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The number of vertebrae in a region can vary but overall the number remains the same. In a human spinal column, there are normally 33 vertebrae. [3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone.
This movement between the atlas and occipital bone is often referred to as the "yes joint", owing to its nature of being able to move the head in an up-and-down fashion. The movement of shaking or rotating the head left and right happens almost entirely at the joint between the atlas and the axis, the atlanto-axial joint .
They allow for flexion and extension and limit lateral flexion in the cervical spine. Pathological processes that can occur in these joints include degenerative changes or hypertrophic arthritis, resulting in foraminal stenosis and nerve compression. Foraminal stenosis at this joint is the most common cause of cervical nerve root pressure.
The spinal nerves arise from the spinal column. The top section of the spine is the cervical section, which contains nerves that innervate muscles of the head, neck and thoracic cavity, as well as transmit sensory information to the CNS. The cervical spine section contains seven vertebrae, C-1 through C-7, and eight nerve pairs, C-1 through C-8.
In other words, the facet joint between C4 and C5 vertebral segments is innervated by the C4 and C5 medial branch nerves. However, there are two exceptions: The facet joint between C2 and C3 is innervated by the third occipital nerve and the C3 medial branch nerve. The facet joint between C7 and T1 is innervated by the C7 and C8 medial branch ...
The spinal cord is an estimated 45 centimetres (18 inches) long in males and about 43 cm (17 in) in females. [citation needed] It is ovoid-shaped and is enlarged in the cervical and lumbar regions. The cervical enlargement, stretching from the C4 to T1 vertebrae, is where sensory input comes from and motor output goes to the arms and trunk.
The supraspinous ligament becomes taut when the spine is fully flexed. [4] The supraspinous ligament, along with the posterior longitudinal ligament, interspinous ligaments and ligamentum flavum, help to limit hyperflexion of the vertebral column.
Articular processes [permanent dead link ] - BlueLink Anatomy - University of Michigan Medical School; Atlas image: back_bone28 at the University of Michigan Health System - "Lumbar Vertebral Column, Posterolateral View" Anatomy figure: 02:01-09 at Human Anatomy Online, SUNY Downstate Medical Center - "Superior and lateral views of typical ...