Anatomy of Skeletal System SKELETAL SYSTEM n COMPOSED

Anatomy of Skeletal System

SKELETAL SYSTEM n COMPOSED OF: -Bones -Cartilage -Joints -Ligaments

Functions of Skeletal System n SUPPORT: Hard framework that supports and anchors the soft organs of the body. n PROTECTION: Surrounds organs such as the brain and spinal cord. n MOVEMENT: Allows for muscle attachment therefore the bones are used as levers. n STORAGE: Minerals and lipids are stored within bone material. n BLOOD CELL FORMATION: The bone marrow is responsible for blood cell production.

Bone Markings · Bone Surface is not smooth, but shows: · Bone markings which reveal where: -muscles, tendons, and ligaments attatched -nerves and blood vessels pass *bone marking may be: 1 -projections or processes or 2 -depressions or cavities Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 9

Structure n Compact bone n n n Outer layer of bone, very hard and dense. Organized in structural units called Haversian systems. Matrix is composed of Ca salts (Ca carbonate and Ca phosphate) Osteocytes – living bone cells that live in matrix. Porous (Spongy) bone n n Located in the ends of long bones. Many spaces that are filled with red bone marrow which produces bone cells.

Structure n Spongy bone (cont’d) n n Trabeculae – needle-like threads of spongy bone that surround the spaces. Add strength to this portion of the bone. Cartilage n Matrix is a firm gel with chondrocytes suspended in the matrix.

Classification of Bones · Long bones · Typically longer than wide · Have a shaft with heads at both ends · Contain mostly compact bone • Examples: Femur, humerus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 4 a

Classification of Bones · Short bones · Generally cube-shape · Contain mostly spongy bone · Examples: Carpals, tarsals Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 4 b

Classification of Bones on the Basis of Shape Figure 5. 1 Slide 5. 4 c

Classification of Bones · Flat bones · Thin and flattened · Usually curved · Thin layers of compact bone around a layer of spongy bone · Examples: Skull, ribs, sternum Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 5 a

Classification of Bones · Irregular bones · Irregular shape · Do not fit into other bone classification categories · Example: Vertebrae and hip Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 5 b

Gross Anatomy of a Long Bone · Diaphysis · Shaft · Composed of compact bone · Epiphysis · Ends of the bone · Composed mostly of spongy bone Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 2 a Slide 5. 6

Structures of a Long Bone · Periosteum · Outside covering of the diaphysis · Fibrous connective tissue membrane · Sharpey’s fibers · Secure periosteum to underlying bone · Arteries · Supply bone cells with nutrients Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 2 c Slide 5. 7

Structures of a Long Bone · Articular cartilage · Covers the external surface of the epiphyses · Made of hyaline cartilage · Decreases friction at joint surfaces Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 2 a Slide 5. 8 a

Structures of a Long Bone · Medullary cavity · Cavity of the shaft · Contains yellow marrow (mostly fat) in adults · Contains red marrow (for blood cell formation) in infants Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 2 a Slide 5. 8 b

Microscopic Anatomy of Bone · Osteon (Haversian System) · A unit of bone · Central (Haversian) canal · Opening in the center of an osteon · Carries blood vessels and nerves · Perforating (Volkman’s) canal · Canal perpendicular to the central canal · Carries blood vessels and nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 10 a

Microscopic Anatomy of Bone Figure 5. 3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 10 b

Microscopic Anatomy of Bone · Lacunae · Cavities containing bone cells (osteocytes) · Arranged in concentric rings · Lamellae · Rings around the central canal · Sites of lacunae Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 3 Slide 5. 11 a

Microscopic Anatomy of Bone · Canaliculi · Tiny canals · Radiate from the central canal to lacunae · Form a transport system Figure 5. 3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 11 b

Changes in the Human Skeleton · In embryos, the skeleton is primarily hyaline cartilage · During development, much of this cartilage is replaced by bone · Cartilage remains in isolated areas · Bridge of the nose · Parts of ribs · Joints Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 12

Bone Growth · Epiphyseal plates allow for growth of long bone during childhood · New cartilage is continuously formed · Older cartilage becomes ossified · Cartilage is broken down · Bone replaces cartilage Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 13 a

Bone Growth · Bones are remodeled and lengthened until growth stops · Bones change shape by gravity &muscle pull · Bones grow in width through periostium Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 13 b

Long Bone Formation and Growth Figure 5. 4 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 14 a

Long Bone Formation and Growth Figure 5. 4 b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 14 b

Types of Bone Cells · Osteocytes · Mature bone cells · Osteoblasts · Bone-forming cells · Osteoclasts · Bone-destroying cells · Break down bone matrix for remodeling and release of calcium · Bone remodeling is a process by both osteoblasts and osteoclasts Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 5. 15

Fractures Closed fracture (simple): skin is intact n Open fracture (compound): skin is open n Fracture reduction : 1 -closed reduction , no surgery is needed 2 -open reduction , surgery is needed n

Repair of fracture n n n Healing time for simple fracture is 6 -8 weeks (longer in elderly people) It occurs in FOUR major events 1 -hematoma formation 2 -fibrocartilage callus formation 3 -bony callus formation 4 -bone remodelling

Skeletal system includes n Axial division Skull and associated bones n Auditory ossicles n Hyoid bones n Vertebral column n Thoracic cage(Ribs+ sternum) n • Appendicular division -Pectoral girdle -Pelvic girdle

The Axial Skeleton n Axial division n Skull and associated bones: n n Auditory ossicles Hyoid bones Vertebral column Thoracic cage n Ribs + sternum

The Skull and Associated Bones

Sutures n n n Sutures – Immovable joints that join skull bones together Form boundaries between skull bones Four sutures: Coronal – between parietal and frontal n Sagittal– between parietal bones n Lambdoid – between the parietal and occipital n Squamous – between the parietal and temporal ü Fontanels – usually ossify by 2 years of age n

Sagittal Frontal (Coronal) Squamous Lambdoid Sutures

The Adult Skull • skull = 22 bones • cranium = 8 bones: frontal, occipital, 2 temporals, 2 parietals, sphenoid and ethmoid • facial bones = 14 bones: nasals, maxillae, zygomatics, mandible, lacrimals, palatines, inferior nasal conchae, vomer. • skull forms a larger cranial cavity -also forms the nasal cavity, the orbits, paranasal sinuses mandible and auditory ossicles are the only movable skull bones • cranial bones also: attach to membranes called meninges -stabilize positions of the brain, blood vessels -outer surface provides large areas for muscle attachment that move the head or provide facial expressions

Bones of the Cranium

Frontal View

Frontal View

Parietal Frontal View

Temporal Frontal View

Nasal Frontal View

Vomer Frontal View

Zygoma Frontal View

Maxilla Frontal View

Mandible Frontal View

Frontal Parietal Temporal Nasal Vomer Maxilla Zygoma Mandible Frontal View

Lateral View

Frontal Lateral View

Parietal Lateral View

Temporal Lateral View

Nasal Lateral View

Zygoma Lateral View

Maxilla Lateral View

Mandible Lateral View

Occipital Lateral View

Mastoid Process Lateral View

External Auditory Meatus Lateral View

Parietal Frontal Sphenoid Temporal Occipital Mastoid Process Nasal Zygoma Maxilla Mandible External Auditory Meatus Lateral View

Figure 6. 4 Sectional Anatomy of the Skull, Part I

n Frontal bone n n n Forms the forehead Roof of the orbit articulates with parietal, sphenoid, lacrimal, nasal, ethmoid, zygomatic and maxilla superior and lateral to glabellar region – frontal sinuses inferior portion – supraorbital ridges with supraorbital notch (supraorbital nerve and artery)

• Parietal bones -Part of the superior and lateral surfaces of the cranium -articulate with each other – sagittal suture -articulate with occipital, frontal, temporal and sphenoid bones

• Temporal bone -Forms wall of jugular foramen -Petrous part: posterior portion -Tympanic part: associated with ear canal -Squamous part: anterior portion, fan-shaped -zygomatic process -forms cranial portion of the TMJ joint -inferior to zygo. process – mandibular fossa (mandibular condyle)

• Temporal bone – petrous portion • houses the inner ear -inferior aspect – mastoid process (air spaces that communicate with the middle ear) -also for attachment of sternocleidomastoid muscle -inferior to mastoid process – mastoid foramen -anterior to mastoid process – external acoustic meatus -inferior and medial to the MP – styloid process (muscle attachment) -stylomastoid foramen (7 th cranial)

n Occipital bone n n n Part of the base of the skull articulates with parietal, temporal and sphenoid Surrounds the foramen magnum lateral to the FM – hypoglossal canal (12 th cranial) projections = occipital condyles Forms part of the jugular foramen

n Sphenoid bone Contributes to floor of cranium n articulates with the frontal, ethmoid, temporal zygomatic, parietal maxillary, palatine, vomer & occipital bones n Bridges cranial and facial bones n Optic canal allows passage of optic nerve n

Ethmoid bone n n n Irregularly shaped bone Forms part of orbital wall Forms roof of nasal cavity articulates with: frontal, sphenoid, lacrimal and maxillary bones connects with the vomer two lateral masses – contain the ethmoid sinuses n projections called the superior and middle nasal conchae two plates: perpendicular plate & the cribiform plate n Cribiform plate: perforations for olfactory nerve, midline is the crista galli n Perpendicular plate = upper part of nasal septum n

14 Facial Bones Nasal (2) Zygomatic (2) Mandible (1) (2) Inferior nasal conchae (2) (1) Maxillae (2) Lacrimal (2) Palatine Vomer

Bones of the Face n Maxillae Paired bone n Largest of facial bones n Form upper jaw n body = orbital, nasal, infratemporal and facial surfaces n body contains the maxillary sinuses n

Maxillary bones: Anterior View n n frontal process – articulates with frontal bone and nasal bones & forms medial orbital rim facial surface – body of maxilla n n n infraorbital foramen – landmark for local inferior to this IF – canine fossa inferior portion of the maxilla – alveolar processes of the teeth (contains the roots of the maxillary teeth

Zygomatic Bones n n n Cheekbones Lateral wall of orbit along with sphenoid Part of zygomatic arch along with part of temporal

n Palatine bones Small, L-shaped n link between maxilla and sphenoid n Form posterior portion of hard palate n Contribute to floor of orbit n made up of horizontal plate and a vertical plate + orbital process n

-two

n Inferior nasal concha n Located on each side of nasal septum n Increase epithelial surface n Create turbulence in inspired air n Lacrimal n Smallest bones in skull n Forms nasolacrimal groove leading to nasolacrimal canal n Delivers tears to nasal cavity

Palatine & Vomer n n n posterior part of nasal septum Forms inferior portion of nasal septum Articulates with maxillae and palatines

Mandible n n n lower jaw only freely movable bone of the skull moving articulations with temporal bone

Mandible: Inferior surface -visible are the genial tubercles – or mental spines -muscle attachment area -two fossas: 1) sublingual (sublingual salivary gl. ) 2) submandibular (submandibular gl. ) -divided by the mylohyoid line (mylohyoid m. ) -mandibular foramen – opening of the mandibular canal -for the exit of the alveolar nerve and vessels -can be lost with alveolar process reabsorption -overhanging the foramen – lingula (attachment of sphenomandibular ligament – TMJ)

The Hyoid Bone n n n Suspended by stylohyoid ligaments Consists of a body, greater horns and lesser horns Base for muscles of the tongue and larynx

Paranasal Sinuses part of the nasal complex n Paired cavities in ethmoid, sphenoid, frontal and maxillary n Lined with mucous membranes and open into nasal cavity though openings called ostia n Resonating chambers for voice, lighten the skull frontal sinuses: frontal bone, separated by a n Sinusitis is inflammation of septum the membrane (allergy) n connects with nasal cavity – frontonasal duct n infection can easily spread sphenoid sinuses: body of the sphenoid bone from one sinus to the other n also drain into nasal cavity through the nasal cavity ethmoid sinuses: or ethmoid air cells, located inn can also spread to other the lateral masses tissues n anterior, middle and posterior sinuses n n n maxillary: body of the maxilla n n n size varies with individual and age largest of the sinuses close proximity to alveolar processes – periodontal tissues may be in direct contact with sinus’ mucus membranes n secondary sinusitis

The Vertebral Column http: //www. wisc-online. com/objects/index. asp? obj. ID=AP 12104

Adult Vertebral Column n 26 vertebrae 24 individual vertebrae n Sacrum n Coccyx n n n Seven cervical vertebrae Twelve thoracic vertebrae Five lumbar vertebrae Sacrum and coccyx are Fused together.

Typical Vertebrae n Body n n weight bearing Vertebral arch pedicles n laminae n n n Vertebral foramen Seven processes 2 transverse n 1 spinous n 4 articular n

Typical Cervical Vert. (C 3 -C 7) n n n Smaller bodies Larger spinal canal Transverse processes n n shorter transverse foramen for vertebral artery Spinous processes of C 2 to C 6 often bifid 1 st and 2 nd cervical vertebrae are

Atlas & Axis (C 1 -C 2)

The Atlas n n n C 1 is termed the atlas Lacks a body and spinous process Supports the skull n n Superior articular facets receive the occipital condyles Allows flexion and extension of neck n Nodding the head “yes”

The Atlas Figure 7. 16 a

The Axis n n Has a body and spinous process Dens (odontoid process) projects superiorly Acts as a pivot for rotation of the atlas and skull n Participates in rotating the head from side to side n

The Axis

Thoracic Vertebrae (T 1 -T 12) n n n All articulate with ribs Have heart-shaped bodies from the superior view Each side of the body bears demifacts for articulation with ribs

Thoracic Vertebrae n Spinous processes are long and point inferiorly n Vertebral foramen are circular n Transverse processes articulate with tubercles of ribs n Allows rotation and prevents flexion and extension

Lumbar Vertebrae n n n Bodies are thick and strong Transverse processes are thin and tapered Spinous rocesses are thick, blunt, and point Vertebral foramina are triangular Allows flexion and extension – rotation prevented

Sacrum (S 1 – S 5) n n n Forms the posterior wall of pelvis Formed from 5 fused vertebrae Superior surface articulates with L 5 Inferiorly articulates with coccyx Sacral promontory n n Where the first sacral vertebrae bulges into pelvic cavity Center of gravity is 1 cm posterior to sacral promontory

Sacrum n Sacral foramina n Ventral foramina n n Passage for ventral rami of sacral spinal nerves Dorsal foramina n Passage for dorsal rami of sacral spinal nerves

Sacrum Figure 7. 18 a, b

Coccyx n n n Is the “tailbone” Formed from 3 – 5 fused vertebrae Offers only slight support to pelvic organs

Bony Thorax n n Forms the framework of the chest Components of the bony thorax Thoracic vertebrae – posteriorly n Ribs – laterally n Sternum and costal cartilage – anteriorly n n Protects thoracic organs Supports shoulder girdle and upper limbs Provides attachment sites for muscles

The Bony Thorax Figure 7. 19 a

The Bony Thorax Figure 7. 19 b

Sternum n Formed from three parts : n Manubrium – superior part n n Body – bulk of sternum n n Articulates with medial end of clavicles Sides are notched as articulations for costal cartilage of ribs 2– 7 Xiphoid process – inferior end of sternum n Ossifies around age 40

Sternum n Anatomical landmarks n Jugular notch n n Central indentation at superior border of the manubrium Sternal angle n A horizontal ridge where the manubrium joins the body

Ribs n All ribs attach to vertebral column posteriorly n True ribs - superior seven pairs of ribs n n Attach to sternum by costal cartilage False ribs – inferior five pairs of ribs , attatch indirectly to the sternum nfloating ribs 11– 12 are short and free anteriuorly.

Ribs Figure 7. 20 a

Ribs Figure 7. 20 b

Disorders of the Axial Skeleton n Abnormal spinal curvatures Scoliosis – an abnormal lateral curvature n Kyphosis – an exaggerated thoracic curvature n Lordosis – an accentuated lumbar curvature – “swayback” n n Stenosis of the lumbar spine n A narrowing of the vertebral canal

The Appendicular Skeleton Allows us to move and manipulate objects n Includes all bones other than axial skeleton, it includes: n n the limbs (upper & lower limbs) n the supportive girdles (pectoral &pelvic girdles)

th Figure 8– 1

What are the bones of the pectoral girdle, their functions, and features?

The Pectoral Girdle n n Also called the shoulder girdle Connects the arms to the body Positions the shoulders Provides a base for arm movement

The Pectoral Girdle Figure 8– 2 a

The Pectoral Girdle n Consists of: 2 clavicles n 2 scapulae n n Connects with the axial skeleton only at the manubrium(claviculosternal joint)

The Clavicles Figure 8– 2 b, c

The Clavicles n n Also called collarbones Long, S-shaped bones Originate at the manubrium (sternal end) Articulate with the scapulae (acromial end)

The Scapulae n n n Also called shoulder blades Broad, flat and triangular Articulate with arms and collarbone

Anatomy of The scapula Figure 8– 3 a

What are the bones of the upper limbs, their functions, and features?

The Upper Limbs n Arms, forearms, wrists, and hands Note: arm (brachium) = 1 bone, the humerus

ANATOMY OF The Humerus Figure 8– 4

The Humerus n n n Also called the arm The long, upper armbone Articulates with the pectoral girdle

The Forearm Figure 8– 5

The Forearm n Also called the antebrachium n Consists nulna of 2 long bones: (medial) nradius (lateral)

Interosseous Membrane n n A fibrous sheet provides strength Connects lateral margin of ulnar shaft to radius

The Wrist Figure 8– 6

The Wrist n 8 carpal bones: n 4 proximal carpal bones n 4 distal carpal bones nallow wrist to bend and twist

Metacarpal Bones n The 5 long bones of the hand n Numbered I–V from lateral (thumb) to medial n Articulate with proximal phalanges

Phalanges of the Hands n Pollex (thumb): n 2 phalanges (proximal, distal) n Fingers: n 3 phalanges (proximal, middle, distal)

What are the bones of the pelvic girdle, their functions, and features?

The Pelvis n Consists of 2 ossa coxae, the sacrum, and the coccyx n Stabilized by ligaments of pelvic girdle, sacrum, and lumbar vertebrae

The Pelvic Girdle Figure 8– 7

The OSSA COXAE Also called hipbones n Strong to bear body weight &stress of movement n Each is made up of 3 fused bones: n n ilium (articulates with sacrum) n ischium n pubis

The Acetabulum (vinegar cup) called the hip socket n Is the meeting point of the ilium, ischium, and pubis n Articulates with head of the femur (Hip joint)) n Also

Marks of the Pubis n Pubic symphysis: n gap between pubic tubercles n padded with fibrocartilage Marks of the Ischium • Ischial tuberosity: posterior projection you sit on • Ischeal spine, superior to the tuberosity , important during labour

The Pelvis Figure 8– 8

Divisions of the Pelvis Figure 8– 9

The Pelvis n Perineum region: inferior edges of true pelvis n forms pelvic outlet n perineal muscles support organs of pelvic cavity n

What are the structural and functional differences between the male and female pelvis?

Comparing the Male and Female Pelvis n Female pelvis: nsmoother nlighter nless prominent muscle and ligament attachments

Comparing the Male and Female Pelvis Figure 8– 10

Pelvis Modifications for Childbearing n n n Enlarged pelvic outlet Broad pubic angle (> 100°) Less curvature of sacrum and coccyx Wide, circular pelvic inlet Broad, low pelvis Ilia project laterally, not upwards

What are the bones of the lower limbs, their functions, and features?

The Lower Limbs n Functions: nweight bearing nmotion Note: leg = lower leg; thigh = upper leg

Bones of the Lower Limbs n Femur (thigh) n Patella (kneecap) n Tibia and fibula (leg) n Tarsals (ankle) n Metatarsals (foot) n Phalanges (toes)

The Femur(longest, heaviest ) Figure 8– 11

The Patella n n Also called the kneecap Formed within tendon of quadriceps femoris

The Tibia and Fibula Figure 8– 13

The Tibia n n Also called the shinbone Supports body weight Larger than fibula Medial to fibula The Fibula • Attaches muscles of feet and toes • Smaller than tibia • Lateral to tibia

Bones of the Ankle n n Talus: Calcaneus (heel bone): transfers weight to ground n attaches Achilles tendon n

The Ankle n Also called the tarsus: n consists of 7 tarsal bones Figure 8– 14 a

Feet: Metatarsal Bones n n n 5 long bones of foot Numbered I–V, medial to lateral Articulate with toes

Feet: Phalanges n Phalanges: n n Hallux: n n bones of the toes big toe, 2 phalanges (distal, proximal) Other 4 toes: n 3 phalanges (distal, medial, proximal)

Feet: Arches n Arches transfer weight from 1 part of the foot to another Figure 8– 14 b

Arches of the Foot n n n Bones are arranged to form THREE strong arches, 2 longitudinal (medial & lateral)& 1 transverse Ligaments & tendons help to hgold the bones firmly in the arched position but still allow a certain amount of spriginess Week arches are referred to as flat foot

Articulations (Joints)

Function n Holds bones together Allows bones to move All bones articulate with at least one other bone except the hyoid.

Classification of joints n n n Functional classification: focuses on the amount of movement (synarthrosis, amphiarthrosis and diarthrosis) Structural classification: based on whether Fibrous, Cartilage or a joint cavity separates the bony regions at the joint. As a general rule, fibrous joints are immovable and synovial joints are freely movable.

Types n n Synarthroses No movements n n n Primarily axial skeleton Bones connected with fibrous tissue ligament Examples: Skull sutures and distal Tibia/Fibula

Types n Amphiarthroses n n Slightly movable Axial skeleton Connected by cartilage Intervertebral joints, pubic symphysis

Types n Diarthroses – freely movable Also called synovial (fluid filled joint cavity) n Primarily found in the limbs n Plane of movement depends on the joint n

Synovial Joints - Structure 1. Articular cartilage: hyaline 2. Joint Cavity: space filled with lubricating fluid 3. Fibrous Capsule: fibrous CT lined with a smooth synovial membrane 4. Reinforcing Ligament: can be inside or outside the joint capsule 5. Synovial Fluid: viscous and lubricating 6. Bursae: fluid filled sacs , see later 7. Tendons sheath an elongated bursa that rapes around a tendon subjected to friction. 8. Menisci: cartilaginous discs

Synovial Joint

Types of synovial joints based on shape n Plane(nonaxial) -Slipping or gliding movements -Intercarpel joints are best examples

Hinge joints( uniaxial) n n Angular movement is allowed in only one plane like a hinge Examples : elbow, ankle and interphalangeal joints

Ball-and-socket joints n n n A spherical head of one bone fits into a round socket in another These Multiaxial joints allow movements in all axes including rotation Shoulder and Hip are examples

Bursae n n Flattened fibrous sac lined with synovial membrane with thin synovial fluid Acts as bags of lubricant to reduce friction where ligaments, muscle, skin, tendon or bones rub together

Disorders of joints n n Dislocation: Bone is forced out of its position, Reduction is done by experts only Bursitis: example falling on the knee Sprain: excessive stretch on a ligament Arthritis: inflammation of joints, may be -Acute: usually bacterial -Chronic: Rheumatoid , Osteoarthritis and Gouty arthritis

Developmental aspects n n n Long bones are formed of Hyaline cartilage Flat bones of skull are formed of fibrous membranes At birth, some fontanels still remain By end of adolescence, the epiphysial plates are fully ossified Adult skull is 1/8 & infant skull is 1/4 of the total body length

n n n At birth, cranium is huge relative to face, it is related to rapid growth of brain By 2 years skull is 3/4 adult size By 9 years, skull become nearly of adult size At birth, the spine is arched (primary) and convex posteriorly Secondary curvature are convex anteriorly, cervical with raising the head & lumber with start of walking S-shaped spine in adult

At birth the UL ratio is 1. 7 to 1 n At 10, UL is 1 to 1 n Bones become stronger with pull of gravity &muscle contractions n Osteoporosis, thin and fragile bones occurs in totally inactive persons. It occurs in half women after 65 and in 20% of men after 70(estrogen maintain healthy bones) n Causes of Osteoporosis: - estrogen deficiency - diet poor in calcium & protein - lack of vitamin D - smoking - lack of exercise - pathologic fracture is the result END of Sk. system n