What makes the upper neck special?
The upper neck also known as the upper cervical spine or craniocervical junction is the vital juncture between the head and neck. It is made up of the occiput, the first cervical vertebrae (C1) and the second cervical vertebrae (C2).
Let's look at what makes craniocervical junction so vital to your health:
Unique anatomy and biomechanics
High neurological density
Cerebrospinal fluid hydrodynamics
Let's look at each in more detail.
1. Unique Anatomy & Biomechanics:
Your spine is made up of 24 individual bones that work together to protect your spinal cord while allowing you the ability to move. 22 out of the 24 bones in your spine have the same design just slightly different variations. They have a vertebral body, an intervertebral disc, and facet joints. These structures keep your spine in its proper position. The top bone of your neck (C1) has none of these structures.
The top bone of your neck is a ring-like structure that pivots around an axis that protrudes from the second bone of your neck (C2). The C1-C2 joint moves very different than the rest of the spine. It is highly mobile, about 50% of the movement of the neck comes from these bones. (1) The top two bones of your neck is held in place by small ligaments and small muscles. As mentioned above C1 lacks a vertebral body, intervertebral disc, and facet joints which allows for so much movement but lacks stability.
2. High Neurological Density
The craniocervical junction is in close proximity to the brain stem and several important cranial & spinal nerves. The muscles in this area are also more neurologically dense. Increased neurological density gives the brain more information. For example the Obliquus Capitis Inferior has a muscle spindle density of 242 muscle spindles per gram of muscle. Compared to the Latissimus Dorsi which has a muscle spindle density of 1.4 muscle spindles per gram of muscle. (2)
In fact all the muscles of the upper neck are neurologically dense.
Red: Obliquus Capitis Inferior 242 muscle spindles/ gram of muscle
Green: Obliquus Capitis Superior 190 muscle spindles/ gram of muscle
Blue: Rectus Capitis Posterior Major 98 muscle spindles/ gram of muscle
Orange: Rectus Capitis Posterior Minor 98 muscle spindles/ gram of muscle
3. Myodural Bridge
The suboccipital muscles (mentioned above) attach DIRECTLY to the spinal cord. (3) This connection is known as the myodural bridge and is not seen in any other part of the spine.
4. Cerebrospinal Fluid Dynamics
Your brain and spinal cord is suspended in fluid this fluid is called cerebrospinal fluid or CSF. Throughout the day your brain is working and creating waste products. At night when you are asleep CSF bathes and cleans your brain then drains the fluid from your skull. New and preliminary research is demonstrating that misalignment of the craniocervical junction can impair this brain draining process. (4) Also that this interruption in brain drain due to a misalignment at the craniocervical junction might also contribute to neurodegenerative diseases. (5)
1. Swartz, E. E., R. T.Floyd, and M. Cendoma. Cervical spine functional anatomy and the biomechanics of injury due to compressive loading. J Athl Train 2005. 403:155–161.
2. V. Kulkarni, M.J. Chandy, K.S. Babu; Quantitative Study of Muscle Spindles in Suboccipital Muscles of Human Foetuses, Neurology India, 49, December 2001: 355-359
3. Zheng N, Chung BS, Li YL, et al. The myodural bridge complex defined as a new functional structure. Surg Radiol Anat. 2019 Sep 28; - PubMed
4. Rosa, Scott & Baird, John & Harshfield, David & Chehrenama, Mahan. (2018). Craniocervical Junction Syndrome: Anatomy of the Craniocervical and Atlantoaxial Junctions and the Effect of Misalignment on Cerebrospinal Fluid Flow. 10.5772/intechopen.72890.
5. Flanagan, Michael. (2015). The Role of the Craniocervical Junction in Craniospinal Hydrodynamics and Neurodegenerative Conditions. Neurology Research International. 2015. 1-20. 10.1155/2015/794829.