Musculoskeletal system

Question 1

What are the 5 functions of bones?

Answer 1

• Structural framework: basic unit of the skeletal system. Forms the shape and frame of the body
• Bodily Movement: Muscle attachment, levers
• Physical protection of vital organs: eg brain, heart, lungs
• Blood cell formation: in bone marrow
• Storage and balance of calcium and phosphate

Question 2

What are the structures in bone?

Answer 2

• Periosteum: is the connective tissue covering the bone on the outside
• Endosteum: is the lining of the inner bone (lines the medullary cavity)
• Medulla: Cavity in diaphysis (a section of bone) that contains bone marrow (yellow
• Epiphyseal plate (line): growth plate of the long bone

Question 3

What are the two forms of bone?

Answer 3

• Cortical (compact) bone: dense bone that forms the outer sections of a bone
• Trabecular bone (cancellous or spongy bone) consists of delicate beams of trabeculae, space and sponge like network in the ends of long bones

Question 4

Talk about the microscopic structure of bone

Answer 4

• The basic unit of a bone is called an osteon. They are like cylinders
• Inside each osteon is a canal which houses blood vessels
• Mature osteocytes are found within small cavities called lacunae
• Lacunae are arranged in layers of concentric circles, called lamellae surrounding, surrounding the central canal
• All lacunae are connected to the central canals by canaliculi
• The canaliculi allow the osteocytes access to nutrients and other materials

Question 5

Describe osteoclasts

Answer 5

• Resorbs bone
• Develop by self-aggregation of macrophages (osteoclast precursors)
• Formation requires the presence of membrane bound proteins RANKL (receptor activator of nuclear factor κβ ligand) and M-CSF (Macrophage colony-stimulating factor)
• OC release H+ and hydrolytic enzymes to resorb bone

Question 6

Describe osteoblasts

Answer 6

• Specialized, terminally differentiated cells arising from mesenchymal stem cells (MSC)
• Synthesize organic matrix of bone (osteoid)
• They synthesize dense, crosslinked collagen and specialized proteins = organic matrix of bone
• OB produce hydroxyapatite which is deposited into matrix

Question 7

Describe osteocytes

Answer 7

• Bone cells trapped in mature bone
• Derived from osteoblasts, they lose most of their organelles
• Live for lifetime of bone
• Mechanosensory cells – stimulate bone remodeling - eg produce RANKL which promotes osteoclast differentiation

Question 8

How is calcium regulated within the body?

Answer 8

• The parathyroid hormone (PTH), secreted by the parathyroid glands, is released whenever blood calcium levels are low. It:
• Stimulaties osteoclasts, which break down bone to release calcium into the blood stream.
• Increases the amount of calcium resorbed by the kidneys
• Triggers the formation of calcitriol, which increases absorption of dietary calcium through the intestines

• Calcitonin, a hormone produced by the thyroid, acts in opposition to PTH by inhibiting osteoclasts, stimulating osteoblasts, and increasing excretion of calcium into the urine by the kidneys.

Question 9

Describe cartillage

Answer 9

• Cartilage is a resilient, elastic tissue
• It is formed by chondroblasts which produce a large amount of collagenous extracellular matrix (collagen type II) tthat is rich in proteoglycan and elastin fibres
• Chondrocytes are chondroblasts that are embedded within cartillage
• The base substance of cartilage is chondroitin sulfate
• No nerves or blood vessels in cartilage

Question 10

What are the 3 types of cartillage?

Answer 10

1. Hyaline cartilage: forms the articular surfaces of long bones. It is predominantly made of collagen. It is covered by a fibrous membrane called the perichondrium
2. Fibrocartilage: has lots of collagen fibers (Type I and Type II). It is what forms tendons and ligament tissue.
3. Elastic cartilage: is stretchy due to high presence of elastin, providing support for flexible structures such as the external ear and nose.

Question 11

What are the 3 types of joints?

Answer 11

1. Fibrous joints: adjacent bones are directly connected to each other by fibrous connective tissue, and thus the bones do not have a joint cavity between them.
   For example, the sutures in our cranium, or the PDL space
2. Cartilaginous joints: adjacent bones are united by cartilage, either hyaline or fibrocartilage. Lacks a joint cavity and involve bones that are joined together by
3. Synovial joints: consist of articular (hyaline) cartilage covering the ends of bones, a fibrous articular capsule (composed of fibrous connective tissue) lined with synovial membrane, a joint cavity containing synovial fluid and reinforcing ligaments to hold the bones together.

Question 12

Describe skeletal muscles

Answer 12

• Three layers; epimysium, perimysium and endomysium
• Sarcolemma is the membrane which wraps each muscle fiber
• The muscle fiber is made of tiny individual units called myofibrils
• Myofibrils are composed of individual units called sarcomeres

Question 13

Describe the sarcomere anatomy

Answer 13

• Actin: thin filament which is anchored to the z-disc
• Myosin: thick filament which is anchored to the m line
• H zone: light zone. Myosin filaments only
• I band: light zone. Actin filaments only
• A band: dark zone. Here, the actin and myosin filaments overlap
• Z disc: is the disc which marks the beginning and ending of a sarcomere unit. This is where two actin filaments attach
• M line: This is where myofilaments attach

Question 14

Describe how muscles contract?

Answer 14

• The sarcoplasmic reticulum is a storage unit for Ca+
• When an action potential occurs, it travel down the t-tubule and into the SR
• This stimulates the release of Ca+ from the SR
• When Ca+ binds to the actin filaments, it exposes the binding sites where the myosin filaments will attach
• The myosin filaments pull the actin along its length
• Because the actin filaments are anchored to the z-line the sarcomere shortens from both sides when they slide across myosin filaments