Musculoskeletal: Anatomy - Overview of the skeletal system Flashcards
What bones make up the axial skeleton?
Head (cranium or skull)
Neck (hyoid bone and cervical vertebrae)
Trunk (ribs, sternum, vertebrae, and sacrum)
What bones make up the appendicular skeleton?
Bones of the limbs, including those forming the pectoral (shoulder) and pelvic girdles
What is cartilage?
Resilient, semirigid form of connective tissue
Role of cartilage
Forms part of the skeleton where more flexibility is required
Role of articular cartilage
Caps the articulating (bearing) surfaces of bones participating in a synovial joint
Provides a smooth, low-friction, gliding surface for movement
How does cartilage obtain oxygen and nutrients?
Is avascular so obtains oxygen and nutrients via diffusion
How does the proportion of bone and cartilage change with body growth?
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
Outline 5 roles of bone
- Support for body and its vital cavities
- Protection for vital structures
- Mechanical basis for movement (leverage)
- Salts storage (e.g. calcium)
- Continuous supply of new blood cells (produced by the marrow in the medullary cavity of many bones)
Types of bone
Compact
Spongy (trabecular)
Describe the structure of bone
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
Outline the 2 different types of bone marrow
Yellow (fatty)
Red (blood cell and platelet-forming)
In long bones, where does the greatest proportion of compact bone occur and why?
Near the middle of the shaft where bones are liable to buckle during weight-bearing
Improves rigidity and function
Outline the 5 different classifications of bone according to their shape, and provide an example of each
- Long bones: tubular (e.g. humerus)
- Short bones: cuboidal (only found in the tarsus and carpus)
- Flat bones: usually serve protective functions (e.g. cranial bones)
- Irregular bones: various shapes other than long, short, or flat (e.g. facial bones)
- Sesamoid bones: develop in certain tendons and are found where the tendons cross the ends of long bones in the limbs (e.g. patella)
What is the role of sesamoid bones?
Protect tendons from excessive wear and often change the angle of tendons as they pass to their attachments
What is periosteum and perichondrium?
Protective fibrous connective tissue surrounding each skeletal element like a sleeve (except where articular cartilage occurs)
Periosteum surrounds bone
Perichrondrium surrounds cartilage
How are bone markings formed?
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
What kind of cells does bone derive from?
Mesenchymal
What are the two processes via which bone can form? Describe each
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
Describe the process of development of a long bone
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
How does ossification of short bones occur?
Similar to the way primary ossification centres of long bones form (via periosteal bud)
What is the only short bone to develop a secondary ossification centre?
The calcaneus
Describe the vascular supply of bones
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
Describe bone innervation
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
How do accessory bones develop? Give two examples
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
Describe the proposed mechanism of heterotropic bone formation in the thighs of horse riders
Chronic muscle strain resulting in small haemorrhagic areas that then undergo calcification and eventual ossification
Describe the process of bone healing after a fracture
- Surrounding fibroblasts (connective tissue cells) proliferate and secrete collagen, forming a collar of callus to hold the bones together
- Remodelling occurs in the fracture area, and the callus calcifies
- Callus is resorbed and replaced by bone
What is a greenstick fracture?
An incomplete break caused by bending of the bones in young children
What is the difference in timing of epiphyseal fusion between boys and girls?
Fusion of epiphyses with diaphysis occurs 1-2 years earlier in girls compared with boys
What causes lines of arrested growth?
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
What are osteochondroses?
Disorders of epiphyses in children resulting from avascular necrosis of unknown aetiology
Describe the blood supply of joints
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
Describe Hilton’s law
Hilton’s law states that nerves supplying a joint also supply the muscles moving the joint and the skin covering their distal attachments
Describe the nerve supply of joints
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
Where are the pain fibres of a joint found?
Pain fibres are numerous in the fibrous layer of the joint capsule and the accessory ligaments, while the synovial membrane is relatively insensitive
What are the three classes of joint?
Synovial
Fibrous
Cartilaginous
What are the 6 major types of synovial joints? Give an example of each
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
Describe the structure of a synovial joint
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
Give an example of a fibrous joint
Cranial sutures
What is a syndesmosis? Give an example
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
What is a dento-alveolar syndesmosis?
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
What is a cartilaginous joint?
Articulating bones are joined by hyaline cartilage or fibrocartilage
What is the difference between a primary and secondary cartilaginous joint? Give an example of each
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)
