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Skeletal System. Types of Animal Skeletons. Endoskeleton Internal skeleton Ex. Humans Exoskeleton External skeleton Ex. Insects, Clams Hydrostatic Internal fluids receive and redistribute applied forces Ex. Annelids. Bone Functions. Movement Protection Support Mineral Storage

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Types of animal skeletons
Types of Animal Skeletons

  • Endoskeleton

    • Internal skeleton Ex. Humans

  • Exoskeleton

    • External skeleton Ex. Insects, Clams

  • Hydrostatic

    • Internal fluids receive and redistribute applied forces

      Ex. Annelids

  • Bone functions
    Bone Functions

    • Movement

    • Protection

    • Support

    • Mineral Storage

      (Ca++, P)

    • Energy Storage

      (Yellow Marrow – Fat)

    • Hematopoiesis - Produce Blood Cells

      (Red Marrow)

    Types of bones








    femur, humerus, other limb bones except wrist, ankles, and patella

    carpals, tarsals


    cranium, ribs, scapula

    vertebrae, mandible, hip bones

    Types of Bones


    Longer than they are wide

    cube shaped

    Sesame seed shaped, formed in tendon

    flattened section

    more than 1 shape

    Classification of bones cont
    Classification of Bones (cont.)

    a = Long Bone

    b = Short Bone

    c = Flat Bone

    d = Irregular Bone

    e = Sesamoid Bone

    Anatomy of a long bone
    Anatomy of a Long Bone

    • Epiphyseal Plate: hyaline cartilage that grows during childhood to lengthen the bone

    • Epiphyseal Line: remnant of epiphyseal plate, found only in adults


    long portion in middle


    shorter section at end



    Bone covering, outer layer of dense irregular c.t.; inner layer of osteoblasts and osteoclasts, supplied with nerves and blood vessels

    Compact Bone:

    dense layer over medullary cavity; supports weight

    Articular Cartliage:

    Covers epiphysis at joints, reduces friction, absorbs shock

    Spongy Bone:

    lattice of trabecula filled with red marrow; nourished directly from circulating blood

    Medullary Cavity:

    Hollow center of diaphysis, contains yellow marrow

    Bone osseous tissue
    Bone (Osseous) Tissue

    Osteocytes – widely spaced, surrounded by intercellular substances

    • Osteoid(organic):

    Osteoblasts: add salts

    Collagenous Fibers

    • Hydroxyapatite

    • (inorganic):

    Osteoclasts: remove salts

    Mineral Salts (calcium, phosphorus)

    - Provides strength and hardness to bone

    Osteon structural unit of matrix and canals
    Osteon: structural unit of matrix and canals

    • Lamella (little plate): rings of calcified matrix, intercellular substance

    • Volkmann’s Canals: horizontal canals; allow blood vessels and nerves to connect

    • Haversian Canals: vertical canals; allow blood vessels and nerves to connect

    • Canaliculi: tiny canals that allow osteocytes to exchange nutrients and wastes

    • Lacunae: space for osteocytes

    Ossification bone formation
    Ossification (bone formation)

    • begins around 6th or 7th week post conception

    • ends by age 25

      2 types

    Intramembranous ossification
    Intramembranous Ossification

    • Bone forms within fibrous membranes (skull, clavicle)

      • Osteoblasts cluster in fibrous membranes: Center of Ossification

      • Calcification: intercellular substances and collagen are secreted into a network where calcium can be deposited

      • Trabecula Formation: complete when osteoblasts are completely surrounded by calcified matrix

      • Trabecula continue to fuse together = spongy bone

      • Red marrow fills in space

    Endochondral ossification most bones
    Endochondral Ossification (most bones)

    • Cartilage is formed in embryonic stage

      • Covered by perichondrium (membrane)

    Primary Ossification:

    Begins at periosteal collar (around middle of diaphysis)

    - Blood vessel penetrates perichondrium

    - Stimulates osteoblast formation

    - Bone replaces cartilage:

    - Intercellular substances calcify

    - Nutrients are cut off by hardened matrix

    Secondary Ossification:

    - Periosteum thickens bones, especially at ends

    - Blood vessel penetrates ends, process repeats


    - 2 areas of cartilage will remain:

    - articulating cartilage

    - epiphyseal plates (allow lengthwise growth of bones)

    Bone remodeling
    Bone Remodeling

    • Normal bone is always undergoing remodeling

    • Removes old bone tissue and replaces it with new bone tissue

    • Remodeling cycle continues throughout life to maintain healthy bone

    • About 20% of all bone tissue is replaced annually

    Bone remodeling1
    Bone Remodeling

    • Sites of remodeling

      • Where bone is experiencing growth

      • Mechanical stress

      • Microfractures

      • Breaks

    Bone remodeling2
    Bone Remodeling

    Five Phases

    • Activation

    • Resorption

    • Reversal

    • Formation

    • Quiescence

    Bone remodeling3
    Bone Remodeling

    • Activation

      • Pre-osteoclasts are attracted to the remodeling sites

      • Pre-osteoclasts fuse to form multinucleated osteoclasts

    • Resorption

      • Osteoclasts dig out a cavity, called a resorption pit, in spongy bone or burrow a tunnel in compact bone

    Bone remodeling4
    Bone Remodeling

    • Calcium can be released into the blood for use in various body functions

    • Osteoclasts disappear

  • Reversal

    • Mesenchymal stem cells, pre-cursors to osteoblasts, appear along the burrow or pit where they…

    • …proliferate (increase in number) and differentiate into preosteoblasts

  • Bone remodeling5
    Bone Remodeling

    • Formation

      • Pre-osteoblasts mature into osteoblasts at the surface of the burrow or pit

      • Osteoblasts release osteoid at the site, forming a new soft matrix

      • The new matrix is mineralized with calcium and phosphorous

    • Quiescence

      • Site remains dormant until the next cycle

    System divisions







    Everything Else

    System Divisions

    Axial skeleton1
    Axial Skeleton

    • Skull

      • All bones immovable except mandible

      • Cranium

        • Paranasal Sinuses

          • Cavities within bones of skull

          • Lined by mucous membranes

        • Fontanels

          • Fetal/Child

            • Soft spots

            • Incomplete Ossification

      • Facial Bones

    Fontanels of fetal skull

    Axial skeleton2
    Axial Skeleton

    • Hyoid Bone

      • No articulation

    Axial skeleton3
    Axial Skeleton

    • Vertebral Column

      • Protects spinal cord

      • Shock absorbers

      • Vertebrae separated by intervertebral disks

        • Fibrocartilage

    Axial skeleton4
    Axial Skeleton

    • 7 Cervical Vertebrae

      • Atlas (C1) and Axis (C2)

        • Allow rotation of the head

    • 12 Thoracic Vertebrae

    • 5 Lumbar Vertebrae

    • Remember the common mealtimes to help you remember the number of vertebrae

      • Breakfast = 7, Lunch = 12, Dinner = 5

    Axial skeleton5
    Axial Skeleton

    • Sacrum

      • Five fused vertebrae

    • Coccyx

      • Tailbone

    • Bony Thorax

      • Sternum

        • Manubrium, Body, Xiphoid process

      • 12 pairs of ribs

    Axial skeleton6
    Axial Skeleton

    • Ribs

      • True ribs

        • Attached to sternum

        • 7 pair

      • False ribs

        • Attached to costalcartilage of 7th rib

        • 3 pair

      • Floating ribs

        • No anterior attachment

        • 2 pair

    Appendicular skeleton1
    Appendicular Skeleton

    • Pectoral (shoulder) girdle

      • Scapula and clavicle (collar bone)

    • Upper limbs

      • Humerus (arm)

      • Radius and ulna (forearm)

    • Carpals (wrist)

    • Metacarpals (palm)

    • Phalanges (fingers and thumb)

    Appendicular skeleton2
    Appendicular Skeleton

    • Pelvic (hip) Girdle

      • Coxal (hip) bones

        Female vs. Male


        Pubic arch = 90˚ Pubic arch = 60˚

        Distance between iliac Bones are heavier

        crest wider Bone markings more


    Appendicular skeleton3
    Appendicular Skeleton

    • Coxal Bones have 3 parts

      • Ilium (superior)

      • Ischium (posterior)

      • Pubis (anterior)

    Appendicular skeleton4
    Appendicular Skeleton

    • Lower Limbs

      • Femur (thigh)

        • Longest bone in body

      • Tibia and Fibula (leg)

        • Tibia = medial, Fibula = lateral

      • Patella (knee cap)

      • Tarsals

        • Ankle

      • Metatarsals

        • Instep

      • Phalanges

        • toes


    • Points of contact between bones

    • Functions

      • Hold skeleton together

      • Mobility

    Joints based on functional differences
    Joints (based on functional differences)


    Synarthroses (axial)

    Amphiarthroses (axial)

    Diarthroses (appendicular)


    (Fibrous Joints)

    • No Movement

    Joining bones connected by fibrous connective tissue

    Example: sutures in skull, gomphosis at teeth, costal cartilage


    (Cartilaginous joints)

    • Slight Movement

    Joining bones connected by cartilage

    Example: vertebral joints



    • Free Movement

    • Surrounded by synovial cavity:

    • lined with synovial membrane

    • - lubricates bones/cartilage

    • - structured like a sleeve

    • bursa often found between the bones

    • ligaments secure bone together

    • - grow out of periosteum

    Types of diarthrotic joints
    Types of Diarthrotic Joints

    Ball and Socket

    Ball-like head of one bone fits in concave socket of

    another bone

    Allows widest range of motion


    Head of one bone fits against concave socket of another

    Allows only flexion and extension


    Small rounded or pointed pin of one bone fits in arch or

    ring of another

    Allows rotation


    Only found where thumb fits wrist, saddle and rider shape

    Allows side-side and back and forth movement


    Flat surfaces of bones fit against each other

    Allows gliding in 2 planes, side – side or front-back


    Oval projection fits into an elliptical socket

    Allows side-side and back and forth movement

    Movement of synovial joints
    Movement of Synovial Joints


    location at which a muscle attaches to a moving bone


    location at which a muscle attaches to a stationary bone

    Movement of synovial joints1
    Movement of Synovial Joints

    • Actions:

      Flexion: Decreasing the angle between


      Dorsiflexion: Moving the top of the foot toward

      the ankle

    Movement of synovial joints2
    Movement of Synovial Joints

    • Actions:

      Extension: Increasing the angle between


      Plantar Flexion: Standing on toes

    Movement of synovial joints3
    Movement of Synovial Joints

    • Actions:

      Hyperextension: Increasing the angle beyond

      normal positions

    Movement of synovial joints4
    Movement of Synovial Joints

    • Actions:

      Abduction: Moving away from the vertical midline of the body

      Adduction: Moving toward the vertical midline

    Movement of synovial joints5
    Movement of Synovial Joints

    Circumduction: Moving a limb so that the distal end

    forms a circular pattern

    Rotation: Moving around a central axis

    Movement of synovial joints6
    Movement of Synovial Joints

    Pronation: Turning the hand to point the palm

    downward or posterior

    Supination: Turning the hand to point the palm

    upward or anteriorly

    Movement of synovial joints7
    Movement of Synovial Joints

    Eversion: Turning the foot to point the sole

    more outward or laterally

    Inversion: Turning the foot to point the sole

    inward or medially

    Movement of synovial joints8
    Movement of Synovial Joints

    Protraction: Moving a body part straight out from

    the midline

    Retraction: Bringing a body part towards the



    Fracture Types:


    Break is incomplete


    Break results in 2 or more pieces


    Break doesn’t puncture skin


    Break punctures skin


    Bone splinters; smaller pieces are found between 2 larger pieces

    Greenstick (children):

    one side breaks, other side bends


    Bone twists


    Bone fractures at a 90 degree angle


    1 fragment is driven into another


    partial fracture due to repeated stress


    Fracture Repair:

    1.) Blood vessels break and fracture hematoma (clot) forms within 6-8 hours of initial injury

    surrounding bone cells die due to lack of circulation

    2.) New bone tissue (callous) begins forming

    3.) Within 48 hours osteoblasts and osteoclasts form periosteum and bone marrow becomes mitotic.

    4.) Remodeling: dead bone is reabsorbed

    healed fracture line sometimes shows up on X-rays as a thickened area


    Fracture Treatments:


    stabilize bone but much muscle and bone

    loss occurs

    Air casts:

    allow more exercise


    realignes bones

    PEMFs (Pulsating Electromagnetic Fields):

    electrotherapy stimulates osteoblasts


    • Spurs:

      • Thick bumps of surplus calcium

    • Rickets (children):

      • Soft bones, much cartilage

      • Due to Vit. D deficiency, calcium and phosphorus aren’t absorbed well by intestines

      • Treatment: UV Ray exposure, Vit. D, calcium, phosphorus supplements

    • Osteomalacia (adults):

      • Bowed legs, shortened backbone, flattened pelvic bone

      • Due to Vit. D deficiency, bones become demineralized

      • Treatment: same as for rickets

    • Osteomyelitis:

      • Microorganism infection in bone

      • Spreads to bones through bloocstream, fractures, sinus infections, tooth abscess

      • Staphylococcus Aureus: most common infection

      • Treatment: antibiotics, but recovery is prolonged and painful

    • Osteoarthritis:

      • Degeneration of cartilage

      • Bony ends touch and produce friction