Question

Which of the following vertebra is formed from four vertebrae? (a) Sacrum (b) \(\operatorname{Coccg} x\) (c) Atlas (d) Axis

Short answer

The correct answer is (b) Coccyx, typically formed by four fused vertebrae. However, the 'Sacrum' may contain four or five, and there is a typo in option (b).

Step-by-step solution

Understanding the Human Vertebral Column

The human vertebral column is divided into different sections, each consisting of a different number of vertebrae. These sections include the cervical, thoracic, lumbar, sacral, and coccygeal regions.

Identifying Characteristics of Options

Each option provided represents a specific vertebra or region in the vertebral column. The Sacrum is formed by the fusion of four to five sacral vertebrae. The Coccyx, commonly referred to as the tailbone, typically consists of four fused vertebrae. The Atlas (C1) and the Axis (C2) are the first and second cervical vertebrae, respectively, and each is a single vertebra.

Determining the Correct Answer

Given that the question asks which of the options is formed from four vertebrae, the Coccyx is the correct choice as it is typically formed by the fusion of four vertebrae. 'Coccg x' likely refers to the Coccyx; however, there is a typographical error. The Sacrum may also be considered correct if it only consists of four fused vertebrae, which is less common but possible.

Key concepts

Sacrum

The sacrum is a critical component in the human vertebral column, serving as the keystone of the pelvis.
It's formed by the fusion of five, sometimes four, sacral vertebrae during adulthood, which is why it might be tempting to consider it as an option in the exercise question.

• The fusion process creates a solid, triangular bone that provides structural integrity and stability to the pelvic girdle.
• It also forms joints with the hip bones known as the sacroiliac joints which are crucial for weight distribution while walking or standing.

Though the majority of people have a sacrum made up of five fused vertebrae, variations do occur and a count of four is less common but still possible.

Coccyx

The coccyx, or tailbone, is the terminal segment of the vertebral column.
Comprised typically of four, and occasionally three to five, small vertebral bones fused together, the coccyx represents a vestigial tail from our evolutionary past.

• Despite its small size, the coccyx plays significant roles in human anatomy, including being an attachment site for various muscles, tendons, and ligaments.
• It also supports and stabilizes a person while sitting, especially in a leaning back position.

In the context of the exercise problem, the coccyx is the vertebra formed from four vertebrae, putting it as the correct answer to the given question.

Vertebrae Fusion

Vertebrae fusion is a biological process where adjacent vertebrae grow together into a single, continuous bone.
This occurs naturally in certain regions of the vertebral column, such as in the sacrum and coccyx, as part of normal human development.

• Fusion provides increased strength and reduces mobility between the bones, which can be beneficial in providing stability to the body's core.
• In the spine's developmental stages, this process can help prevent potential injuries that could occur from independent movement of these vertebrae.

However, in other contexts, such as medical conditions or surgical procedures, vertebral fusion can be a corrective measure to alleviate pain or stabilize the spine.

Cervical Vertebrae

The cervical vertebrae represent the first segment of the vertebral column, consisting of seven vertebrae (C1 through C7) located in the neck.
These vertebrae are very distinct in their design and function compared to other spinal segments.

• The first two cervical vertebrae, the atlas (C1) and axis (C2), play crucial roles in supporting the head's rotation and pivotal movement.
• They are distinctively shaped: the atlas has no body and consists of a delicate ring, while the axis has a unique odontoid process, called the dens, which creates a pivotal joint.

The cervical spine overall is known for its high degree of flexibility and mobility, allowing for a wide range of head and neck movements.