Anatomic.us > Skeletal System Posterior

Atlas

The vertebral column (backbone of) human body is made up of almost similar small bones (33 in number) called vertebrae. The vertebrae present in neck are called the cervical vertebrae. They are seven in number, extending from the base of the skull to the thoracic region where the thoracic vertebrae are continued.

The first cervical vertebra, at the base of the skull is called the atlas vertebra. It is an atypical vertebra which means it is not having usual typical features like other typical cervical vertebrae (3rd to 6th cervical vertebrae are typical).

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Atlas

BONY FEATURES OF THE ATLAS VERTEBRA

Following are the specific bony features of the atlas vertebra. By the help of these features, it can be identified easily:

  • It is ring shaped

  • It does not have a body or a spinous process like other typical vertebrae

  • It has a short anterior arch. This arch, on anterior aspect, has a median anterior tubercle and on posterior aspect, has an oval facet (which articulates with the dens)

  • It has a long posterior arch. This arch, on upper surface, is marked by a groove and on posterior surface, has a median posterior tubercle

  • It has right and left lateral masses. The upper surface of each lateral mass has superior articular facet and the lower surface has inferior articular facet. The medial surface of each lateral mass has a tubercle.

  • It has transverse processes. These are the processes which project laterally from the lateral masses. These are very long.

 

ATTACHMENTS

Following muscles are attached to this vertebrae:

  • Longus colli ( inserted on anterior tubercle)

  • Following muscles are originated from the atlas vertebra:

  • Rectus capitis posterior (from posterior tubercle)

  • Rectus capitis anterior (from anterior surface)

  • Rectus capitis lateralis, superior oblique, inferior oblique and levator scapulae (from transverse process)

 

FUNCTION

This is a very important bone of neck region. It makes joint with the base of the skull, which connects the head with the rest of the body. It allows the brain to connect to the rest of the body and it allows the necessary flexibility for free movement of head. It also protects, along with other cervical vertebra, the medulla and spinal cord with its meanings.

 

SOME CLINICAL ASPECTS

Jefferson fracture is the burst fracture of cervical vertebra. Spinal cord is not damaged commonly in this case. This fracture occurs most commonly by falling on head from a height and motor vehicle accidents etc.

It is one of the most common vertebrae, involved in cervical fracture in young children. The size of head of young children is large and bones are comparatively soft that may result in fracture of these vertebrae easily on trauma.


BONY FEATURES OF THE ATLAS VERTEBRA

Following are the specific bony features of the atlas vertebra. By the help of these features, it can be identified easily:

  • It is ring shaped

  • It does not have a body or a spinous process like other typical vertebrae

  • It has a short anterior arch. This arch, on anterior aspect, has a median anterior tubercle and on posterior aspect, has an oval facet (which articulates with the dens)

  • It has a long posterior arch. This arch, on upper surface, is marked by a groove and on posterior surface, has a median posterior tubercle

  • It has right and left lateral masses. The upper surface of each lateral mass has superior articular facet and the lower surface has inferior articular facet. The medial surface of each lateral mass has a tubercle.

  • It has transverse processes. These are the processes which project laterally from the lateral masses. These are very long.

 

ATTACHMENTS

Following muscles are attached to this vertebrae:

  • Longus colli ( inserted on anterior tubercle)

  • Following muscles are originated from the atlas vertebra:

  • Rectus capitis posterior (from posterior tubercle)

  • Rectus capitis anterior (from anterior surface)

  • Rectus capitis lateralis, superior oblique, inferior oblique and levator scapulae (from transverse process)

 

FUNCTION

This is a very important bone of neck region. It makes joint with the base of the skull, which connects the head with the rest of the body. It allows the brain to connect to the rest of the body and it allows the necessary flexibility for free movement of head. It also protects, along with other cervical vertebra, the medulla and spinal cord with its meanings.

 

SOME CLINICAL ASPECTS

Jefferson fracture is the burst fracture of cervical vertebra. Spinal cord is not damaged commonly in this case. This fracture occurs most commonly by falling on head from a height and motor vehicle accidents etc.

It is one of the most common vertebrae, involved in cervical fracture in young children. The size of head of young children is large and bones are comparatively soft that may result in fracture of these vertebrae easily on trauma.

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