SKELETAL SYSTEM

FUNCTIONS

1. Support the body2. Attachment of muscles3. Protection of internal organs4. Acts as levers for movement5. Gives stability and framework and shape

to the body6. Production of blood cell (in mammals)

TYPES OF SKELETON

As to Formation

Membrane or dermal bone-formed by direct ossification in

connective tissue without an intervening cartilage stageEndochondral or cartilage bone

-formed by replacement of pre-existing cartilage

As to Kinds of Bone Tissue

Spongy bone tissue-located at the ends and interiors of long

bones-also called bone marrow-composed of an open lattice of bone-within this lattice framework, RBC are

producedCompact bone tissue

-surrounds the spongy bone tissue-also found at the core of bones-gives strength to withstand mechanical

stress

As to LocationExoskeleton or dermal skeleton

-built up outside the body-muscles are attached to the inner surface-limits the size of the animal-formed from a secretion called chitin which is

made hard by the deposition of calcium salts-characteristics of arthropods

Endoskeleton-built up inside the body surrounded by soft

tissue-muscles are attached to the outer surface-characteristics of vertebrates-divided into axial and appendicular skeletons

AXIAL SKELETON

Notochord

the primitive axial skeleton, replaced by the vertebral column

unsegmented and composed of dense fibrous connective tissue

the first skeletal element to appear in the embryo of chordates

Vertebral Columnthe main axial support of vertebratescommonly called back bonecomposed of segmentally arranged vertebrate from

the base of the skull to the tip of the tailprotects the spinal cordprovides rigidity to the bodyprovides direct or indirect attachment of the

appendicular skeleton in man, there are 26 vertebrae: 7 cervical (the first

vertebrae is the atlas and the second is the axis), 12 thoracic, 5 lumbar, 1sacral (five fused to form sacrum), and 1 caudal vertebrae (three to five fused to form the coccyx)

Regions of the vertebral column

in fishes - two regions, trunk tallin frogs - four regions, no neckin salamanders, reptiles, birds, and

mammals - five regions, neck or cervical, chest or thoracic, lower back or lumbar, pelvic or sacral, and tail or caudal

Ribs series of cartilaginous or elongated bony structures attached

to the vertebrae stout, arched structures surrounding the thoracic cavity and

uniting ventrally with the sternum forms the thoracic cage composed of the neck, shaft and the angle in man, there are 12 pairs of ribs, the first seven pairs are

called vertebrosternal or true ribs, the next three pairs are false ribs, and the last two pairs are floating ribs

Types of ribs1. true ribs - directly connected to the sternum2. false ribs - the distal cartilaginous ends unite with the

costal cartilages of the last true ribs3. floating ribs - the distal cartilaginous ends terminate

freely

Sternumcommonly called as the breast boneelongated structure lying in the mid-ventral

region of the anterior trunkarticulates with the pectoral girdlestrengthen the anterior part of the trunknot present in snakes, limbless lizards, and

turtles (with plastron) in man, th sternum is flat and narrow, divided

into three parts: manubrium, the upper part; gladiolus, the middle or body and largest part; xiphoid or ensiform process, the lowest portion

the first two parts are notches for the reception of sternal ends of the upper seven costal cartilages, while xiphoid has no ribs attached to it but some abdominal muscles

Skullthe framework of the headthe most complex of all parts of the

endoskeleton because of its origincartilaginous during embryonic stage

Origin of the skull1. chondrocranium - composed of cartilage; base of

the skull, including sense capsule; replaced by bone

2. dermatocranium - composed of membrane bones; roof over the chondrocranium

3. splanchnocranium - derived from the visceral skeleton; cartilaginous covered by membrane bones

Parts of the skull

1. cranium - the brain case2. three pairs of sense capsule for the organs of smell,

sight and hearing3. visceral skeleton - in lower vertebrates: paired

arches providing the jaws, the support for the tongue (hyoid apparatus), and support for the gill region; in higher vertebrates; the hyoid apparatus, the ear ossicles (incus, malleus, and stapes) for sound conduction, the laryngeal or thyroid cartilage and the tracheal or cricoid cartilages

APPENDICULAR SKELETON

Composition of the Appendicular Skeleton

Pectoral girdle1. scapula - shoulder blade2. coracoid3. clavicle - collarbone

Forelimbs1. humerus - upper arm2. radius and ulna - forearm3. carpals - wrists4. metacarpals - palm5. phalanges - fingers

Pelvic girdle (hip bones)

1. ilium2. ischium3. pubis

Hindlimbs1. femur - thigh2. tibia and fibula - shank3. patella - knee cap4. tarsals - ankle5. metatarsals - sole6. phalanges - toes

DISTRIBUTION OF BONES IN HUMAN ADULT

there are a total of 206 bones in an adult human infants have more bones that adult due to

numerous jointsdistributed as follows:skull (cranium + face) - 22 (8 + 14)ears - 6hyoid - 1vertebral column - 26sternum - 1ribs - 24pectoral girdle and forelimbs - 64pelvic girdle and forelimbs - 62

JOINTS

Types as to Amount of Movement and Structural Composition

Synarthroses immovable joints connected by fibrous tissue or cartilage-like sutures,

which are the lines of junction of the skullAmphiarthroses slightly movable joints

Types of diarthroses1. symphysis, a joint where two long bony surfaces are

connected by a broad, flat disc of fibrocartilage2. synchondrosis, a temporary form of joint made of

cartilage; found between the epiphysis and bodies of long bones

Diarthroses freely movable joints, most common joint in the bodyTypes of diarthroses1. gliding joint - gliding movement only; wrists, ankles,

vertebrae2. hinge joint - angular movement in one direction; humerus

and ulna, knee, ankle, phalanges3. condyloid joint- angular movement in two directions, as

when the condyle is received into an elliptical cavity as in the wrist joint

4. saddle joint - concave in one direction and convex in another; metacarpal bone of the thumb

5. pivot joint - rotary movement in one axis; atlas and axis, radius and ulna, hand to the lower end of the radius

6. ball-and-socket joint - angular movement in all directions; head of the femur in the acetabulum, and the head of the humerus in the glenoid cavity, shoulder joint is the most freely movable joint in the body

GAIT

Types of Gait

1. plantigrade - entire sole of the foot touches the ground; man, apes, bears, raccoons

2. digitigrade - digits with pads touch the ground and the rest of the foot is elevated; cat family

3. ungultigrade - tips of the digits (specialized into hoofs) touch the grounds; ungulates or hoofed animals, cows, carabaos, pigs, horse, goats

BONE STRUCTURE AND FORMATION

bone is a special form of cartilage in which the collagen fibers are coated by a calcium phosphate salt

bone is formed in two stages:1. collagen is laid down in a matrix of fibrils along lines of

stress2. calcium-containing minerals (hydroxyapatite0

impregnate the fibrilhydroxyapatite provides rigidity, while the collagen

provides flexibilitybone is laid down in concentric layers called

lamellae lamellae are laid down as a series of tubes around

narrow channels called Haversian canalsHaversian canals are interconnected containing

blood vessels and nerve