Lecture Notes on the Skeletal System (HUB2019F)

Skeletal System
Bone (general)
- Is a connective tissue
- Shapes and reshaped by the cells that reside within it, conforms to mechanical needs
- Morphology (size and shape) altered in life

Function
Musculoskeletal System Function:
- Protect and support soft tissues
- Anchor muscles, tendons and ligaments
- Rigid levers that operate muscles
- Locomotion

Physiological Function:
- Critical for red-blood cell production (marrow cavity)
o Hematopoiesis = blood cell production
o Erythropoiesis = formation of red blood cells
o Old red blood cells must be replenished by new cells
o All red blood cells formed in bone marrow in 8 stages
 7 stages in marrow, the cell released into bloodstream as a
reticulocyte where it matures 1-2- days later into an erythrocyte
o Derived in marrow from pluripotent Myeloid stem cells that give rise to all
blood cells
- Fat storage
o 70% of bone marrow is fat = 10% of adipose mass in the body
o Suggested to be primarily for hematopoietic (blood stem cell production)
process rather than the total energy of the animal needs
- Calcium reserve and release metabolism (main function of skeleton)
o 99% of calcium is in the skeleton as calcium phosphate
o Binds proteins and to do so it is required in the blood plasma


Properties
- Living tissue, responds to external stress-deposits where needed and absorbs where
it is not
- Strength (due to minerals):
o High tensile strength (stretching)
o High compression strength (top to bottom pressure)
o Low torsion (twisting)
- Elasticity (from proteins) – slightly higher than wood


Anatomical terms
- Supine = standard anatomical position of the body (spine on table face looking up)
- Crania = skull
- Postcranial = below the skull

, Skeletal System
Motions
- Origin = stable site during contraction
- Insertion = site moved during contraction
- Types of motion:
o Extension (movement of limb away from
midline)/ Flexion (movement of limb
back to site of origin)
o Abduction (away from body like snow
angel)/Adduction (reverse, i.e. back
towards body)
o Pronation (rotate hand so finger nails
face ceiling)/Supination (so nails face
down)
o Rotation (windmill)


Planes of reference
- Sagittal = split body into left and right
- Coronal = (frontal) split body into front and back
- Transverse = body into upper and lower parts


Directional terms
- Proximal
o close to midline
- Distal
o away from midline
- Anterior
o Front
- Posterior
o Back
- Superior
o above
- Inferior-
o Below
- Medial
o towards midline
- Lateral
o away from midline

, Skeletal System
Joints
Fibrous Joints
- Bands of collagen, dense, fibrous connective tissue that allows for no movement
- Mostly there for growth and development
- E.g. cranial sutures


Cartilaginous Joints
- Cartilage between bones allows for some movement
- For growth and shock absorption
- E.g. Synchondrosis (with hyaline cartilage): little movement – in the ribs and sternum
- E.g. Symphysis (with fibrocartilage) – in the vertebrae


Synovial Joints
- Move freely
- Hyaline cartilaginous plates with a space and pocket for synovial fluid between them
6 Types:
1. Plane/Gliding - slides across one another (foot arch & wrist)
2. Hinge – 1 direction (knee, ulna & humerus)
3. Ball-and-Socket – move in many directions (shoulder girdle, hip)
4. Saddle – movement in 2 directions (base of the thumb)
5. Pivot – ovoid surface, provides rotation (atlanto-axial joint)
6. Ellipsoid – (Condyloid joint) irregular surface (radiocarpal)


Bones (continued)
Classification by Shape
- Flat: protection and muscular attachment
- Long (tubular): marrow cavity
- Short (compact): as tall as they are wide
- Irregular
- Sesamoid: (Patella)


Bone Anatomy
- Compact/Cortical
o Solid & dense, bone shaft walls
- Spongy/cancellous/trabecular
o Lightweight, honey comb structure
o Ends of long bones
o Short bones and between flat bones