The Skeletal System 1. The human skeleton consists of 206 named bones Bones of the skeleton are...

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The Skeletal System

1The human skeleton consists of 206 named bonesBones of the skeleton are grouped into two principal divisions:Axial skeletonConsists of the bones that lie around the longitudinal axis of the human body: Skull bones, auditory ossicles (ear bones), hyoid bone, ribs, sternum (breastbone), and bones of the vertebral column.The primary function is protection of vital organs.Appendicular skeletonConsists of the bones of the upper and lower limbs (extremities), plus the bones forming the girdles that connect the limbs to the axial skeleton. The primary function of this division is movement.Divisions of the Skeletal System2

3Bones of the Human Body

4Bone TissueBone is a specialized type of connective tissue characterized by the presence of a calcified extracellular matrix (called bone matrix) and three types of cells: Osteoblasts, Osteocytes and Osteoclasts.Functions of bones:Support fleshy structures.Protect vital organs (example: the skull protects the brain).Assist in movement.Synthesis of blood elements.Storage of fat.Storage of minerals (calcium and phosphate).5Cells of bones:6Bone matrix:Bone matrix is formed of various organic and inorganic molecules.Collagen fibers is abundant in bone matrix.

Periosteum:A thick connective tissue layer that covers the bone.Its important for the nourishment of bone, in the formation of bone and in fracture repair.

Endosteum:A thin connective tissue layer that lines the cavities inside the bone.7Classification of bones8In a cross section, bones may appear as a dense area with generally no cavities. These are called Compact Bones.

Others have several interconnected cavities. These are called Spongy (Cancellous) Bones

Histologically, both the compact bone and the trabeculae of the spongy bone have the same features.According to Gross Morphology:9According to Histological Features:Primary (woven) bone in which the collagen fibers of the matrix have no specific arrangement.

Secondary (lamellar) bone in which the collagen fibers are arranged in layers called lamellae.

In secondary bone, the lamellae usually form concentric circles around a central cavity in whats called Osteons.10

An osteon is formed of:Central Canal: this contains blood vessels, nerves and loose connective tissue.Several concentric lamellae.Several lacunae containing osteocytes and located between the lamellae.Several canaliculi that connect the lacunae together. These canaliculi are narrow passages in the bone through which process of osteocytes pass.11Bones can be classified into five types based on shape:LongShortFlatIrregularSesamoidAccording to Shape:12

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, navicular, cuboid Flat bones Thin and composed of two nearly parallel plates of compact bone tissue enclosing a layer of spongy bone tissue Cranial bones, 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 Found within tendons. Protect the tendons from excessive wear and tear Patellae13

Various parts of long bones.ProximalEndDistalEndShaft14Bones have characteristic surface markingsStructural features adapted for specific functionsThere are two major types of surface markings:1) Depressions and openingsAllow the passage of blood vessels and nerves2) ProcessesProjections or outgrowths that form joints or serve as attachment points for ligaments and tendonsBone Surface Markings15


The Axial Skeleton17The skull (Cranium) Consists of 22 bonesBones of the skull are grouped into two groups:Cranial bonesEight cranial bones form the cranial cavity which encloses the brainFrontal bone, two parietal bones, two temporal bones, the occipital bone, the sphenoid bone and the ethmoid bone

Facial bonesFourteen facial bones form the faceTwo nasal bones, two maxillae, two zygomatic bones, two lacrimal bones, two palatine bones, two inferior nasal conchae, vomer and the mandible.The Skull18The cranial and facial bones protect and support special sense organs and the brainBesides forming the large cranial cavity, the skull also forms several smaller cavitiesNasal cavityOrbits (eye sockets)Oral cavityParanasal sinuses Small cavities which house organs involved in hearing and equilibriumFeatures of the Skull19Immovable joints called sutures fuse most of the skull bones togetherThe skull provides a large area of attachment for muscles that move various parts of the headSkull and facial bones provide attachment for muscles that produce facial expressionsThe facial bones form the framework of the face and provide support for the entrances to the digestive and respiratory systems20Cranial Bones:Frontal BoneForms the foreheadParietal BonesForm the sides and roof of the cranial cavityTemporal BonesForm the lateral aspects and floor of the craniumConsists of 5 parts: squamous part, petrous part, tympanic part, mastoid part and the styloid processOccipital BoneForms the posterior part and most of the base of the craniumThe perceptible protrusion on the back of the head is the external occipital protuberance21



Sphenoid BoneLies in the middle part of the base of the skullIts formed of:Body2 Lesser wings2 Greater wings2 Pterygoid processes24


Ethmoid BoneLocated in the midline in the anterior part of the cranial floor medial to the orbits and forms the roof of the nasal cavityContains thin projections called conchaeHas a transverse and a perpendicular plate26Facial Bones:27Nasal BonesForm the bridge of the noseMaxillaeForm the upper jawboneHas the following processes: Frontal process superiorlyZygomatic process laterallyPalatine process posteriorlyForms most of the hard palateSeparates the nasal cavity from the oral cavityAlveolar process inferiorly. Contains sockets for the teeth.Zygomatic Bonescommonly called cheekbones, form the prominences of the cheeksThe temporal process of this bone unites with the zygomatic process of the temporal bone to form the zygomatic arch.Lacrimal BonesForm a part of the medial wall of each orbit. Related to the lacrimal (tear) sac.Palatine BonesForm the posterior portion of the hard palateInferior Nasal ConchaeForm a part of the lateral wall of the nasal cavityVomerForms the inferior portion of the nasal septumMandibleLower jawboneThe largest, strongest facial boneThe only movable skull bone28



Parts of the Mandible:31

The Nasal Septum:A partition that divides the nasal cavity into right and left parts (not exactly equal).Its formed of:The perpendicular plate of the ethmoid bone and the vomer bone posteriorly.Septal cartilage anteriorly.32

The Orbital Cavity:The bones that participate in the formation of the orbital cavity are: the frontal, lacrimal, ethmoid, sphenoid, zygomatic and maxillary.33

Main Sutures:Coronal Suture: between the frontal and the two parietal bones.Sagittal Suture: between the two parietal bones.Lambdoid Suture: between the two parietal and the occipital bones.34

Paranasal Sinuses:Cavities within cranial and facial bones near the nasal cavitySecretions produced in the sinuses drain into the nasal cavityServe as resonating chambers that intensify and prolong soundsFound in the Frontal, ethmoid, sphenoid and maxillary bones35

Areas of unossified tissue that link the cranial bones at birthEventually, they are replaced with bone to become suturesProvide flexibility to the fetal skull, allowing the skull to change shape as it passes through the birth canalFontanels:Anterior FontanelPosterior FontanelLocationBetween the frontal and parietal bonesBetween the parietal and occipital bonesShapeDiamond Triangular SizeLarger than the posteriorSmaller than the anteriorClosesLater than the posteriorBefore the anterior36Located in the upper part of the neckThe only bone in the body that does not articulate with any other boneSupports the tongue, providing attachment sites for some tongue muscles and for muscles of the neck and pharynx and some ligamentsFormed of body, greater horns and lesser horns

The Hyoid Bone37Also called the spine, backbone, or spinal columnFunctions to:Protect the spinal cordSupport the headServe as a point of attachment for the ribs, pelvic girdle, and musclesComposed of a series of bones called vertebrae (Adult=26)7 cervical are in the neck region12 thoracic are posterior to the thoracic cavity5 lumbar support the lower back1 sacrum consists of five fused sacral vertebrae1 coccyx consists of four fused coccygeal vertebraeThe Vertebral Column38The vertebral column is curved to varying degrees in different locationsCurves increase the column strengthHelp maintain balance in the upright positionAbsorb shocks during walking, and help protect the vertebrae from fracture

These curves are:CervicalThoracicLumbarSacral39

40Vertebrae typically consist of:A Body anteriorly (weight bearing)A vertebral arch posteriorly (surrounds the spinal cord)Several processes (points of attachment for muscles and ligaments)The body and the vertebral arch surrounds a foramen called the vertebral foramen. When the vertebrae are stacked on each other, the vertebral foramina will line together to form the vertebral canal through which the spinal cord passes

Found between the bodies of adjacent vertebrae are the Intervertebral Discs (formed of fibrocartilage). The function of these discs is to:Form strong jointsPermit various movements of the vertebral columnAbsorb vertical shockThe Vertebrae:41

Parts of vertebrae:42Cervical RegionCervical vertebrae (C1C7)The atlas (C1) is the first cervical vertebra. It a