skeletal system and its mobility and function

System

1. SKELETAL SYSTEM

2. The skeletal system consists of bone and cartilage. The skeleton can be divided into 2 subgroups axial skeleton ( skull, vertebral column, thorax) appendicular skeleton ( pectoral girdle, upper limb, pelvic girdle, lower limb)

3. axial skeleton skull - 29 Cranium - 8 (frontal, occipital, sphenoid, ethamoid, parietal-2, temporal-2) Facial bones - 14 (zygomatic bone -2, maxilla-2, palatine-2, lacrimal bone- 2, nasal bone-2, inferior nasal oncha-2, vomer-1, mandile-1) Hyoid - 1 Ear ossicles - 6 (malleus-2, stapes-2, incus-2)

4. VERTEBRAL COLUMN - 26 cervical vertebrae - 7 thoracic vertebrae - 12 lumbar vertebrae - 5 sacrum - 1 coccyx -1

5. thorax - 25 sternum - 1 ribs - 24 1 - 7 ( attaches directly to sternum) 8 - 10 ( attaches to 7th rib) 11 - 12 ( floating ribs)

6. appendicular skeleton pectoral girdle- 4 clavicle - 2 scapula - 2 upper limb - 60 humerus - 2 radius - 2 ulna - 2 carpals - 16 ( 8 + 8) metacarpals - 10 (5 + 5) phalanges - 28 (14 + 14)

7. pelvic girdle - 2 hip bone - 2 ileum ischium pubis lower limb - 60 femur - 2 tibia - 2 fibula - 2 tarsals - 14 ( 7 + 7) metatarsals - 10 ( 5 + 5) phalanges - 28 (14 + 14)

8. bone Bone is a calcified and rigid connective tissue consisting of cells (osteocytes) embedded in a matrix of ground substance and collagen fibers. highly vascular tissue with high cell density low metabolic rate supportive sturctures of the body protectors of vital organs resoervoirs of calcium and phosphorus biochemical levers on which muscles act to produce movement containers for blood producing cells

9. types Based on structure of the bone : compact bone - is a dense bone that forms the outer shell of all bones or cortex of mature bones. spongy/trabecular/cancellous bone - consists of spicules of bone enclosing cavities containing blood- forming cells (marrow) or honeycombed by large cavities

10. Based on shape of the bone : long bones (clavicle, humerus, radius, ulna, metacarpals, femur, tibia, fibula, metatarsals) miniature long bones (phalanges of hand and foot) short bones (carpals and tarsals) irregular bones ( vetebra , hip bone, hyoid, temporal, ethamoid , zygomatic , maxilla, sphenoid, mandible, palatine, inf. nasal concha, ear osscicles ) flat bones (scapula, sternum, ribs, frontal, parietal, occipital, nasal, lacrimal,vomer ) sesamoid bones pneumatic bones

11. sesamoid bone Sesamoid bones develop in certain tendons and reduce friction on the tendon, thus protecting it from excessive wear. In the ear: The lenticular process of incus In the hand: Two sesamoid bones in the distal portions of the first metacarpal bone (within the tendons of adductor pollicis and flexor pollicis brevis). In the wrist: The pisiform (within the tendon of flexor carpi ulnaris) In the knee: The patella (within the quadriceps tendon) Fabella in the lateral head of gastrocnemius behind the knee joint. Sesamoid bone in the tendon of peroneus longus where it binds around the cuboid bone. In the foot: Two sesamoid bones in the distal portions of the first metatarsal bone (within the tendons of flexor hallucis brevis).

12. pneumatic bones Pneumatic bones are the irregular bones which contain air-filled cavities within them. provides resonance for the voice because of their hollow chambers makes the bone light in weight. E.g., maxilla, frontal, sphenoid, and ethmoid bones and a part of the mastoid process of the temporal bone. Note: At birth the mastoid is not pneumatized, but becomes aerated over the first year of life.

13. parts of bone It has a superficial thin layer of compact bone around a central mass of spongy bone, and contain internal soft tissue, the marrow, where blood cells are formed. Long bones are tubular and have a shaft (diaphysis) and two ends (epiphyses). The metaphysis is a part of the diaphysis adjacent to the epiphyses. Diaphysis Metaphysis Epiphyses

14. Diaphysis Forms the shaft (central region) and is composed of a thick tube of compact bone that encloses the marrow cavity. Metaphysis Is a part of the diaphysis, the growth zone between the diaphysis and epiphysis during bone development. Epiphyses Are expanded articular ends, separated from the shaft by the epiphyseal plate during bone growth and composed of a spongy bone surrounded by a thin layer of compact bone.

15. types of epiphysis There are four types of epiphysis: Pressure epiphysis are the parts of bone involved in weight transmission (and are intracapsular) e.g. head of humerus and femur and condyles of humerus, femur, tibia etc. Traction epiphysis are present at the ends of bones and develop due to traction by the attached muscles (and are extracapsular) e.g. tubercles of the humerus (greater and lesser ), and trochanters of the femur (greater and lesser). Mastoid process is also a traction epiphysis.

16. Atavistic epiphysis: These types of fused bones are called atavistic e.g. the coracoid process of the scapula, which has been fused in humans with the main bone. Aberrant epiphysis : These epiphyses are deviations from the normal anatomy and are not always present. e .g. the epiphysis at the head of the first metacarpal bone .

17. The periosteum is a membrane that covers the outer surface of all bones, except at the articular surfaces (i.e. the parts within a joint space) of long bones. Endosteum lines the inner surface of the medullary cavity of all long bones.

18. There are four types of cells that are found within bone tissue Osteogenic cells are undifferentiated and develop into osteoblasts Osteoblasts are bone-forming cell osteoclasts resorb or break down bone osteocytes are mature bone cells. An equilibrium between osteoblasts and osteoclasts maintains bone tissue

19. cell type function location osteogenic cells develop into osteoblasts Deep layers of the periosteum and the marrow osteoblasts bone formation Growing portions of bone, including periosteum and endosteum osteocytes Maintain mineral concentration of matrix Entrapped in matrix osteoclasts Bone resorption Bone surfaces and at sites of old, injured bone

20. structure of compact bone : The compact bone is made up of a system of Haversian (longitudinal) canals connected by Volkmann's (transverse) canals.

21. haversian system Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the osteonic (haversian) canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels ( canaliculi ) radiate from the lacunae to the osteonic (haversian) canal to provide passageways through the hard matrix. The osteonic canals contain blood vessels that are parallel to the long axis of the bone.

22. volkmann’s canal Volkmann's canals are inside osteons. They interconnect the haversian canals with each other and the periosteum. Volkmann's canals are the small channels in the bone that transmit blood vessels from the periosteum into the bone and that communicate with the haversian canals.

23. structure of spongy bone :

24. Spongy bone contains osteocytes housed in lacunae, but they are not arranged in concentric circles. Instead, the lacunae and osteocytes are found in a lattice-like network of matrix spikes called trabeculae The canaliculi connect to the adjacent cavities, instead of a central haversian canal, to receive their blood supply. Functions: storage of bone marrow site of erythropoiesis low density of songy bone balances out the denser compact bone trabeculae provides strength and flexibility to bone mineral storage

25. compact and spongy bone

26. cartilage It is an avascular and aneural type of supporting connective tissue and has no lymphatics. Cartilage is composed of specialized cells called  chondrocytes that produce a large amount of collagenous extracellular matrix, abundant ground substance that is rich in  proteoglycan, and elastin fibers . Nutrition is supplied to the chondrocytes by diffusion . Functions: Supports soft tissue Provide a smooth, gliding surface for bone articulation Enable the development and growth of bone

27. cells of cartilage are of 3 types chondrogenic cells : found in perichondrium and differentiate into chondroblasts chondroblasts : young cartilage cells chrondrocytes : mature cartilage cells cartilage has 2 types of fibrous cartlage : type 1 collagen fibers (fibro- cartilage) type 2 collagen fibes ( hyaline and elastic cartilage )

28. ground substance consist of : proteoglycans : chondroitin sulphate + keratan sulphate glycoproteins ( chondronectin, chondrocalcin - a calcium binding protein) water ( tissue fluid)

29. Types of cartilage Hyaline cartilage : matrix contains moderate amount of collagen fibers Example  : Connection between ribs and sternum, nasal cartilage and articular cartilage (which covers opposing bone surfaces in many joints ). Elastic cartilage : matrix contains collagen fibers along with large number of elastic fibers Example  : the auricle of the outer ear. Fibro- cartilage : matrix contains a limited number of ground substance amidst a substantial amount of collagen fibers Example  : Intervertebral discs

30. Types of cartilage Hyaline cartilage Elastic cartilage Fibro cartilage Color Bluish opalescent Yellow White Collagen type Type 2 Type 2 Type 1 & 2 Perichondrium Present ( except at epiphysis and articular cartilage) Present Absent Calcification Occurs with old age No calcification Occurs only with bone repair Cells Chondrocytes & chondroblasts Chondrocytes & chondroblasts Chondrocytes & fibroblasts Fibers Thin collagen Elastic fibers Thick collagen Examples Cricoid cartilage Thyroid cartilage Trachea & bronchi Articular cartilage of bone Epiphyseal plate Costal Cartilage (ribs) Apices of arytenoid Epiglottis Corniculate cartilage Cuneiform cartilages Eustachian tube Pinna (auricle) Ext. auditory meatus Articular discs - TMJ Intervertebral discs Menisci Glenoid and acetabular labrum Pubic symphysis Manubriosternal jt

31. ossification Ossification is the process of laying down new bone material by cells called osteoblasts . It is of two types : Membranous ossification is the direct laying down of bone into the mesenchyme (embryonic connective tissue ). Example: some flat bones of the skull and face Endochondral ossification involves osteogenesis in a precursor model of cartilage. Example: The bones of the extremities, vertebral column and thoracic cage. Membrano-cartilaginous ossification, in which bones are initially formed in membrane but later partly in cartilage Example: clavicle.

32. Types of Cartilaginous ossification The point from where ossification begins is called a center of ossification. Cartilaginous ossification involves two centres of ossification. Primary center of ossification Secondary center of ossification

33. Primary center of ossification In long bones, bone tissue first appears in the diaphysis (middle of shaft ). Primary centers starts appearing at 6th week of intrauterine life . Chondrocytes multiply and form trabeculae . cartilage is progressively eroded and replaced by bone, extending towards the epiphysis . A perichondrium layer surrounding the cartilage forms the periosteum, which generates osteogenic cells that make a collar to encircles the exterior of the bone and remodels the medullary cavity on the inside.

34. Nutrient foramen The nutrient artery enters via the nutrient foramen from a small opening in the diaphysis. It invades the primary center of ossification, bringing osteogenic cells (osteoblasts on the outside, osteoclasts on the inside ) e.g. The growing ends of bones in upper limb are upper end of humerus and lower ends of radius and ulna. In lower limb, the lower end of femur and upper end of tibia are the growing ends. The nutrient foramen is directed away from the growing end of the bone; their directions are indicated by a memory aid: ‘Towards the elbow I go, from the knee I flee’ .

35. Secondary center of ossification The secondary centres generally appear at the ends (epiphysis) of long bones . Secondary ossification mostly occurs after birth The epiphyseal arteries and osteogenic cells invade the epiphysis, depositing osteoblasts and osteoclasts which erode the cartilage and build bone

36. radiograph of ossification of bones

37. LAWS OF OSSIFICATION Primary ossification center is single and appears before birth. Exceptions : carpal bones ossify after birth Clavicle has 2 primary ossification centers Secondary ossification centers can be single or multiple and appear after birth. Exceptions : secondary center for lower end of femur appears before birth (9 th month of fetal life). Proximal epiphysis of tibia may appear before birth in some individuals Secondary centers of ossification which appear first are last to unite. Exceptions : secondary center at the lower end of fibula appears during 1 st yr (before the upper end which appears in 3 rd or 4 th yr ) but fuses between 15 th and 17 th yr (before the fusion of upper end between 17 th and 19 th year)

38. LAWS OF OSSIFICATION The secondary ossification centers fuse together to form a single epiphysis, which then fuses with diaphysis. Exceptions : the 3 secondary centers at the upper end of femur ( head - 1 st yr, greater trochanter - 4 th yr, lesser trochanter - 12 th yr) fuse independently with the shaft. The direction of the nutrient artery is opposite to the direction of the growing end of the bone.

39. Time period Bones affected Second month of fetal development Ossification of long bones begins Fourth month Most primary ossification centers have appeared in the diaphyses of bone. Birth to 5 years Secondary ossification centers appear in the epiphyses 5 years to 12 years in females, 5 to 14 years in males Ossification is spreading rapidly from the ossification centers and various bones are becoming ossified 17 to 20 years Bone of upper limbs and scapulae becoming completely ossified 18 to 23 years Bone of the lower limbs and os coxae become completely ossified 23 to 25 years Bone of the sternum, clavicles, and vertebrae become completely ossified By 25 years Nearly all bones are completely ossified

40. blood supply The long bone is supplied by four set of arteries nutrient artery periosteal artery metaphyseal artery epiphyseal artery

41. Nutrient artery enters the middle of shaft through nutrient foramen. divides into ascending and descending branches in medullary cavity each branches subdivides into smaller paralle branches and enters into metaphysis this forms the hair- pin loops / bends these loops anastomose with other arteries

42. joints The site where two skeletal structures come together are termed as joints Union between bones can be in one of three types: by fibrous tissue; by cartilage; or by synovial joints structural classificaion : Fibrous joints Cartilaginous joint Synovial joints regional classifiation : skull type : immovable vertebral type : slightly movable limb type : freely movable

43. Functional classification : Synarthrosis (immovable) Amphiarthrosis (slight mobile) Diarthrosis (freely mobile) According to the number of articulating bones : simple joint - Two bones articulate (eg : interphalangeal joints ) compound joint - More than two bones articulate within one capsule. (eg : wrist / elbow joint ) complex joint - the joint cavity is divided by an intra- articular disc ( eg : temporo- mandibular joint )

44. classification of joints

45. Synarthrosis Fibrous joints occur where bones are separated only by connective tissue and movement between them is negligible. Types of fibrous joint Suture Gomphosis - Tooth and socket joints Syndesmosis - The bones are connected by the interosseous ligament (eg. Middle radioulnar joint and Inferior radioulnar joint)

46. sutures Sutures: These are peculiar to skull, and are immovable. According to the shape of bony margins, the sutures can be: Plane, e.g. internasal suture Serrate, e.g. interparietal suture Squamous, e.g. temporo-parietal suture Denticulate, e.g. lambdoid suture Schindylesis type, e.g. between rostrum of sphenoid and upper border of vomer

47. types of sutures

48. Amphiarthrosis Cartilaginous joints are of two varieties, primary and secondary . Types of cartilaginous joint Synchondrosis - Spheno -occipital joint Epiphysio-diaphyseal joint (growing bone) Symphysis - Midline intervertebral joint Sacrococcygeal joint

49. synchondroses Primary Cartilaginous Joints ( synchondroses ) are united by hyaline cartilage and permit no movement but growth in the length. synchondrosis is one where bone and hyaline cartilage meet. All epiphyses are primary cartilaginous joints and the junctions of ribs with their own costal cartilages Epiphysio- diaphyseal joint spheno -occipital joint manubrio -sternal joint.

50. Symphysis Secondary cartilaginous joints (Symphysis) have bones are united by hyaline plus fibrocartilage. union between bones whose articular surfaces are covered with a thin lamina of hyaline cartilage. The hyaline laminae are united by fibrocartilage.

51. There may be a cavity in the fibrocartilage, but it is never lined with synovial membrane and it contains only tissue fluid. A limited amount of movement is possible, depending on the amount of fibrous tissue within them. All symphyses occur in the midline of the body. Examples pubic symphysis manubrio-sternal joint intervertebral joints.

52. Diarthrosis Synovial joints are freely mobile joints . connections between skeletal components where the bones involved are seperated by a narrow aticular cavity

53. These joints possess a cavity and articular ends of bones forming joints are enclosed in a fibrous capsule. Narrow cavity is called as articular cavity Filled by synovial fluid It consist of fibrous capsule synovial membrane articular cartilage ligaments articular disc bursae fat pads

54. characteristic feature of synovial joints Articular surfaces are covered by a thin plate of hyaline catilage. Joint cavity is enveloped by an articular capsule (an outer fibrous capsule and inner synovial membrane) Cavity of joint is lined everywhere by synovial membrane except over the articular cartilages. The cavity is filled with synovial fluid ( secreted by synovial membrane) which provides lubrication of articular surfaces and nutrition Sometimes joint cavity is completely and incompletely divided by articular disc / meniscus.

55. FIBROUS CAPSULE : It completely encloses the joint and the synovial cavity. It consists of longitudinal and interlacing bundles of white connective tissue fibers. The fibrous capsule along with synovial membrane together forms articular capsule. FUNCTIONS : stabilizes the joint , so that it permits movements and resists dislocation. watch- dog action of the capsule : Numerous sensory nerve endings ramify on the capsule. The stimulation of these muscles action on the joint in such a way that joint is brought in a position of maximum comfort to protect the joint.

56. fibrous capsule

57. LIGAMENTS : These are thickened bands of collagen fibers it is of two types: true ligaments : they are not seperated from the capsular ligaments. they permit movements in one plane and stabilize the joint. accessory ligaments : are seperate from fibrous capsule ( may be intra / extracapsular ) they provide additional reinforcement to the joint

58. synovial membrane : Thin vascular membrane of connective tissue lining inside the fibrous capsule functions : produces synovial fluid to enable lubrication of the joint synovial fluid i s slippery like an egg- white. it is a dialysate of blood plasma + mucin called hyaluronic acid.

59. articular cartilage : it is made up of hyaline cartilage the cartilage consists of proteoglycan - hyaluronic acid aggregates. the hyaluronic acid retains water which resists compresion. function : provides smooth friction- free movements

60. articular disc / meniscus : The articular discs are pads of fibro- cartilage interposed between the articular surfaces of some joints eg : temporo- mandibular joint sterno- clavicular joint acromio- clavicular joint function : Helps in lubrication Divides the joint completely into 2 compartments Prevents wear and tear of articular cartilages by providing a cushioning effect.

61. bursae : These are pouch like sacs of connective tissue filled with synovial fluid ( in synovial joint) Commonly located between tendon and bone / between muscle and bone / between skin and bone / between tendon and skin. Function : cushions certain muscles and to facilitate the movement of tendon/ muscle over bony surfaces. The synovial tendon sheath is a modified bursa that surrounds and lubricates the tendon of certain muscles ( eg : that crosses the wrist and ankle joint)

62. fat pads : also kown as haversian glands pads of fat placed between synovial membrane and bone eg : acetabular fat of hip joint infra patellar fat of knee joint

63. classification of synovial joints According to the shape of articular surfaces : plane joints hinge / ginglymus joints pivot / tricoid joints condylar joints ellipsoidal joints saddle or sellar joints ball and socket / spheroidal joints According to the plane of movement : uniaxial joints biaxial joints multi / polyaxial joints According to the number of articulating bones : simple joints complex joints

64. plane joints - The articular surfaces are nearly flat (plane) they permit gliding movements (eg: side to side , back to forth ) hinge / ginglymus joints - the articular surfaces are pulley shaped movements are permitted only in one plane around transverse axis. pivot / tricoid joints - the articular surface of one bone is rounded and fits into concavity of another bone movement is limited totation around a central axis

65. condylar joints - The round articular of one bone fits into socket type articular sace of another bone. they permit movements in 2 directions (biaxial) eg : side to side / up and down ellipsoidal joints - the elliptical convex surface of one bone articulates with the elliptical concave surface of another bone. movements are permitted in 2 direction (flexion & extension around a transverse axis) saddle or sellar joints - articular surfaces are reciprocally saddle shaped ( conco - convex) it is a modified condyloid joint.

66. Ball and socket / spheroidal joints Rounded convex surface of one bone fits into the cup - like socket of another bone it provides the greatest range of movement eg : hip joint shoulder joint incudo - stapedial joint (smallest ball & socket joint)

67. Types of synovial joint Examples Plane Acromioclavicular Intercarpal & Intertarsal Hinge Elbow & Interphalangeal Pivot ( Trochoid ) Atlanto -axial / Superior radio-ulnar & Inferior radio-ulnar Condylar Temporo -mandibular & Knee joint Ellipsoid Atlanto -occipital Wrist (radio-carpal) Metacarpo -phalangeal (knuckle) Saddle Malleus-incus joint Sternoclavicular First carpo -metacarpal Calcaneocuboid Ball and socket Incus-stapes joint Shoulder & Hip Talo-calcaneo-navicular

68. According to the plane of movement : uniaxial joints - movement occur only in one plane or axis eg : hinge joints, pivot joints biaxial joints - movement occur in two planes or axes eg : condylar joints, ellipsoidal joints, saddle joints multi / polyaxial joints - movements occur in three planes or axes eg : ball and socket joints According to the number of articulating bones : simple joints - only two bones take part in the formation of a joint complex joints - more than two bones take part in the formation of a joint. eg : ankle joint, elbow joint, radio- carpal joint