Bone structure and Axial Skeleton Flashcards
What is the only substance harder than bone?
Enamel
Functions of bone?
Support, protection, leverage, storage, blood cell formation
o Hormone from thyroid gland
o Prevents hypercalcemia – too high a level of calcium in the blood
- Calcitonin
o Hormone that prevents hypocalcemia – too low a level of calcium in the blood
- Parathyroid hormone
- Serve as a site for blood cell formation
Hematopoiesis
- 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
Surround by Haversian systems
Contains blood vessels, lymph nodes and nerves that supply osteocytes
Haversian canal
Tiny channels through the bone
Allow osteocytes to contact each other and exchange nutrients
Like slots in the jail cell doors
Canaliculi
Hard intercellular substance where a sparse population of cells are embedded
Matrix
Areas in the ossified matrix where osteoblasts become trapped
Lacunae
- 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
- Membrane that lines the hollow interior surfaces of bones
- Contains osteoblasts
Endosteum
The cells that form bone
Secrete the matrix of bone and then supply the minerals necessary to harden it
Osteoblasts
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
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
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
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
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
o Primary growth center (fetal growth)
o Shaft of bone
Diaphysis
o Secondary growth center
o Ends of bone
Epiphysis
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)
o Flared transition of bone from physis (growth plates) to diaphysis
Metaphysis
Bone develops from fibrous tissue membranes
Occur only in certain skull bones
Creates flat bones of the cranium
o Intramembranous membrane bone formation
Longer than they are wide
Most bones of the limbs
Proximal epiphysis and distal epiphysis
Long bones
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
