What is the Difference Between Typical and Atypical Vertebrae

The main difference between typical and atypical vertebrae is that typical vertebrae consist of a body, vertebral arch, and transverse processes, whereas atypical vertebrae contain deviated structures based on their functional requirements. Furthermore, cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacrum, and coccyx are the types of vertebrae occur in the vertebral column while the cervical vertebrae, C1, C2, and C7, thoracic vertebrae, T1, T9, and T12, lumbar vertebrae, L5, are atypical vertebrae. Moreover, other vertebrae are typical vertebrae. 

Typical and atypical vertebrae are two types of vertebrae in the vertebral column. Generally, each vertebra has a different structure based on their function. 

Key Areas Covered 

1. What are Typical Vertebrae
     – Definition, Types, Structure
2. What are Atypical Vertebrae
     – Definition, Types, Structure
3. What are the Similarities Between Typical and Atypical Vertebrae
     – Outline of Common Features
4. What is the Difference Between Typical and Atypical Vertebrae
     – Comparison of Key Differences

Key Terms 

Atypical Vertebrae, Cervical, Coccyx, Lumbar, Sacrum, Thoracic, Typical Vertebrae

What are Typical Vertebrae 

Typical vertebrae are the vertebrae, which have the standard structure of a vertebra of the vertebral column. Generally, the vertebral column contains 33 individual vertebrae; 24 presacral vertebrae (7 cervical, 12 thoracic, and 5 lumbar) followed by the sacrum (5 fused sacral vertebrae) and the coccyx (4 frequently fused coccygeal vertebrae). Except for the sacrum and the coccyx, intervertebral columns occur in between all other vertebrae. 

Figure 1: A Typical Vertebra

Furthermore, one of the main characteristic features of a vertebra is the presence of a large body. Also, the posterior part of the vertebra forms the vertebral arch. Significantly, this vertebral arch contains eleven parts, including two pedicles, two laminae, and seven processes. Also, pedicles like vertebral notches form intervertebral foramina while articulating the vertebra. For instance, these foramina are the entry and exit points for the spinal nerves. In the meanwhile, the central opening, which accommodates the spinal canal is the vertebral foramen formed by the body and the vertebral arch. Also, this vertebral foramen is responsible for enclosing and protecting the spinal cord. 

What are Atypical Vertebrae 

Atypical vertebrae are the vertebrae in the vertebral column with different structures when compared to the structure of a typical vertebra. However, only cervical, thoracic, and lumbar vertebrae contain atypical vertebrae.  

Atypical Cervical Vertebrae 

Cervical vertebrae are the vertebrae in the neck, occurring immediately below the skull. The bifid spinous process, transverse foramina, and a small vertebral body are the characteristic features of cervical vertebrae. However, the three cervical vertebrae are atypical. They include C1, C2, and C7. Here, C1 or atlas is the most superior cervical vertebra, which connects to the occipital condyles, forming the atlantooccipital joint – a synovial hinge joint. However, instead of a vertebral body, C1 contains two lateral masses, providing the fossae for the occipital condyles to rest in. Also, it contains very distinct anterior and posterior tubercles for the attachment of ligaments. Also, C1 has a small groove called the facet for the odontoid process (dens) of C2. Moreover, C1 contains a groove for the vertebral artery.

Figure 2: Cervical Vertebrae

Furthermore, C2 or the axis has three joints: the two lateral atlantoaxial joints and a single medial atlantoaxial joint to perform its main function: rotating the head. Also, it contains two lateral masses along with a vertical finger-like projection known as the odontoid process or dens. Moreover, C7 or the vertebral prominens is the most inferiorly located cervical vertebrae with striking similarities to thoracic vertebrae, containing a single, long, posteroinferior projecting spinous process.  

Atypical Thoracic Vertebrae 

Thoracic vertebrae are the strong vertebrae located in the middle of the vertebral column between the cervical and the lumbar vertebrae. Out of the twelve of them, five are atypical. They include T1, T9, T10, T11, and T12. Here, T1 is the superior-most thoracic vertebra, which contains a complete facet for the first rib as well as a demi-facet for the second rib.

Figure 3: Atypical Thoracic Vertebrae

Besides, T1 has a straighter spinous process, more closely resembling C7. Also, T9 does not contain inferior demi-facet to connect to the T10. Additionally, T10, T11, and T12 have a single costal facet to articulate with their respective ribs. Moreover, T11 and T12 have similar spinous processes, which are shorter and posteriorly-oriented.  

Atypical Lumbar Vertebrae 

Lumbar vertebrae are the largest and heavier vertebrae occur below thoracic vertebrae. Also, their main characteristic feature is the large vertebral body. However, L5 is the only atypical vertebrae among the other 5 lumbar vertebrae.

Figure 4: L5

Generally, it has the largest vertebral body as well as transverse processes. Also, it has the most inferiorly located discovertebral unit.  

Similarities Between Typical and Atypical Vertebrae  

• Typical and atypical vertebrae are two types of vertebrae occur in the vertebral column.  
• Except for the sacrum and the coccyx, other vertebrae consist of a vertebral body, vertebral arch, and transverse processes.  
• They are mainly responsible for protecting the spinal cord while providing support to the body. 

Difference Between Typical and Atypical Vertebrae 

Definition 

Typical vertebrae refer to the vertebrae, consisting of a body, vertebral arch, and several processes while atypical vertebrae refer to the vertebrae whose structure is highly modified by function and position.  

Types 

Cervical vertebrae, thoracic vertebrae, lumbar vertebrae, sacrum, and coccyx are the types of vertebrae occur in the vertebral column while the cervical vertebrae, C1, C2, and C7, thoracic vertebrae, T1, T9, T10, T11, and T12, lumbar vertebrae, L5 are atypical vertebrae. 

Regions

Vertebrae occur in the middle portion of the cervical, thoracic, and lumbar vertebrae, the sacrum, and the coccyx are typical vertebrae while atypical vertebrae occur in the transitioning regions of the vertebral column. 

Conclusion 

Typical vertebrae are the vertebrae of the vertebral column, consisting of the general structure of a vertebra. Also, this includes the presence of a vertebral body, vertebral arch, and transverse processes. However, the transitioning regions of the cervical, thoracic, and lumbar vertebrae contain atypical vertebrae with specific structures. Generally, C1, C2, C7, T1, T9, T10, T11, T12, and L5 are the atypical vertebrae of the vertebral column. On that account, the other vertebrae in the cervical, thoracic, and lumbar regions, as well as the sacrum and coccyx, are typical vertebrae. Therefore, the main difference between typical and atypical vertebrae is their structure and position. 

References:

1. “Vertebra, Vertebrae (Plural).” SPINE-Health, Available Here.
2. Maish, William. “Atypical Vertebrae of the Vertebral Column: Spine.” Geeky Medics, 12 May 2019, Available Here.

Image Courtesy:

1. “718 Vertebra-en” By Jmarchn – Own work (CC BY-SA 3.0) via Commons Wikimedia   
2. “723 Cervical Vertebrae” By OpenStax College – Anatomy & Physiology, Connexions Web site. Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia   
3. “Gray91” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 91 (Public Domain) via Commons Wikimedia   
4. “Gray94” By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See “Book” section below)Bartleby.com: Gray’s Anatomy, Plate 94 (Public Domain) via Commons Wikimedia