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Chapter 6 EDocFind com by 87bn1yX0


									Chapter 6
The Skeletal System
Functions of Bone
• Support and Protection
   • It provides a framework for the body and gives it
   • It supports and protects organs from injury.
• Leverage
   • It provides a place for muscles, tendons,
     ligaments and tendons of the body to attach.
   • It helps make movement possible.
• Storage
   • It stores minerals (Calcium)
• Blood Cell Formation
   • It provides a place for hemotpoeisis
Bone Structure
• Two main types of bone:
   • Cancellous Bone
      • Light and spongy inner layer of bone.
      • Consists of tiny spicules with bone marrow
      • Provides strength but prevents damage.
   • Compact Bone
      • Heavy and dense layer of outer bone
      • Found in shafts of long bones
      • Composed of haversian systems around a
        haversian canal
Bone Structure continued
• Osteocytes- bone cells.
• Periosteum- covering of bone
   • Inner layer contains osteoblasts.
• Endosteum- membrane that lines the
  hollow interior surface of bones.
                  Haversian Systems
• Concentric layers of ossified bone matrix arranged around a
  central Haversian canal
• Layers of ossified bone matrix
Bone Cells
       • Osteoblasts
          • Cells that form bone.
       • Osteocytes
          • Once osteoblasts are trapped
            inside matrix of osseous material.
          • Can revert back to osteoblasts
            (remember this from last chapter?)
       • Osteoclasts
          • Eat bone away.
          • Are the remodelers of bone
          • Withdraw calcium when needed
            from bone
          • Why is this important?
Blood Supply to Bone
• Tiny vessels penetrate the periosteum.
• Volkmann’s canals- tiny channels in the
  bone matrix that vessels pass through.
   • Are at right angles to Haversian canals
     that run lengthwise in the bone.
• Nutrient Foramina- Where large vessels
  enter the bone.
   • Carry blood into and out of bone
   • Can be mistaken for fracture on
  Bone Formation
• Bone is formed in 2 ways:
   • Endochondral Bone formation
   • Intramembranous Bone

• Bone formation and growth is
  stimulated by Growth Hormone
  (GH) from the anterior pituitary
  (adenohypophysis) gland in the
Endochondral Bone Formation
  • Endochondral Bone formation
     • Cartilage bone formation
         • Cartilage first, then bone
     • How most bones develop
     • Start as cartilage rods in long bones in
       diaphysis (shaft).
         • Contains primary growth center
              • Cartilage is removed gradually as
                bone is created and growth center
         • Secondary growth center
              • Develop in epiphysis (ends) of
Growth plates
• Located between diaphysis and epiphysis.
• May be called epiphyseal growth plates.
• Sites of creation of new bone that allows bone to
  lengthen as animal grows.
• Cartilage is created on epiphyseal side while bone
  is created on diaphyseal side.
• When bone reaches full length, all cartilage is
  replaced by bone and plates “Close”.
• Remodeling may take place but bone will not get
  any longer.
• Young animals may have epiphyseal fractures
  because this area is weaker than rest of bone.
• “Growing Pains” in dogs.
• Inflammation of various bone layers
• Seen prevalently in young giant breed
• Basically, body can not keep up as bones
  are growing very quickly.
• Can be confirmed through Radiographs.
• May cause “Shifting Leg Lameness”
• Treated with rest and anti-inflammatories
• Usually occurs in the center of the bone.
Intramembranous Bone
• Occurs only in certain skull bones
• Bone forms in the fibrous membranes that
  cover the brain in fetus.
• Bone forms directly from osteoblasts with
  no cartilage intermediary.
      Bone Shapes
•   Long Bones
•   Short Bones
•   Flat Bones
•   Irregular Bones
Long Bones
    • Longer than they are wide.
    • Has a proximal and distal epiphysis
      consisting of cancellous bone.
    • Main part of bone is diaphysis which
      composed of compact bone.
    • Found in digits and limbs.
Short Bones
• Shaped like cubes.
• Have core of cancellous bone covered by
  compact bone.
• Carpal and tarsal bones.
Flat Bones
• Thin and flat bones
• Consists of two layers of compact bone
  separated by cancellous bone.
• Bones in skull, pelvis, and scapula are
Irregular Bones
          • Miscellaneous bones that
            do not fit into another
          • May have characteristics of
            more than one category.
          • Include vertebrae and
            sesamoid bones.
             • Patella is largest
               sesamoid bone in body.
Bone Marrow
• Fills the spaces within bones
• Has two types:
   • Red bone marrow
         • Hematopoietic tissue forms new blood cells.
         • Majority of bone marrow in young animals
           but less of older animals
   • Yellow bone marrow
         • Consists primarily of adipose connective
         • Common type of marrow in adult animals
         • Does not produce blood cells but can revert
           to red marrow if needed.
Common Bone Features
• Articular Surfaces
   • Joint surfaces where bones come in
     contact with each other to form joints.
   • Consists of:
       • Condyles
       • Head
       • Facet
   • Covered by articular cartilage
       • Composed of what type of cartilage?
• Large, round articular surface.
• Major condyle is located on end of
  humerus and femur.
• Also located in skull.
• Somewhat spherical articular surface on
  the proximal end of a long bone.
• Found on humerus, femur and rib.
• Head is usually joined with rest of bone by
  a neck.
Femoral Head Osteotomy (FHO)
• Head of femur is removed in cases of
  trauma or severe arthritis.
• A “false joint” forms which gives more
  comfort to the patient.
• A flat articular surface.
• Found in carpal and tarsal bones as well
  as in vertebrae, radius and ulna.
• All projections of a bone.
• Heads and condyles are considered to be
• Tendons may attach to processes
Holes and Depressed Areas
• Foramen: A hole in bone.
   • Usually allow the passage of nerve or
     blood vessel.
   • May exist simply to lighten structure
     (pelvis-obturator foramen)
• Fossa: A depressed of sunken area on the
  surface of a bone.
   • Usually occupied by muscles or
Types of Skeletons
• Bones of head and trunk are Axial
• Bones of limbs and appendages are
  Appendicular Skeleton.
• Some animals may have Visceral
  Skeleton- bones formed in the viscera or
  soft organs.
       Axial Skeleton
                        bones of head & trunk
•   Skull
•   Hyoid bone
•   Spinal column
•   Ribs
•   Sternum
• Usually consists of 37 or 38 separate bones
• Most skull bones joined by sutures (fibrous joint)
• Mandible is connected to skull by a synovial joint (TMJ)
External bones:
   Frontal bones (2)
   Occipital bones (1)
   Parietal bones (2)
   Temporal bones (2)
   Incisive (2 )
   Nasal (2)
   Maxillary (2)
   Zygomatic (2)
   Mandible (2)
   Palatine (2)
   Turbinates (2)
Skull Bones Continued
• Categorized by:
   • Bones of Cranium
   • Bones of the ear
   • Bones of the face
Bones of the Cranium
• Cranium-portion of skull that surrounds the
• External Bones of Cranium:
   • Frontal Bones (2)
   • Interparietal Bones (2)
   • Occipital Bone (1)
   • Parietal Bones (2)
   • Temporal Bones (2)
• Internal Bones of Cranium:
   • Ethmoid Bone (1)
   • Sphenoid Bone (1)
External Bones of Cranium
Occipital Bone
• Forms caudoventral portion or base of
  skull, most caudal skull bone.
• Important because:
   • Where spinal cord exits skull
   • Skull bone that articulates with first
     cervical (neck) vertebrae.
• Foramen Magnum is in center of occipital
   • Occipital Condyles are on either side of
     foramen magnum
Interparietal Bones
• Small bones located on dorsal midline
  between occipital and parietal bones
• Clearly visible in young animals, may fuse
  together in older animals.
Parietal Bones
• Form the lateral walls of the cranium
• Well developed in dogs, cats and humans,
  but relatively small in horses and cattle.
    Temporal Bones
•   Located ventral to the Parietal bones
•   Form walls of the cranium
•   Contain middle and inner ear structures
•   Form Temporamandibular Joints (TMJ’s)
    with the mandible (Lower jaw)
          Frontal Bones
• Form forehead region of skull.
• Located rostral to parietal bone.
• Frontal sinus is contained within frontal
• Horns are extension of frontal bone.
Internal Bones of the Cranium
• Sphenoid Bone
   • Forms ventral portion of the cranium and
     contains the pituitary fossa.
       • This contains the pituitary gland.
   • Contains the sphenoidal sinus in most animals.
• Ethmoid Bone
   • Located rostral to sphenoid bone.
   • Contains cribriform plate which has branches of
     olfactory nerve passing through.
   • In horses and humans also have ethmoidal
     sinus in the ethmoid bone.
Bones of the Ear
• Hidden in the middle ear from the outside
   • The Malleus- hammer
   • The incus- anvil
   • The stapes- stirrup

• Function is to transmit vibrations from the
  tympanic membrane (eardrum) to cochlea
  where vibrations are changed into nerve
External Bones of the Face
• Incisive Bones:
   • Also called premaxillary bones
   • In common domestic animals house
     upper incisor teeth. (Ruminants have a
     dental pad instead)
• Nasal Bones:
   • Form the bridge of the nose.
   • Size depends on length of nose of
External Bones of the Face
• Maxillary Bones:
   • Make up upper jaw.
   • House upper canine teeth, premolars
     and molars.
   • Houses maxillary sinuses.
   • Forms hard palate with palatine bones.
• Lacrimal Bones:
   • Form medial portion of the orbit of the
   • Contain lacrimal sac which is part of
     tear system.
External Bones of the Face
• Zygomatic Bones:
   • Also known as the malar bones.
   • Join process from temporal bones to form
     zygomatic arch.
• Mandible:
   • The lower jaw.
   • Houses all lower teeth and is the only moveable
     part of the skull.
   • Forms TMJ with the temporal bone on each
   • Unite at mandibular symphysis at rostral end.
   • Composed of shaft (horizontal portion) and
     ramus (vertical portion).
Internal Bones of the Face
• Palatine Bones:
   • Make up part of hard palate
• Pterygoid Bones:
   • Support part of the lateral walls of the pharynx
• Vomer Bone:
   • Forms part of nasal septum (wall between left
     and right nasal passages).
• Turbinates:
   • Also called nasal conchae.
   • Thin and scroll-like that fill most of nasal cavity
Hyoid Bone
• Also called hyoid apparatus.
• Supports base of tongue, the pharynx, and
  the larynx and assists in swallowing.
• Composed of several parts that are united
  by cartilage.
                Spinal Column
•   Also called the vertebral column
•   Made up of vertebrae that extends from skull to tip of tail.
•   Vertebrae are divided into 5 portions:
     • Cervical (neck)
          • Abbreviated C
          • Contain 7 vertebrae in dogs and cats
     • Thoracic (chest)
          • Abbreviated T
          • Contain 13 vertebrae in dogs and cats
     • Lumbar (abdomen)
          • Abbreviated L.
          • Contain 7 vertebrae in dogs and cats.
     • Sacral (pelvis)
          • Abbreviated S.
          • Contain 3 vertebrae in dogs and cats.
     • Coccygeal (tail)
          • Abbreviated Cy.
          • Number is variable.

•   Refer to vertebrae by letter designation and number designation.
Vertebrae Characteristics
•   Consists of:
     • Body
          • The main, ventral portion of the bone.
          • Separated from other vertebrae by intervertebral disks
            of cartilage.
               • What type of cartilage makes this up?
     • Arch (neural arch)
          • Arch helps to make up vertebral foramen which allows
            passage of the spinal cord.
     • Processes
          • Transverse Processes
               • Laterally projecting
               • Site of muscle attachement.
          • Articular Processes
               • Found on cranial and caudal ends of vertebrae,
                 help to join adjacent vertebrae.
          • Spinous Processes
               • Single and projects dorsally
Intervetebral Disk Disease (IVDD)
• When disks “slip”
• More predominant in long-backed breeds
  (dachsunds, Bassets).
• Can confirm with radiographs.
• Usually once it occurs, animal is
• Curative procedure is surgery to fuse
  spinal column together.
• Animals may become paralyzed (dragging
  rear legs).
Cervical Vertebrae
   • Atlas is C1
      • Holds up head.
      • Has “wings of the
      • Has no vertebral
        body, just is a ring
        which spinal cord
        passes through.
   • Axis is C2
      • Has large spinous
Thoracic Vertebrae
• Have tall spinous processes.
• Have articular facets which communicate
  with the ribs.
Lumbar Vertebrae
• Dorsal to abdominal region.
• Most massive-looking bones in spinal
Sacral Vertebrae
• Fuse together to form one single, solid
• Called the sacrum.
• Joins pelvis via sacroiliac joint.
Coccygeal Vertebrae
• Bones of the tail.
• Appearance changes as bones progress
  down the tail.
• In humans fuse into coccyx.
• Flat bones that form the lateral walls of the
• Usually rib number is equal to the number
  of thoracic vertebrae.
• Have more of a moveable joints which is
  allows lungs to expand.
• Term for rib is costal.
• Sternal ribs attach to sternum
• Asternal ribs make up caudal part of
• Unattached ribs are called floating ribs.
•   Breastbone
•   Made up of sternebrae.
•   Most cranial sternebrae is manubrium
•   Most caudal sternebrae is called xiphoid
     • May be broken during CPR.
           Appendicular Skeleton
•   Made up of bones of limbs.
     • Thoracic limbs (front leg)
         • Scapula
         • Humerus
         • Radius
         • Ulna
         • Carpal bones
         • Metacarpal bones
         • Phalanges
     • Pelvic Limbs (back leg)
         • Pelvis
              • Ilium
              • Ischium
              • pubis
         • Femur
         • Tibia
         • Fibula
         • Tarsal bones
         • Metatarsal bones
         • Phalanges
Appendicular Skeleton (limb bones)

      Thoracic Limb
      •   Scapula
      •   Humerus
      •   Radius
      •   Ulna
      •   Carpal bones (carpus)
      •   Metacarpal bones
      • Phalanges
• Most proximal bone of the thoracic limb.
• Flat and triangular.
• Has prominent ridge on lateral surface
  referred to as “spine of the scapula”
• Glenoid cavity at distal end forms portion
  of ball and socket shoulder joint.
• Long bone of upper arm (brachium)
• Has head at proximal end with tubercles
  (processes) where muscles attach.
• Condyle at distal end is composed of
  trochlea, capitulum, medial and lateral
  epicondyles, and olecranon fossa.
• Is not “funny bone” (actually is a nerve not
  a bone).
• One of two bones that form antebrachium
• Forms major portion of elbow joint with
  distal end of the humerus.
• Has large olecranon process at proximal
  end which forms the point of the elbow.
   • Trochlear notch makes elbow tight.
   • End of trochlear notch forms anconeal
• Where triceps brachii muscle attaches.
• Coronoid process articulates with the
• Main weight bearing bone of the
• Articulates with humerus and ulna.
• Styloid process articulates with carpus.
Carpal Bones
     • Carpus has two rows of bones.
     • Is the “wrist” of the animals
     • Proximal row bones have names
       (radial carpal bone, ulnar carpal
       bone, accessory carpal bone)
     • Distal row bones numbered
       medial to lateral (1st carpal, 2nd
       carpal, etc)
Metacarpal Bones
• Extend distally from distal row of carpal
  bones to proximal phalanges of the digits.
• Numbered from medial to lateral (dewclaw
  being number 1 in dogs and cats).
• Horses have one large metacarpal bone
  (cannon bone) and two non-weight
  bearing splint bones.
• Cattle have fused metacarpal bones with
  sesamoid bones (proximal and distal).
• Each digit is made up of two or three
  phalanges (single bones are phalanx)
• In horses phalanges are the long and short
  pastern bone and coffin bone.
• Also have 2 proximal and 1 distal
  (navicular bone) sesamoid bones.
• Dogs and cats have a ungual process that
  surrounds the claw.
Appendicular Skeleton- Hind Limb
  •   Connected to the axial skeleton at sacroiliac joint

  Pelvic Limb:
  • Pelvis
       • Ilium
       • Pubis
       • Ischium
  •   Femur
  •   Tibia
  •   Fibula
  •   Tarsal bones (tarsus)
  •   Metatarsal bones
  •   Phalanges
• May be referred to as the os coxae
• Develops as three separate bones on each side
  that fuse into a solid structure.
• Joined at pelvic symphysis.
• Bones are:
   • Ilium
        • Cranial most bone of pelvis
        • “Wings of the ilium” or hips.
   • Ischium
        • Most caudal pelvic bone
        • Tailbone is ischial tuberosity.
   • Pubis
        • Smallest of the pelvic bones
Pelvic landmarks
• Acetabulum- portion of hip bone that forms
  ball and socket joint with femur.
   • We look at this area in cases of hip
• Obturator foramen- large holes in pelvis
  that help to lighten weight of pelvis.
   • We look at this as landmark if
     radiograph is straight or not.
 • Long Bone of thigh
 • Proximal end is the ball portion is called
 • Proximal end also contains the
   trochanters where muscles attach.
 • Distal end forms stifle joint (knee) with
• Kneecap is largest sesamoid bone in the body.
• Formed in the distal tendon of the quadriceps
  femoris muscle on the cranial aspect of the stifle
• Helps to protect tendon as it passes down over
  the trochlea of the femur.
Patellar Luxation
• When trochlear groove is not deep enough
  to contain patella so it slips in and out of
• Usually will cause brief episodes of
  lameness which can correct.
• May hear or feel “popping” in and out of
• Found in small, toy breeds most
• Can be surgically corrected.
• Two small sesamoid bones located in the
  proximal gastrocnemius or calf muscles.
• Not present in cattle or horses.
• Main weight bearing bone of the lower leg
• Forms stifle joint with femur.
• Forms hock (ankle) with tarsus.
• Medial malleolus- medial to distal articular
  surface, knob of ankle.
• Tibial tuberosity of proximal end forms the
  tibial crest.
   • Where patellar tendon attaches.
• Thin but complete bone in dogs and cats.
• Consists of proximal extremity, shaft, and
  distal extremity.
• Serves as a muscle attachment site.
• Horses and cattle do not have shaft of
• Forms lateral malleolus at distal end.
Tarsal Bones
• Ankle but in four legged animals is termed
  the “hock”
• Consists of two rows of tarsal bones
  (similar to carpal bones in wrist).
• Proximal row is named and distal row is
• Contains calacaneal tuberosity which
  forms the point of the hock. Site of
  attachment for tendon of the
  gastrocnemius muscle.
Metatarsal Bones
     • Dogs and cats: four
       metatarsal bones (II to V)
     • Horses: 1 large metatarsal
       bone (cannon bone) and 2
       small metatarsal bones
       (splint bones)
                        Pelvic Limb Phalanges
• Similar to thoracic limb phalanges
• Exceptions: dogs and cats
   • Usually only 4 digits (II to V)
   Visceral Skeleton
• Bones that form in organs
• Examples
   • os cordis: in heart of cattle and sheep
   • os penis: in penis of dogs, beaver, raccoons, and walruses
   • os rostri: in nose of swine
•   Junctions between bones
•   Can be moveable or immovable.
•   Arthro and articular refer to joints.
•   3 Types of joints:
     • Fibrous Joints (synarthroses)
         • Immovable
         • Found in sutures of skull bones
     • Cartilaginous Joints (amphiarthroses)
         • Slightly moveable
         • Vertebral disks between vertebrae
         • Pelvic and mandibular symphisis
     • Synovial Joints (diarthroses)
         • Freely moveable
Characteristics of Synovial Joints
  • Have Articular surfaces on bones
      • Articular cartilag covering articular
  • Fluid-filled joint cavity
  • Enclosed by a joint capsule
      • Synovial membrane- outer
          • Synovial fluid- lubricates joint
  • Ligaments - fibrous Connective tissue
    that join bones to other bones.
Synovial Joint Movements
• Flexion and Extension
   • Opposite movements
   • Increase (extension) or decrease (flexion) angle
      between two bones
• Adduction and Abduction
   • Opposite movements
   • Move an extremity toward (Adduction) or away
      from (Abduction) medial plane
• Rotation
   • Twisting movement of a part on its own axis
• Circumduction
   • Movement of an extremity so that the distal end
      moves in a circle
Types of Synovial Joints
•   Hinge Joints
     • One joint surface swivels around another
     • Only capable of flexion and extension
•   Gliding Joints
     • Rocking motion of one joint surface on another
     • Primarily capable of flexion and extension
     • Abduction and adduction possible in humans
       not dogs/cats
•   Pivot Joints
     • One bone pivots (rotates) on another
     • Only capable of rotation
•   Ball-and-socket joints
     • Allow for all joint movements

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