Anatomical References

Now that we have reviewed the root terms used for developing our nomenclature, we need to take a moment to look at how we go about referencing the various locations of the human body.  When discussing anatomical terms, the references that we use will depend on where you are attempting to reference.   First there needs to be a means for referencing to ensure that the body is being portrayed in the same position regardless of the point of view being taken.  In this manner we utilize what is referred to as the anatomical position, figure 1, of the body.

Anatomical Planes

From this anatomical position we are able to divide the body for reference of location of body segments based on geometric planes.  These geometric planes are given the reference of planes of the body.   And are based on the relative relationship of the plane to an imaginary “X-axis, Y-axis, or Z-axis” being overlaid the body, figure 2.  The result of this overlaid geometric axis is the development of three reference planes that are generally used to divide the body, or regions of the body, about the imaginary geometric axis.  These planes are the coronal (frontal), the transverse (cross-sectional or transaxial), and the sagittal (mid-sagittal) planes. The Coronal (Frontal), within the X-axis, will divide the body or region of the body into being dorsal and ventral, or posterior and anterior (commonly determined as back to front). The Transverse (Cross-sectional), within the Z-axis, plane will divide the body or region of the body into cranial and caudal, or superior and inferior (commonly determined as above or below).  The Sagittal plane, within the Y-axis, divides the body or region of the body into medial and lateral, or right and left.  There is a special case within the sagittal plane (mid-sagittal) that divides the body, or region of the body, directly down the long axis that divides the body, or region of the body, evenly into two halves. 

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Relationship References

Following which, there can then be references as to the position of a structure relative to other parts of the body, or body segments. This type of reference is utilized; it is dependent upon the point of reference that is being taken in explaining the location of the structure of interest.  With that in mind, we must discuss the anatomical terminology based on reference to the body as a whole or based on a regional area of the body or body segment, figure 3.

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In which we discuss locations in terms of the body as a whole using the paired references: ventral and dorsal, cranial and caudal, and ipsilateral and contralateral, figure 3.  Where ventral is the indication of being toward the stomach side of the body (front of the body) while dorsal as the indication of being toward the vertebral side of the body (back of the body).  Then there is cranial indicating being toward the head (upper half of the body) as caudal will reference being toward the tail (lower half of the body).  Lastly there is ipsilateral that is an indication of the structures being on the same side of the body, and contralateral indicating that the structures are on opposite sides of the body. 

Following which anatomical terminology will then be used to reference locations in reference to the regions and segments of the body where we are attempting to show relative relationship, figure 3.  Just as with the whole body, these references are performed in comparison pairs.  Where the reference pairs include: anterior and posterior, proximal and distal, and superficial and deep.  In which anterior provides a reference toward the front of the region while posterior indicates being toward the back of the region.  While proximal is an indication that the structure is closer to the torso and distal gives an indication of being further away from the torso.  Lastly we get a reference for the depth of the structure, where superficial is indicating being closest to the outer surface and deep is the indication for being furthest from the outer surface.

Additionally, there are anatomical terms that can be interchanged between references to locations at the level of the whole body and within regions of the body, figure 3.  Once again, these references are provided in relative pairs: lateral and medial, and superior and inferior.  In which the reference of medial and lateral are indications of relationship to the midline of the segment (or body). Lateral indicates being away from the midline of the long axis of the body or region of the body, while medial indicates being closer to the midline of the long axis of the body or region of the body.  And superior and inferior gives an indication of location along the long axis of the body (or segments of the body). Superior is the indication that the region is above, while inferior is the indication of being below, along the long axis of the body or region of the body.

While these terms give us reference for localization and relationship between structures of the body.  It does not provide us with a reference for the actual structure that we are referencing.  In this case, we describe the body by gross (aka large) anatomical divisions and superficial landmarks that we can observe, figure 4.(Greathouse et al., 2004; Kachlik et al., 2009)  

Gross Anatomical Identification

The anatomical divisions can be broken into seven (7) generalized regions of the body. (Greathouse et al., 2004; Kachlik et al., 2009) The axial region refers to the area around the skull, thorax and spine. In the axial region there are three (3) regions. The vertebral region is in reference to the spine.  The thorax is going to be referring to the trunk of the body (area of the body housing the internal organs). Then there is the pelvic region referring to the pelvis (area of the body housing the reproductive organs, rectum/anus, and urinary bladder). Lateral and distal to the axial region is the appendicular region.  This gives us reference to the extremities or areas around the extremities.  In the appendicular region there are two (2) regions.  There is the upper extremity, or the region referring to the arm, forearm, wrist and hand of the body.  And there is the lower extremity, region of the body region referring to the thigh, leg, ankle and foot of the body.

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Additionally there are distinct terms that are used to describe landmarks of the body that may be very different from how one may commonly discuss the region of landmark, figure 4 and table 4.(Greathouse et al., 2004; Kachlik et al., 2009)   The regions of the body can be subdivided into openings that provide areas for the reference to the location of the internal organs of the body, figure 5.  These openings are termed “cavities” and first divided into the ventral and dorsal cavities and then are further subdivided into smaller cavities that provide distinct identifiable locations for each of the internal organs of the body.  Cavities are then bounded by a series of connective membranes, which are divided into two types of membranes. The visceral membranes are the membranes that will surround organs themselves.  While the parietal membranes are the membranes that enclose the inner surface of the cavities that surrounds the organs covered by the visceral membranes. There are also references given to the abdominopelvic cavity for location of the organs based on the concept of regions (think a tic-tac-toe grid) overlaying the ventral view of the abdominopelvic cavity.

Lastly, there are references that we can use to describe how movements are occurring within the various body segments.  In these references there are distinct methods used to discuss the means of movements that the body, regions of body, or body segments can perform, see Musculoskeletal Chapter for more detail.  Just as with the references used for location of structures, these movements often occur in paired relationships while a few are unpaired.  These pairs include: flexion with extension, abduction with adduction, internal (medial) with external (lateral) rotation, elevation with depression, and protraction with retraction.  Along unpaired motions: circumduction, deviation, lateral flexion, and axial rotation.