Vertebrae in Human Body

The vertebrae and accompanying intervertebral discs are the basic skeletal components that make up the back. The skull, pelvic bones, scapulae and ribs contribute to the back skeletal structure and serve as attachment points for muscles. Here, let’s learn more about the anatomy and functions of vertebrae in the human body.

Table of Contents

• Vertebrae Anatomy
• Vertebral Column – Diagram
• Cervical Vertebrae
• Thoracic Vertebrae Anatomy
• Lumbar Vertebrae
• Sacral Vertebrae
• Coccygeal Vertebrae
• Vertebrae Functions
• Frequently Asked Questions

Vertebrae Anatomy

The 33 vertebrae are the primary bones of the back. The number of vertebrae and their specific properties varies according to the bodily location with which they are related. There are seven cervical vertebrae, five lumbar vertebrae, twelve thoracic vertebrae, five sacral vertebrae, and three to four coccygeal vertebrae. The sacral vertebrae unite to form a single bone structure known as the sacrum.

The coccygeal vertebrae have a simple form, range in number from three to four (4 being most common), and frequently unite into a single coccyx. The total number of cervical thoracic and lumbar vertebrae comes to 24; along with unfused sacral and coccygeal vertebrae, they make 33. Thus the number of vertebrae present in humans is 33. In adult humans, the five sacral vertebrae fuse to form a single sacrum and four coccygeal vertebrae fuse to form a single coccyx. Thus, adult humans have only 26 vertebrae.

Typical Vertebrae

A typical vertebra comprises a vertebral arch as well as a vertebral body. The characteristic features in a typical vertebra are as follows:

Parts of Vertebrae

• The vertebral body is typically the most weight-bearing component of the bone and is located anteriorly. It becomes larger from the cervical vertebra (C2) to the lumbar vertebra (L5). It is connected to other vertebrae by ligaments and intervertebral discs.
• Intervertebral discs made of fibrocartilaginous material divide the vertebral bodies of neighbouring vertebrae.
• The vertebral arch is responsible for the posterior and lateral portions of the foramen vertebrae. Each vertebra’s vertebral arch is made up of laminae and pedicles.
• A vertebral foramen is an opening formed by the posterior portion of the vertebral arch and the anterior portion of the vertebral body.
• A spinous process emerges inferiorly and posteriorly from the intersection of the 2 laminae and serves as a location for ligament and muscle attachment.
• On each side, a transverse process protrudes posterolaterally from the pedicle-lamina junction.
• Superior and inferior articular processes also protrude from the area where the laminae and pedicle join.

Vertebral Column – Diagram

Typically there are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral and 4 caudal (coccygeal) vertebrae.

Cervical Vertebrae

The vertebrae are named after the region they occupy. The human cervical vertebrae are found in the neck region, immediately below the skull. The seven (C1 to C7) cervical vertebrae that connect the thorax to the skull are distinguished by their tiny size as well as the presence of a vertebral foramen (opening) in the transverse processes.

The cervical vertebrae anatomy is as follows:

• When seen from above, the vertebral body is square in form and short in height, with a convex inferior surface as well as a concave superior surface.
• The transverse processes are typically trough-shaped, with a circular foramen transversarium perforating it.
• Spinous process is bifid and short, with a triangular foramen.

The first (atlas-C1) and second (axis-C2) cervical vertebrae are designed to support the head movement. The primary differentiating characteristic of C1 is the absence of a vertebral body. During development, the vertebral body of C1 merges with the body of C2 to form the dens of C2. The cervical vertebrae from C3 to C6 are small structures. The C7 bone has a long spinous process, whose tip can be felt through the skin.

Thoracic Vertebrae Anatomy

The number of thoracic vertebrae are 12. The attachment of the twelve thoracic vertebrae with the ribs distinguishes them all. Although all vertebrae have rib elements, they are small and are incorporated into the transverse processes. However, in the thorax, the ribs are separate bones that articulate via synovial joints with the associated vertebrae’s vertebral bodies and transverse processes.

The presence of facets that function as the site of attachment with the corresponding tubercle of the rib distinguishes the thoracic vertebrae from the vertebral bones. Also, when viewed from above, the vertebral body is slightly heart-shaped, and the vertebral foramen is round.

• The thoracic vertebrae are numbered from T1 to T12. T1 is closest to the skull and the T2 is typically larger than the T1.
• The first four thoracic vertebrae are slightly similar to the cervical vertebrae. Whereas the last four have characteristics similar to that of lumbar vertebrae.

Lumbar Vertebrae

The thoracic vertebrae are followed by five lumbar vertebrae, which create the skeletal support for the posterior abdominal wall and are distinguished by their large-sized bones. The other characteristics featured in the lumbar vertebrae anatomy are –

• A normal lumbar vertebral body is cylindrical, and the vertebral foramen is triangular and bigger than the ones in the thoracic vertebrae.
• The L1 is levelled with the anterior end of the 9th rib.
• The lumbar vertebrae also lack facets for rib articulation, except for those on vertebra L5. It is a large and slightly conical-shaped structure where the iliolumbar ligaments attach.

See more: Bones of Spine

Sacral Vertebrae

Next, the five sacral vertebrae fused into a single bone known as the sacrum. It articulates with the pelvic skeleton on either side and is a component of the pelvic wall. The anatomy of sacral vertebrae is as follows:

• It has a triangular form with an inferiorly pointed apex and is bent to have convex posterior and concave anterior surfaces.
• It articulates with the L5 vertebra above and the coccyx below.
• It features two big L-shaped facets for forming a connection with the pelvic skeleton, one on each lateral side.

Coccygeal Vertebrae

A three to four (common) variable number of coccygeal vertebrae are located inferior to the sacrum and merge into a single small triangular bone known as the coccyx. The coccyx has attachments with tendons, muscles and ligaments and is not entirely useless. But facilitating attachments is not the only original purpose of cervical vertebrae. Hence they are considered vestigial.

• The coccyx (tailbone) articulates with the sacrum’s inferior end and comprises 3 to 4 fused coccygeal vertebrae.
• The sacrococcygeal joint is the articulation between the base of the coccyx and the apex of the sacrum.
• It is distinguished by its tiny size and absence of vertebral canal and vertebral arches.
• The first portion of these vertebrae is large and resembles the last sacral vertebrae.

Vertebrae Functions

The spinal column is a complex structure comprising various bones, joints, nerves, muscles, ligaments and tendons woven together to form a strong structure. This spinal or vertebral column is made up of a series of vertebrae. These vertebrae serve various purposes like support, protection, movement, etc. Let’s have a look at the functions of vertebrae in humans.

• Cervical vertebrae functions – It supports the head and aids in its movements (up-down and left-right movement). It also houses eight pairs of spinal nerves that innervate the shoulder, arm, neck and hand regions.
• Thoracic vertebrae functions – It supports the neck and anchors the rib cage. Also, it helps transfer the force from the torso to the lower segment of the spine. It houses twelve pairs of spinal nerves that control various sensory and motor signals.
• Lumbar vertebrae functions – It protects the cauda equina (a bundle of lower spinal nerves) along with the coccyx and sacrum. It provides support and stabilises the upper body and also controls leg movement.
• Sacrum and coccyx – They form the back wall of the pelvis and hip. It also facilitates sitting, walking and running movements.

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