Overview
This lecture introduces the axial skeleton, focuses on the bones of the cranium, and highlights key features, functions, and names to support lab study.
Axial Skeleton Overview
- The axial skeleton includes the skull, thoracic cage, and vertebral column (about 80 bones).
- It excludes the arms, legs, and bones that support limbs (clavicle, scapula, pelvis).
- The appendicular skeleton consists of limb bones and their supporting structures.
Bones of the Cranium
- The cranium encloses and protects the brain.
- Skull bones are grouped as facial bones, cranial bones, and associated bones.
Frontal Bone
- Forms the forehead; main flat part is the squamous part ("scale"-like).
- Zygomatic process connects toward the zygomatic bone.
- Supraorbital margin is the ridge above the eye, containing a notch (supraorbital notch/foramen).
- Contains frontal sinus (cavity inside the bone).
Parietal Bones
- Paired bones forming the sides (walls) of the cranium.
- Parietal eminence: prominent corners of the skull.
- Internal grooves house meningeal vessels.
Temporal Bones
- Located near the ears; main ear region of the skull.
- Squamous part: flat region.
- External auditory meatus: ear canal through the bone.
- Mastoid process: large, palpable lump behind the ear.
- Styloid process: thin, spike-like projection.
- Zygomatic process reaches toward zygomatic bone.
- Mandibular fossa: jaw joint connection point.
- Internal auditory meatus: inner ear canal.
- Petrous region is the rocky, thick part.
- Contains carotid canal/foramen for the carotid artery and stylo-mastoid foramen for nerves.
- Contains three auditory ossicles (malleus, incus, stapes).
Occipital Bone
- Found at the base of the skull; contains the foramen magnum for spinal cord connection.
- Has hypoglossal canals for nerves.
- External occipital crest and superior/inferior nuchal lines serve as muscle attachments.
- External occipital protuberance is a palpable bump.
- Occipital condyles articulate with the atlas (C1 vertebra) for head nodding.
- Jugular notch forms the jugular foramen when the skull is assembled.
Sphenoid Bone
- Irregular, butterfly-shaped bone spanning the skull's width.
- Contains optic foramen/canal for optic nerve and superior orbital fissure for nerves.
- Sella turcica holds the pituitary gland.
- Greater and lesser wings project from the body.
- Foramina include spinosum, ovale, and rotundum.
- Pterygoid processes extend downward.
Ethmoid Bone
- Located between the eyes, behind the nose.
- Cribriform plate contains foramina for olfactory nerves.
- Crista galli projects upward (resembles a rooster's comb).
- Perpendicular plate extends downward.
- Superior and middle nasal conchae create nasal airflow turbulence.
- Contains ethmoid sinus.
Key Terms & Definitions
- Axial Skeleton — Central skeleton: skull, thoracic cage, vertebral column.
- Appendicular Skeleton — Limbs and limb-supporting bones.
- Squamous — Flat, thin region of a bone.
- Process — Bone projection pointing toward another structure.
- Fossa — Dish-shaped bone depression.
- Foramen — Opening or hole in a bone.
- Condyle — Rounded bone projection for articulation.
- Auditory Ossicles — Three small bones in the middle ear (malleus, incus, stapes).
- Sella Turcica — Saddle-shaped depression in the sphenoid bone holding the pituitary gland.
- Concha — Curved nasal bone increasing turbulence.
Action Items / Next Steps
- Practice palpating bone landmarks on your own head.
- Study skull models to identify each bone and structure.
- Prepare for the next topic: bones of the face.