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Functions of the Skeletal System Support Protection Attachment sites for skeletal muscles Blood cell production Mineral storage 2

Bone Structure Bones are composed of a number of tissues Bone tissue is the bulk of each bone There are four basic types of bone based on shape Long bones Short bones Flat bones Irregular bones 3

Structure of a long bone Epiphysis Articular cartilage Diaphysis Medullary cavity Endosteum Epiphyseal disk Periosteum 4

Spongy bone Interior of small bones, skull bones, and epiphyses Consists of trabeculae and spaces filled with red bone marrow Reduces bone weight without reducing strength 5

Compact bone Wall of diaphysis and surface of diaphysis Tightly packed tissue with no spaces Strong and gives supportive strength 6

Microscopic structure Bone cells lie inside lacunae Compact bone Osteons Osteonic canals Lamellae Foramen Canaliculi Spongy bone Lack osteons Receive nutrients by diffusion through canaliculi 7

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Bone Formation Ossification is the process of bone formation during the 6th or 7th week of embryonic life Two types of bone formation Intramembranous ossification Endochondral ossification 9

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For both types of bone formation Primitive connective tissue cells become osteoblasts Osteoblasts deposit bone matrix around them Once trapped in matrix, osteoblasts become osteocytes 11

Intramembranous ossification Forms most skull bones Steps involved Connective tissue membranes form at sites of future intramembranous bones Some cells become osteoblasts Osteoblasts deposit spongy bone beginning at center of bone Osteoblasts form layer of compact bone atop the spongy bone 12

To produce the correct bone shape Use osteoclasts to remove bone matrix Use osteoblasts to reform new bone matrix 13

Endochondral ossification Forms most bones of the body Example: long bones Steps involved Bones are preformed in hyaline cartilage 14

Primary ossification center forms in center of cartilage Periosteal osteoblasts form a compact bone collar around primary ossification center Cartilage in the primary center calcifies and chondrocytes die 15

Osteoblasts form spongy bone at the primary ossification center Blood vessels and nerves penetrate the center, bring osteoblasts with them Osteoblasts form spongy bone at the primary ossification center 16

Secondary ossification center forms in the epiphyses Osteoclasts remove the spongy bone and form the medullary cavity 17

Bone continues to grow At the end of the process, the epiphyseal disk separates the epiphyses from the diaphysis 18

Continued growth in length takes place at the epiphyseal disk Continued growth in diameter due to formation of compact bone beneath the periosteum Continued growth in length takes place at the epiphyseal disk Cartilage grows on the epiphyseal side Cartilage is converted into bone on the diaphysis side 20

Osteoblasts and osteoclasts continually reshape the bone as it grows Bone growth in length continues until age 25 Epiphyseal disk is completely replaced by bone Epiphyseal line is all that remains 21

Homeostasis of bone Bone is continually remodeled due to activity of osteoclasts and osteoblasts Remodeling can be affected by Physical activity Dietary calcium intake Age 22

Divisions of the Skeleton Skeleton is divided into two divisions Axial skeleton Bones along the longitudinal axis of the body Appendicular skeleton Pectoral girdle and upper extremities Pelvic girdle and lower extremities

Axial Skeleton Skull Divided into two segments Bones joined by sutures Cranium Facial bones Bones joined by sutures Immovable joints

Several bones possess paranasal sinuses

Cranium Frontal bone Parietal bones Occipital bones Temporal bones Anterior part of cranium Parietal bones Sides and roof of cranium Occipital bones Posterior portion and floor of cranium Temporal bones Inferior to parietal bones on each side of the cranium Temporomandibular joint

Sphenoid bone Ethmoid bone Forms part of cranium floor, lateral posterior portions of eye orbits, lateral portions of cranium anterior to temporal bones Ethmoid bone Anterior portion of cranium, including medial surface of eye orbit and roof of nasal cavity Nasal conchae

Facial bones Maxillae Palatine bones Form upper jaw, anterior portion of hard palate, part of lateral walls of nasal cavity, floors of eye orbits Maxillary sinus Palatine bones Form posterior portion of hard palate, lateral wall of nasal cavity

Zygomatic bones Lacrimal bones Nasal bones Cheek bones Also form floor and lateral wall of each eye orbit Lacrimal bones Medial surfaces of eye orbits Nasal bones Form bridge of nose

Inferior nasal conchae Vomer In midline of nasal cavity Forms nasal septum with the ethmoid bone Inferior nasal conchae Attached to lateral walls of nasal cavity Mandible Lower jawbone Only movable skull bone

Hyoid bone Found in anterior portion of neck, inferior to mandible Does not articulate with any other bones Used as attachment site for tongue muscles

The infant skull Newborn skull is incompletely developed Possess fontanels Non-ossified areas Allow for flexibility during birth and growth afterwards

Vertebral column Extends from skull to pelvis Flexible and sturdy longitudinal support for trunk Formed by 24 movable vertebrae, a sacrum, and a coccyx Possess intervertebral discs Shock absorbers Possess four distinct curvatures

Structure of a vertebra All vertebrae have common features Neural arch Vertebral foramen Spinous process Transverse process Superior and inferior articulating process Intervertebral foramina

Cervical vertebrae Support neck Possess unique transverse foramen

Atlas: cervical vertebra 1 Articulate occipital condyles of occipital bone Supports head

Axis: cervical vertebra 2 Possesses the odontoid process Serves as a pivot point for axis

Thoracic vertebrae Larger vertebra with longer spinous process then cervical vertebrae Ribs articulate on the transverse processes and bodies

Lumbar vertebrae Heavy, thick bodies to support greater stress and weight Larger processes for attachment of back muscles

Sacrum Coccyx Five fused sacral bones Forms posterior wall of pelvic girdle Coccyx Tailbone Three to five fused rudimentary vertebrae

Thoracic cage Composed of Functions Thoracic vertebrae Ribs Costal cartilages Sternum Functions Protection of internal organs Support of upper body

Ribs Attached to thoracic vertebrae True ribs (#1-7) Attached to sternum directly by costal cartilages False ribs (#8-10) Attach to costal cartilage of superior ribs Floating ribs (#11-12) Do not attach anteriorly, no costal cartilages

Sternum Flat, elongated bone in the anterior midline of thoracic cage Composed of three fused bones Manubrium Body Xiphoid process

Appendicular Skeleton Consists of Pelvic girdle and upper extremity Pelvic girdle and lower extremity Composed of 126 individual bones

Pectoral girdle Composed of Clavicle Two clavicles Two scapula Articulates with sternum and scapula

Scapula Located on each side of vertebral column Held in place by muscles to allow free shoulder movement

Upper extremity Humerus Articulates with scapula at the shoulder and ulna and radius at the elbow

Ulna Radius Medial bone in forearm Bone does not move with hand rotation Radius Lateral bone in the forearm Bone that rotates when the hand is rotated

Carpals Metacarpals Phalanges Wrist bones Bones of the palm of the hand Phalanges Bones of the fingers

Pelvic girdle Consists of Forms a rigid, bony pelvis Two coxal bones Sacrum Forms a rigid, bony pelvis

The pelvic girdles of males and females have several structural differences

Coxal bones Formed by three fused bones Attachment site for the legs Ilium Ischium Pubis Attachment site for the legs Symphysis pubis

Lower extremity Femur Patella Thigh bone Largest and strongest bone in the body Patella Kneecap Sesamoid bone in tendon that extends anterior to knee

Tibia Fibula Shinbone Larger of the lower leg bones Bears body weight Slender, lateral bone in lower leg

Tarsals Metatarsals Phalanges Ankle bones Bones of the instep Toe bones

Articulations An articulation is a joint or junction between two bones Joints allow for varying degrees of movement Three categories of joints Immovable Slightly movable Freely movable

Immovable joints (synarthrosis) Bones are tightly joined and separated by thin fibrous connective tissue No movement at the joint Example: sutures

Slightly movable joints (amphiarthrosis) Bones separated by layer of cartilage or fibrous connective tissue Limited flexibility Example: joints between vertebrae

Freely movable joints (diarthrosis) Joints are freely movable Structurally more complex Several types of freely movable joints

Gliding joints Condyloid joints Involve sliding of bones across each other Example: carpal and tarsal bones Condyloid joints Allow movement from side to side and back and forth Example: between carpals and bones of forearm

Hinge joints Allow movement in one direction only Example: knee and elbow joints

Saddle joints Pivot joints Ends of each bone are saddle shaped Movement is side to side and back and forth Example: joint between trapezium and metacarpal of thumb Pivot joints Allow rotational movement Example: atlas on the axis

Ball-and-Socket joints A rounded head of one bone fits into a concavity on another bone Movement may be rotational or in any plane Example: hip and shoulder joint

Movements at freely movable joints Movement is caused by contraction of muscles that span the joint Movement depends upon joint type and location of muscle(s) involved

Disorders of the Skeletal System Common disorders can be characterized as Disorders of bones Disorders of joints Orthopedics Branch of medicine that specializes in treating skeletal disease and abnormalities

Disorders of Bones Fractures: broken bones Complete Incomplete Compound Simple Greenstick Comminuted Impacted

Osteomyelitis Osteoporosis Inflammation of bone and bone marrow due to bacterial infection Osteoporosis Weakening of bone due to loss of calcium salts Common in older people, especially postmenopausal women Caused by inactivity and decrease in hormone production

Rickets Childhood disease Due to deficiency of calcium salts in bones Dietary deficiency in calcium or Vitamin D Children have a bowlegged appearance

Disorders of Joints Arthritis Rheumatoid arthritis Osteoarthritis Characterized by inflammation, swelling, and pain Rheumatoid arthritis Most painful and crippling type Result is ossification of joint, making it immovable Auto-immune dissorder Osteoarthritis Most common type Loss of articular cartilage makes movement restricted and painful

Bursitis Dislocation Herniated disk Inflammation of bursa Displacement of bones forming the joint Herniated disk Intervertebral disc protrudes out beyond vertebrae Caused by excessive pressure May apply pressure to nerves

Spinal curvatures Sprain Kyphosis (hunchback) Lordosis (swayback) Excessive thoracic curvature Lordosis (swayback) Excessive lumbar curvature Scoliosis Abnormal lateral curvature Sprain Tearing or stretching of ligaments and tendons without dislocation