The Axial Skeleton

THE SKELETAL SYSTEM The Axial Skeleton The skeleton consists of – Bones (206) – Cartilages – Joints – also called articulations, are the junctions between skeletal elements – Ligaments – connect bones Divided into axial and appendicular

Axial skeleton - forms long axis of body – Skull – Vertebral column – Thoracic cage Appendicular skeleton – appendages and what they attach to – Upper limbs (arms) – Pectoral girdle (shoulder) – Lower limbs (legs) – Pelvic girdle

Axial skeleton Skull Vertebral column Thoracic cage Axial skeleton is shown in green

The Skull Cranial bones (or cranium) – Enclose the cranial cavity, which supports and protects the brain – Attachment sites for some head and neck muscles Facial bones (anterior aspect of skull) – Form framework of face – Form cavities for sense organs of sight, taste and smell – Provides openings for passage of air and food – Hold the teeth – Anchor the muscles of the face

Cranium Vault – “calvaria” = skullcap – Forms superior, lateral and posterior aspects of skull, and forehead Base or floor: inferior part – Prominent bony ridges divide cranial base into 3 “fossae” (steps) – anterior, middle and posterior Anterior cranial fossa Middle cranial fossa Posterior cranial fossa (looking down on the floor of the skull)

Cranial bones Frontal bone Parietal bones (paired) Occipital bone Temporal bones (paired) Sphenoid bone Ethmoid bone

Cranial bones parietal frontal temporal parietal occipital _______sphenoid _____ethmoid occipital

Temporal bones this is the right temporal bone looking at it from the right side

Sphenoid Ethmoid Small cranial bones…

Sutures Immovable, interlocking joints of flat bones of skull Irregular, saw-toothed appearance Largest 4 skull sutures: where bones articulate with parietal bones – Coronal – Sagittal – Squamous – Lambdoid

Find: coronal, squamous and lamboid sutures

Find: sagittal and lambdoid sutures

Cranial “cavity” – houses brain Smaller cavities – Housing middle and inner ear – Nasal cavity – Orbits – Sinuses Openings (foramina, canals, fissures) for: – Spinal cord – Blood vessels – Twelve cranial nerves: I-XII

Remember, the skull is composed of: 1.Cranial bones (or cranium) and 2.Facial bones (anterior aspect of skull) – Form framework of face – Form cavities for sense organs of sight, taste and smell – Provides openings for passage of air and food – Hold the teeth – Anchor the muscles of the face

Facial bones Mandible Vomer Maxillae (paired) Zygomatics (paired) Nasal (paired) Lacrimal (paired) Palatines (paired) Inferior nasal conchae (paired)

Mandible Vomer Maxillae (paired) Zygomatics (paired) Nasal (paired) Lacrimal (paired) Palatines (paired) Inferior nasal conchae (paired) Facial bones:

Mandible (lower jaw) Maxilla (there are 2 which fuse, forming the upper jaw)

Nasal cavity Of bone and cartilage nasal bone maxilla___________

Orbit Cone-shaped bony cavities holding the eyes, muscles that move the eyes, some fat and tear-producing glands optic nerve passes out through it

Paranasal sinuses Air-filled sacs in the bones “Paranasal” because they cluster around and connect to the nasal cavity

Hyoid bone Only bone which does not articulate with any other bone Moveable base for the tongue Points of attachment for neck muscles that raise and lower the larynx during swallowing

Skull Vertebral column Thoracic cage Axial skeleton is shown in green

The Vertebral Column Fetus and infant: 33 separate bones or vertebrae Adult: 24 vertebrae – Inferior 9 have fused forming The sacrum (5) and The coccyx (4)

Vertebrae Cervical – 7 Thoracic - 12 Lumbar - 5 Sacrum (5 fused) Coccyx (4 fused)

Spinal curvatures Cervical and lumbar are concave posteriorly* (lordosis) Thoracic and sacral are convex posteriorly* (kyphosis) Abnormal: – Too much of either – Scoliosis (more than 10 degrees of lateral curvature) * when viewed from the side

Abnormal curvatures

Disorders of the axial skeleton Scoliosis (over 10% curvature) Kyphosis Lordosis Vertebral compression fractures Spinal stenosis

Non-bony parts Intervertebral discs – anulus fibrosis and nucleus pulposus) Anterior longitudinal ligament Posterior longitudinal ligament Ligamentum flavum

Anterior longitudinal ligament: wide, strong and attaches to vertebrae as well as discs (prevents hyperextension) Posterior longitudinal ligament: narrow and relatively weak, attaching only to discs *

Structure of a typical vertebra

Cervical vertebrae (C1-C7) C1 (atlas) C2 (axis)

Smallest Lightest Most flexible Triangular vertebral foramen Transverse processes have foramina (transverse foramen) Spinous process bifid (forked) except for C7 Cervical Vertebrae

Heart shaped body Additional small costal facets (costal=ribs) Round or oval vertebral foramen Form posterior part of rib cage Thoracic Vertebrae T1-T12

Massive blocklike bodies Short, thick hatchet-shaped spinous processes Limited mobility Lumbar Vertebrae L1-L5

The Sacrum Shapes posterior wall of pelvis Composite bone of 5 fused vertebrae Sacral foramina allow passage of vessels & nerves Coccyx (the tailbone)

Remember that the Axial skeleton includes: Skull Vertebral column Thoracic cage Axial skeleton is shown in green

The Thoracic Cage

Sternum Ribs Manubrium Body Xiphoid process True ribs 1-7 False ribs 8-12 Floating ribs 11,12