Ch. 5 Skeletal system

Canal

Bone marking: large passageway (eg. optic canal)

Condyle

Rounded prominence providing support to hyaline cartilage and forms joints

Foramen

Hole in bone through which nerves and blood vessels pass

Fossa

Shallow depression in bone surface

Meatus

Tube-like channel that goes through bone, may provide passageway for nerves + vessel + sound

Process

Bony projection for muscle attachment, eg. spinal processes

Protuberance

A bump/outgrowth on bone

Compact bone structure + where is it found on the body

Osteon / Haversian system

• Cylindrical bone matrix (concentric lamellae) w/ a central canal and bone cells + canaliculi in layers

Compact bone is in areas of high compressional stress and the outer portions of all bones

Spongy bone structure

“Cross beam” trabeculae with space (dipole) in btwn

Bone classifications

1. Long - long, medullary cavity w/ marrow (femur, tibia, fingers)

2. Short - approximately equal height/width, lack projections and holes (eg carpus and tarsus)

3. Flat - flat with thin spongy bone layer and no cavity (eg. ribs, sternum, scapula)

4. Irregular - many projections, do not fit other categories (vertebrae)

5. Sesamoid - small bones typically embedded in tendons (eg patella)

6. Sutural/wormian - extra bones variable across individuals that develop along cranial sutures

Long bone anatomy

red marrow - place of erythropoiesis

yellow - replaced with adipose with age

Periosteum and endosteum

Periosteum

• primarily dense irregular connective; membrane surrounding bone composed of dense fibers extending from the inside to form a strong attachment point

• continuous with synovial joint capsule

• inner osteogenic layer: growth and repair

Endosteum

• Membrane lining medullary cavities and trabeculae

Cells of the bone

Osteoprogenitor / osteogenic

• Stem cells of perio + endosteum that differentiate into osteoblasts: growth and repair

Osteoblast

• Cells actively secreting matrix in osteoid (soft uncalcified matrix)

Osteocyte

• Mature cell in solid matrix, monitors stress + remodeling

Osteoclast

• Macrophage WB stem cell-derived multinucleated cell that breaks down bone (remodeling)

Interstitial vs appositional growth

• Interstitial: within/inside tissue, lengthens bone

• Appositional: along circumference, increases diameter

Intramembranous vs endochondral growth

Intramembranous - No cartilage frame, bone grows around embryonic mesenchyme and forms trabeculae. Closed off then outer portions remodeled into compact bone while inside spongey

Endochondral - Cartilage frame, primary ossification center where calcium accumulates + chondrocytes die to leave behind cavities (lacunae) for osteoblasts and vessels to occupy. Secondary centers emerge and all cart except for joints and line replaced with bone

Growth plate zones

1. Resting - regular cartilage

2. Proliferating

3. Hypertrophic - chondrocytes stop dividing but incr in size

4. Calcification - calcium accumulates, chondrocytes die

5. Ossification - hardening of matrix

Types of fractures

+Pott’s (ankle)

Cranial bones

8 total:

Parietal, temporal (paired)

Frontal, occipital, sphenoid, ethmoid

Temporal bone structures (inside of skull)

Petrous: Ridge on cranial cavity floor

Stylomastoid foramen: exit point for cranial nerves between styloid process and mastoid process

Carotid canal: passage for major brain artery, outside base of skull anteromedial to styloid process

Sphenoid bone

• “moth”like, keystone bone: joints with almost every other skull bone

• Forms base of skull, has passageways for nerves, optic canals, arteries

Ethmoid bone

• Located in midline of skull, embedded behind nasus

• Forms roof and lateral wall of nasal cavity, part of orbit medial walls, upper nasal septum

Fontanelles

“Soft spots” on infant head: dense connective tissue separating fetal cranial bones to allow for growth and passage through the birth canal

Disappear around age 2 but bones remain separated at sutures before fusing