Cervical spinal canal
The volume and diameter of the cervical spinal canal are not constant; rather, the shape of the spinal canal changes from extension to flexion as the diameter of the osseous canal narrows during extension and widens during flexion 1).
1)
Bartlett RJ, Hill CA, Rigby AS, Chandrasekaran S, Narayanamurthy H. MRI of the cervical spine with neck extension: is it useful? Br J Radiol. 2012 Aug;85(1016):1044-51. doi: 10.1259/bjr/94315429. Epub 2012 Jan 3. PMID: 22215879; PMCID: PMC3587072.