Welcome to Easy Anatomy! In this video, we are going to discuss basic directional terms, anatomical axes, and body planes.
This knowledge helps in describing the structures of the human body, identifying their exact location, and understanding their relationships to each other and to the standard anatomical position.
In this position, the person is standing straight, with the upper limbs down at their sides, palms facing forward, and thumbs pointing outward. The lower limbs are positioned parallel, with the toes pointing forward.
Anatomical body planes
There are three main imaginary anatomical planes that intersect the body:
- Sagittal plane
It divides the body into right and left parts. The sagittal plane can pass either off-center or perfectly along the midline of the body. In the latter case, it is called the median or mid-sagittal plane.
- Frontal (or coronal) plane
It divides the body into anterior (front) and posterior (back) parts.
Transverse (or axial) plane It divides the body into superior (upper) and inferior (lower) parts.
Anatomical axes of movement
An anatomical axis is a line around or along which movement occurs. Knowing these axes will be useful when studying muscles and joints.
There are three anatomical axes:
- Sagittal axis – passes from front to back
- Frontal axis – passes from left to right
- Vertical axis – passes from top to bottom
Anatomical terminology. Directional terms
There are several paired characteristics used to describe anatomical structures:
- Superior and inferior. Superior means closer to the head, while inferior means closer to the feet.
For example, the sternum is superior to the pelvis but inferior to the frontal bone.
You may also encounter the terms cranial and caudal. These are almost the same as superior and inferior.
The closer a structure is to the skull, the more cranial it is called (derived from Latin: cranium), and the closer it is to the “tail”, the more caudal it is referred to (derived from Latin: cauda). These terms are often used to describe embryonic structures.
The next pair of terms are anterior and posterior.
The synonyms are ventral and dorsal.
Derived from the Latin “venter” meaning belly, and “dorsum” meaning back.
If referring to a structure of the head or brain, instead of “ventral”, the term rostral is used, from the Latin “rostrum” meaning beak.
When describing the feet or hands, the term “dorsal” refers to their back surface.
The front surface of the hand is described by the more obvious term palmar, and the sole by the term plantar.
The next pair of terms describe the proximity of a structure to the median plane.
- Medial means closer to the median plane, and lateral means further from the median plane.
For example, our eyes are medial to our ears, and the ears are lateral to the eyes.
- Another pair of terms are external and internal. They usually describe the position of a structure relative to the center of a particular organ or cavity. For example, within the thoracic cavity, the heart is located more internally compared to the ribs.
- The terms superficial and deep describe the position of an object relative to the body surface. For example, the skin is more superficial than the muscles.
The last pair of terms are proximal and distal.
They are used to describe structures that have a beginning and an end. The closer to the beginning, the more proximal, and the closer to the end, the more distal.
For example, the proximal part of the humerus is involved in forming the shoulder joint, while the distal part is involved in forming the elbow joint.
There are also 4 terms of laterality:
1. Unilateral – the structure is located only on one side of the body (e.g., the spleen).
2. Bilateral – the structure is located on both sides of the body (e.g., the kidneys or lungs).
3. Ipsilateral – several structures are located on the same side of the body (e.g., the left kidney and the left lung).
4. Contralateral – one structure is located on one side of the body, and another on the opposite side, – contralaterally (e.g., the left eye and the right kidney).
Directional terms
- Anterior
- Refers to the front of the body or a structure; synonymous with ventral
- Posterior
- Refers to the back of the body or a structure; synonymous with dorsal
- Ventral
- Relates to the belly side of the body; synonymous with anterior
- Dorsal
- Relates to the back side of the body; synonymous with posterior
- Distal
- Describes a structure that is farther from the point of origin or attachment
- Proximal
- Describes a structure that is closer to the point of origin or attachment
- Median
- Refers to a structure situated in the middle or midline of the body
- Medial
- Describes a structure closer to the median plane of the body
- Lateral
- Describes a structure farther from the median plane of the body
- Superior
- Indicates a structure that is closer to the head
- Inferior
- Indicates a structure that is closer to the feet
- Cranial
- Refers to a structure closer to the skull; similar to superior
- Caudal
- Refers to a structure closer to the tail or lower part of the body; similar o inferior
- External
- Describes a structure located more towards the outside of an organ or cavity
- Internal
- Describes a structure located more towards the inside of an organ or cavity
- Superficial
- Refers to a structure closer to the body surface
- Deep
- Refers to a structure further away from the body surface
- Palmar
- Refers to the front (palm) surface of the hand
- Dorsal (of hand)
- Refers to the back surface of the hand
- Plantar
- Refers to the sole of the foot
- Dorsal (of foot)
- Refers to the top surface of the foot
