Human skeleton

Human skeleton



The human skeleton consists of both fused and individual

bones supported and supplemented by ligaments,

tendons, muscles and cartilage. It serves as a scaffold

which supports organs, anchors muscles, and protects

organs such as the brain, lungs and heart. The biggest

bone in the body is the femur and the smallest is the

stapes bone in the middle ear. In an adult, the skeleton

comprises around 13% of the total body weight, and half

of this weight is water.



Fused bones include those of the pelvis and the cranium.

Not all bones are interconnected directly: There are three

bones in each middle ear called the ossicles that

articulate only with each other. The hyoid bone, which is

located in the neck and serves as the point of attachment

for the tongue, does not articulate with any other bones

in the body, being supported by muscles and ligaments.

Organization



Much of the human skeleton maintains the ancient
segmental pattern present in all vertebrates
(mammals, birds, fish, reptiles and amphibians)
with basic units being repeated. This segmental
pattern is particularly evident in the vertebral
column and in the ribcage.There are 206 bones in
the adult human skeleton, a number which varies
between individuals and with age - newborn
babies have 270 bones some of which fuse
together. These bones are organized into a
longitudinal axis, the axial skeleton, to which the
appendicular skeleton is attached.

Function



Support
The skeleton provides the framework which supports the

body and maintains its shape. The pelvis and associated

ligaments and muscles provide a floor for the pelvic

structures. Without the ribs, costal cartilages, and the

intercostal muscles the lungs would collapse.



Movement
The joints between bones permit movement, some allowing

a wider range of movement than others, e.g. the ball and

socket joint allows a greater range of movement than the

pivot joint at the neck. Movement is powered by skeletal

muscles, which are attached to the skeleton at various sites

on bones. Muscles, bones, and joints provide the principal

mechanics for movement, all coordinated by the nervous

system.

Function c.d.



Protection
The skeleton protects many vital organs:
The skull protects the brain, the eyes, and the middle

and inner ears.
The spine protects the spinal cord.
The rib cage, spine, and sternum protect the lungs,

heart and major blood vessels.
The clavicle and scapula protect the shoulder.
The ilium and spine protect the digestive and

urogenital systems and the hip.
The patella and the ulna protect the knee and the

elbow respectively.
The carpals and tarsals protect the wrist and ankle

respectively.

Function c.d.



Blood cell production
The skeleton is the site of haematopoiesis, which takes place

in red bone marrow. Marrow is found in the center of long

bones.



Storage
Bone matrix can store calcium and is involved in calcium

metabolism, and bone marrow can store iron in ferritin and

is involved in iron metabolism. However, bones are not

entirely made of calcium, but a mixture of chondroitin

sulfate and hydroxyapatite, the latter making up 70% of a

bone.



Endocrine regulation
Bone cells release a hormone called osteocalcin, which

contributes to the regulation of blood sugar (glucose) and fat

deposition. Osteocalcin increases both the insulin secretion

and sensitivity, in addition to boosting the number of insulin-

producing cells and reducing stores of fat.

Gender-based differences



There are many differences between the male and

female human skeletons. Most prominent is the

difference in the pelvis, owing to characteristics

required for the processes of childbirth. The shape of a

female pelvis is flatter, more rounded and proportionally

larger to allow the head of a fetus to pass. Men tend to

have slightly thicker and longer limbs and digit bones

(phalanges), while women tend to have narrower rib

cages, smaller teeth, less angular mandibles, less

pronounced cranial features such as the brow ridges

and external occipital protuberance (the small bump at

the back of the skull), and the carrying angle of the

forearm is more pronounced in females. Females also

tend to have more rounded shoulder blades.



In the skull (22):



The Cranial bones:

–

frontal bone

–

parietal bone (2)

–

temporal bone (2)

–

occipital bone

–

sphenoid bone

–

ethmoid bone



Facial bones:

–

mandible

–

maxilla (2)

–

palatine bone (2)

–

zygomatic bone (2)

–

nasal bone (2)

–

lacrimal bone (2)

–

vomer bone

–

inferior nasal conchae (2)

Bones



In the middle ears (6):

- malleus (2)
- incus (2)
- stapes (2)



In the throat (1):

- hyoid bone



In the shoulder girdle (4):

- scapula or shoulder blade (2)
- clavicle or collarbone (2)

Bones



In the thorax (25 or 27):

- sternum

–

Can be considered as three different bones;

manubrium, body of sternum (gladiolus) and xiphoid

process

- ribs (2 x 12)



In the vertebral column (24):

- cervical vertebrae (7)
- thoracic vertebrae (12)
- lumbar vertebrae (5)

Bones



In the arms (2):

- humerus (2)



In the forearms (4):

- radius (2)
- ulna (2)



In the hands (54):



Carpal (wrist) bones:

–

scaphoid bone (2)

–

lunate bone (2)

–

triquetral bone (2)

–

pisiform bone (2)

–

trapezium (2)

–

trapezoid bone (2)

–

capitate bone (2)

–

hamate bone (2)



Metacarpus (palm) bones:

–

metacarpal bones (5 × 2)



Digits of the hands (finger bones or

phalanges):

–

proximal phalanges (5 × 2)

–

intermediate phalanges (4 × 2)

–

distal phalanges (5 × 2)

Bones



In the pelvis (4):

- coccyx (4 or 5 fused)
- sacrum (5 fused)
- hip bone (innominate bone or coxal bone)

(2)



In the thighs (2):

- femur (2)

Bones



In the legs (6):

- patella (2)
- tibia (2)
- fibula (2)



In the feet (52):



Tarsal (ankle) bones:

–

calcaneus (heel bone) (2)

–

talus (2)

–

navicular bone (2)

–

medial cuneiform bone (2)

–

intermediate cuneiform bone

(2)

–

lateral cuneiform bone (2)

–

cuboid bone (2)



Metatarsus bones:

–

metatarsal bone (5 × 2)



Digits of the feet (toe bones or

phalanges):

–

proximal phalanges (5 × 2)

–

intermediate phalanges (4 × 2)

–

distal phalanges (5 × 2)

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