The axial skeleton is one of two major divisions of the human skeleton and includes the following three regions: skull, vertebral column, and thoracic cavity. Bones and associated structures of the axial skeleton are grouped and described according to their location and function. The axial skeleton consists of that part of the skeleton that includes the regions of head and the core of the upper body. It plays important roles in supporting and enabling critical body systems. Among other functions, the axial skeleton protects the brain and nervous system, provides structures that facilitate eating and gathering of sensory information, shields central body organs, makes breathing possible, and anchors upright mobility. It provides areas where muscles attach to allow for motion.
At A Glance
- The axial skeleton consists of 80 bones and includes the cranium and its parts, the thorax, and the vertebral column, while the appendicular skeleton includes the limbs and connective bone structures.
- Eight cranial bones form the cranial cavity: frontal, parietal, temporal, occipital, sphenoid, and ethmoid bones.
- Cranial bones are fused together at sutures, the seam-like immovable junctions between two bones, such as those of the skull.
- There are 14 facial bones, each having distinguishing features that reflect function.
Nasal cavities, oral cavities, orbital cavities, paranasal cavities, and middle-ear cavities in the skull envelop and protect the brain and sensory organs, as well as function to resonate sound during speech and reduce the skull's weight.
- At birth, the cranial bones are attached by fibrous membranes called fontanels, which allow flexibility in the cranium, but bones fully fuse by the time the head is finished growing.
- The vertebral column consists of 33 vertebrae in five different regions of the spine: cervical, thoracic, lumbar, sacrum, and coccyx.
- At birth, the vertebral column is C-shaped and later in life takes on an S-shape, where scoliosis, lordosis, and kyphosis could result in abnormal curvatures of the spine.
- Most vertebrae have a body, vertebral arch, and superior and inferior articular processes and some fuse together to form the sacrum and coccyx.
- The thoracic cavity protects the heart and lungs and is made up of the thoracic vertebrae, 12 pairs of ribs, and the sternum.