Human Anatomy: Skeletal System

Axial Skeleton

• The skeletal system can be classified into axial skeleton and appendicular skeleton
• Axial skeleton consists of the skull, vertebral column, ribs, and sternum

Skull

• The skull is composed of 22 separate bones united at immobile joints called sutures
• The connective tissue between the bones is called a sutural ligament
• The mandible is an exception, united to the skull by the mobile temporomandibular joint

Cranium

• The cranium consists of 8 bones: 2 parietal, 2 temporal, 1 frontal, 1 sphenoid, 1 occipital, and 1 ethmoid
• The vault is the upper part of the cranium, and the base of the skull is the lowest part of the cranium
• The skull bones are made up of external and internal tables of compact bone separated by a layer of spongy bone called the diploë

Facial Bones

• The facial bones consist of 14 bones: 2 zygomatic, 2 maxillae, 2 nasal, 2 lacrimal, 2 palatine, 2 inferior conchae, 1 mandible, and 1 vomer

Frontal Bone

• Characteristics:
  • Contains the frontal paranasal sinuses
  • 1 frontal bone
  • 3 parts: squamous portion, orbital portion, and nasal portion

Parietal Bone

• Characteristics:
  • Forms the majority of the cranial vault
  • 2 parietal bones
  • Relatively square, forming the roof and sides of the cranial vault
  • Parts: All parts undergo intramembranous ossification

Occipital Bone

• Characteristics:
  • Forms the posterior part of the cranial vault
  • Articulates with the atlas
  • 1 occipital bone
  • 3 parts: squamous portion, lateral portion, and basilar portion

Temporal Bone

• Characteristics:
  • Helps form the base and lateral walls of the skull
  • Houses the auditory and vestibular apparatuses
  • Contains mastoid air cells
  • 2 temporal bones
  • 4 parts: squamous part, petrous part, tympanic part, and styloid process

Sphenoid Bone

• Characteristics:
  • Forms the majority of the middle portion of the cranial base
  • Contains the sphenoid paranasal sinus
  • 1 sphenoid bone
  • 4 parts: body, greater wing, lesser wing, and pterygoid process

Ethmoid Bone

• Characteristics:
  • A porous bone that forms the major portion of the middle part of the face between the orbits
  • Helps form the orbit, nasal cavity, nasal septum, and anterior cranial fossa
  • 1 ethmoid bone
  • 3 parts: perpendicular plate, cribriform plate, and ethmoid labyrinth