Anatomical Position of Human Body
Anatomical position is the basic premise or central tenet, the very core on which all the details of anatomy are based.
Thus, to understand the anatomy of the human body, the anatomical position has always to be remembered.
The anatomical position of the human body is
- The person standing erect and face forward.
- Arms are straight along the sides of the trunk with hands held by the hips, palms facing forward
- Feet parallel and toes pointing forward.
Anatomical Planes of Body
After the anatomical position, planes of the body are crucial to understanding the terminology and relation of the different organs relative to each other.
Just for orientation purposes, a plane is a two-dimensional slice through three-dimensional space. There can be many planes through a given space. For example, vertical plane, horizontal plane, oblique plane. There are infinite possibilities theoretically.
But for purpose of anatomy following planes are important- sagittal, coronal and transverse.
- Sagittal plane divides the body into two equal halves – left and right.
- A plane parallel to sagittal plane is called parasagittal plane
- Parasagittal plane is also called as longitudinal plane
- Coronal plane divides the body into anterior and posterior section.
- Transverse plane divides the body into a superior section and a lower inferior section.
For example, to description may say that it is a transverse section of the arm. That means we are looking at the content of the section from above or below.
The transverse section may be referred to as horizontal section in some labels. Again, the anatomical position comes to our help as for the horizontal section to be understood we know the position of the body and conclude that it is the same as transverse. [a horizontal section of lying person would mean different than standing.]
Anatomical Locations and Relations
After position and planes, we now move to terms that denote the location and relation of different organs or indicate the direction of motion of a joint.
To avoid any ambiguity, we cannot use terms like left, right, front, back, above or below because they are position-dependent. While head is above neck, it reverses position when one is upside down.
Similarly, the base of the nose is right of the left eye and left or right eye. It fails to describe its position as an absolute anatomical location.
Therefore, we use terms that offer unchanging relations and locations in spite of the position of the body and communicate without faltering or ambiguity.
Thus, the base of the nose is medial to both eyes.
Not only it saves left or right confusion, but it also denotes a symmetrical relation of both eyes to the base of the nose.
In fact, when we address the locations through standard anatomical terms, we can marvel at how the sagittal plane divides the body into two symmetrical halves.
Following terms are used
Medial and Lateral
Medial denotes towards the midline in the sagittal plane. The line denoting the sagittal plane divides the body into right and left halves. This line is called midline.
Medial means towards the midline. Lateral means away from this midline.
As we noted before, the nose is medial to the eye. Therefore eye is lateral to nose.
Take the example of the hand. In anatomical position, the thumb is lateral to the index finger. In fact, the thumb is the most lateral digit and the little finger is the most medial.
The term lateral is also used to indicate the side. For example, in surgical positioning, left lateral position means the patient lies on his left side and the right side is up.
Other meaningful terms are made by adding suffixes
Unilateral – single side. For example a unilateral lesion
Bilateral – Both sides. For example, the disease involves bilateral hips [hips on both sides]
Contralateral – Opposite side. The patient also has an injury to contralateral femur
Ipsilateral – Same side. The patient has an injury to ipsilateral femur and tibia.
Anterior and Posterior
Anterior means front refers to the front, and the posterior refers to the back. Thus the scapula bone is posterior to the thoracic cage.
The tongue is anterior to the pharynx.
Terms ventral and dorsal are also used by medical professionals for anterior and posterior respectively though in humans these are more of embryological terms [see later]
Superior and Inferior
Superior and inferior are terms that describe vertical relations along the vertical lines.
The higher structure is superior and the lower structure is inferior. Thus the nipple is superior to the navel.
Similarly, hips is superior to knee and ankle is inferior to knee in anatomical position.
These terms work very well in axial structures but in limbs, because of their mobility, the relative position will change and the superior-inferior relation may not hold absolutely and lead to a difference in communication. A similar problem also occurs in structures that have a beginning and end, like nerves and vessels.
Therefore, we have another set of terms proximal and distal.
Proximal and Distal
These terms are used in structures which to have a beginning and an end. Limbs, vessels, nerves, and muscles are few such structures.
The proximal and distal describe the position or part of the structure in relation to its origin. Thus proximal means closer to its origin, distal means further from the origin.
The elbow is distal to the shoulder. Toes are distal to ankles etc.
Terms used in Embryology
Let us briefly touch the terms used in embryology too.
- Cephalic or cranial – towards the head
- Caudal – towards the tail or inferior end
- Ventral – Front side of the embryo [anterior]
- Ventral – posterior or back and Dorsal
In addition to this rostral and caudal are used to describe structures within the central nervous system.
- The rostral means towards the beak [nose].
- Caudal refers to the posterior (back) of the head.
Various Other Terms of Location and Their Usage
Palmar/Dorsal and Plantar/Dorsal
To describe hand structures, the following two terms are used.
- Palmar – describe the front or palmar side of the hand
- Dorsal – backside of the hand
Examples are palmar fascia, dorsal veins
Similarly, for foot, the terms are plantar and dorsal.
Term volar is also used in place of palmar and plantar.
Thus the volar side of the hand is palmar and the volar side of the foot is plantar.
These terms are more specific and explanatory and avoid confusion of anterior/posterior due to the rotation of the forearm that leads to change in the relative orientation of the hand.
Radial/Ulnar
[In the forearm, to avoid the same confusion, the sides of the forearm are denoted by terms after the bones. The lateral side is radial and the medial side is ulnar. Similarly, the relations can also be described as ulnarward or radialward structures.
In leg, the terms are tibial and fibular, named on the same patterns.]
It must be reiterated that standard anterior-posterior, medial-lateral are used and quite sufficient but because of the prolonged use in literature, the usage still continues especially in clinical specialties. SO it s better to acquaint oneself with these terms too.
Anteversion and retroversion are terms which denote forward or backward tilting.
Read more| Anteversion and Retroversion
Axial
Axial refers to around the central axis of the whole body or the extremity. Abaxial means away from axis and adaxial means toward the central axis.
Parietal and Visceral
Parietal and visceral are used in visceral structures. Parietal means pertaining to the wall of a body cavity.
For example, the parietal peritoneum is the lining on the inside of the abdominal cavity. [Parietal is also a bone in the skull.]
Visceral means associated with organs within the body’s cavities.
For example, The visceral lining of the stomach.
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