The human skull is a protective structure, safeguarding the brain. While its overall shape appears smooth, closer examination reveals subtle contours and prominences. Understanding these features helps demystify the “bumps” one might feel on the back of the head.
Key Anatomical Features
The most prominent “bump” on the back of your head is the External Occipital Protuberance (EOP). This bony projection is located on the outer surface of the occipital bone, which forms the lower back part of the skull. You can feel it in the center, where the neck meets the head. The highest point of this protuberance is called the inion.
Extending horizontally outwards from the External Occipital Protuberance are bony ridges known as the superior nuchal lines. These curved lines stretch across the occipital bone. Together, the EOP and these lines form a boundary between the scalp and the neck, and they are palpable as distinct ridges under the skin.
Purpose of These Bumps
These bony features serve important functional roles in supporting the head and facilitating movement. The External Occipital Protuberance and the superior nuchal lines act as attachment points for several muscles and ligaments of the neck and back. For instance, the large trapezius muscle, which extends from the EOP down to the shoulder blade, attaches here.
The nuchal ligament, a strong fibrous band that helps support the head, connects to the External Occipital Protuberance. Other muscles like the sternocleidomastoid and splenius capitis also attach to the superior nuchal lines. These muscle and ligament attachments are important for movements such as rotating, extending, and flexing the head and neck, allowing for a wide range of motion and maintaining proper posture.
Normal Variations and Considerations
The size and prominence of the External Occipital Protuberance and the nuchal lines can vary significantly among individuals. These differences are normal anatomical variations, often influenced by genetics. For example, the EOP may be more palpable in males. Therefore, feeling a bump on the back of your head is a natural characteristic of your skull’s structure.
While most bumps on the back of the head are benign anatomical features, certain types of lumps or changes might warrant medical attention. These include bumps that appear after a recent injury, new or growing lumps, those that are painful, or any accompanied by other concerning symptoms. Other potential causes for bumps on the head can range from cysts, such as pilar cysts that commonly develop on the scalp, to fatty growths called lipomas, or even inflamed hair follicles.