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THE AXIAL SKELETON.docx

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Department
Biology
Course Code
BIOL 301
Professor
Vivian Dayeh

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Description
CHAPTER 7 – THE AXIAL SKELETON − The skeleton consists of: o Bones 206 of them in the human skeleton. Grouped into:  Axial skeleton  Appendicular skeleton o Cartilages o Joints/articulations  junctions between skeletal muscles o Ligaments connect bones and reinforce most joints AXIAL SKELETON − Forms the long axis of the body. − Consists of 80 bones divided into: skull, vertebrate column and thoracic cage SKULL − Body’s most complex bony structure. − Geography: o Facial bones form anterior aspect; cranium forms the rest o Cranium can be divided into:  Cranial vault/calvaria/skullcap  forms superior, lateral and posterior aspect of the skull and the forehead region  Cranial base/floor  forms the inferior part • Internally, prominent bony ridges divide the cranial base into 3 distinct steps/fossae  anterior, middle and posterior cranial fossae (all completely enclosed by cranial vault). o Brain occupies cranial cavity. o Skull also contains smaller cavities:  Middle and inner ear cavities  carved into lateral aspects of cranial base  Nasal cavities  lies in and posterior to nose  Orbits  house eyeballs  Paranasal sinuses  air-filled sinuses that occur in several bones around the nasal cavity. o Skull has ~85 named openings (foramina, canals, fissures)  Provide passageways for spinal cord, major blood vessels serving the brain, and 12 cranial nerves. • Foramen magnum is the opening for spinal cord. − Formed by: − Cranial bones (8)  does not mean skull! Enclose and protect the brain. They are attachment points for some head and neck muscles. o Paired  Temporal bones • Lies inferior to parietal bones and forms inferolateral region of skull and parts of cranial floor. • 1 region to start getting grey hair with age. • Each has 4 major regions: o Squamous  has zygomatic process, which together with zygomatic bone forms zygomatic arch (cheek bone).  Mandibular fossa on inferior surface of zygomatic process receives mandible and forms the temporomandibular/jaw joint. o Tympanic  surrounds external acoustic meatus/external ear canal.  Styloid process projects inferiorly from tympanic region and is attachment point for tongue muscles and pharynx, and for ligament connecting skull to hyoid bone of neck. o Mastoid  has mastoid process, an anchoring site for some neck muscles.  Stylomastoid foramen is located between styloid and mastoid processes and a branch of cranial nerve VII leaves skull through it.  Also has air sinuses called mastoid air cells. o Petrous (rocky process)  projects medially and contributes to cranial base. Posterior slope lies in posterior cranial fossa, while anterior slope is in the middle cranial fossa, the fossa holding the temporal lopes of the brain.  Middle and inner ear cavities lie in this region, which contain sensory apparatus for hearing and balance.  Jugular foramen located in this region, through which jugular vein (largest vein of the head) passes through.  Parietal bones • Bulk of cranial vault; most superior part and its lateral walls. • Has 4 large sutures where it articulates with other cranial bones: o Coronal  occurs anteriorly, where it meets frontal bone o Squamous  occurs where it meets temporal bone inferiorly on lateral aspect of the skull o Sagittal (midline)  where right and left parietal bones meet superiorly in middle of cranium o Lambdoid  occurs where it meets occipital bone superiorly (looks like Greek letter lambda, ). o Unpaired  Frontal bone • Forms forehead; roofs of orbits o Supraorbital margin of each orbit is pierced by a hole/notch called supraorbital foramen/notch.  Transmits supraorbital nerve and artery, which supply the forehead • Contributes internally to anterior cranial fossa holds large frontal lobes of brain • Glabella  region with no hair in between eye brows • Contains frontal sinus (air-filled) lateral to glabella  Occipital bone • Posterior portion of cranium and cranial base • Articulates with temporal bones at the occipitomastoid sutures and with the parietal bones at the lambdoid suture • Internally forms posterior cranial fossa  holds cerebellum • Foramen magnum located at its base connects with spinal cord • Contains: o Occipital condyles  articulates with 1 vertebrate; enables head to nod ‘yes’ o External occipital protuberance knob in the midline; connects neck vertebrae to skull o Superior and inferior nuchal lines  tendons and musculature attach; superior marks the upper limit of the neck. o Hypoglossal canal for cranial nerve XII/hypoglossal nerve (important exit point)  Sphenoid bone • Looks like butterfly; spans width of cranial floor • Articulates with every other cranial bone • Consists of a central body and 3 pairs of processes: o Greater wings  projects laterally forming parts of middle cranial fossa and the orbit. o Lesser wing  horn-shaped; forms part of floor of anterior cranial fossa and part of orbit o Pterygoid process  projects inferiorly from greater wings. • Superior part of body has saddle-shaped prominence called sella turcica (Turkish saddle) o Hypophyseal fossa (seat of saddle) holds pituitary gland • Contains sphenoid sinuses within the sphenoid body • Has 5 openings for cranial nerves  Ethnoid bone • Lies between nasal and sphenoid bones • Forms most of the medial bony region between nasal cavity and orbits • Most deeply situated bone of the skull. • Superior surface formed by paired, horizontal cribriform plates that are perforated by tiny holes called olfactory foramina. o Crista galli  superior projection between the 2 cribriform plates in the midline. • Superior and middle nasal conchae extend medially from lateral masses and protrude into nasal cavity. − Facial bones (14) Provides: framework for face; cavities for the sense organs; openings for air/food passage; teeth anchor; attachment for facial muscles. o Paired  Maxillary bones/maxilla • Forms upper jaw and central part of facial skeleton • Articulates with all other facial bones except mandible. • Contains maxillary sinuses (largest paranasal sinus) • Forms part of inferior orbital fissure • Palatine process projects medially from alveolar margins  forms anterior region of hard palate  Zygomatic bones/cheek bones • Posteriorly  joins zygomatic process of temporal bone • Superiorly  joins zygomatic process of frontal bone • Anteriorly  joins zygomatic process of maxilla  Nasal bones • Join medially to form bridge of nose. • Superiorly  articulate with frontal bone • Laterally  join with maxilla • Posteriorly  join with perpendicular plate of ethnoid bone • Inferiorly  attach to cartilage that form most of skeleton of external nose  Lacrimal bones • Located in medial orbital walls; contain lacrimal fossa that contain lacrimal sac that gathers tears. • Superiorly  articulate with frontal bone • Posteriorly  join with ethmoid bone • Anteriorly  join with maxilla  Palatine bones • Lie anterior to maxilla • Articulate with each other at their inferior horizontal plates  complete posterior part of hard palate • Perpendicular plates form posterior part of lateral walls of nasal cavity  Inferior nasal concha • Largest of he three pairs of conchae; lie inferior to middle nasal conchae of the ethmoid bone. o Unpaired  Mandible • Lower jaw bone; largest, strongest facial bone • Articulates with temporal bone • Composed of 2 main parts: o Horizontal body  anchors lower teeth and forms chin  Superior border is alveolar margin  tooth sockets (alveoli) open into it.  Anteriorly, fusion between 2 halves of mandible is called mental protuberance. o 2 upright rami/ramus  meet body posteriorly at a mandibular angle.  2 processes at superior margin of each ramus: • Coronoid process  temporalis muscle that elevates mandible inserts here. • Condylar process  forms mandiblular condyle/head of
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