Classification Of Bones

Question 1

Classification of bones according to shape

Answer 1

Long bones 
Short bones 
Flat bones
Irregular bones 
Pneumatic bones 
Sesamoid bones 
Accessory (supernumerary) bones

Question 2

Long bones are divided into

Answer 2

Typical
Short long or miniature
Modified

Question 3

Long bone

Answer 3

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.

Question 4

Examples of types of long bones

Answer 4

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

Question 5

Speciality of clavicle

Answer 5

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

Question 6

Short bones

Answer 6

Their shape is usually cuboid , scaphoid or cuniform . Examples - tarsals and carpals. These are pierced by blood vessels

Question 7

Flat bones

Answer 7

Resembles shallow plates and forms boundaries of certain body cavities. Eg - scapula , bones of vault of skull , ribs and sternum

Question 8

Irregular bones

Answer 8

Eg : hip bones and bones in the base of the skull eg - sphenoid and first and second vertebrae

Question 9

Pneumatic bones

Answer 9

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

Question 10

Sesamoid bones

Answer 10

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

Question 11

Examples of sesamoid bones

Answer 11

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

Question 12

Functions of sesamoid bones

Answer 12

Resists pressure
Minimises friction
Alters the direction of pull of muscle
Maintains the local curculation , protects the vessels and nerves

Question 13

Accessory bones

Answer 13

These bones are not generally present in the body. If present they do not cause any harm . They are often mistakes for fractures.

Question 14

Accessory bones are formed due to

Answer 14

Appearance of extra ossification centres in skull sutures - sutural or wormian bones commonly present in hydrocephalic bones.

Question 15

Developmental classification

Answer 15

Membraneous 
Cartilaginous
Membrano-cartilaginous 
Somatic 
Visceral

Question 16

Membrane (dermal) bones

Answer 16

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

Question 17

Cartilaginous bones

Answer 17

Ossifies in cartlage , derived from preformed cartilage models. Eg :- bones of limbs like femur , humerus etc

Endochindral or intracartilagenous ossification

Question 18

Membrano-cartilaginous

Answer 18

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

Question 19

Somatic and visceral bones

Answer 19

Most bones are somatic bones

Visceral - formed from pharyngeal arches , eg ear ossicles , hyoid bone and part of mandible

Question 20

Regional classification

Answer 20

Axial and appendicular

Axial - skull , ribs , sternum and vertebral column
Appendicular - includes bones of the limbs eg pelvic girdle

Question 21

Structural classification

Answer 21

Macroscopic - compact and cancellous

Microscopic - lamellar , woven , dentine , cement and fibrous

Question 22

Compact bone

Answer 22

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)

Question 23

Cancellous or spongy or trabecular

Answer 23

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.

Question 24

Wolff’s law or trajectory theory of wolff

Answer 24

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

Question 25

Microscopic - lamellar

Answer 25

Most of the mature bones in humans are made up of thin plates of bone called lamellae. These are arranged as branching curved plates in cancellous bones and as concentric circles (haversian system) in compact bones

Question 26

Woven

Answer 26

Seen in fetal bones , fracture bones and cancer bone. The collagen fibres and bone crystals are arranged randomly

Question 27

Fibrous bone

Answer 27

Found in young fetal bones , common in reptiles and amphibia

Question 28

Dentine and cement

Answer 28

Occur in teeth