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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.
Lordosis is historically defined as an abnormal inward curvature of the lumbar spine. [1] [2] However, the terms lordosis and lordotic are also used to refer to the normal inward curvature of the lumbar and cervical regions of the human spine. [3] [4] Similarly, kyphosis historically refers to abnormal convex curvature of the spine.
However, the cervical spine is comparatively mobile, and some component of this movement is due to flexion and extension of the vertebral column itself. 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.
Looking directly at the front or back of the body, the 33 vertebrae in the spinal column should appear completely vertical. From a side view, the cervical (neck) region of the spine (C1–C7) is bent inward, the thoracic (upper back) region (T1–T12) bends outward, and the lumbar (lower back) region (L1–L5) bends inward.
The atlas is the topmost vertebra and the axis (the vertebra below it) forms the joint connecting the skull and spine. The atlas and axis are specialized to allow a greater range of motion than normal vertebrae. They are responsible for the nodding and rotation movements of the head.
The four main divisions of the spinal column, from top to bottom: cervical, thoracic, lumbar, and sacral. The lateral grey column (lateral column, lateral cornu, lateral horn of spinal cord, intermediolateral column) is one of the three grey columns of the spinal cord (which give the shape of a butterfly); the others being the anterior and posterior grey columns.
Within these compartments, the neck houses the cervical vertebrae, the cervical portion of the spinal cord, upper parts of the respiratory and digestive tracts, endocrine glands, nerves, arteries and veins. The muscles of the neck, which are separate from the compartments, form the boundaries of the neck triangles. [2]
Spinal accessory nerve (Cranial Nerve XI) Branches of cervical plexus; Roots and trunks of brachial plexus; Phrenic nerve (C3,4,5) B) Vessels: Subclavian artery (Third part) Transverse cervical artery; Suprascapular artery; Terminal part of external jugular vein; C) Lymph nodes: Occipital; Supraclavicular; D) Muscles: Inferior belly of omohyoid ...