VT 111 Lec. 6 Skeletal System: General & Axial Skeleton

Divisions of the Skeleton

Axial skeleton:

• Skull

• Ribs

• Vertebral column

Appendicular skeleton:

• Pelvic girdle

• Pectoral girdle

• Appendages

About Bone

• Osseous connective tissue

  • Most rigid type

  • Well vascularized

    • Haversian canal

• Osteoblasts

  • Make bone by secreting matrix and then hardening it via ossification

• Osteocytes

  • Osteoblasts that are trapped in ossified matrix

  • Can revert to osteoblasts if repair needed

• Osteoclasts

  • Break down bone; reshape and remodel

Bone: Functions

• Support

• Protection

• Movement/leverage

• Storage

  • Minerals (Ca++)

• Hematopoiesis

  • Blood cell formation

Bone Type Classification: Cancellous Bone

• Light, spongy

• Many spaces between spicules of bone

  • Occupied by bone marrow

Bone Type Classification: Compact Bone

• Heavy, dense

• Shafts of long bones and outside layer of all bones

• Haversian systems (osteon)

  • Tightly compacted cylinders of bone surrounding Haversian canal (where blood vessels run)

    • Run lengthwise to bone

Cancellous vs Compact

Bone Structure

• Periosteum: membrane covers the outer surfaces of bones

  • Outer layer – fibrous tissue

  • Inner layer – osteoblasts

• Endosteum: membrane lines hollow interior surfaces

Bone Marrow

• Red bone marrow

  • Hematopoietic

    • Forms blood cells

    • Large amounts in young animals

• Yellow bone marrow

  • Adipose connective tissue

    • Large amount in adult marrow

      • Can revert to red bone marrow if animal becomes anemic

Brown Growth (Osteogenesis)

• Bone formation starts in utero

• Bone development continues throughout adulthood

  • Repair

  • Remodeling

• Two types of ossification:

  • Intramembranous—forms from fibrous tissue membranes that cover brain in developing fetus

  • Endochondral—grows from a cartilage template

Endochondral Bone Formation

• New bone develops along epiphyseal plates of cartilage located between shaft and ends of bones

• Allows long bones to lengthen

• Cartilage cells create new cartilage on epiphyseal surface of the plate

• Osteoblasts replace cartilage with bone on diaphyseal surface

• When bone is full size the epiphyseal plates ossify

Bone Shapes

• Long

  • Longer than they are wide

  • Most limb bones

  • Have Diaphysis is the main part of long bones

• Short

  • Shaped like small cubes

  • Examples include carpal and tarsal bones

• Flat

  • Relatively thin and flat

  • Many skull bones, scapulae, and pelvic bones are flat

• Irregular

  • Miscellaneous category

  • All bones that don’t fit other categories

  • Examples include vertebrae, some skull bones, and sesamoid bones

Forces Placed Upon Bones

• Compression: force placed on bone along the long axis of the shaft toward an object

• Tension/distraction: force that tends to pull the ends of bone apart along the long axis

• Torsion: twisting force on bone

• Shearing: parallel forces in opposite direction, usually perpendicular to the long axis of a bone

Fracture Types: Complete Fracture

• Transverse: fracture line transverse to long axis

• Oblique: fracture line oblique to long axis

• Spiral: torsional forces fracture bone; spirals along long axis; edges of fracture are very sharp

• Comminuted: fragmented into 3 or more pieces; fracture lines interconnect

• Multiple: 3 or more fracture fragments, but the lines do not connect

• Impacted: bone ends are forced into each other

  • Compression: cancellous bone (vertebrae) is crushed

Fracture Types: Incomplete Fracture

• Greenstick: incomplete break

• Fissure: crack on long or flat bone as a result of direct pressure

• Depression: bone is depressed inward; multiple fissures lines intersect

Fracture Type: Simple/Closed

• No skin penetration of bone

Fracture Type: Compound/Open

• Bone broken ends protrude through skin

Epiphyseal Plate Fractures

• Immature animals

• Salter-Harris classification

Fracture Repair

2. Osteoblasts gradually bridge fracture gap

3. Mineralization

4. To return bone to original size and shape

Axial & Appendicular Skeletons

Bone Terminology

• Holes

  • Foramen

    • Plural foramina

• Sunken area

  • Fossa

• Groove

  • sulcus

• Flat articular surface

  • Facet

Bone Processes

• Any and all projections on bones

  • Head

  • Condyle

    • Epicondyle

  • Process

  • Trochanter

  • Spine

  • Crest

  • Wing

  • Trochlea

Condyle vs Epicondyle

• Condyle:

  • a rounded protuberance at the end of some bones

  • forms an articulation with another bone

  • smooth surface

• Epicondyle:

  • a protuberance above or on the condyle of a long bone

  • site for attachment of muscles

  • rough surface

Tuberosity vs Tubercle

• Tuberosity: a large prominence on a bone usually serving for the attachment of muscles or ligaments

• Tubercle: a small rounded projection or protuberance, especially on a bone 

Components of the Axial Skeleton

• Axial: bones of head and trunk

  • Skull

    • Cranial and Facial

    • Mandible

  • Spinal column

    • Cervical

    • Thoracic

    • Lumbar

    • Sacrum

    • Caudal

  • Ribs

  • Sternum

Skull

• ~38 bones united by sutures which are immovable, fibrous joints

• The mandible is connected to the skull by a freely movable synovial joint

• Temporomandibular joint (TMJ)

• Skull is divided into regions: cranial, facial, ear

Cranial Bones: External

• Occipital (1)

• Interparietal (2)

• Parietal (2)

• Temporal (2)

• Frontal (2)

External Skull

• Occipital

  • Base of skull

  • Most caudal

  • Where spinal cord exits

    • Foramen magnum

  • Forms a joint with C1

    • Occipital condyles articulate with atlas(C1)

• Interparietal

  • Dorsal midline between occipital and parietal

  • May fuse with age

• Parietal

  • Forms dorsolateral walls of cranium

    • Small in horses/cattle

External Skull Continued…

• Temporal

  • Form lateral walls of cranium

  • Contain middle and inner ear structures

    • External acoustic meatus

  • Forms temporomandibular joint (TMJ) with mandible

• Frontal

  • Forehead region

  • In front of parietal bones

  • Concave portion of orbit

  • Contain frontal sinus

  • Horned animals – cornual process

    • Horn core; communicates with frontal sinus

Skull: Internal View

• Ethmoid (1)

  • Separates nasal cavity from brain

  • Forms part of medial orbit wall

  • Cribriform plate

    • Passage of olfactory nerve branches

• Sphenoid (1)

  • Bottom of cranium rostral to occipital bone

  • Bat shaped

  • Has pituitary fossa

    • Sella turcica

  • What lives here???

Difference Among Species

Horse

Facial Bones: External

• Incisive (2)

• Nasal (2)

• Maxillary (2)

• Lacrimal (2)

• Zygomatic (2)

• Mandible (1)

External Facial Bones

• Incisive

  • AKA premaxillary

    • Most rostral

    • House upper teeth

      • Exceptions → ruminants

• Nasal

  • Bridge of nose (dorsal nasal cavity)

  • Shape depends upon length of face

    • Dolichocephalic vs. brachycephalic

External Facial Bones Continued…

• Maxillary

  • Upper jaw (with incisive)

  • Upper canines, PM’s and M’s

  • Maxillary sinuses

  • Hard palate (separates mouth and nasal cavity)

  • Infraorbital foramen

• Lacrimal

  • Medial portion of orbit

• Zygomatic

  • Forms portion of orbit

  • Join with portion of temporal bone process to make zygomatic arch

Internal Facial Bones

• Palatine (2)

  • Caudal portion of hard palate

• Pterygoid (2)

  • Support lateral pharynx

• Vomer (1)

  • Midline

  • Forms part of nasal septum

• (Ethmo)turbinates (4)

  • AKA nasal turbinate or conchae

  • Thin, scroll-like bones that fill nasal cavity

  • Covered in nasal epithelium

    • Cleans, humidifies and warms air before lungs

Clinically Important Areas of the Face

• Carnassial tooth abscesses

• Zygomatic arch fractures

• Fractured maxillae

• Fractured mandibles

• Separation of mandibular symphysis

  • Mandibular symphysial fracture

Mandible

• Houses all lower teeth

• Only movable skull bone

• Forms TMJ with temporal bone on each side

• 2 sides fused at mandibular symphysis at rostral end

  • Joint is cartilaginous: amphiarthrosis

  • Dogs, cats, cattle

• Ramus is site of jaw muscle attachment

Hyped Bone

• AKA hyoid apparatus

• Located just above larynx

• Made up of several small bones untied by cartilage

• Supports base of tongue, pharynx and larynx

  • Aids in swallowing

• Attached to temporal bone

Spinal Cord: Vertebrae

• Vertebral formulae of dog

  • Cervical 7

  • Thoracic 13

  • Lumbar 7

  • Sacral 3

  • Coccygeal - varies; tail length

Cervical, Thoracic & Lumbar

Cervical

• Constant number among mammalian species (7)

• C1 = atlas

  • articulates with occipital condyles

  • wings, but no vertebral body

• C2 = axis

  • dens

Cervical Continued…

Thoracic

• Tall spinous processes

• Lateral articular facets

  • Form joints with head of ribs

• Number varies among species

Lumbar

• Large and bulky

  • Support weight of abdominal organs and structures

• Number varies by species

Sacrum

• Fused vertebrae

• Solid platform to connect to ilium

• Sacral foramina

  • passage of nerves

• Sacroiliac joint

  • articulation between sacrum and pelvis

  • Fibrocartilaginous

• Most species number 3-5 (fused vertebrae)

Sacroiliac Joint

Coccygeal/Caudal

• Tail

• Number varies among and within species

Ribs (Costals)

• 13 ribs in dog

  • 13th rib is floating

• Form walls of thorax

• Heads form joints with thoracic vertebrae

  • Freely movable – allow expansion of chest wall

• Dorsal part

  • Bone

• Ventral part

  • Costal cartilage

• Dorsal and ventral part joined by costochondral junctions

• Ends of costal cartilage attach to sternum, adjacent costal cartilage (asternal ribs) or nothing (floating ribs)

Ribs

Sternum

• AKA breastbone

• Forms floor of thorax

• Formed of sternebrae

  • 1st: manubrium

  • Last: xiphoid process

    • Has extension of cartilage - xiphoid cartilage