standing orientation.[1]
The axes and sagittal plane are the same for bipeds and quadrupeds, but the orientations of the coronal and transverse planes switch. The axes on particular pieces of equipment may or may not correspond to the axes of the body, especially since the body and the equipment may be in different relative orientations.
When describing anatomical motion, these planes describe theaxis along which an action is performed. So by moving through the transverse plane, movement travels from head to toe. For example, if a person jumped directly up and then down, their body would be moving through the transverse plane in the coronal and sagittal planes.
Alongitudinal plane is any plane perpendicular to the transverse plane. Thecoronal plane and thesagittal plane are examples of longitudinal planes.
Sometimes the orientation of certain planes needs to be distinguished, for instance inmedical imaging techniques such assonography,CT scans,MRI scans, orPET scans. There are a variety of different standardized coordinate systems. For theDICOM format, the one imagines a human in the anatomical position, and an X-Y-Zcoordinate system with the x-axis going from front to back, the y-axis going from right to left, and the z-axis going from toe to head. Theright-hand rule applies.[8]
In humans, reference may take origin fromsuperficial anatomy, made toanatomical landmarks that are on the skin or visible underneath. As with planes, lines and points are imaginary. Examples include:
In addition, reference may be made to structures at specific levels of thespine (e.g. the 4thcervical vertebra, abbreviated "C4"), or the rib cage (e.g., the 5thintercostal space).
Occasionally, in medicine,abdominal organs may be described with reference to thetrans-pyloric plane, which is a transverse plane passing through thepylorus.
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In discussing theneuroanatomy of animals, particularlyrodents used inneuroscience research, a simplistic convention has been to name the sections of the brain according to the homologous human sections. Hence, what is technically atransverse (orthogonal) section with respect to the body length axis of a rat (dividing anterior from posterior) may often be referred to in rat neuroanatomical coordinates as acoronal section, and likewise acoronal section with respect to the body (i.e. dividing ventral from dorsal) in a rat brain is referred to astransverse. This preserves the comparison with the human brain, whose length axis in rough approximation is rotated with respect to the body axis by90 degrees in the ventral direction. It implies that the planes of the brain are not necessarily the same as those of the body.
However, the situation is more complex, since comparative embryology shows that the length axis of the neural tube (the primordium of the brain) has three internal bending points, namely two ventral bendings at thecervical andcephalic flexures (cervical flexure roughly between themedulla oblongata and thespinal cord, and cephalic flexure between thediencephalon and themidbrain), and a dorsal (pontine or rhombic flexure) at the midst of the hindbrain, behind thecerebellum. The latter flexure mainly appears in mammals and sauropsids (reptiles and birds), whereas the other two, and principally the cephalic flexure, appear in all vertebrates (the sum of the cervical and cephalic ventral flexures is the cause of the 90-degree angle mentioned above in humans between body axis and brain axis). This more realistic concept of the longitudinal structure of vertebrate brains implies that any section plane, except the sagittal plane, will intersect variably different parts of the same brain as the section series proceeds across it (relativity of actual sections with regard to topological morphological status in the ideal unbent neural tube). Any precise description of a brain section plane therefore has to make reference to the anteroposterior part of the brain to which the description refers (e.g., transverse to the midbrain, or horizontal to the diencephalon). A necessary note of caution is that modern embryologic orthodoxy indicates that the brain's true length axis finishes rostrally somewhere in the hypothalamus where basal and alar zones interconnect from left to right across the median line; therefore, the axis does not enter the telencephalic area, although various authors, both recent and classic, have assumed a telencephalic end of the axis. The causal argument for this lies in the end of the axialmesoderm -mainly the notochord, but also the prechordal plate- under the hypothalamus. Early inductive effects of the axial mesoderm upon the overlying neuralectoderm is the mechanism that establishes the length dimension upon the brain primordium, jointly with establishing what is ventral in the brain (close to the axial mesoderm) in contrast with what is dorsal (distant from the axial mesoderm). Apart from the lack of a causal argument for introducing the axis in the telencephalon, there is the obvious difficulty that there is a pair of telencephalic vesicles, so that a bifid axis is actually implied in these outdated versions.
In quadrupeds the coronal plane is called the dorsal plane.
Some of these terms come from Latin.Sagittal means "like an arrow", a reference to the position of the spine that naturally divides the body into right and left equal halves, the exact meaning of the term "midsagittal", or to the shape of the sagittal suture, which defines the sagittal plane and is shaped like an arrow.