Musculoskeletal: Anatomy - Overview of the skeletal system

Question 1

What bones make up the axial skeleton?

Answer 1

Head (cranium or skull)
Neck (hyoid bone and cervical vertebrae)
Trunk (ribs, sternum, vertebrae, and sacrum)

Question 2

What bones make up the appendicular skeleton?

Answer 2

Bones of the limbs, including those forming the pectoral (shoulder) and pelvic girdles

Question 3

What is cartilage?

Answer 3

Resilient, semirigid form of connective tissue

Question 4

Role of cartilage

Answer 4

Forms part of the skeleton where more flexibility is required

Question 5

Role of articular cartilage

Answer 5

Caps the articulating (bearing) surfaces of bones participating in a synovial joint
Provides a smooth, low-friction, gliding surface for movement

Question 6

How does cartilage obtain oxygen and nutrients?

Answer 6

Is avascular so obtains oxygen and nutrients via diffusion

Question 7

How does the proportion of bone and cartilage change with body growth?

Answer 7

Proportion of bone and cartilage changes with growth: younger people have more cartilage
Newborn bones are soft and flexible because they are mostly composed of cartilage

Question 8

Outline 5 roles of bone

Answer 8

1. Support for body and its vital cavities
2. Protection for vital structures
3. Mechanical basis for movement (leverage)
4. Salts storage (e.g. calcium)
5. Continuous supply of new blood cells (produced by the marrow in the medullary cavity of many bones)

Question 9

Types of bone

Answer 9

Compact
Spongy (trabecular)

Question 10

Describe the structure of bone

Answer 10

All bones have a superficial thin layer of compact bone around a central mass of spongy (trabecular) bone, except where the latter is replaced by a medullary (marrow) cavity

Question 11

Outline the 2 different types of bone marrow

Answer 11

Yellow (fatty)
Red (blood cell and platelet-forming)

Question 12

In long bones, where does the greatest proportion of compact bone occur and why?

Answer 12

Near the middle of the shaft where bones are liable to buckle during weight-bearing
Improves rigidity and function

Question 13

Outline the 5 different classifications of bone according to their shape, and provide an example of each

Answer 13

1. Long bones: tubular (e.g. humerus)
2. Short bones: cuboidal (only found in the tarsus and carpus)
3. Flat bones: usually serve protective functions (e.g. cranial bones)
4. Irregular bones: various shapes other than long, short, or flat (e.g. facial bones)
5. Sesamoid bones: develop in certain tendons and are found where the tendons cross the ends of long bones in the limbs (e.g. patella)

Question 14

What is the role of sesamoid bones?

Answer 14

Protect tendons from excessive wear and often change the angle of tendons as they pass to their attachments

Question 15

What is periosteum and perichondrium?

Answer 15

Protective fibrous connective tissue surrounding each skeletal element like a sleeve (except where articular cartilage occurs)
Periosteum surrounds bone
Perichrondrium surrounds cartilage

Question 16

How are bone markings formed?

Answer 16

By the attachment of tendons, ligaments, and fascias, or by the passage of arteries lying adjacent to or entering bones
Other formations relate to joints, the passage of tendons, and the provision of increased leverage

Question 17

What kind of cells does bone derive from?

Answer 17

Mesenchymal

Question 18

What are the two processes via which bone can form? Describe each

Answer 18

Intramembranous ossification: directly from mesenchyme (mesenchymal models form during the embryonic period and direct ossification occurs in the foetal period)
Endochondral ossification: from a cartilaginous model derived from mesenchyme during the foetal period

Question 19

Describe the process of development of a long bone

Answer 19

Via endochondral ossification
Mesenchymal cells condense and differentiate into chondroblasts to form the cartilaginous bone model (this occurs during the foetal period)
Cartilage in the midregion of the model calcifies
Periosteal capillaries grow into the calcified cartilage and together with osteogenic cells form the periosteal bud
Capillaries initiate the primary ossification centre - ossified bone from this centre is called the diaphysis
Secondary ossification centres appear in other parts of the developing bone after birth - ossified bone from these centres are called the epiphyses
Flared part of the diaphysis nearest to the epiphysis is called the metaphysis
Once the bone reaches its adult size, the cartilaginous epiphysial plates (between the diaphysis and epiphyses) are ossified
When this occurs, bone growth ceases and the diaphysis fuses with the epiphyses via synstosis, forming the epiphysial line

Question 20

How does ossification of short bones occur?

Answer 20

Similar to the way primary ossification centres of long bones form (via periosteal bud)

Question 21

What is the only short bone to develop a secondary ossification centre?

Answer 21

The calcaneus

Question 22

Describe the vascular supply of bones

Answer 22

Nutrient arteries arise as branches of adjacent arteries outside the periosteum, and pass obliquely through the compact bone of the shaft via nutrient foramine
Nutrient artery divides in the medullary cavity into longitudinal branches which supply each end of the bone marrow, spongy bone, and deeper compact bone
Small arteries from the periosteal arteries nourish most of the compact bone
Blood reaches osteocytes in compact bone via haversian systems or osteons (microscopic canal systems)
Ends of bone are supplied by metaphyseal and epiphysial arteries arising mainly from the arteries supplying the joints (in limbs these are typically part of a peri-articular arterial plexus)
Veins accompany arteries through the nutrient foramina, as well as through foramina near the articular ends of bones
Lymphatic vessels are abundant in the periosteum

Question 23

Describe bone innervation

Answer 23

Nerves accompany blood vessels
Periosteal nerves carry pain fibres
Bone itself has relatively few sensory endings
Within bones, vasomotor nerves control blood vessel constriction and dilation to regulate blood flow through the marrow

Question 24

How do accessory bones develop? Give two examples

Answer 24

When an ossification centre fails to fuse with the main bone
E.g. in the cranium where sutural bones can form between the flat bones of the skull, or in the foot

Question 25

Describe the proposed mechanism of heterotropic bone formation in the thighs of horse riders

Answer 25

Chronic muscle strain resulting in small haemorrhagic areas that then undergo calcification and eventual ossification

Question 26

Describe the process of bone healing after a fracture

Answer 26

1. Surrounding fibroblasts (connective tissue cells) proliferate and secrete collagen, forming a collar of callus to hold the bones together 2. Remodelling occurs in the fracture area, and the callus calcifies 3. Callus is resorbed and replaced by bone

Question 27

What is a greenstick fracture?

Answer 27

An incomplete break caused by bending of the bones in young children

Question 28

What is the difference in timing of epiphyseal fusion between boys and girls?

Answer 28

Fusion of epiphyses with diaphysis occurs 1-2 years earlier in girls compared with boys

Question 29

What causes lines of arrested growth?

Answer 29

During periods of starvation and illness, proliferation of cartilage at the metaphyses slows whilst degeneration of cartilage cells in the column continues, producing dense lines of provisional calcification which then become thickened trabeculae, or lines or arrested growth

Question 30

What are osteochondroses?

Answer 30

Disorders of epiphyses in children resulting from avascular necrosis of unknown aetiology

Question 31

Describe the blood supply of joints

Answer 31

Receive blood from articular arteries that arise from vessels around the joint Vessels often anastamose to form networks (peri-articular arterial anastamoses) Articular veins accompany arteries and, like the arteries, are located in the joint capsule, mostly in the synovial membrane

Question 32

Describe Hilton's law

Answer 32

Hilton's law states that nerves supplying a joint also supply the muscles moving the joint and the skin covering their distal attachments

Question 33

Describe the nerve supply of joints

Answer 33

Rich nerve supply provided by articular nerves with sensory nerve endings in the joint capsule Most articular nerves are branches of nerves supplying the muscles that cross and therefore move the joint In distal limbs, articular nerves are branches of cutaneous nerves supplying the overlying skin

Question 34

Where are the pain fibres of a joint found?

Answer 34

Pain fibres are numerous in the fibrous layer of the joint capsule and the accessory ligaments, while the synovial membrane is relatively insensitive

Question 35

What are the three classes of joint?

Answer 35

Synovial Fibrous Cartilaginous

Question 36

What are the 6 major types of synovial joints? Give an example of each

Answer 36

Plane, e.g. ACJ Hinge, e.g. elbow Saddle, e.g. carpometacarpal Condyloid, e.g. metacarpophalangeal Ball and socket, e.g. hip Pivot, e.g. atlanto-axial

Question 37

Describe the structure of a synovial joint

Answer 37

Articulating bones are united by a joint (articular) capsule composed of an outer fibrous layer lined by a serous synovial membrane Joint cavity is a potential space containing a small amount of synovial fluid, secreted by the synovial membrane Inside the capsule, articular cartilage covers the articulating surfaces of the bones; all other internal surfaces are covered by synovial membrane The periosteum investing the participating bones external to the joint blends with the fibrous layer of the joint capsule Usually reinforced by accessory ligaments that are either separate (extrinsic) or are a thickening of a portion of the joint capsule (intrinsic) If articulating surfaces of bones are incongruent, there may be a fibrocartilaginous articular disc or meniscus

Question 38

Give an example of a fibrous joint

Answer 38

Cranial sutures

Question 39

What is a syndesmosis? Give an example

Answer 39

A type of fibrous joint in which bones are united with a sheet of fibrous tissue (either a ligament of fibrous membrane), and is therefore partially movable E.g. interosseous membrane joining radius and ulna

Question 40

What is a dento-alveolar syndesmosis?

Answer 40

Also known as a gomphosis or socket Fibrous joint in which a peg-like tooth fits into a socket, forming an articulation between the root of the tooth and the alveolar process of the jaw

Question 41

What is a cartilaginous joint?

Answer 41

Articulating bones are joined by hyaline cartilage or fibrocartilage

Question 42

What is the difference between a primary and secondary cartilaginous joint? Give an example of each

Answer 42

In primary cartilaginous joints, or synchondroses, bones are united by hyaline cartilage, which permits slight bending during early life - they are usually temporary unions (e.g. epiphysial plate in developing long bones) Secondary cartilaginous joints, or symphyses, are strong, slightly movable joints united by fibrocartilage (e.g. fibrocartilaginous intervertebral discs)