Anatomical Directions and Positions
To describe the relative positions of structures in anatomy, a system of paired terms is used that allows precise orientation within the human body regardless of its posture.
- Lateral position (lateralis) — location of a structure further away from the median plane of the body. For example, the hand is located lateral to the clavicle; the eye is lateral to the nose.
- Medial position (medialis) — location closer to the median plane. The nose is medial to the eye; the clavicle is medial to the hand.
- Cranial direction (cranialis, from cranium — skull) — direction toward the skull. For example, the common carotid artery runs in this direction.
- Caudal direction (caudalis) — direction toward the lower end of the body. The aorta descends in the caudal direction after the ascending part and the aortic arch.
The same principles apply to the limbs: the ulna (ulna) is located medially, and the radius (radius) is located laterally in the anatomical position of the body.
Body Planes and Sections
Standard planes of section are used to study the internal structure of organs and bones.
- Sagittal plane (planum sagittale) — a vertical plane dividing the body into right and left parts. The median sagittal plane runs exactly along the midline.
- Transverse (horizontal) plane (planum transversale) — a plane perpendicular to the longitudinal axis of the body, dividing it into upper and lower parts.
- Frontal plane (planum frontale) — a vertical plane dividing the body into anterior and posterior parts.
Vertebral Column: General Characteristics
The vertebral column (columna vertebralis) is formed by a set of vertebrae (vertebrae) and constitutes the axial skeleton of the trunk. The standard vertebral formula includes:
- 7 cervical vertebrae (vertebrae cervicales);
- 12 thoracic vertebrae (vertebrae thoracicae);
- 5 lumbar vertebrae (vertebrae lumbales);
- 5 sacral vertebrae fused into the sacrum (os sacrum);
- 3–5 coccygeal vertebrae forming the coccyx (os coccygis).
Despite differences between regions, all vertebrae are built according to a single plan, which allows their general structure to be distinguished.
General Structure of a Vertebra
When describing an isolated vertebra, it is oriented so that the body faces forward, and the spinous process points backward and downward. A typical vertebra comprises the following parts.
- Vertebral body (corpus vertebrae) — the massive anterior part that performs a supporting function. Its surface features nutrient foramina (foramina nutricia) for the passage of vessels and nerves.
- Vertebral arch (arcus vertebrae) — the posterior part, bounding the vertebral foramen posteriorly and laterally.
- Pedicles of the vertebral arch (pedunculi arcus vertebrae) — paired segments connecting the arch to the body.
- Vertebral foramen (foramen vertebrale) — the space between the body and the arch. The combination of vertebral foramina forms the vertebral canal (canalis vertebralis), which houses the spinal cord (medulla spinalis).
Vertebral Processes
Seven processes extend from the vertebral arch, providing attachment sites for muscles and ligaments, as well as articulation between vertebrae.
- Spinous process (processus spinosus) — unpaired, extending backward from the arch along the midline.
- Transverse processes (processus transversi) — paired, directed laterally from the arch.
- Superior articular processes (processus articulares superiores) — paired, directed upward and bearing articular surfaces for articulation with the vertebra above.
- Inferior articular processes (processus articulares inferiores) — paired, directed downward and articulating with the vertebra below.
Vertebral Notches and Intervertebral Foramina
Depressions, known as vertebral notches, are located on the upper and lower margins of the arch pedicles.
- Superior vertebral notch (incisura vertebralis superior) — usually less pronounced.
- Inferior vertebral notch (incisura vertebralis inferior) — more deeply pronounced.
When adjacent vertebrae articulate, the superior and lower notches form the intervertebral foramen (foramen intervertebrale), through which spinal nerves exit the vertebral canal and blood vessels pass.
Key points
- Lateral and medial positions are determined relative to the median plane of the body.
- The cranial direction points toward the skull, while the caudal direction points toward the lower end of the body.
- The vertebral column (columna vertebralis) includes 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 3–5 coccygeal vertebrae.
- A typical vertebra consists of a body (corpus), an arch (arcus), and pedicles (pedunculi) that bound the vertebral foramen (foramen vertebrale).
- Seven processes extend from the arch: one spinous, two transverse, and four articular (superior and inferior).
- The vertebral body features nutrient foramina (foramina nutricia) for blood vessels and nerves.
- The combination of vertebral foramina forms the vertebral canal, which contains the spinal cord.
- The superior and inferior vertebral notches of adjacent vertebrae form the intervertebral foramen for the exit of spinal nerves.