The Axial Skeleton
Divisions of the Skeleton
Axial Skeleton:
Consists of bones of the head and trunk
Forms the longitudinal axis of the body
Appendicular Skeleton:
Consists of bones that support the limbs
The Axial Skeleton
Comprises 80 bones in total:
Skull:
8 cranial bones
14 facial bones
Associated Bones:
6 auditory ossicles
1 hyoid bone
Thoracic Cage:
1 sternum
24 ribs
Vertebral Column:
24 vertebrae
1 sacrum
1 coccyx
Functions of the Axial Skeleton
Provides support and protection for organs in body cavities
Offers points of attachment for muscles that:
Adjust the positions of the head, neck, and trunk
Perform breathing movements
Stabilize parts of the appendicular skeleton
The Skull
Contains 22 bones:
Cranial Bones (8):
Form the cranium, encloses the cranial cavity which contains the brain
Includes Calvaria (skullcap)
Facial Bones (14):
Protect and support entrances to digestive and respiratory tracts
Cranial and Facial Subdivisions of the Skull
Cranial Bones:
Occipital bone
Parietal bones (2)
Frontal bone
Temporal bones (2)
Sphenoid bone
Ethmoid bone
Total: 8 cranial bones
Facial Bones:
Maxillae (2)
Palatine bones (2)
Nasal bones (2)
Inferior nasal conchae (2)
Zygomatic bones (2)
Lacrimal bones (2)
Vomer (1)
Mandible (1)
Total: 14 facial bones
Associated Bones of the Skull
Auditory Ossicles:
6 bones enclosed in temporal bones
They transmit sound vibrations from tympanic membrane to internal ear
Hyoid Bone:
1 bone not attached to any other bone, supports the larynx
Skull Sutures
Sutures: Immovable joints of the skull, including:
Lambdoid Suture: Separates occipital from parietal bones
Coronal Suture: Attaches frontal bone to parietal bones
Sagittal Suture: Between parietal bones, running from lambdoid suture to coronal suture
Squamous Sutures: Join temporal bones with parietal bones
Major Structures of the Adult Skull
Anatomy includes landmarks such as:
Occipital condyle
External occipital protuberance
Mastoid process
Styloid process
Important foramina include:
Foramen magnum
Jugular foramen
Hypoglossal canal
Sinuses of the Skull
Sinuses: Air-filled chambers in the skull that:
Decrease weight of the skull
Are lined with mucous membranes that produce mucus to moisten and clean the air
Serve as resonating chambers in speech production
Vertebral Column
Composition:
Protects the spinal cord
Supports the head and body
Composed of 26 bones:
24 vertebrae
1 sacrum
1 coccyx
Spinal Curves
Curvatures:
Cervical curve
Thoracic curve
Lumbar curve
Sacral curve
Primary Curves: Thoracic and sacral, present at birth
Secondary Curves: Cervical and lumbar, develop postnatally
Vertebral Regions
Cervical (7 vertebrae), Thoracic (12 vertebrae), Lumbar (5 vertebrae)
Each vertebral region has distinct structural characteristics determined by their specific functionalities
Vertebra Structure
A typical vertebra consists of:
Vertebral Body: Transfers weight along the spine
Vertebral Arch: Forms the posterior margin and consists of pedicles and laminae
Articular Processes: Projections for articulations with neighboring vertebrae
Intervertebral Anatomy
Intervertebral Discs: Pads of fibrocartilage that separate adjacent vertebral bodies
Intervertebral Foramina: Gaps between pedicles that allow for nerve connections to the spinal cord
Vertebral Canal: Formed by vertebral foramina of consecutive vertebrae, it encloses the spinal cord
Sacrum and Coccyx
Sacrum Composition:
Comprises 5 fused sacral vertebrae
Articulates with the coccyx
Thoracic Cage
Composition:
Thoracic vertebrae
Ribs
Costal cartilages
Sternum
Functions of Thoracic Cage
Protects organs of the thoracic cavity (heart, lungs)
Provides attachment points for muscles involved in breathing
Ribs
Types of Ribs:
True Ribs: Ribs 1-7, attach directly to the sternum
False Ribs: Ribs 8-12, do not attach directly to the sternum
Sternum Structure: Consists of the manubrium, body, and xiphoid process