Human skeleton

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Overview

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 longest and heaviest 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 20% of the total body weight.

Fused bones include those of the pelvis and the cranium. Not all bones are interconnected directly: There are 6 jnbones in the middle ear called the ossicles (three on each side) 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. Early in gestation, a foetus has a cartilaginous skeleton from which the long bones and most other bones gradually form throughout the remaining gestation period and for years after birth in a process called endochondral ossification. The flat bones of the skull and the clavicles are formed from connective tissue in a process known as intramembranous ossification, and ossification of the mandible occurs in the fibrous membrane covering the outer surfaces of Meckel's cartilages. At birth a newborn baby has approximately 300 bones, whereas on average an adult human has 206 bones (these numbers can vary slightly from individual to individual). The difference comes from a number of small bones that fuse together during growth, such as the sacrum and coccyx of the vertebral column. The sacrum (the bone at the base of the spine) consists of five bones which are separate at birth but fuse together into a solid structure in later years. An infant is born with zones of cartilage, called epiphyseal plates, between segments of bone to allow further growth. Growing is usually completed between ages 13 and 18, at which time the epiphyseal plates of long bones close allowing no further growth.

Segmental pattern

Much of the human skeleton maintains the ancient segmental pattern present in all vertebrates (mammals, birds, fishes, reptiles and amphibians) with basic units being repeated. This segmental pattern is particularly evident in the vertebral column and in the ribcage.

Function

The skeleton has five main functions:

Support

The skeleton provides the framework which supports the body, and maintains its shape. 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

Movement in vertebrates is powered by skeletal muscles, which are attached to the skeleton by tendons. Without the skeleton to give leverage, movement would be greatly restricted. However, biologically speaking, the skeleton does not enable movement.

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.

Blood cell production

The skeleton is the site of haematopoiesis – the generation of blood cells, which takes place in red bone marrow.

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.

Organization

The human skeleton can be divided into the axial skeleton and the appendicular skeleton.

Bones

See also: List of bones of the human skeleton

There are more than 200^[1] bones in the human body.

v • d • e Bones (Axial skeleton, Appendicular skeleton)
VERTEBRAL COLUMN	vertebrae (cervical - thoracic - lumbar) - sacrum - coccyx
THORAX	sternum - rib
cranial bones of SKULL	occipital - parietal - frontal - temporal - sphenoid - ethmoid
facial bones of SKULL	nasal - maxilla - lacrimal - zygomatic - palatine - inferior nasal conchae - vomer - mandible - THROAT: hyoid (greater cornu, lesser cornu, body)
UPPER EXTREMITY	SHOULDER GIRDLE:clavicle - scapula - ARM: humerus - ulna - radius- HAND:carpals (scaphoid - lunate bone - triquetral - pisiform - trapezium - trapezoid - capitate - hamate) - metacarpals - phalanges (prox - int - dist)
LOWER EXTREMITY	PELVIS:pelvis (ilium, ischium, pubis) - LEG: femur - patella - fibula - tibia - FOOT: tarsals (calcaneus - talus - navicular - cuneiform - cuboid ) - metatarsals - phalanges (prox - int - dist)
MIDDLE EAR OSSICLES	malleus - incus - stapes

v • d • e Bones of head and neck: the facial bones of the skull
Maxilla	Surfaces Anterior: fossae (Incisive fossa, Canine fossa) - Infraorbital foramen - Anterior nasal spine Infratemporal: Alveolar canals - Maxillary tuberosity Orbital: Infraorbital groove - Infraorbital canal Nasal: Pterygopalatine canal Processes Zygomatic process Frontal process (Agger nasi, Anterior lacrimal crest) Alveolar process Palatine process (Incisive foramen, Incisive canals, Foramina of Scarpa, Incisive bone, Anterior nasal spine) Other Body of maxilla - Maxillary sinus
Zygomatic	Orbital process (Zygomatico-orbital) - Temporal process (Zygomaticotemporal) - Lateral process (Zygomaticofacial)
Palatine	Fossae Pterygopalatine fossa - Pterygoid fossa Plates Horizontal plate (Posterior nasal spine) - Perpendicular plate (Pterygopalatine canal, Sphenopalatine foramen, Pyramidal process) Processes Orbital - Sphenoidal
Mandible	Body external surface (Symphysis menti, Mental protuberance, Mental foramen) - internal surface (Mental spine, Mylohyoid line, Sublingual fovea, Submandibular fovea) - Alveolar part of mandible Ramus Mylohyoid groove (Mandibular canal, Lingula) - Mandibular foramen - Angle Coronoid process - Mandibular notch - Condyloid process
Minor/ nose	Nasal bone: Internasal suture - Nasal foramina Inferior nasal concha: Ethmoidal process - Maxillary process Vomer: Wing Lacrimal: Posterior lacrimal crest - Lacrimal groove - Lacrimal hamulus

v • d • e Bones of head and neck: the cranium of the skull
Occipital	Squama external (Inion/External occipital protuberance, Nuchal lines) - planes (Occipital, Nuchal) - internal (Cruciform eminence, Internal occipital protuberance, Sagittal sulcus, Internal occipital crest) Lateral parts Condyle (Condyloid fossa, Condylar canal) - Hypoglossal canal - jugular (Jugular process, Jugular tubercle) Basilar part Pharyngeal tubercle Other Foramen magnum
Parietal	Parietal eminence - Temporal line - Parietal foramen
Frontal	Squama Frontal suture - Frontal eminence - external (Superciliary arches, Glabella) - foramina (Supraorbital, Cecum) - Zygomatic process - internal (Sagittal sulcus, Frontal crest) Orbital part Ethmoidal notch - Lacrimal fossa - Trochlear fovea - Frontal sinus - Frontonasal duct
Temporal	Squama Articular tubercle - Suprameatal triangle - Mandibular fossa - Petrotympanic fissure - Zygomatic process Mastoid part Mastoid foramen - Mastoid process (Mastoid cells) - Mastoid notch - Occipital groove - Sigmoid sulcus - Mastoid antrum (Entrance) Petrous part Carotid canal - Facial canal (Hiatus) - Internal auditory meatus - Aqueduct of cochlea - Stylomastoid foramen fossae (Subarcuate fossa, Jugular fossa) - canaliculi (Inferior tympanic, Mastoid) - Styloid process - Petrosquamous suture (note: ossicles in petrous part, but not part of temporal bone) Tympanic part Suprameatal spine
Sphenoid	Surfaces Superior surface: Sella turcica (Dorsum sellae, Tuberculum sellae, Hypophysial fossa, Posterior clinoid processes) - Ethmoidal spine - Chiasmatic groove - Middle clinoid process - Petrosal process - Clivus Lateral surface: Carotid groove - Sphenoidal lingula Anterior surface: Sphenoidal sinuses Great wings foramina (Rotundum, Ovale, Vesalii, Spinosum) - Spine - Infratemporal crest - Sulcus for auditory tube Small wings Superior orbital fissure - Anterior clinoid process - Optic canal Pterygoid processes fossae (Pterygoid, Scaphoid) - pterygoid plates (Lateral, Medial) - Pterygoid canal - Hamulus Other Body - Sphenoidal conchae
Ethmoid	Plates Cribriform plate (Crista galli, Olfactory foramina) - Perpendicular plate Surfaces Lateral surface Orbital lamina - Uncinate process Medial surface Superior nasal concha - Superior meatus - Middle nasal concha - Middle meatus Labyrinth Ethmoid sinus - ethmoidal foramina (Posterior, Anterior)

v • d • e Bones of head and neck: cranial sutures, fontanelles, and related regions
Cranial sutures	Cranial: Frontoethmoidal - Frontal or Metopic (Frontal/Frontal) - Coronal (Frontal/Parietal) - Occipitomastoid (Occipital/Temporal) - Lambdoid (Parietal/Temporal) - Sagittal (Parietal/Parietal) - Sphenoethmoidal - Sphenofrontal - Sphenoparietal - Sphenosquamosal (Sphenoid/Temporal) - Sphenopetrosal (Sphenoid/Temporal) -Squamosal (Temporal/Parietal) - Petrosquamous (Temporal/Temporal) Facial: Palatomaxillary suture Cranial-facial: Sphenozygomatic - Zygomaticotemporal - Zygomaticofrontal
Fontanelles	Anterior fontanelle - Posterior fontanelle - Sphenoidal fontanelle - Mastoid fontanelle
Foramina of multiple bones	Inferior orbital fissure - Foramen lacerum - Jugular foramen - Nasolacrimal canal
Fossae	Anterior cranial fossa - Middle cranial fossa - Posterior cranial fossa - Cranial cavity
Other compound structures	Cranial: Asterion - Pterion - Calvaria - Stephanion - Bregma - Lambda Facial: Nasion Cranial-facial: Dacryon - Zygomatic arch - Temporal fossa - Infratemporal fossa - Pterygomaxillary fissure - Pterygopalatine fossa

v • d • e Bones of upper limbs
Pectoral girdle, clavicle	conoid tubercle - trapezoid line - costal tuberosity - subclavian groove
Scapula	fossae (subscapular, supraspinatous, infraspinatous) - suprascapular notch - glenoid cavity tubercles (infraglenoid, supraglenoid) - spine of scapula - acromion - coracoid process borders (superior, lateral/axillary, medial/vertebral) - angles (superior, inferior, lateral)
Humerus	upper extremity: necks (anatomical, surgical) - tubercles (greater, lesser) - intertubercular sulcus body: radial sulcus - deltoid tuberosity lower extremity: capitulum - trochlea - epicondyles (lateral, medial) - supracondylar ridges (lateral, medial) - fossae (radial, coronoid, olecranon)
Forearm	radius: upper extremity (head, tuberosity) - body - lower extremity (ulnar notch, styloid process) ulna: upper extremity (tuberosity, olecranon, coronoid process, radial notch, trochlear notch) - body - lower extremity (head, styloid process)
Hand	carpus: scaphoid - lunate - triquetral - pisiform - trapezium - trapezoid - capitate - hamate (hamulus) metacarpus: 1st metacarpal - 2nd - 3rd - 4th - 5th phalanges of the hand: proximal - intermediate - distal

v • d • e Bones of torso
Sternum	Suprasternal notch, Manubrium, Sternal angle, Body of sternum, Xiphisternal joint, Xiphoid process
Rib	specific ribs (1, 2, 9, 10, 11, 12, false - 8-12, floating - 11-12) - parts (Angle, Tubercle, Costal groove, Neck, Head)
General vertebral structures	body of vertebra, vertebral arch (pedicle, lamina, vertebral notch), foramina (vertebral, intervertebral), processes (transverse, articular / zygapophysis, spinous)
Cervical vertebrae	C1 (anterior arch, posterior arch, lateral mass), C2 (dens), C3, C4, C5, C6, C7 anterior tubercle, posterior tubercle, foramen transversarium
Thoracic vertebrae	T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12 costal facets (superior, inferior, transverse)
Lumbar vertebrae	accessory process, mammillary process, L5
Sacrum	pelvic surface (anterior sacral foramina), dorsal surface (posterior sacral foramina, median sacral crest, medial sacral crest, lateral sacral crest), lateral surface (sacral tuberosity), base, sacral hiatus - presacral space - sacral promontory - sacral canal - ala of sacrum - sacrovertebral angle

v • d • e Bones of lower limbs
Femur	head of femur (fovea capitis femoris) · neck of femur · greater trochanter · trochanteric fossa · lesser trochanter · tubercle of the femur · intertrochanteric line · intertrochanteric crest · linea quadrata body (linea aspera, third trochanter, pectineal line, adductor tubercle) lower extremity (lateral condyle, medial condyle, lateral epicondyle, medial epicondyle, patellar surface)
Tibia	upper extremity medial condyle · lateral condyle · intercondyloid eminence · tuberosity of the tibia · posterior intercondyloid fossa · anterior intercondyloid fossa body soleal line lower extremity medial malleolus
Fibula	head of fibula · body of fibula · lateral malleolus
Tarsus	calcaneus (sustentaculum tali, trochlear process) · talus · navicular · cuboid · cuneiform (medial, intermediate, lateral)
Metatarsus	1st metatarsal · 2nd · 3rd · 4th · 5th
Other	patella · phalanges of the foot

v • d • e Bones of pelvis/pelvic cavity
General	sacrum, coccyx, hip bone
Ilium	Body (Arcuate line) Wing: gluteal lines (Posterior, Anterior, Inferior) - Fossa - iliac spines (Anterior superior, Anterior inferior, Posterior superior, Posterior inferior) - Crest - Tuberosity
Ischium	Body (Ischial spine, Lesser sciatic notch) - Superior ramus (Tuberosity of the ischium) - Inferior ramus
Pubis	Body - Superior ramus (Pubic tubercle, Pubic crest, Obturator crest) - Inferior ramus (Pectineal line)
Compound	Acetabulum (Acetabular notch) - Iliopubic eminence/Iliopectineal line - Linea terminalis - Ischiopubic ramus/Pubic arch Obturator foramen - Greater sciatic foramen/Greater sciatic notch - Lesser sciatic foramen Lesser pelvis (Pelvic inlet, Pelvic brim, Pelvic outlet) - Greater pelvis

Gender 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 parturition (childbirth). The shape of a female pelvis is flatter, more rounded and proportionally larger to allow the head of the 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.

Disorders

See also: List of skeletal disorders

There are many disordes of the skeleton. One of the more prominent is osteoporosis.

Osteoporosis

Main article: Osteoporosis

Osteoporosis is a disease of bone - leading to an increased risk of fracture. In osteoporosis, the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. Osteoporosis is defined by the World Health Organization (WHO) in women as a bone mineral density 2.5 standard deviations below peak bone mass (20-year-old sex-matched healthy person average) as measured by DXA; the term "established osteoporosis" includes the presence of a fragility fracture.^[1] Osteoporosis is most common in women after the menopause, when it is called postmenopausal osteoporosis, but may develop in men and premenopausal women in the presence of particular hormonal disorders and other chronic diseases or as a result of smoking and medications, specifically glucocorticoids, when the disease is called steroid- or glucocorticoid-induced osteoporosis (SIOP or GIOP).

Osteoporosis can be prevented with lifestyle advice and medication, and preventing falls in people with known or suspected osteoporosis is an established way to prevent fractures. Osteoporosis can be treated with bisphosphonates and various other medical treatments.

External links

• A skeleton page for kids
• Skeletal System & Bones of Human Body

Gallery

Drawing of the reverse of a female skeleton giving an impression of the location relative to surface markings

A medical drawing by a German physician from 1910

Annotated skeleton

v • d • e Bones (Axial skeleton, Appendicular skeleton)
VERTEBRAL COLUMN	vertebrae (cervical - thoracic - lumbar) - sacrum - coccyx
THORAX	sternum - rib
cranial bones of SKULL	occipital - parietal - frontal - temporal - sphenoid - ethmoid
facial bones of SKULL	nasal - maxilla - lacrimal - zygomatic - palatine - inferior nasal conchae - vomer - mandible - THROAT: hyoid (greater cornu, lesser cornu, body)
UPPER EXTREMITY	SHOULDER GIRDLE:clavicle - scapula - ARM: humerus - ulna - radius- HAND:carpals (scaphoid - lunate bone - triquetral - pisiform - trapezium - trapezoid - capitate - hamate) - metacarpals - phalanges (