Bones consist of a specialized type of dense connective tissue that forms a rigid structure known as "osseous" tissue designed to support the body. Each bone in the body has a specific shape according to its location and purpose. In addition to a particular shape, each bone has certain distinctive surface features to allow the attachment of soft tissue, muscles, tendons, and nerves that permits the body parts to move individually or in unison with other parts of the body. The occipital bone, for example, has what is known as the external occipital protuberance, a bony protrusion or bump where the muscles that keep the head upright and allow the head to tilt backward attach.
The human skull is actually formed by the fusion of 22 different bones to create a protective covering for the brain. Of those bones, however, the occipital bone is one of eight that creates what is known as the "neurocranium" or "braincase," the back area of the skull that houses the brain. The occipital bone is a thick, bowl-shaped bone with an uneven surface that provides the rounded appearance at the bottom of the base of the skull. The external occipital protuberance, also referred to as the "inion," is located roughly in the center of this bone.
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At the base of the occipital bone, there is a circular opening called the foramen magnum. This cavity allows the medulla oblongata, an extension of the spinal cord, to communicate with the brain. Above and behind the foramen magnum is the occipital squama, a curved plate-like section of the bone. The external occipital protuberance is situated near the middle of the occipital squama, between two curved slightly raised lines — the superior nuchal line and the highest nuchal line — the site where muscles, such as the occipitalis and the trapezius, the muscles of the head and neck, attach. Also attached to the area is the ligamentum nuchae, a thick fibrous band that aids in the ability of the body to hold the weight of the head upright.
When the muscles, tendons, or ligaments that attach to this area become irritated, sufferers may experience tenderness, pain, and tightness at the base of the skull. This can cause movement of the head and neck to become difficult and painful. Symptoms can also radiate up into the head and down into the shoulders or upper back area.