Block 5 ALS Revision Questions

What is the gait cycle?

Period from the heel strike of one limb until the next time that heel hits the ground

What is the stance phase?

Time from when the heel strikes until the toe begins to lift off the ground

What is the swing phase?

Period when the limb has lost contact with the ground

What conditions can alter gait?

• Aging

• Structural damage

• Inflammatory or degenerative conditions

• Neurological conditions

What does the axial skeleton develop from?

Mesodermal somites (sclerotome portion)

What are the four cells of bone tissue?

• Osteogenic cells

• Osteoblasts

• Osteocytes

• Osteoclasts

What are osteogenic cells?

Unspecialised bone stem cells

What are osteoblasts?

Bone building cells

What are osteocytes?

Mature bone cells

What are osteoclasts

Break down bone for reabsorption

What are the two methods of bone formation?

• Endochondral ossification

• Intramembranous ossification

Where does bone form in endochondral ossification?

Within hyaline cartilage

Where does bone form in intramembranous ossification?

Directly within mesenchyme

What are the four stages of intramembranous ossification?

• Development of ossification centre

• Calcification

• Formation of trabeculae

• Development of periosteum

What is the process of developing the ossification centre in intramembranous ossification?

Chemical messages, at site where bone will develop, cause clustering and differentiation of mesenchymal cells into osteogenic cells then osteoblasts

What is the process of calcification in intramembranous ossification?

Secretion of extracellular matrix stops and osteoblasts become osteocytes

Minerals are deposited in ECM and it hardens

What is the process of forming trabeculae in intramembranous ossification?

Bone ECM develops into trabeculae that fuse to form spongy bone

Associated connective tissue forms red bone marrow

What is the process of developing the periosteum in intramembranous ossification?

Mesenchyme condenses at periphery to for periosteum

Compact bone replaces spongy at outside

Regions (left)

• Epiphysis

• Diaphysis

• Epiphysis

Parts (right)

• Articular cartilage

• Epiphyseal line

• Spongy bone

• Medullary cavity

• Nutrient foramen

• Endosteum

• Periosteum

• Articular cartilage

What allows growth in length of a bone?

Epiphysial growth plate

What is the basic unit of compact bone?

Osteon

• Osteon (haversian system)

• Osteoclasts (in lacunae)

• Lamella

• Central canal

• Canaliculi

What is resorption?

Removal of collagen fibres and minerals by osteoclasts

What is deposition?

Addition of minerals and collagen fibres by osteoblasts

What is the process of bone resorption?

• Osteoclasts attach tightly to bone surface at periosteum or endosteum, and form a leak-proof seal at the edges of the ruffled border

• Releases lysosomal enzymes, which digest collagen fibres and other organic structures, and acids, which dissolve bone minerals

• Degraded proteins and minerals enter the osteoclast by endocytosis, cross the vesicle and are exocytosed to the other side of the ruffles border

• Interstitial fluid and other products diffuse into blood capillaries

What is a Colles fracture?

Fracture of the distal radius with dorsal displacement of the wrist and hand

What is osteoporosis?

Progressive bone disease characterised by decrease in bone mass and density

What is the effect of parathyroid hormone on blood calcium?

Increases blood calcium

What is the effect of calcitonin?

Decreases blood calcium levels

What are the four stages of fracture repair?

• Formation of fracture haematoma

• Formation of fibrocartilaginous callous

• Formation of bony callus

• Bone remodelling

What is the process of forming a fracture haematoma?

• Blood vessels broken at fracture line

• Blood collects around the site to form haematoma

• Nearby bone cells die causing inflammation and swelling

What is the process of forming a fibrocartilaginous callus?

• Periosteal fibroblasts enter fracture site and produce collagen fibres

• Cells develop into chondroblasts which produce the callus

What is the process of forming a bony callus?

• Osteoblasts develop in area closer to well-vascularised bone

• Produce spongy bone trabeculae which replace fibrocartilage

What is the process of bone remodelling?

• Dead bone is reabsorbed by osteoclasts

• Spongy bone is replaced by compact bone

• Remains as a thickened area on bone surface

What is the smallest functional unit of the nervous system?

Neuron

What are unipolar, bipolar and multipolar neurons?

• Unipolar - one axon off cell body

• bipolar - two axons

• Multipolar - multiple axons

What are the three cranial meninges?

• Dura mater

• Arachnoid mater

• Pia mater

Which meningeal space is potential in the brain and actual in the spinal cord?

Extradural (epidural) space