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Skeletal System
aka Musculoskeletal system
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Arthro-
joints (places where bones meet)
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Arthti-
joints (places where bones meet)
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Skeletal system functions
- support - soft tissues
- protection - organs
- leverage - allows movement
- storage - mineral, energy
- blood cell formation
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Histology of bone
- connective tissue
- osteoblasts
- osteocytes
- osteoclasts
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Osteoblasts
form new bone
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Osteocytes
- maintain formed bone
- live in lacunae
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Osteoclasts
- destroy bone in a process called remodeling
- osteoblasts can use the waste product to make new bone (eg in other places)
- release calcium to build bone in fetus
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Skeletal system vascular supply
- highly vascular
- Volksmans Canals
- - perpendicular to long axis (cross-wise)
- Haversian Canals
- - parallel to long axis
- Nutrient Foramina
- - grossly visible on diaphysis (shaft)
- - artery goes in here
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Bone formation
- 2 methods:
- - endochondral - inside cartilage
- - intramembranous bone formation - inside membranes
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Endochondral
- cartilage template
- - appendicular skeleton mostly
- primary growth center
- - in center - nutrient foramen hole
- secondary growth center
- - at ends
- - when bone gets too long, turns into...
- growth plates
- approx 3rd trimester:
- - blood vessel intrudes into cartilage
- - then cells shift from chondroblasts to osteoblasts (differentiation -> specialization)
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Intramembranous Bone Formation
- fibrous connective tissue
- flat bones of the skull
- allows for further development of the brain
- fontanelles:
- - humans close at approx 1 year
- - dogs close approx 1 week
- chihuahuas - lots of skull misformations
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Divisions of the skeletal system
- axial
- appendicular
- visceral
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Axial skeleton
- bones of the head and trunk:
- - skull
- - vertebrae
- - hyoid bone
- - ribs
- - sternum (sternabrae)
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Appendicular skeleton
- limbs:
- - thoracic limb
- - pelvic limb
- - pelvis
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Visceral skeleton
- skeleton of the hollow organs
- os cordis - in cow heart
- os penis - walrus is ~ 3 ft long
- os rostri - snouted animals, e.g. pigs; stiffens snout
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Joint
- junction between two bones
- diseases of musculoskeletal system are mostly joint related
- - once in a while, broken bones, although less common since leash laws
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Articular
describes surfaces of joints
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Arthrology
study of joints
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Arthritis
- inflammation of joints
- types:
- - septic - info
- - immune mediated - caused by immune system
- - degenerative - caused by wear & tear
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Types of joints
- immovable
- slightly moveable
- freely moveable
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Immovable joints
- fibrous joints
- aka syntharthroses - held together tightly
- bones held together in an immoveable joint of fibrous connective tissue
- - bones of skull - sutures
- - equine metacarpals & metatarsals aka splint bones
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Slightly moveable joints
- cartilaginous joints
- aka amphiarthroses
- slight rocking motion
- symphyses:
- - pelvis
- - mandible
- - intervertebral
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Freely moveable joints
- synovial joints
- aka diarthroses
- multiple structures to give support for movement in all directions:
- - articular surfaces
- - joint capsule
- - ligaments
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Articular surfaces in synovial joints
- articular cartilage
- - hyaline cartilage
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Joint capsule in synovial joints
- defines joint space
- fibrous outer layer
- synovial membrane:
- - inner layer
- - produces synovial fluid - normally thick, clear, tacky - like mucus
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Ligaments in synovial joints
hold bone to bone
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Synovial joint movements
- flexion - decreases angle between the bones
- extension - increases the angle between the bones
- adduction - movement towards the median plane
- abduction - movement away from the median plane
- rotation - twisting of a part around its own axis; hoofed mammals have very little capacity to rotate
- circumduction - movement of a limb causing the distal extremity to move in a circular motion
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Types of synovial joints
- hinge
- gliding
- pivot
- ball & socket
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Hinge joint
- ginglymus
- can only flex & extend
- eg elbow
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Gliding joint
- arthroidal or rocking joints
- flexion & extension in animals
- adbuction & adduction in humans & animals
- carpal joints
- - knee in horse
- - carpus in dog & cat
- - wrist in human
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Pivot joints
- trochoid joints
- bones pivot or rotate against each other
- rotation
- C1-C2 - cervical vertebrae
- atlanto-axial joint - joint between atlas & axis
- "no" joint
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Ball and socket joints
- spheroidal joints
- all movements possible
- shoulder & hip joints
- greatest range of motion, so most likely to wear out in older animals (osteoarthritis)
- hip displaysia (flattened joint) can lead to osteoarthritis
- can tell on radiograph
- - healthy hip - femur head fits nice & tight in acetabulum
- osteophytes - body makes bony spurs to try to stabilize bone
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