Bone structure and Axial Skeleton Flashcards by Liz Dywiak

What is the only substance harder than bone?

Enamel

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Functions of bone?

Support, protection, leverage, storage, blood cell formation

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o Hormone from thyroid gland
o Prevents hypercalcemia – too high a level of calcium in the blood

Calcitonin

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o Hormone that prevents hypocalcemia – too low a level of calcium in the blood

Parathyroid hormone

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Serve as a site for blood cell formation

Hematopoiesis

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Tiny, tightly compacted cylinders of bone
Runs lengthwise to the bone
Multilayered (laminated) cylinder composed of concentric layers of ossified bone matrix
Like rings on a tree
Osteocytes are located on the junctions between layers of bone

Haversian systems

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 Surround by Haversian systems
 Contains blood vessels, lymph nodes and nerves that supply osteocytes

Haversian canal

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 Tiny channels through the bone
 Allow osteocytes to contact each other and exchange nutrients
 Like slots in the jail cell doors

Canaliculi

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 Hard intercellular substance where a sparse population of cells are embedded

Matrix

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 Areas in the ossified matrix where osteoblasts become trapped

Lacunae

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Membrane that covers the outer surface of bones
Outer layer
o Composed of fibrous tissue
Inner layer
o Contains osteoblasts
 Enables bones to increase in diameter
 Involved in the healing of bone fractures

Periosteum

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Membrane that lines the hollow interior surfaces of bones
Contains osteoblasts

Endosteum

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 The cells that form bone
 Secrete the matrix of bone and then supply the minerals necessary to harden it

Osteoblasts

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 Osteoblasts trapped in the ossified matrix
 Always ready to revert to their former lives as osteoblasts and form new bone if an injury makes that necessary

Osteocytes

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 Necessary for remodeling to take place by removing bone from where it is not needed
 Allow the body to withdraw calcium from the bones when it is needed to raise the calcium level in the blood

Osteoclasts

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 Large channels where large blood vessels, lymph vessels and nerves enter the bone marrow by many large bones, especially long bones
 Location is fairly predictable
 On xray, can resemble a crack type fracture of the bone cortex

o Nutrient foramina

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 Tiny channels in the bone matrix that vessels pass through
 Come in at right angels to the long axis of the hone and at right angels to the Haversian canals

o Volkmann’s canals

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 Most bone develops this way
 Bone grows into and replaces a cartilage model
 Body first creates a cartilage “template” that is replaced by bone

o Endochondral or cartilage bone formation

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o Primary growth center (fetal growth)
o Shaft of bone

Diaphysis

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o Secondary growth center
o Ends of bone

Epiphysis

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o Located between the shaft (diaphysis) of the bone and the ends (epiphysis)
o Sites where the creation of new bone allows the long bones to lengthen
o Cartilage cells create new cartilage on the outside (epiphyseal surface) of the plate
o Osteoblasts replace the cartilage on the inside (diaphyseal surface)
o When the bone has reached its full size, the epiphyseal plates completely ossify (all of the cartilage is replaced by bone)

Physis (epiphyseal growth plates or growth plates)

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o Flared transition of bone from physis (growth plates) to diaphysis

Metaphysis

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 Bone develops from fibrous tissue membranes
 Occur only in certain skull bones
 Creates flat bones of the cranium

o Intramembranous membrane bone formation

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 Longer than they are wide
 Most bones of the limbs
 Proximal epiphysis and distal epiphysis

Long bones

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 Shaped like cubes or marshmallows  Spongy bone covered by a thin layer of compact bone  Carpal and tarsal bones

Short bones

 Relatively thin and flat  Two thin plates of compact bone separated by a layer of cancellous bone  Skull bones and scapula

Flat bones

 Miscellaneous category * Do not fit into long, short or flat categories   Vertebrae, oddly shaped skull bones, sesamoid bones * Patella is the largest sesamoid bone

Irregular bones

 Hematopoietic tissue (blood – formation) * Forms blood cells  Majority of bone marrow for young animals, only a small portion of marrow in older animals

Red bone marrow

 Consists primarily of adipose connective tissue  Most common type in adult animals  Does not produce blood cells but it can revert to red bone marrow if the body needs

Yellow bone marrow

* Joint surfaces, smooth areas of compact bone where bones come in contact with each other to form joints

 Articular surfaces

o A smooth, thin layer of hyaline cartilage that covers each articular cartilage

* Articular cartilage

Three types of articular surfaces?

Condyle, head and facet

 Usually large and round articular surface  Located on the distal end of the humerus and femur as well as the occipital bone of the skull

o Condyle

 Somewhat spherical articular surface  Proximal end of the humerus, femur and ribs  Ball and socket shoulder and hips joints

Head

 Flat articular surface  Carpal and tarsal bones, vertebrae, long bones of radius and ulna

Facet

* Projections on a bone where tendons attach * Includes all the lumps, bumps and other projections on a bone * The larger the feature, the more powerful the muscular pull on the area of the bone

Processes

o Hole in the bone, usually for something important like a nerve or blood vessels

Foramen

o Depressed or sunken area on the surface of the bone o Usually occupied by muscles or tendons

Fossa

* Most complex part of the skeleton * Most domestic animals 37 or 38 separate bones

Skull

o Jagged, immoveable, fibrous joints that unite most skull bones

Sutures

o Only the mandible (lower jaw) is connected to the rest of the skull with this free moving joint

Synovial joint in skull

o Portion of the skull that surrounds the brain o 11 bones

Cranium

* Single bone that forms the caudoventral portion or base of the skull

Occipital bone

o Large hole in the center of the occipital bone where spinal cord exits the skull

* Foreman magnum

o On either side of the foreman magnum, articular surfaces that join with the first cervical vertebra called the atlas (atlantooccipital joint)

* Occipital condyles

External bones are also called?

Landmarks

* Two small bones located dorsal midline between the occipital bone and the parietal bones * Visible in young animals * In older animals they may fuse together into one bone or they may fuse to the parietal bones and become indistinguishable

Interparietal bones

* Two bones that form the dorsolateral walls of the cranium * Large and well developed in dogs, cats and humans * Relatively small in horses and cattle

Parietal bones

* Two bones located below (ventral) to the parietal bones * Form the lateral walls of the cranium * Contains the middle and inner ear structures

Temporal bones

o Formed by skull bones, joint between the mandible and the cranium

* Poromandibular joints (TMJs)

o The only ear structure that is visible from the outside o Bony canal that leads into the middle and inner ear cavities

* External acoustic meatus

* Form the forehead region of the skull * Form the rostrolateral portion of the cranium and a portion of the orbit o Concave socket that holds the eye

Frontal bones

o In horned breeds of cattle, the cornual process of the frontal bone is the horn core around which the horn develops o Process is hollow and communicates with the frontal sinus

* Frontal sinus (paranasal sinus)

Another name for internal bones?

Hidden bones

* Single bone forms the ventral part (bottom) of the cranium * Pituitary fossa o Houses the pituitary gland * Just rostral to the occipital bone * Look like a bat with its wings and legs expanded

 Sphenoid bone

* Single bone located just rostral to (in front of) the sphenoid bone * Cribriform plate o Where many branches of the olfactory (sense of smell) nerve pass from the upper portion of the nasal cavity to the olfactory bulbs of the brain

 Ethmoid bone

 Group of three ear bones, hidden in middle ear

Ossicles

What are the three bones in the ear?

Malleus, incus and stapes

o The bones in the ear transmit vibrations from what, across the middle ear cavity to an inner ear structure called the what?

tympanic membrane (ear drum) and cochlea

 In the cochlea, receptor cells for hearing convert the vibrations to nerve impulses that are interpreted by what as sound

The brain

* Two bones that are the most rostral * Sometimes called the premaxillary bones * House the upper incisor teeth

Incisive bones

* Two bones form the bridge of the nose * Doral or upper part of the nasal cavity

Nasal bones

Long faced animals

o Dolichocephalic

Short faced animals

o Brachycephalic

* Two bones make up most of the upper jaw * House the upper canine teeth and all upper cheek teeth (premolars and molars * Form the hard pallet (roof of the mouth)

Maxillary bones

* Two smalls bones that form part of the medial portion of the orbit of the eye * Houses the part of the tear drainage system of the eye

 Lacrimal bones

* Two bones known as the malar bones * Form a portion of the orbit of the eye and join with a process from the temporal bones to form the _____ arches

 Zygomatic bones

Easily palpable, o Bony landmarks below and behind the eyes

zygomatic arches

* Lower jaw * Houses all the lower teeth * Is the only moveable skull bone * Forms the TMJ with the temporal bone

Mandible

o Cartilaginous joint where the two sides of the mandible are separated at their rostral (front) ends

* Mandibular symphysis

o Horizontal portion of the mandible that houses all of the teeth

Shaft of the mandible

vertical portion of mandible

Ramus of the mandible

* Two bones that make up the caudal portion of the hard pallet (roof of mouth)

Palatine bones

* Two small bones that support part of the lateral walls of the pharynx (throat)

 Pterygoid bones

* Single bone located on the midline of the skull and forms part of the nasal septum

Vomer bone

central “wall” between the left and right nasal passages

Nasal septum

* Four thin, scroll like bones that fill most of the space in the nasal cavity * Each side has a dorsal and ventral turbinate, covered by the moist, very vascular soft tissue lining * Force in air inhaled by the nose o Helps warm, humidify and trap any tiny particles in air

 Turbinates (nasal conchae)

* U shaped structure * Supports the base of the tongue, the pharynx and the larynx – helps the animal swallow * Composed of several individual portions united by cartilage * Attached to the temporal bone by two small rods of cartilage

Hypoid bone (hypoid apparatus)

o A series of individual irregular bones that make up the spinal column o Extend from the skull to the tip of the tail o Consists of a body, an arch (neural arch) and a group of processes

* Vertebrae (singular, vertebra)

* Separates the bodies of adjacent vertebrae

 Intervertebral discs (body)

* Long flexible tunnel formed when all arches of all the vertebrae line up * Houses and protects the spinal cord

Spinal canal (arches)

o Single, dorsally projecting process

* Spinous process

o Two laterally projecting processes, vary in size among vertebrae

* Transverse process

o Process located on the cranial and caudal ends of the vertebral arches  Help form the joints between adjacent vertebrae

* Articular process

Cranial portion of verterbrea

Cervical (neck) verterbrea

C1, “holds up” the head

Atlas

C2 vertibrea

Axis

 Located dorsal to the thorax  Numbers vary among species and can even vary within a species  Same number as pairs of ribs  Tall, spinous processes and their lateral articular facets form joints with the heads of the ribs

Thoracic (chest) verterbrea

 Dorsal to the abdomen region  Number varies amount species and within a species  Most massive looking bones in the spinal column * Bodies are large and bulky to support all of the weight from abdominal organs

o Lumbar (abdomen) verterbrea

 Fused to form a single, solid structure * Number of vertebrae fused varies among species * Located dorsal to the pelvis region

o Sacral (pelvis) verterbrea

 Joint between sacrum and the pelvis on each side

o Sacroiliac joint

 Bones of the tail  Number varies greatly between species and within species  Appearance varies, even within an individual animal

o Coccygeal (tail) vertebrea

* The single bone in humans formed from fused coccygeal vertebrae

 Coccyx (tailbone)

* Flat bones that form the lateral walls of the thorax * Number of pairs of ribs equals the number of thoracic vertebrae * At their dorsal ends, the heads of ribs form joints with the thoracic vertebrae o Help the process of ventilation * Ventral ends are more variable

Ribs

End of rib made of bone

Dorsal

End of rib made of cartilage

Ventral

o Cartilage part of rib

Costal cartilage

o Junction between the costal cartilage and the bony part of the rib

* Costochondral junction

o Ribs whose cartilages join the sternum

* Sternal ribs

o Ribs that join the costal cartilage

* Asternal ribs

o Unattached ribs at bottom of rib cage

* Floating ribs

* Forms the floor of the thorax

 Sternum (breastbone)

o Series of rodlike bones that make up the sternum

* Sternebrae

 First, most cranial sternebrae

o Manubrium (manubrium sterni)

 Last, most caudal sternebrae

o Xiphoid (xiphoid process)

* Extends caudally from the xiphoid process

 Xiphoid cartilage