VET 120 Skeletal System

The skeleton is…

The framework of bones that supports & protects the soft tissues of the body

Medical term for bone

Os/osteo-

What is the hardest natural substance in the body? What is the second?

1st = tooth enamel, 2nd = bone

Describe bones

> Vital, living tissue with an excellent capacity to repair itself after injury
> Composed of cells embedded in matrix

Matrix

> Intracellular substance that surrounds bone cells, providing structure & strength, & forms most of the mass of bones
> Composed of collagen fibers in a gelatin-like substance composed of protein & polysaccharides

Osteoblasts

Cells that form bones by secreting matrix

Osteocytes

> Aka bone cells
> Mature osteoblasts trapped within the bone

Osteoclasts

> Cells that remove & remodel bone
> Are also involved in withdrawing calcium from the bone storage to raise levels in the bloodstream

Ossification

Hardening of the matrix when calcium & phosphate infiltrate the matrix, forming hydroxyapatite crystals

Process of bone formation

> Osteoblasts secrete a soft flexible matrix
> Osteoblasts harden through ossification
> As they create areas of bone, the osteoblasts become trapped in the lacunae
> Once this process is complete, osteoblasts develop into osteocytes

What gives bone its characteristic hardness?

Hydroxyapatite crystals

Lacunae

Spaces within the matrix

Canaliculi

Thread-like channels in the bone that provide osteocytes communication & blood supply

Functions of bones

Support, protection, leverage, storage, & hematopoiesis

Bone support function

The scaffolding for the other body tissues

Bone protection function

Surround delicate tissues; eg. the skull protects the brain, eyes, & ears

Bone leverage function

In conjunction with muscles, allows for body movement

Bone storage function

Calcium storage with quick access by the body to keep calcium levels in the bloodstream normal

Clinical relevance of calcium storage in the body

Improper calcium levels can cause eclampsia or calcinosis cutis

Bone blood cell formation function

Blood cells are produced within the bone marrow of some bones

Cancellous bone

> Spongy, consisting of many tiny spicules, with bone marrow occupying the space between spicules
> Keeps bones lightweight, yet very strong

Compact bone

> Aka cortical bone
> Heavy, dense outer layer of all bones composed of tightly compacted cylinders of bone with small Haversian canals

Haversian canals

Small channels within compact bone, running parallel to the bone, that supply blood vessels, nerves, & lymph to the bone cells

Articular surface

Aspect of bone that touch other bones, smooth areas of compact bone covered by a thin layer of hyaline cartilage (articular cartilage)

Periosteium

> Membrane covering all bone except the articular surface
> The outer layer is fibrous & the inner layer contains osteoblasts to allow bones to increase in diameter

Endosteum

Membrane lining the hollow interior surface of bones, also contains osteoblasts

Volkmann’s canals

Small channels within compact bone that run perpendicular & join up with Haversian canals to form a blood supply to the bone cells

Nutrient foramina

> Large channels in large bones that supply the bone marrow with blood vessels, lymph vessels, & nerves
> Can be mistaken for bone fractures on radiographs

Endochondral bone formation

> The body first creates a cartilage template that is subsequently replaced by bone
> Bone gradually replaces cartilage & the epiphyses develop
> When the animal reaches full size, the growth plates ossify & bone growth is halted

Epiphyseal plates

Growth plates between the diaphysis & epiphysis that allow the bones to grow in length as the animal matures

What is the primary growth center of long bones?

The diaphysis

Diaphysis

Shaft of long bones, composed of compact bone

What is the secondary growth center of long bones?

Epiphysis

Epiphysis

Rounded end of long bones, composed of cancellous bone

Intramembranous bone formation

Occurs only in certain skull bones, where bone replaces the fibrous tissue membrane covering the brain

Long bones

Bones of the limbs, eg. humerus, femur, radius, ulna

Short bones

Small cube-like bones, eg. carpal & tarpal bones

Flat bones

Thin & flat bones, eg. skull, shoulder, blades, individual pelvic bones

Irregular bones

Miscellaneous category of irregularly shaped bones, eg. vertebrae, some skull bones, patella, sesamoid

Red bone marrow

Predominant type of marrow in young animals, involved in making blood cells - hematopoietic tissue

Yellow bone marrow

> Predominant type of marrow in adult animals, composed of adipose tissue
> Can revert to red bone marrow if the body suffers chronic blood loss

Condyle

Large, round articular surface on the distal end of a long bone

Head

Spherical articular surface on the proximal end of a long bone

Facet

Flat, articular surface of a bone

Foramen

Hole in a bone, typically where blood vessels or nerves pass through

Fossa

Depressed or sunken area on a bone, usually occupied by muscles or tendons

Axial skeleton

Bones of the head & trunk

Appendicular skeleton

Bones of limbs & appendages

Process

Lumps, bumps, & other projections on a bone, typically where tendons attach to the bone

Visceral skeleton

Bones formed in soft organs, eg. os penis

How many skull bones are there?

37-38

Suture joints

Jagged, immovable, fibrous joints of most bones of the skull

What kind of joint connects the mandible to the skull?

Synovial

Ossicles

Bones of the ear - malleus, incus, & stapes

Features of vertebrae

Consist of a body, an arch, & processes

Fibrous joint

> Aka synarthrosis
> Immovable fixed joint connected by fibrous tissue
> eg. sutures of the skull

Cartilaginous joint

> Aka amphiarthrosis
> Slightly movable joint that connected by cartilage or ligaments
> eg. spine, pelvis, ribs

Synovial joint

> Aka diarthrosis
> Freely movable joint characterized by a synovial cavity filled with synovial fluid
> eg. shoulder, hip, elbow, knee, wrist, ankle

3 types of joints

Fibrous, cartilaginous, & synovial

Types of synovial joints

Hinge, gliding, pivot, & ball & socket

Hinge synovial joint

> One joint surface swivels around another, providing only flexion & extension movements
> eg. elbow, knee

Gliding synovial joint

> Rocking motion of one bone on another, primarily providing flexion & extension movements with some abduction & adduction possible
> eg. carpus & tarsus bones

Pivot synovial joints

> One bone rotates on another, providing only rotational movement
> alanto-axial joint is the only true pivot joint

Ball & socket synovial joint

> Allows for all 6 types of joint movement
> eg. shoulder, hip

6 types of synovial joint movements

Flexion & extension, abduction & adduction, rotation, & circumduction

Rotation joint movement

Twisting movement of a bone on its own axis

Circumduction joint movement

Movement of an extremity so that the distal end moves in a circle

Which limbs have no bony connection to the axial skeleton?

The thoracic limbs

Where do the pelvic limbs connect to the axial skeleton?

At the sacroiliac joint

Bones of the thoracic limb, proximal to distal from the axial skeleton

Scapula > humerus > radius (medial) & ulna (lateral) > carpal bones > metacarpal bones > phalanges

Bones of the pelvic limb, proximal to distal from the axial skeleton

Pelvis > femur > patella & fabellae > tibia & fibula > tarsal bones > metatarsal bones > phalanges

Bones of the pelvis

Ilium (most cranial), ischium, & pubis (most caudal)

Joint where the femur meets the pelvis

Coxofemoral joint

What is the bone that sits just rostral of the occipital bone?

Parietal bone

How many thoracic vertebrae do cats & dogs have?

13

Which fused vertebrae does the pelvis attach to?

The sacrum

Maxilla

Upper jaw

Mandible

Lower jaw

Are the ribs part of the appendicular skeleton?

No

Which digit is usually absent in the rear leg of dogs?

#1

What is the weight bearing bone of the forelimb?

Radius

Does the frog of the hoof never bear weight?

No

Which bone is P3 of horses?

Coffin bone

What is the smallest pelvic bone?

Pubis

How many cervical vertebrae do cats & dogs have?

7

Which metatarsals are the splint bones in horses?

2 & 4

How many lumbar vertebrae do cats & dogs have?

7

Tendons attach…

Bones to muscle

Ligaments attach…

Bones to bone

Where are the phalanx bones located?

In the foot

C1 vertebrae

Atlas - yes joints

C2 vertebrae

Axis - no joint

What feature of the skull does the spinal cord exit?

Foramen magnum

Occipital bone

Single bone that forms the base of the skull

Interparietal bones

2 small bones located on the dorsal midline between the occipital & parietal bones

Parietal bones

2 bones that form the dosolateral walls of the cranium

Temporal bones

2 bones located ventral to the parietal bones that form the lateral walls of the cranium & the joint with the mandible

Which skull bones contain the structures for the middle & inner ears?

The temporal bones

Frontal bones

2 bones that form the forehead region of the skull & part of the eye socket & contains the paranasal/frontal sinus

What are the ribs that directly attach to the sternum?

Sternal ribs