Axial Skeleton: Cranial Bones

Nestor T. Hilvano, M.D., M.P.H.(Illustrations Copyright by Frederic H. Martini, Pearson Publication

Inc., and The McGraw-Hill Companies Inc.)

Learning Objectives You should be able to: 1. Identify the bones of axial skeleton and

their functions. 2. Identify the cranial bones including its parts

and surface markings.3. Describe the differences among the skull

of infants and children compared to adults.4. Define craniostenosis and discuss the

consequences associated with this anomaly.

Overview of Skeletal System • Number of bones

– 206 in adult skeleton– start at 270 at birth

• Regions of the skeletonI- Axial skeleton = 80 bones

1) Skull and associated bones2) Thoracic cage 3) Vertebral column

II- Appendicular skeleton = 126 bones

1) Pectoral (shoulder) girdle and Upper limbs 2) Pelvic (hip) girdle and Lower limbs

Skull: Cranial Bones • 8 Cranial bones – frontal (1),

parietal (2), occipital (1), temporal (2), sphenoid (1), and ethmoid (1)

• 7 associated bones – auditory ossicles (6) and hyoid bone (1)

Sutures

• Calvaria (skullcap) is formed by frontal, parietal, and occipital bones

• Sutures:

___ between the frontal bone and parietal bone.

___ between the parietal bone and occipital bone.

___ between the two parietal bones.

___ between the parietal bone and temporal bone.

a. sagittal suture b. squamous suture

c. lambdoid suture d. coronal suture

Frontal Bone• Forms the anterior part

of the ___________ and roof of the _________

• Contains frontal sinus

• Landmarks: frontal squama, supraorbital margin, lacrimal fossa

• Supraorbital foramen

Parietal Bone

• Form part of the

____ and ____ surfaces of cranium

• Bordered by 4 sutures• Landmarks: Temporal

lines for attachment of _________ muscle

Temporal Bone• ________ wall and part of ______ of cranial cavity• Consists of: a. Squamous part

- zygomatic process

- mandibular fossa b. Mastoid processc. Styloid process d. Petrous (bone) part

- houses middle and inner ear cavities - internal acoustic (auditory) meatus - jugular foramen

Right Temporal Bone

Openings in Temporal Bone

Carotid canalpassage for __________artery

Jugular foramenPassage for __________

Occipital Bone • ______________ of skull• Foramen magnum • Skull rests on atlas (C1) at

occipital condyles• Hypoglossal canal

transmits ___________ nerve

• External occipital protuberance

• Nuchal lines mark neck muscles

Sphenoid Bone• Part of the floor of the

cranium

• Lesser wing

• Greater wing

• Body of sphenoid

• Medial and lateral pterygoid processes

- attachment sites for

muscles that move the

mandible and soft palate

• ___________ sinus

Sphenoid Bone• Body of the sphenoid

– sella turcica (hypophyseal fossa) contains ____.

• Lesser wing– optic foramen

• Greater wing

– foramen rotundum and ovale for brs. trigeminal nerve

– foramen spinosum for meningeal artery

Ethmoid Bone

• Medial orbital wall• Lateral walls and roof

nasal cavity• Cribriform plate and crista

galli• Ethmoid air cells form

ethmoid sinus• Perpendicular plate forms

_______ septum• Superior and middle

Conchae on lateral wall

Ethmoid Bone

• Superior and middle concha

• Perpendicular plate of nasal septum

Skull of infants and children • Spaces between unfused

bones = fontanelles (fontanels)

– What purpose does a fontanel serve? ______.

– Anterior fontanel closes at 2 yrs. old.

• 2 frontal bones fuse by age six (metopic suture)

• Skull reaches adult size by 8 or 9

• Craniostenosis – premature closure of cranial sutures

Craniostenosis

• Long and narrow head is formed by early closure of sagittal suture

• Broad (tower) skull results from premature closure of coronal suture

Bones Associated With Skull • Ossicles

– malleus, incus, and stapes

• Hyoid bone– suspended from styloid process of

skull by muscle and ligament– Supports larynx and attachment site

for muscles of pharynx, larynx, and tongue

– Body, greater and lesser cornua (horns)

– Only bone in the body that does not articulate with another bone

* What are the smallest bones? _____

Homework 1. Describe the cranial sutures and fontanelles. 2. Identify the cranial bones associated with the following

regions or landmarks. __ temporal lines a) occipital__ sella turcica, lesser/greater wings b) frontal__ roof of orbits, bone of forehead c) parietal__ crista galli & cribriform plate d) temporal__ mastoid process, petrous bones e) ethmoid __ base of skull, foramen magnum f) sphenoid

• What is craniostenosis? • The internal acoustic meatus is located in which bone? • What is the content of the hypophyseal fossa of the

sella turcica?