Complete Lecture Notes - The Skeleton PDF

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General information of the skeleton...

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The Skeletal System Openstax – Chapter 7 The Skeletal System • Two subdivisions of the skeleton 1. Axial skeleton 2. Appendicular skeleton  Parts of the skeletal system o Bones (skeleton) o Joints o Cartilages o Ligaments Functions of Bones  Support the body  Protect soft organs • Skull and vertebrae protect brain and spinal cord • Rib cage protects thoracic cavity organs • Attached skeletal muscles allow movement • Store minerals and fats • Calcium and phosphorus • Fat in the internal marrow cavity • Blood cell formation (hematopoiesis) The Axial Skeleton • Forms the longitudinal axis of the body • Divided into three parts 1. Skull 2. Vertebral column 3. Bony thorax The Skull • Two sets of bones 1. Cranium bones enclose the brain 2. Facial bones • Hold eyes in anterior position • Allow facial muscles to express feelings • Bones are joined by sutures • Only the mandible is attached by a freely movable joint

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The Skull • 8 cranial bones protect the brain 1. Frontal bone 2. Occipital bone 3. Ethmoid bone 4. Sphenoid bone 5–6. Parietal bones (pair) 7–8. Temporal bones (pair) •

There are 14 facial bones. All are paired except for the single mandible and vomer. 1–2. Maxillae 3–4. Zygomatics 5–6. Palatines 7–8. Nasals 9–10. Lacrimals 11–12. Inferior nasal conchae 13. Mandible 14. Vomer

Overview of Skull Geography • Facial bones form anterior aspect, with cranium forming the rest of skull • Cranium is divided into a vault and a base • Cranium also contains other cavities: – Middle and internal ear cavities – Nasal cavity – Orbits that house eyeballs • Skull has 85 named openings – Foramina, canals, fissures – Provide passageways for spinal cord, major blood vessels, and the 12 cranial nerves Cranium • Frontal bone: shell-shaped bone forms anterior portion of cranium – Vertical part, called squamous region, is also known as the forehead – Inferior portion ends at supraorbital margins • Area underneath eyebrows – Forms superior wall of the orbits and most of anterior cranial fossa – Supraorbital foramen (notch) allows supraorbital artery and nerve to pass to forehead – Glabella is area of frontal bone between orbits • Frontal sinuses located just lateral to glabella

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Cranium (cont.) • Parietal bones and the major sutures – Two large parietal bones form most of superior and lateral aspects of cranial vault – Four sutures mark articulations of parietal bones with frontal, occipital, and temporal bones: 1. Coronal suture: between parietal bones and frontal bone 2. Sagittal suture: between right and left parietal bones 3. Lambdoid suture: between parietal bones and occipital bone 4. Squamous (squamosal) sutures: between parietal and temporal bones on each side of skull • Occipital bone – Forms most of skull’s posterior wall and posterior cranial fossa – Articulates with parietal, temporal, and sphenoid bones – Foramen magnum: “large hole” through which brain connects with spinal cord • Flanked by pair of occipital condyles that articulate with 1st vertebra – Hypoglossal canal allows cranial nerve XII to pass through – External occipital protuberance: protrusion just superior to foramen magnum – External occipital crest: ridges that are site of attachment for ligamentum nuchae – Superior and inferior nuchal lines: site of attachment for many neck and back muscles •

Temporal bones: paired bones that make up inferolateral aspects of skull and parts of cranial base – Three major regions: 1. Squamous: zygomatic processes articulate with zygomatic bone to form zygomatic arch and mandibular fossa makes up part of temporomandibular joint 2. Tympanic: surround external acoustic meatus (external ear canal) 3. Petrous: houses middle and internal ear cavities • Makes up part of the middle cranial fossa • Several foramina penetrate petrous region: » Jugular foramen allows passage of three cranial nerves » Carotid canal: passageway for internal carotid artery » Foramen lacerum: jagged opening covered by cartilage in living human » Internal acoustic meatus and styloidmastoid foramen: cranial nerve passageways • Mastoid and styloid processes: areas for attachment of several neck and tongue muscles

The Hyoid Bone • Closely related to mandible and temporal bones • The only bone that does not articulate with another bone • Serves as a movable base for the tongue • Aids in swallowing and speech Paranasal Sinuses

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Facial Bones • Mandible: largest, strongest bone of face – U-shaped lower jawbone made up of body (chin) and two upright rami • Mandibular angle: point where rami and chin meet • Coronoid process: superior end of rami serves as insertion point for large temporalis muscle • Condylar process: posterior to coronoid forms part of temporomandibular joint • Mandibular notch: separates processes • Body consists of alveolar process that contains sockets for teeth and mandibular symphysis ridge • Foramina include mandibular (for nerves) and mental foramina (for nerves and blood vessels) •

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Maxillary bones (maxillae): medially fused to form upper jaw and central facial skeleton – Upper teeth held in alveolar processes – Anterior nasal spine forms just below nose – Palatine process forms two-thirds of hard palate – Frontal process: forms lateral bridge of nose – Zygomatic processes articulate with zygomatic bones – Maxillary sinuses: flank nasal cavity laterally – Openings for nerves and blood vessels include: • Inferior orbital fissure • Infraorbital foramen • Incisive fossa and canal Zygomatic bones – Form cheekbones and inferolateral margins of orbits – Articulate with zygomatic processes of temporal, frontal, and maxillary bones Nasal bones – Form bridge of nose – Articulate with frontal, maxillary, and ethmoid bones – Attach to cartilage that forms tip of nose Lacrimal bones – Form medial walls of orbits – Articulate with frontal, maxillary, and ethmoid bones – Lacrimal fossa that houses lacrimal sac allows passageway for tears to drain

Special Characteristics of the Orbits and Nasal Cavity • Orbits – Cavities that encase eyes and lacrimal glands – Sites of attachment for eye muscles – Formed by parts of seven bones • Frontal, sphenoid, zygomatic, maxilla, palatine, lacrimal, and ethmoid • Nasal cavity: formed by parts of several bones – Roof: cribriform plates of ethmoid – Lateral walls: superior and middle conchae of ethmoid, perpendicular plates of palatine and Inferior nasal conchae © 2015 Pearson Education, Inc.

• Spaces between conchae called meatuses • Conchae increase turbulence of air flow – Floor: processes of palatine and maxillary bones – Nasal septum • Bony posterior formed by vomer and perpendicular plate of ethmoid • Anterior formed by septal cartilage The Paranasal Sinuses • Hollow portions of bones surrounding the nasal cavity • Functions of paranasal sinuses • Lighten the skull • Amplify sounds made as we speak The Vertebral Column – General Characteristics • Extends from skull to pelvis • Also called spine or spinal column • Functions to transmit weight of trunk to lower limbs, surround and protect spinal cord, provide attachment points for ribs and muscles • Flexible curved structure contains 26 irregular bones called vertebrae in five major regions • Regions and curvatures • Regions: ~28 long vertebral column broken into five major regions: 1. Cervical: consists of 7 vertebrae 2. Thoracic: 12 vertebrae 3. Lumbar: 5 vertebrae • Remember meal times: 7 am, 12 noon, and 5 pm 4. Sacrum: one bone, formed from fusion of several bones, articulates with hip 5. Coccyx: also fused bones that form terminus of column • Primary curvatures • Spinal curvatures of the thoracic and sacral regions • Present from birth • Form a C-shaped curvature as in newborns • Secondary curvatures • Spinal curvatures of the cervical and lumbar regions • Develop after birth • Form an S-shaped curvature as in adults •

Ligaments: along with trunk muscles, help support vertebral column • Anterior and posterior longitudinal ligaments: continuous bands from neck to sacrum that run down front and back of spine • Support and prevent hyperextension (backward) or hyperflexion (forward) bending • Ligamentum flavum: connects adjacent vertebrae • Short ligaments: connect each vertebra to those above and below

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Intervertebral discs • Cushionlike pad sandwiched between vertebrae that act as shock absorbers • Composed of two parts • Nucleus pulposus – Inner gelatinous nucleus – Gives disc its elasticity and compressibility • Anulus fibrosus – Outer collar composed of collagen and fibrocartilage – Limits expansion of nucleus pulposus when compressed

Vertebral Column (Spine) • Parts of a typical vertebra • Body (centrum) • Vertebral arch • Pedicle • Lamina • Vertebral foramen • Transverse processes • Spinous process • Superior and inferior articular processes Regional Vertebral Characteristics  Cervical vertebrae • C1 to C7: smallest, lightest vertebrae • C3 to C7 share following features: • Oval-shaped body • Exception: C7 spinous processes are split (bifid) • Large, triangular vertebral foramen • Transverse foramen found in each transverse process for artery passageways • C7 is vertebra prominens; large and can be felt through skin, so used as a landmark • C1 (atlas) and C2 (axis) have unique features • Atlas (C1) • No body or spinous process • Consists of anterior and posterior arches, and two lateral masses • Superior surfaces of lateral masses articulate with occipital condyles – Occipital condyles “carry” skull • Movement for nodding head “Yes” • Axis (C2) • Has body and processes like other vertebrae • Major feature is knoblike dens that projects superiorly into anterior arch of atlas – Dens is the “missing” body of atlas • Dens is a pivot for rotation of atlas © 2015 Pearson Education, Inc.

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Movement allows side to side rotation for saying “No”

Regional Vertebral Characteristics (cont.)  Thoracic vertebrae • T1 to T12 increase in size and articulate with ribs • Unique characteristics: • Body is heart shaped with two small demifacets that articulate with ribs – T10 to T12 have only single facet, not two • Vertebral foramen is circular • Long, sharp spinous process points inferiorly • Transverse processes have transverse costal facets that articulate with ribs (except T11, T12) • Location of articular facets allows rotation of this area of spine  Lumbar vertebrae • L1 to L5 “small of back”; receives most stress, so bodies are massive • Other characteristics: • Short, thick pedicles and laminae • Flat, hatchet-shaped spinous processes point posteriorly • Vertebral foramen is triangular • Orientation of articular facets locks lumbar vertebrae together to prevent rotation • Sacrum: triangular bone shapes posterior wall of pelvis; made from five fused vertebrae (S1– S 5) • Superior articular process articulates with L5 • Articulates inferiorly with coccyx and laterally with hip bones via its auricular surfaces, forming sacroiliac joints • Sacral promontory: anterosuperior margin • Transverse ridges mark lines of fusion • Anterior sacral foramina: lie at lateral ends of ridges; act as openings for nerves and vessels • Alae: winglike expansions • Median sacral crest: roughened bumps on posterior midline and lateral sacral crest; roughened area seen laterally on posterior side • Posterior sacral foramina: large openings for sacral spinal nerves • Sacral canal: continuation of vertebral canal • Sacral hiatus: large opening at end of canal • Coccyx: tailbone formed from three to five fused vertebrae; articulates superiorly with sacrum • Very little function

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The Bony Thorax • Forms a cage to protect major organs • Consists of three parts 1. Sternum 2. Ribs • True ribs (pairs 1–7) • False ribs (pairs 8–12) • Floating ribs (pairs 11–12) 3. Thoracic vertebrae Sternum  Also called the breastbone; consists of three fused bones: • Manubrium: superior portion that articulates with clavicular notches and ribs 1 and 2 • Body: midportion that articulates with costal cartilages of ribs 2 through 7 • Xiphoid process: inferior end that is site of muscle attachment • Not ossified until ~age 40  Sternum has three important anatomical landmarks: • Jugular notch • Central indentation in superior border of manubrium • Sternal angle • Horizontal ridge across front of sternum • Xiphisternal joint • Point where sternal body and xiphoid process fuse Ribs  12 pairs form sides of thoracic cage  All attach posteriorly to bodies and transverse processes of thoracic vertebrae  True (vertebrosternal) ribs (pairs 1–7) • Attach directly to sternum by individual costal cartilages  False (vertebrochondral) ribs (pairs 8–10) • Attach indirectly to sternum by joining costal cartilage of rib above  Vertebral (floating) ribs (pairs 11–12) • No attachment to sternum  Main parts of rib: • Shaft: flat bone that makes up most of rib  Costal groove: houses nerves and vessels • Head (posterior end)  Articulates with facets (demifacets) on bodies of two adjacent vertebrae • Neck: constricted portion beyond head • Tubercle: knoblike structure lateral to neck  Articulates posteriorly with transverse costal facet of same-numbered thoracic vertebra

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