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Axial Skeleton Part 1

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Slides to accompany an anatomy lecture to introduce axial skeleton and go through each bone of the skull

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Page 1: Axial Skeleton   Skull

Axial Skeleton Part 1

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There are approximately 206 bones in the adult skeleton, although the exact number varies from individual to individual

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The axial skeleton (dark bones in this picture) are the skull and associated bones, the vertebral column, and the bones of the rib cage. The appendicular skeleton (pale bones in this picture) are the bones of the extremities and the shoulder and pelvic girdle

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Hollywood feels that skulls are scary and remind us of our mortality

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There are typically 8 cranial bones and 14 facial bones.

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The configuration of the facial bones contribute greatly to the individuality of the human face.

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Cranial cavity (superior portion of dorsal body cavity) houses the brain

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The calvaria, the upper dome-like portion of the skull, consists of portions of the frontal, parietal, and occipital bones.

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Frontal bone

Sphenoid bone

Temporal bone

Occipital bone

Ethmoid bone

The base of the cranium is composed of portions of the frontal, ethmoid, sphenoid, temporal, and occipital bones

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The nasal septum, composed of bone and cartilage, divides the nasal cavity into left and right halves.

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There are 4 sets of paranasal sinuses that all drain into the nasal cavity.

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WHICH OF THE FOLLOWING IS NOT PART OF THE CALVARIA?

A WORMIAN BONES

B CORONAL SUTURE

C SAGITTAL SUTURE

D ETHMOID BONE

E OCCIPITAL BONE

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The author begins with an overview of the entire skull. Feel free to look it over. However, I will go into details as I discuss each bone.

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The 8 cranial bones are those bones that directly surround the brain. Injuries that penetrate these bones are often fatal. In contrast, damage to the facial bones, while disfiguring, are usually not fatal.

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The single frontal bone forms the anterior roof and anterior floor of the cranium, the forehead, a portion of the nasal cavity roof, and the superior arch of the orbits.

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Anterior view of frontal bone

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Inferior view of frontal bone. Note central gap where the ethmoid bone is normally located in roof of nose.

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Lacerations from car crashes can expose the frontal bone. Bleeding in tissues around eyes possibly suggests intracranial bleeding.

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Supraorbital margin

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The supraorbital foramina allow passage of small nerves and blood vessels. Forceful pressure at this site can cause great pain!

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The frontal sinus may or may not be present. When present is contains air, mucous, and ciliated cells. It drains into the nasal cavity.

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The sinuses, and the nose, are lined with ciliated cells with an overlying layer of mucous.

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The distinctive shape of the frontal sinuses can be used to identify crime victims if a previous dental x-ray has been kept.

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The parietal bones form the lateral walls and roof of the cranium. They are divided along the midline by the sagittal suture and separated from the frontal bone by the coronal suture.

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The two parietal bones form the upper sides and roof of the cranium

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Note that the parietal bones have an inner layer of diploë

Cancellous bone

Compact bone

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Skull from pre-Columbian Larsen village demonstrating scalping marks on parietal bone.

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First blow

Second blow

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Read about craniosynostosis (premature fusion of the sagittal suture) in you text

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The temporal bones form the lower sides and part of the floor of the cranium

Squamosal suture

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The petrous portion of the temporal bone contains the carotid canal and the jugular foramen

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Close-up of petrous portion of temporal bone showing the carotid canal and the jugular foramen. Note that the internal carotid artery (which brings blood to the brain) enters the carotid canal at an angle and then exits into the cranial cavity via the foramen lacerum. The jugular foramen, located between the temporal and occipital bones, allows the internal jugular vein (which drains blood from the brain) to exit.

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Note internal auditory canal that allows nerves and blood vessels to travel to and from the inner and middle ear.

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The mastoid portion of the temporal bone contains the hollow mastoid process.

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The squamous region of the temporal bone is the lateral flat surface below the squamosal suture. Included are the zygomatic process and the mandibular fossa.

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Temporomandibular joint (TMJ)

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Close-up of temporomandibular joint (TMJ)

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The tympanic portion of temporal bone contains the external acoustic meatus and the styloid process.

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ACCORDING TO THE ARTICLE “A LIFETIME OF PAIN”, WHICH OF THE FOLLOWING IS A SYMPTOM OF TEMPOROMANDIBULAR JOINT (TMJ) DSYFUNCTION?

A BLINDNESS

B MEDIASTINAL PAIN

C RUNNY NOSE (RHINORRHEA)

D FACIAL FLUSHING

E CERVICAL PAIN

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The single occipital bone (#15) forms the back and much of the base of the skull. Note the lambdoidal suture as #14.

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Inferior view of occipital bone. Note the formen magnum

Foramen magnum

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The occipital condyles rock on the upper surface of the first vertebra

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There are two prominent horizontal ridges on the posterior of the occipital bone: the inferior nuchal line and the superior nuchal line.

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The single sphenoid bone, with its bat-like shape, contributes to the base of the skull.

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The single sphenoid bone is often referred to as the “bridging bone” because it unites many of the cranial bones and facial bones.

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The sphenoid bone is hollow and contains the sphenoidal sinuses. Because of these sinuses, and the numerous foramina in this bone, it is often fractured by traumatic movements of the brain.

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The sella turcica houses the pituitary gland, which produces a wide variety of hormones, including growth hormone.

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Traumatic shifts in the brain’s position can shear the pituitary stalk.

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Beware “head in the dashboard syndrome”!

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There are numerous foramina in the sphenoid bone.

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Foramen lacerum is an opening between the sphenoid and the temporal bones.

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WHICH OF THE FOLLOWING IS CORRECT ABOUT THE SPHENOID BONE?

A IT ARTICULATES WITH THE OCCIPITAL BONE

B IT CONTAINS THE STAPES

C IT ALLOWS PASSAGE OF THE INTERNAL JUGULAR VEIN

D IT CONTAINS THE CAROTID CANAL

E ALL OF THE ABOVE

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The single ethmoid bone is located in the anterior floor of the cranium between the orbits where it contributes to the roof of the nasal cavity.

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The ethmoidal sinuses (shown in blue) contain air, mucous, and ciliated epithelial cells. They empty into the nasal cavity.

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The most inferior portion of the ethmoid is the perpendicular plate, which contributes to the nasal septum.

The crista galli (“cock’s comb”) is the most superior portion of the ethmoid

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Cock’s comb

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“Falx” means “scythe” (referring to the shape)

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The cribriform plate of the ethmoid contributes to the floor of the cranium and the roof of the nose. It is a weak structure!

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Cribriform means “like a sieve.”

What passes through the holes of the cribriform plate?

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Branches of the olfactory nerve (cranial nerve I) pass through the holes in the cribriform plate to innervate the roof of the nasal cavity for our sense of smell.

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Fractured cribriform plate can allow the fluid around the brain to escape into the nose and microbes to enter into meninges

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If bacteria from the nose enter through a fractured cribriform plate into the cerebrospinal fluid within the meninges, deadly meningitis can result.

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Egyptian mummies typically had their brains removed during the embalming process.

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A small curved rod, with a spoon-like tip at the other end, was punched through the cribriform plate to scoop out the brain through the roof of the nose. The brain was then thrown away.

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Egyptian embalming tools. Note one used for removing brain.

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The perpendicular plate is the most inferior portion of the ethmoid

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The superior and middle nasal conchae (turbinates), shown in green, are medial projections of the ethmoid into the nasal cavity. The inferior nasal conchae are separate facial bones and not part of the ethmoid.

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Facial bones

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There are 14 facial bones

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Facial bones provide the basic shape of the face

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Zygomatic bones form the bony prominence of the cheeks. They also contribute to the zygomatic arch and the lateral margin of the orbits.

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Zygomatic bone

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The tear ducts drain just inferior to the inferior nasal conchae

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Nasal bones contribute to the roof of the nasal cavity. They are easily fractured.

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Major injury to nasal bones

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Fractured nasal bones

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The vomer bone contributes to the inferior portion of the nasal septum

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“Vomer” means “plow”

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The nasal septum consists of the perpendicular plate of ethmoid, the vomer, and septal cartilage

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This killing blow is actually harder to do than fictional novels suggest. Master Long does know how to do it right! Moreover, it is not the septal cartilage that does the penetrating but rather is the ethmoid.

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Mister Miyagi also knows how to do this killing blow, especially when dealing with evil senseis who show no mercy.

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Inferior nasal conchae (inferior turbinates)

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Inferior nasal conchae, along with the rest of the inner nose, are covered with highly vascular moist mucous membrane.

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The left and right palatine bones form the posterior third of the hard palate (the palatine processes of the maxillae form the front two thirds), a portion of the nasal cavity, and, surprisingly, a portion of the orbits.

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The two maxillae unite along the midline to form the upper jaw.

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The teeth of the maxillae are located in sockets (alveoli).

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The palatine processes of the maxillae, along with the left and right palatine bones, form the hard palate and the floor of the nasal cavity.

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Note infraorbital foramen which allows passage of a nerve and blood vessels.

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(hare lip)

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Cleft palate and a hare lip repair

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The huge maxillary sinuses contain air, mucous, and ciliated epithelial cells. They drain into the nasal cavity through an opening high on the medial side (poor drainage).

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Note large maxillary sinuses

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Note maxillary sinus has thin overlying bone anteriorly and superiorly.

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Drainage route

Note that the drainage opening for the maxillary sinuses is high up on the medial side. This allows fluid to accumulate more easily, and infection to happen more easily, than occurs in the other sinuses.

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Fracture of the maxillary sinuses can occur with blows to the face

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WHICH OF THE FOLLOWING IS A CORRECT STATEMENT?

A FRACTURE OF THE NASAL BONES WILL TYPICALLY LEAD TO MENINGITIS

B THE TEAR DUCTS DRAIN INTO THE MOUTH JUST BELOW THE TONSILS

C NERVE ENDINGS ASSOCIATED WITH THE NASAL SEPTUM CAN CHANGE OVULATION

D THE ZYGOMATIC BONES CONTAIN ALVEOLI

E MUMMIFICATION INVOLVED PUNCHING THROUGH THE FRONTAL SINUS TO REMOVE THE BRAIN

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Fractured zygomatic bone and fractured maxillary sinus from punch to the face. When palpated crepitus was noted.

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A blow to the eye and orbit can fracture the floor of the orbit and the and its muscles may drop down into upper portion of maxillary sinus (“blow out fracture”).

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Blowout fracture

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Blowout fracture of left eyePatient is asked to look up with both eyes, but the muscles of the left eye are trapped

Normal eye

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WHICH OF THE FOLLOWING CONTRIBUTES TO THE LATERAL WALLS OF THE NASAL CAVITY?

A PALATINE BONES

B MAXILLAE

C ETHMOID

D LACRIMAL BONES

E ALL OF THE ABOVE

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Hamlet is evaluating Ophelia’s mandible

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Note the alveoli of the single mandible (lower jaw) that contain teeth.

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The mandibular foramen is a target of your dentist when he/she is injecting anesthesia.

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To numb the lower jaw the dentist will aim for the mandibular foramen

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Nasal complex

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Paranasal sinuses

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Orbital complex

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Auditory ossicles are inside petrous portion of temporal bone

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Relative size of auditory ossicles

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Besides the obvious bruising, this strangulation victim had a fractured hyoid bone

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Intramembranous ossification (shown in gold) leads to formation of flat bones of skull, zygomatic (cheek) bone, maxilla (upper jaw), mandible (lower jaw), collar bone (clavicle), and sesamoid bones.

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Fibrous sutures and many fontanels (soft spots) allow for molding of the head during birth (parturition).

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Parturition (birth)

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The fibrous sutures and fontanels also allow the cranium to expand to accommodate the growing brain in children.

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A bulging fontanel could be a sign of increased intracranial pressure caused by meningitis

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ACCORDING TO THE ARTICLE “ROUNDING IT OUT”, WHAT CONTRIBUTES THE MOST TO CURRENT CASES OF PLAGIOCEPHALY?

A LACK OF FOLIC ACID

B FEAR OF CRIB DEATH (SIDS)

C ILL-FITTING HELMETS

D FAILURE OF FONTANELS TO FUSE

E BIRTH TRAUMA

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Tooth loss is associated with erosion of the alveolar processes of the mandible and maxillae.