Axial Skeleton (Skull)

Lab 6

Human Skeleton # bones

206

Axial Skeleton

Bones lying on the body’s longitudinal axis (80 bones)

Skull

22 bones (Cranial and Facial)

Cranial

8 bones

Facial bones

14 bones

Hyoid bone

• U-shaped bone in neck

• No direct joint with other bones

• Supports tongue, aids swallowing & speech

• Between mandible & larynx

Cervical

7 bones

Thoracic

12 bones

Lumbar

5 bones

Sacrum 1 bone

• Triangular bone at the base of the spine

• Formed by the fusion of 5 vertebrae

• Connects spine to pelvis

• Supports weight in sitting & standing

Coccyx 1 bone

• Also called the tailbone

• Small, triangular bone at the spine’s base

• Formed by 3-5 fused vertebrae

• Provides attachment for ligaments & muscles

• Helps support body weight when sitting

Sternum 1 bone

• Flat, breastbone in the chest

• Located in the center of the ribcage

• Consists of manubrium, body, and xiphoid process

• Protects vital organs (heart, lungs)

• Attachment point for ribs and clavicles

Ribs 24 bones

• 12 pairs of curved bones in the chest

• Protect vital organs (heart, lungs)

• True ribs (1-7): directly attach to sternum

• False ribs (8-10): connect to cartilage of rib 7

• Floating ribs (11-12): no anterior attachment

Auditory ossicles 6 bones

• Three small bones in the middle ear

• Malleus (hammer), Incus (anvil), Stapes (stirrup)

• Transmit sound vibrations from the eardrum to the inner ear

• Smallest bones in the human body

Appendicular skeleton

Bond of the limbs & girdles which anchor the limbs to the axil skeleton (126 bones)

Pectoral girdle

4 bones (clavicle and scapula)

Clavicle

2 bones

Scapula

2 bones

Upper extremities (60 bones)

Humerus (2), radius (2), ulna(2), carpals (16), Meta carpals (10), phalanges (28)

Pelvic girdle

2 coxal bones

Lower extremities (60 bones)

Femur (2), Tibia (2), Fibula (2), patella (2), Tarsals (14), Metatarsals (10), Phalanges (28)

The cranium consists of 8 cranial bones:

1 frontal, 2 parietal, 1 occipital, 2 temporal, 1 ethmoid, 1 sphenoid

Cranial cavity

fluid filled chamber housing and protecting the brain

Sutures

The articulation points where one cranial bone meets another, clear bone unions

Frontal bone

Forms the forehead, roof of the orbits and most of the anterior portion of the cranial floor

Frontal squama

flattened expanse commonly referred to as the forehead

Supraorbital foramen or notch

of forehead

superior margin of the orbit, passage for blood vessels & nerves. of the forehead

Lacrimal fossa

Location of the lacrimal (tear) gland. Located in the superior- lateral boarder of orbit

*A 2nd lacrimal fossa exists in the lacrimal bone of the face to accommodate the lacrimal duct

Frontal Sinus

Air filled cavity. Mucus membrane lined cavities (not visible in all skulls)

Parietal bones (2)

Forms most of the lateral/posterior wall of cranium. Functions as muscle attachment site for temporalis muscle

Occipital bone (1)

Forms posterior, lateral and inferior surfaces of the cranium

Foramen Magnum

Large hole in the base of the skull- allows for the passage of spinal chord, lower brain regions and vertebral &spinal arteries (connects the cranial & spinal cavities

Occipital condyles

Convex surfaces on either side of foremen magnum- articulates w. first vertebrae (Atlas C1)

External occipital protuberance

prominent projection o back of skull- serves as attachment for ligaments and muscles

Hypoglossal canal

Small passage present along lateral boarder of foramen magnum- allows passage of the hypoglossal nerve (CN XII) innervating the tongue

Temporal bones (2)

Form inferior, lateral walls of cranium

External structures (7 of them)

Temporal squama

External auditory canal

zygomatic process

mandibular fossa

mastoid process

Styloid process

stylomastoid foreman

Temporal squama

Flattened lateral portion of skull, provides attachment site for muscle (temporalis)

External auditory canal

Ear canal. Opening into interior of ear, conducting sound waves to the interior of the ear (ends at eardrum- tympanic membrane)

mandibular fossa

Depression anterior to external auditory canal which articulates w/ mandible (lower jaw)

mastoid process

Breast shaper, posterior- ventral process just posterior to external auditory canal serves as site for neck muscle attachment

stylomastoid foreman

Between the styloid and mastiod process is a small passage. It allows passage of the facial nerves (CN VII)

Styloid process

process serves as attachment for muscles of the tongue & neck

Internal Structures (5 of them)

Petrous portion

Internal acoustic canal

Jugular foramen

Carotid canal

Foramen lacerum

Petrous portion

Large raised region on cranial floor, contains inner & middle ear structures

Internal acoustic canal

Small canal on the posterior medial surface of the petrous portion; carries auditory nerve (CN VIII) and facial nerve (CN VII)

Carotid canal

Medium sized canal seen from both the cranial floor and the inferior skull surface. From the inferior skulls surface, the canal lies anterior to the jugular foramen. The canal runs in a lateral inferior to the medial superior directions. Carries internal carotid artery

Foramen lacerum

Jagged opening inferior to the exit of the carotid canal on the medial surface. Extends between occipital & temporal bone

Normally filled w/ hyaline cartilage in living skull

Jugular foramen

Medium sized jagged hole visible from both the cranial floor and the inferior skull surface. From the inferior skull surface, the passage lies between the mastoid process and the occipital condyles

Allows passage of jugular vein, glossopharyngeal nerve (CN IX), vagus nerve (CN X) & spinal accessory nerve (CN XI)

Sphenoid bone (1)

Lies at the base of cranium, “Keystone” of skull as it articulates with all other cranial bones. Connects to facial and cranial bones displays distinct bat like shape

Sphenoid bones Lesser wing

The anterior margin of the sphenoid is the bat shaped lesser wings. Most superior projection of bones anterior to Sella Turcica

Sphenoid bones Greater wing

Lying posterior to the lesser wing, the greater wing contributes to the anterior floor of the cranium and forms back of eye orbits

Pterygoid process

Sharp process off of greater wings- serves as attachment sites for jaw & tongue muscles

Sella turcica Hypophyseal fossa

“turkish saddle” middle portion of sphenoid.

Supports the pituitary gland

Body of sphenoid

Cube shaped central mass of bone between the occipital and ethmoid bones

optic canal

paired canals inferior to the lesser wing carriers optic nerve CN II

Superior orbital fissure

Superior elongated opening in the orbit. Carries nerves

3 foramen on the lateral sides of the sella turcica

Foramen rotundum

Foramen ovale

Foramen spinosum

Foramen rotundum

Small paired passages on the surface of the greater wing just inferior to the superior orbital fissure. Allows passage of the maxillary division of the trigeminal nerve (CN V2)

Foramen ovale

Paired medium sized oval foramen in the posterior region of greater wing. Allows passage of the mandibular division of trigeminal nerve (CN V3)

Foramen spinosum

Paired small holes posterior to foremen ovale. Allows for passage of blood vessels

Ethmoid bone (1)

Sponge like bones forms majority of nasal structure.majority of this bone lies within the nasal cavity, but a prominent projection through the frontal bone (crista galli) communicates with the cranium. The ethmoid is directly behind the nasal bones and medial to the eye orbits.

Crista galli

 Vertical projection, site for attachment of the

brain's coverings (meninges: brain CT)

Cribriform plate

Superior porous bone projection through the frontal bone. Allows

entrance of olfactory nerves (CN I). Small olfactory foramina allow passage of olfactory nerves.

Lateral masses (2)

delicate scrolled bones called conchae or turbinates; function to circulate inhaled air.

The lateral masses are a combination of the superior and middle nasal conchae.

perpendicular plate

Superior nasal septum. Thin sheet of bone dividing the nasal cavity in half.

Sutures

The tight immovable joints found only in the skull. Sutures bind cranial bones together with dense irregular CT.

1. coronal suture 2. sagittal sutures 3. lambdoid suture 4. squamosuture.

(Metopic suture: fusion line within frontal bone; disappears ~ 8 years of age)

Fontanels

Temporary fibrous connections between adjacent cranial bones in the infant skull. A newborn infant has six fontanels; the anterior and posterior, two mastoid, and two sphenoid.

Facial bones (14)

Mandible (1)

Maxillary bones (2)

Zygomatic bones (2)

Nasal bones (2)

Lacrimal bones (2)

vomer (1)

INferior nasal conchae (2)

Palatine bones (2)

Mandible

Foramen spinosum

Mandible body

U-shaped horizontal portion bending posteriorly at the angle to 2 lateral raised walls (ramus)

Mandible ramous

2 lateral raised "walls". Perpendicular portions serve as muscle

attachment sites (masseter muscle)

Mandible

Coronoid process

2 lateral raised "walls". Perpendicular portions serve as muscle

attachment sites (masseter muscle)

Mandible

Condylar process

Posterior-superior rounded process - Articulates w/ temporal bone forming the temporomandibular joint (TMJ at the mandibular fossa, the ONLY synovial joint in the skull

Mandible

Alveolar processes

Oral margins accommodating the teeth within the superior surface of the body

Mental foramen:

 Small holes on the lateral-anterior surfaces of the mental region. Allow passage of mental nerve (chin & lips)

7. Mandibular foramen (canal):

Medium sized hole on the medial aspect of the ramus: Allows passage of mandibular nerve and blood vessels to the teeth & gums

Maxillary Bones

 (2): Bones unite to form the upper jaw. Articulates w/ every bone in face except the mandible

Maxillary

Alveolar processes:

 Oral margins accommodating the teeth (alveoli)

Maxillary sinus:

 Mucus membrane lined cavity within maxillary bone. Lateral to nasal cavity. Drains fluids into nasal cavity

Maxillary

Palatine process:

forms anterior 3/4 of hard palate

Maxillary

Inferior orbital fissure:

Inferior elongated hole in the inferior aspect of the orbit (formed by union with sphenoid bone within the orbit)

Maxillary

teeth

"Bilateral" dental formula - Adult: 2, 1, 2, 3. On top and bottom, right and left, from midline, teeth are:

2 incisors, 1 cuspid (canine), 2 bicuspid (premolars), 3 tricuspid (molars)

Incisors: 

Blade-shaped teeth with a single root found at the front of the mouth. Incisors are useful in nipping and cutting. First teeth to appear at ~ 7.5 - 9 months and then at 7-9

Cuspids (canines):

 Conical- shaped teeth with one root, lateral to incisors. Used for tearing or slashing.

First appear at 18 months and then at 11-12 yrs.

bicuspids

 (premolars): Flat wide teeth with usually 2 roots, just posterior to cuspids. Useful for grinding, crushing, and tearing. First appear at 14 months and then at 10-12 years

Tricuspids (molars_

Flat wide teeth with usually 3-4 roots. Useful for grinding crushing and tearing.

First appear at 24 months and then at 6 - 21 yrs (with the third molar - wisdom tooth cutting at ~21 yrs).

Zygomatic bones (2)

"cheek bones"; Form the lateral wall of orbit & anterior portion of zygomatic arch

1. Temporal process: Articulation with temporal bone. Forms anterior portion of the zygomatic arch

Nasal bones (2)

Paired bones forming the bridge of nose (most of nose is hyaline & elastic cartilage)

Lacrimal bones (2)

Smallest bones in skull. Forms the medial, anterior portion of orbit

Smallest bones in skull. Forms the medial, anterior portion of orbit

1. Lacrimal foramen:

2. Lacrimal fossa:

Lacrimal foramen:

Passages located at the inferior medial aspect of the eyes orbit. Allows passage of nasolacrimal duct - "tear duct". Functions to drain eye fluids into the nasal cavity

Lacrimal fossa:

Depression almost encompassing the whole bone, allows passage of lacrimal duct into nasal cavity

Vomer (1):

Inferior portion of nasal septum. Thin triangle or "plow"-shaped bone. Unites

with the perpendicular plate of the ethmoid bone.

Inferior nasal conchae (2):

Lateral, inferior fold of scroll-shaped bone projecting into nasal cavity (turbinates). Inferior to the middle and superior nasal conchae of the ethmoid bone. Similar structure and function, but are considered paired facial bones (not part of any cranial bone).

Palatine bones (2)

Paired "L" shaped bones; Form the posterior 1/3 of the hard palate, contribute to floor and lateral walls of nasal cavity, and to the floor of the orbits.

Hyoid bone:

Unique "U-shaped"

inferior to the skull, provides attachment for muscles of tongue, neck, and pharynx to aid in tongue movement and swallowing. The hyoid does NOT articulate with any other bones.

Middle ear ossicles

located within the middle ear, in the petrous portion of the temporal bone.

Mnemonic: lateral→ medial; "MIS"

1. Malleus: "hammer"

2. Incus: "anvil"

3. Stapes: "stirrup"

A:

olfactory foramina

B:

B: optic canal

C

Superior orbital fissure