ANP 1001 Skeletal System Part 1 PDF

Bones The Support System and More  Skeletal Cartilage ◼ Contains no blood vessels or nerves ◼ Surrounded by the perichondrium (dense irregular connective tissue) that resists outward expansion ◼ Three types ◼ Hyaline ◼ Elastic ◼ fibrocartilage  Hyalin...

Bones The Support System and More  Skeletal Cartilage ◼ Contains no blood vessels or nerves ◼ Surrounded by the perichondrium (dense irregular connective tissue) that resists outward expansion ◼ Three types ◼ Hyaline ◼ Elastic ◼ fibrocartilage  Hyaline Cartilage ◼ the most abundant skeletal cartilage ◼ Support, flexibility, and resilience ◼ Present in these cartilages: ◼ Articular – covers the ends of long bones ◼ Costal – connects the ribs to the sternum ◼ Respiratory – makes up the larynx and reinforces air passages ◼ Nasal – supports the nose  Elastic Cartilage ◼ Similar to hyaline cartilage but contains elastic fibers ◼ Found in: ◼ the external ear ◼ the epiglottis  Fibrocartilage ◼ Highly compressed with great tensile strength ◼ Contains collagen fibers ◼ Found in: ◼ menisci of the knee ◼ intervertebral discs  Growth of Cartilage ◼ Appositional ◼ cells in the perichondrium secrete matrix against the external face of existing cartilage ◼ Interstitial ◼ lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within ◼ Calcification of cartilage occurs ◼ During normal bone growth ◼ During old age  Classification of Bones: By Shape ◼ Long bones are longer than they are wide (e.g., humerus)  Classification of Bones: By Shape ◼ Flat bones are thin, flattened, and a bit curved (e.g., sternum, and most skull bones)  Classification of Bones: By Shape ◼ Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)  Bone Functions ◼ Support -form the framework that supports the body and cradles soft organs ◼ Protection – provide a protective case for the brain, spinal cord, and vital organs ◼ Leverage – provide levers for muscles ◼ Mineral storage – reservoir for minerals, especially calcium and phosphate ◼ Blood cell formation – hemopoiesis occurs within the marrow cavities of bones  Gross Anatomy of Bones: Bone Textures ◼ Compact bone – dense outer layer ◼ Spongy bone – honeycomb of trabeculae filled with yellow/red bone marrow Structure of Long Bone Figure 6.3  Structure of Long Bone ◼ Long bones consist of a diaphysis and an epiphysis ◼ Diaphysis ◼ Tubular shaft that forms the axis of long bones ◼ Composed of compact bone that surrounds the medullary cavity/marrow cavity ◼ Yellow bone marrow (fat) is contained in the medullary cavity  Structure of Long Bone ◼ Epiphyses ◼ Expanded ends of long bones ◼ Exterior is compact bone (cortex), and the interior is spongy bone ◼ Joint surface is covered with articular (hyaline) cartilage ◼ Epiphyseal line separates the diaphysis from the epiphyses Structure of Long Bone Figure 6.3  Bone Membranes ◼ Periosteum – double-layered protective membrane ◼ Outer fibrous layer is dense regular connective tissue ◼ Inner layer is composed of osteoblasts and osteoclasts ◼ Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina ◼ Secured to underlying bone by Sharpey’s fibers ◼ Endosteum – delicate membrane covering internal surfaces of bone Structure of a Flat Bone  Structure of Short, Irregular, and Flat Bones ◼ Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside ◼ Have no diaphysis or epiphyses ◼ Contain bone marrow between the trabeculae Microscopic Structure of Bone: Compact Bone  Microscopic Structure of Bone: Compact Bone ◼ Haversian system, or osteon – the structural unit of compact bone ◼ Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen ◼ Haversian, or central canal – central channel containing blood vessels and nerves ◼ Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal  Microscopic Structure of Bone: Compact Bone ◼ Osteocytes – mature bone cells ◼ Lacunae – small cavities in bone that contain osteocytes ◼ Canaliculi – hairlike canals that connect lacunae to each other and the central canal  Cells of Bone ◼ Osteoblasts – bone-forming cells ◼ Osteocytes – mature bone cells ◼ Osteoclasts – large cells that resorb or break down bone matrix  Chemical Composition of Bone: Organic ◼ Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen  Chemical Composition of Bone: Inorganic ◼ Hydroxyapatites, or mineral salts ◼ Sixty-five percent of bone by mass ◼ Mainly calcium phosphates ◼ Responsible for bone hardness and its resistance to compression  Developmental Aspects of Bones ◼ Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton ◼ The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms ◼ At birth, most long bones are well ossified (except for their epiphyses)  Developmental Aspects of Bones ◼ By age 25, nearly all bones are completely ossified ◼ In old age, bone resorption predominates ◼ A single gene that codes for vitamin D docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life  Formation of Bone (Osteogenesis) ◼ Intramembranous ossification – bone develops from a fibrous membrane ◼ Formation of most of the flat bones of the skull and the clavicles ◼ Endochondral ossification – bone forms by replacing hyaline cartilage ◼ Uses hyaline cartilage as models for bone construction ◼ Requires breakdown of hyaline cartilage prior to ossification  Stages of Intramembranous/Dermal Ossification Figure 6.7.1 Stages of Intramembranous Ossification Figure 6.7.2 Stages of Intramembranous Ossification Figure 6.7.3 Stages of Intramembranous Ossification Figure 6.7.4  Stages of Intramembranous Ossification ◼ An ossification center appears in the fibrous connective tissue membrane ◼ Bone matrix is secreted within the fibrous membrane ◼ Woven bone and periosteum form ◼ Bone collar of compact bone forms, and red marrow appears  Endochondral Ossification ◼ Begins in the second month of development ◼ Uses hyaline cartilage as models for bone construction ◼ Requires breakdown of hyaline cartilage prior to ossification  Stages of Endochondral Ossification Secondary Articular ossification cartilage center Epiphyseal Spongy Deterioratingg blood vessel bone Hyaline cartilage matrix cartilage Spongy Epiphyseal bone plate Primary formation Medullary cartilage ossification center cavity Bone Blood collar vessel of periosteal bud 1 2 Formation of bone Cavitation 3 collar of the 4 hyaline Invasion of around Formation of the 5 cartilage internal cavities Ossification of the hyaline medullary cavity as within the by the epiphyses; when cartilage ossification continues; cartilage periosteal bud completed, hyaline model. appearance of model. and spongy cartilage remains bone formation. secondary ossification only in the centers in the epiphyseal plates epiphyses in and articular preparation for stage 5. cartilages  Stages of Endochondral Ossification ◼ Formation of bone collar ◼ Cavitation of the hyaline cartilage ◼ Invasion of internal cavities by the periosteal bud, and spongy bone formation ◼ Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses ◼ Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates and the joint cavity  Functional Zones in Long Bone Growth ◼ Growth zone – cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis ◼ Transformation zone – older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate ◼ Osteogenic zone – new bone formation occurs Long Bone Growth in Length  Long Bone Growth and Remodeling ◼ Growth in length – cartilage continually grows and is replaced by bone as shown ◼ Remodeling – bone is resorbed and added by appositional growth (increase in diameter) as shown in the next slide  Appositional Growth of Bone Central canal of osteon Periosteal ridge Artery Periosteum Penetrating canal 1 Osteoblasts beneath 2 As the bony ridges 3 The periosteum 4 As the osteoblasts the periosteum enlarge and meet, lining the tunnel is beneath the endosteum secrete bone matrix, the groove transformed into an form new lamellae, a new forming ridges that containing the endosteum and the osteon is created. follow the course of blood vessel osteoblasts just Meanwhile new periosteal blood becomes a tunnel. deep to the tunnel circumferential lamellae vessels. endosteum secrete are elaborated beneath bone matrix, the periosteum and the narrowing the canal. process is repeated, continuing to enlarge bone diameter. Hormonal Regulation of Bone Growth During Youth ◼ During infancy and childhood, epiphyseal plate activity is stimulated by growth hormone and thyroxine ◼ During puberty, androgen and estrogens: ◼ Initially promote adolescent growth spurts ◼ Cause masculinization and feminization of specific parts of the skeleton ◼ Later induce epiphyseal plate closure, ending longitudinal bone growth  Bone Deposition ◼ Occurs where bone is injured or added strength is needed ◼ Requires a diet rich in protein, vitamins C, D, and A, calcium, phosphorus, magnesium, and manganese ◼ Alkaline phosphatase is essential for mineralization of bone ◼ Sites of new matrix deposition are revealed by the: ◼ Osteoid seam – unmineralized band of bone matrix ◼ Calcification front – abrupt transition zone between the osteoid seam and the older mineralized bone  Bone Resorption ◼ Accomplished by osteoclasts ◼ Resorption bays – grooves formed by osteoclasts as they break down bone matrix ◼ Resorption involves osteoclast secretion of: ◼ Lysosomal enzymes that digest organic matrix ◼ Acids that convert calcium salts into soluble forms ◼ Dissolved matrix is transcytosed across the osteoclast’s cell where it is secreted into the interstitial fluid and then into the blood Importance of Ionic Calcium in the Body ◼ Calcium is necessary for: ◼ Transmission of nerve impulses ◼ Muscle contraction ◼ Blood coagulation ◼ Secretion by glands and nerve cells ◼ Cell division  Control of Remodeling ◼ Two control loops regulate bone remodeling ◼ Hormonal mechanism maintains calcium homeostasis in the blood ◼ Mechanical and gravitational forces acting on the skeleton  Hormonal Mechanism ◼ Rising blood Ca2+ levels trigger the thyroid to release calcitonin ◼ Calcitonin stimulates calcium salt deposit in bone ◼ Falling blood Ca2+ levels signal the parathyroid glands to release PTH ◼ PTH signals osteoclasts to degrade bone matrix and release Ca2+ into the blood Hormonal Mechanism Figure 6.12  Response to Mechanical Stress ◼ Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it ◼ Observations supporting Wolff’s law include ◼ Long bones are thickest midway along the shaft (where bending stress is greatest) ◼ Curved bones are thickest where they are most likely to buckle  Response to Mechanical Stress ◼ Trabeculae form along lines of stress ◼ Large, bony projections occur where heavy, active muscles attach Response to Mechanical Stress Figure 6.13  Bone Fractures (Breaks) ◼ Classified by: ◼ The position of the bone ends after fracture ◼ The completeness of the break ◼ The orientation of the bone to the long axis ◼ Whether or not the bones ends penetrate the skin  Types of Bone Fractures ◼ Nondisplaced – bone ends retain their normal position ◼ Displaced – bone ends are out of normal alignment ◼ Complete – bone is broken all the way through ◼ Incomplete – bone is not broken all the way through ◼ Linear – the fracture is parallel to the long axis of the bone  Types of Bone Fractures ◼ Transverse – the fracture is perpendicular to the long axis of the bone ◼ Compound (open) – bone ends penetrate the skin ◼ Simple (closed) – bone ends do not penetrate the skin  Common Types of Fractures ◼ Comminuted – bone fragments into three or more pieces; common in the elderly ◼ Spiral – ragged break when bone is excessively twisted; common sports injury ◼ Depressed – broken bone portion pressed inward; typical skull fracture ◼ Compression – bone is crushed; common in porous bones  Common Types of Fractures ◼ Epiphyseal – epiphysis separates from diaphysis along epiphyseal line; occurs where cartilage cells are dying ◼ Greenstick – incomplete fracture where one side of the bone breaks and the other side bends; common in children Common Types of Fractures Table 6.2.1 Common Types of Fractures Table 6.2.2 Common Types of Fractures Table 6.2.3 Stages in the Healing of a Bone Fracture ◼ Hematoma Hematoma formation ◼ Torn blood vessels hemorrhage ◼ A mass of clotted blood (hematoma) forms at the fracture site ◼ Site becomes swollen, painful, and 1 Hematoma formation inflamed Figure 6.14.1 Stages in the Healing of a Bone Fracture ◼ Fibrocartilaginous External callus forms callus ◼ Granulation tissue (soft callus) forms a few days after the New fracture blood Internal vessels Capillaries grow callus ◼ (fibrous into the tissue tissue and Spongy and phagocytic cartilage) bone trabeculae cells begin cleaning debris 2 Fibrocartilaginous callus formation Figure 6.14.2 Stages in the Healing of a Bone Fracture ◼ Bony callus formation Bony ◼ New bone trabeculae callus of spongy appear in the bone fibrocartilaginous callus ◼ Fibrocartilaginous callus converts into a bony (hard) callus ◼ Bone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later 3 Bony callus formation Figure 6.14.3 Stages in the Healing of a Bone Fracture ◼ Bone remodeling ◼ Excess material on the bone shaft exterior and in the medullary canal is removed Healing ◼ Compact bone is fracture laid down to reconstruct shaft walls 4 Bone remodeling Figure 6.14.4  Stages in the Healing of a Bone Fracture ◼ The fibrocartilaginous callus forms when: ◼ Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone ◼ Fibroblasts secrete collagen fibers that connect broken bone ends ◼ Osteoblasts begin forming spongy bone ◼ Osteoblasts furthest from capillaries secrete an externally bulging cartilaginous matrix that later calcifies  Homeostatic Imbalances ◼ Rickets ◼ Bones of children are inadequately mineralized causing softened, weakened bones ◼ Bowed legs and deformities of the pelvis, skull, and rib cage are common ◼ Caused by insufficient calcium in the diet, or by vitamin D deficiency  Homeostatic Imbalances ◼ Osteoporosis ◼ Group of diseases in which bone reabsorption outpaces bone deposit ◼ Spongy bone of the spine is most vulnerable ◼ Occurs most often in postmenopausal women ◼ Bones become so fragile that sneezing or stepping off a curb can cause fractures Bones, Part I: The Axial Skeleton Chapter 7  Types of Bones ◼ Long Bones ◼ Greater length than width and are slightly curved for strength ◼ Femur, tibia, fibula, humerus, ulna, radius, phalanges ◼ Short bones ◼ Cube-shaped and are nearly equal in length and width ◼ Carpal, tarsal ◼ Flat bones ◼ Thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue ◼ Cranial, sternum, ribs, scapulae ◼ Irregular bones ◼ Complex shapes and cannot be grouped into any of the previous categories ◼ Vertebrae, hip bones, some facial bones, calcaneus ◼ Sesamoid bones ◼ Protect tendons from excessive wear and tear ◼ Patellae, foot, hand ◼ Sutural bones ◼ Small bones located in sutures of cranial bones Copyright 2009, John Wiley & Sons, Inc.  Bone Surface Markings ◼ Bones have characteristic surface markings ◼ Structural features adapted for specific functions ◼ There are two major types of surface markings: ◼ 1) Depressions and openings ◼ Allow the passage of blood vessels and nerves or form joints ◼ 2) Processes ◼ Projections or outgrowths that form joints or serve as attachment points for ligaments and tendons Copyright 2009, John Wiley & Sons, Inc. Bone Surface Markings Copyright 2009, John Wiley & Sons, Inc. The Skeleton ◼ Bones, cartilage, joints and ligaments ◼ 206 bones grouped into 2 divisions ◼ Axial skeleton - 80 ◼ Appendicular - 126 The Axial Skeleton ◼ Supports the head, neck, and trunk ◼ Protects brain, spinal cord, thoracic organs ◼ Cranium ◼ Vertebral Column ◼ Thoracic Cage  Bone Markings ◼ Projections that provide attachment for muscles and ligaments ◼ Projections that help form joints ◼ Depressions and openings for passage of nerves and blood vessels The Skull – formed by cranial and facial bones Fig 7.2  The Skull Formed by cranial and facial bones ◼ Cranium- cranial bones enclose & protect the brain - provide attachment sites for head and neck muscles ◼ Facial bones 1) form framework of the face 2) form cavities for the sense organs of sight, taste, smell 3) provide openings for the passage of air, food, smell 4) hold the teeth 5) anchor muscles of the face ◼ Sutures – skull bones (flat) are united by  Overview of Skull Geography ◼ Facial bones form the anterior aspect, and the cranium forms the rest ◼ Cranium is divided into a cranial vault and a base - cranial vault or skullcap includes the forehead - cranial base, or floor, is the inferior part ◼ Internally, prominent bony ridges divide skull into distinct fossae  Skull Geography The skull contains smaller cavities ◼ Middle and inner ear cavities – in lateral aspect of cranial base ◼ Nasal cavity – lies in and posterior to the nose ◼ Orbits – house the eyeballs ◼ Air-filled sinuses – occur in several bones around the nasal cavity  Skull Openings ◼ Skull contains ~85 named openings - foramina, canals, and fissures ◼ Provide openings for important structures - spinal cord - blood vessels serving the brain - 12 pairs of cranial nerves  Cranial and Frontal Bones ◼ Cranium - formed from 8 large bones - paired bones: temporal and parietal - unpaired bones: frontal, occipital, sphenoid, and ethmoid ◼ Frontal bones - forms the forehead and roofs of the orbits - forms superciliary arches - internally, contributes to the anterior cranial fossa - contains frontal sinuses  Parietal Bones and Sutures ◼ Pariental bones form superior and lateral parts of the skull ◼ 4 sutures of the cranium include: - coronal suture – runs in the coronal plane, located where parietal bones meet the frontal bone - squamous suture – occurs where each parietal bone meets a temporal bone inferiorly - sagittal suture – occurs where right and left parietal bones meet superiorly - lambdoid suture – occurs where the parietal bones meet the occipital bone posteriorly  Occipital Bone ◼ Forms the posterior portion of the cranium and cranial base ◼ Articulates with the temporal bones and parietal bones ◼ Forms the posterior cranial fossa ◼ Foramen magnum located at its base ◼ Features and structures (bone markings) - occipital condyles - hypoglossal foramen, - external occipital protuberance - superior and inferior nuchal lines Fig 7.4  Temporal Bones ◼ Lie inferior to parietal bones ◼ Form the inferolateral portion of the skull ◼ ‘Temporal’ – latin word for time ◼ Specific regions of temporal bone - squamous, temporal, petrous, and mastoid regions Fig 7.3 The Temporal Bone Fig 7.5  The Sphenoid Bone ◼ Spans the width of the cranial floor ◼ Resembles a butterfly or bat ◼ Consists of a body and 3 pairs of processes ◼ Contains 5 important openings The Sphenoid Bone Fig 7.6 The Sphenoid Bone Fig 7.6  The Ethmoid Bone ◼ Lies between nasal and sphenoid bones ◼ Forms most of the medial bony region between the nasal cavity and orbits The Ethmoid Bone  Facial Bones ◼ Unpaired bones - mandible and vomer ◼ Paired bones - maxillae - zygomatic bones - nasal bones - lacrimal bones - palatine bones - inferior nasal conchae  Mandible ◼ Lower jawbone is the largest and strongest facial bone ◼ Composed of 2 main parts - horizontal body - 2 upright rami  Mandible Fig 7.8  Maxillary Bones ◼ Articulate with all other facial bones except the mandible ◼ Contain maxillary sinuses – largest paranasal sinuses ◼ Forms part of the inferior orbital fissure Maxillary Bones Fig 7.8  Other Bones of the Face ◼ Zygomatic bones – form lateral wall of orbits ◼ Nasal bones – form bridge of nose ◼ Lacrimal bones – located in the medial orbital walls ◼ Palatine bones – completes the posterior part of the hard palate ◼ Vomer – forms the inferior part of the nasal septum ◼ Inferior nasal conchae – thin, curved bones that project medially form the lateral walls of the Bones of the Face Fig 7.2  Special Parts of the Skull ◼ Orbits ◼ Nasal cavity ◼ Paranasal sinuses ◼ Hyoid bone Nasal Cavity Fig 7.9 Nasal Septum Orbits  Paranasal Sinuses ◼ Air-filled sinuses are located within - Frontal bone - Ethmoid bone - Sphenoid bone - Maxillary bones ◼ Lined with mucous membrane ◼ Serve to lighten the skull Paranasal Sinuses Fig 7.11  The Hyoid Bone ◼ Lies inferior to the mandible ◼ Only bone with no direct articulation with any other bone ◼ Acts as a movable base for the tongue  The Vertebral Column ◼ Formed from 26 bones in the adult ◼ Transmits weight of trunk to the lower limbs ◼ Surrounds and protects the spinal cord ◼ Serves as attachment sites for muscles of the neck and back ◼ Held in place by ligaments: - anterior and posterior longitudinal ligaments - ligamentum flavum The Vertebral Column  Intervertebral Discs ◼ Cushion-like pads between vertebrae ◼ Act as shock absorbers ◼ Compose about 25% of height of vertebral column ◼ Composed of: - nucleus pulposus: gelatinous inner sphere of intervertebral disc; enables spine to absorb compressive stresses - annulus fibrosis: an outer collar of ligaments and fibrocartilage that contains the nucleus pulposus; functions to bind vertebrae together, resist tension & absorb stress Ligaments and Intervertebral Discs Fig 7.14  Herniated Disc ◼ May be caused by trauma to the spine ◼ Aging is also a contributing factor ◼ Nucleus pulposes loses cushioning properties ◼ Anulus fibrosis weakens  Regions and Normal Curvatures ◼ Vertebral column is ~70 cm (28 in) and is divided into 5 major regions ◼ Cervical vertebrae – 7 in the neck region ◼ Thoracic vertebrae – 12 in the thoracic region ◼ Lumbar vertebrae – 5 of the lower back ◼ Sacrum – inferior to lumbar vertebrae and articulates with coxal bones ◼ Coccyx – most inferior region of the column  Normal Curvature ◼ 4 distinct curvatures give an S-shape ◼ Cervical & lumbar curves are concave posteriorly ◼ Thoracic & sacral curves are convex posteriorly ◼ Curvatures increase the resilience of the spine General Structure of Vertebrae Fig 7.16  Regional Vertebral Characteristics ◼ Specific regions of the spine perform specific functions ◼ Types of movement that occur between vertebrae - Flexion and extension - Lateral flexion - Rotation in the long axis  Cervical Vertebrae ◼ 7 cervical vertebrae (C1 – C7) – smallest and lightest ◼ C3 – C7 are typical cervical vertebrae - body is wider laterally - spinous processes are short and bifid (except C7) - vertebral foramen are large and triangular - transverse processes contain transverse foramina - superior articular facets face superoposteriorly Cervical Vertebrae Table 7.2 Fig 7.17  The Atlas ◼ The atlas - C1 ◼ Lacks a body and spinous process ◼ Supports the skull - superior articular facets receive the occipital condyles ◼ Allows flexion and extension of neck - nodding the head ‘yes’ Fig 7.16  The Axis ◼ Has a body and spinous process ◼ Dens (odontoid process) projects superiorly - formed from fusion of the body of the atlas with the axis - acts as a pivot for rotation of the atlas and skull - participates in rotating the head from side to side  Thoracic Vertebrae (T1 – T12) ◼ All articulate with ribs ◼ Have heart-shaped bodies from the superior view ◼ Each side of the body of T1 – T10 bears demifacts for articulation with ribs - T1 has a full facet for the first rib - T10 – T12 only have a single facet Table 7.2  Thoracic Vertebrae ◼ Spinous processes are long and point inferiorly ◼ Vertebral foramen are circular ◼ Transverse processes articulate with tubercles of ribs ◼ Superior articular facets point posteriorly ◼ Inferior articular processes point anteriorly - allows rotation and prevents flexion and extension  Lumbar Vertebrae (L1 – L5 ) ◼ Bodies are thick and robust ◼ Transverse processes are thin and tapered ◼ Spinous processes are thick, blunt, and point posteriorly ◼ Vertebral foramina are triangular ◼ Superior and inferior articular facets are directly medially ◼ Allows flexion and extension – rotation prevented Table 7.2 Fig 7.17  Sacrum (S1 – S5) ◼ Shapes the posterior wall of the pelvis ◼ Formed from 5 fused vertebrae ◼ Superior surface articulates with L5 ◼ Inferiorly articulates with coccyx ◼ Sacral promontory - where the 1st sacral vertebrae bulges into the pelvic cavity ◼ Center of gravity is 1cm posterior to sacral promontory  Sacrum Sacral foramina: ◼ Ventral foramina - passage for ventral rami of sacral spinal nerves ◼ Dorsal foramina - passage for dorsal rami of sacral spinal nerves Sacrum Fig 7.18  Coccyx ◼ ‘Tailbone’ – formed from 3 – 5 fused vertebrae ◼ Offers only slight support to pelvic organs  Bony Thorax ◼ Forms the framework of the chest ◼ Components include: thoracic vertebrae – posteriorly ribs – laterally sternum and costal cartilage – anteriorly ◼ Protects thoracic organs ◼ Supports shoulder girdle and upper limbs ◼ Provides attachment sites for muscles The Bony Thorax Fig 7.19 The Bony Thorax Fig 7.19  Sternum Formed from 3 sections ◼ Manubrium – superior section articulates with medial end of clavicles ◼ Body – bulk of sternum - sides are notched at articulations for costal cartilage of ribs 2-7 ◼ Xiphoid process – inferior end of sternum - ossifies around age 40 ◼ Jugular notch – central indentation at superior border of the manubrium ◼ Sternal angle – horizontal ridge where the manubrium joins the body  Ribs All ribs attach to vertebral column posteriorly ◼ True ribs – superior 7 pairs attach to sternum by costal cartilage ◼ False ribs – inferior 5 pairs ◼ Floating ribs – ribs 11 - 12 Fig 7.20 Disorders of the Axial Skeleton ◼ Abnormal spinal curvatures ◼ Scoliosis – an abnormal lateral curvature ◼ Kyphosis – an exaggerated thoracic curvature ◼ Lordosis – an accentuated lumbar curvature ◼ Stenosis of the lumbar spine – a narrowing of the vertebral canal The Axial Skeleton – Throughout Life ◼ Membrane bones begin to ossify in 2nd month of development ◼ Bone tissue grows outward from ossification centers ◼ Fontanels – unossified remnants of membrane Fontanels Fig 7.21  Axial Skeleton Throughout Life ◼ Many bones of the face and skull form by intramembranous ossification ◼ Endochondral bones of the skull - Occipital bone - Sphenoid - Ethmoid bones - Parts of the temporal bone