Classification Of Bones Flashcards
Classification of bones according to shape
Long bones Short bones Flat bones Irregular bones Pneumatic bones Sesamoid bones Accessory (supernumerary) bones
Long bones are divided into
Typical
Short long or miniature
Modified
Long bone
Each long bone has an elongated shaft called diaphysis and two expanded ends called epiphysis which is smooth and articular.
The diaphysis has 3 surfaces separated by 3 borders. A central medullary cavity , and a nutrient foramen directed away from the growing end.
Examples of types of long bones
Typical long bones- humerus , radius , ulna , femur , tibia and fibula . With 2 secondary epiphyses
Short long bones - they have only one epiphysis. Metacarpals , metatarsals and phalanges
Modified long bones - have no meduallry cavity like clavicle . It transmits wright from appendicular skelton to axial skeleton
Speciality of clavicle
Its the only long bone that is horizontally placed and has no meduallry cavity. It transmits weight from axial to appendicular skeleton.its also the first bone to ossify
Short bones
Their shape is usually cuboid , scaphoid or cuniform . Examples - tarsals and carpals. These are pierced by blood vessels
Flat bones
Resembles shallow plates and forms boundaries of certain body cavities. Eg - scapula , bones of vault of skull , ribs and sternum
Irregular bones
Eg : hip bones and bones in the base of the skull eg - sphenoid and first and second vertebrae
Pneumatic bones
Variety of irregular bones. They contain large air spaces (para nasal air sinuses) lined by epithelium . Eg - maxilla , sphenoid and ethmoid . They make the skull 1) light in weight 2) helps in resonance of voice 3) acts as ac chambers for inspired air 4) it the timbre or quality of voice
Sesamoid bones
These are bony nodules found embedded in tendons or joint capsules. They arise from tendons . They have no perisosteum and ossify after birth .
They are related to an articular or non artocular bony surface and surgaces of contact are covered by hyaline cartilage and lubricated by bursa or synovial membrane.
These bones have no medullary cavity , haversian system or periosteum
Examples of sesamoid bones
Patella in tendon of quadriceps femoris in front of the knee joint
The cartilage covering the patella is the largest articular cartilage .
Flabella in the lateral head of gastrocnemius behind the knee joint.
Pisiform in the tendon of flexor carpi ulnaris
Riders bone developed in tendon of adductor longus in professional horse riders
Functions of sesamoid bones
Resists pressure
Minimises friction
Alters the direction of pull of muscle
Maintains the local curculation , protects the vessels and nerves
Accessory bones
These bones are not generally present in the body. If present they do not cause any harm . They are often mistakes for fractures.
Accessory bones are formed due to
Appearance of extra ossification centres in skull sutures - sutural or wormian bones commonly present in hydrocephalic bones.
Developmental classification
Membraneous Cartilaginous Membrano-cartilaginous Somatic Visceral
Membrane (dermal) bones
Ossifies in membrane, and are derived from mesenchymal condensations. Eg: bones in the vault of skull like frontal , parietal and facial bones like maxilla. Known as mesenchymal ossification
Cartilaginous bones
Ossifies in cartlage , derived from preformed cartilage models. Eg :- bones of limbs like femur , humerus etc
Endochindral or intracartilagenous ossification
Membrano-cartilaginous
Ossifies partly from cartilage and partly from membrane. Eg in clavicle the sternal end is formed from endochondral ossification and the rest of the bone is formed by intra membranous ossification. , mandible , maxilla , occipital , temporal and sphenoid
Somatic and visceral bones
Most bones are somatic bones
Visceral - formed from pharyngeal arches , eg ear ossicles , hyoid bone and part of mandible
Regional classification
Axial and appendicular
Axial - skull , ribs , sternum and vertebral column
Appendicular - includes bones of the limbs eg pelvic girdle
Structural classification
Macroscopic - compact and cancellous
Microscopic - lamellar , woven , dentine , cement and fibrous
Compact bone
Dense in texture like ivory but extremely porous in nature. It is best developed in the cortex of long bones. This is an adaptation to bending and twisting ( combo of compression, tension and shear)
Cancellous or spongy or trabecular
Its open in texture , made up of a meshwork of traveculae (rods and plates) . There are marrow spaces in between them. Three types of trabecular netwroks :
Rod meshwork
Rod and plate meshwork
Plate meshwork
Its an adaptation to compressive forces.
Wolff’s law or trajectory theory of wolff
Acc to this law bone formation is directly proportional to stress and strain. There are two forces , tensile and compressive force. They can stimulate bone formation in proper conditions
The architecture of cancellous bone is often interpreted in terms of trajectorial theory.
The arrangementof bony trabeculae is governed by the lines if maximal internal stress in the bone .
The pressure lamellae are parallel to the line of transmissof weight and the tension lamellae lie perpendicular to the pressure lamellae .
The compact arrangement of pressure lamellae forms a bony buttress for additional support like calcar femorale
