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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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Skeletal System

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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