In biology, the skeleton or skeletal system is a strong framework that supports the body. The human skeleton consists of both fused and individual Bones supported and supplemented by Ligaments Tendons Muscles and Cartilage An endoskeleton is an internal support structure of an Animal. Foundations of modern biology There are five unifying principles External rigid frameworks, such as those found in some invertebrates (e. An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate g. insects), are termed exoskeletons. Insects ( Class Insecta) are a major group of Arthropods and the most diverse group of Animals on the Earth with over a million described An exoskeleton is an external Skeleton that supports and protects an animal's body in contrast to the internal Endoskeleton of for example a Human. Internal rigid frameworks, such as those found in most vertebrates (e. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes g. mammals), are termed endoskeletons. Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands An endoskeleton is an internal support structure of an Animal.

The average adult human skeleton has around 206 bones ^[1] These bones meet at joints, the majority of which are freely movable, making the skeleton flexible and mobile. The human skeleton consists of both fused and individual Bones supported and supplemented by Ligaments Tendons Muscles and Cartilage Bones are rigid organs that form part of the Endoskeleton of Vertebrates They function to move support and protect the various organs of the body produce A joint is the location at which two or more Bones make contact The skeleton also contains cartilage for elasticity. Cartilage is a type of dense Connective tissue. It is composed of specialized cells called chondrocytes that produce a large amount of extracellular matrix Ligaments are strong strips of fibrous connective tissue that hold bones together at joints, thereby stabilizing the skeleton during movement. In Anatomy, the term ligament is used to denote three different types of structures Fibrous tissue that connects Bones to other bones

Contents 1 Main functions 2 The Skull 3 Sinuses 4 Skull development 5 Backbone and ribs 6 Intervertebral discs 7 Vertebral curves 8 Regions of the backbone 9 Bony thorax 10 Ribs 11 References 12 See also

Main functions

A skeleton provides "cages" to protect the delicate organs. For example: the ribcage helps protect the lungs, heart, etc. Moreover, it gives muscles "sides" or edges to attach to (through tendons). It also maintains balance, supports the body's shape and allows for motion. Another function of the skeleton is to make red and white blood cells. The Marrow in the bone produces these cells for when the body needs them. But all these functions are perhaps secondary to the primary function of locomotion. The bones allow the muscles of the body to move the limbs. Bones come in different sizes; the longest bone is the femur, and the shortest, the stapes. The femur is the thigh bone In Humans, it is the longest, most voluminous and strongest Bone. The stapes or stirrup is the stirrup-shaped small Bone or ossicle in the Middle ear which attaches the Incus to the Fenestra ovalis The First layer of a bone is called the Periostium. It is a thin membraine coarting the compact bone. The next layer of bones are called compact bones, and the middle, called spongy or cancellous bone, which are hollow and contain bone marrow. Joints of bones are held together by ligaments, which are fine fibers attaching to each bone at joints. In order for bones to not scrape against each other, slippery cartilage and synovial fluid are covered atop the bones.

The Skull

The human skull shapes the head and face, protects the fragile brain, and houses and protects special sense organs for taste, smell, hearing, vision, and balance. It is constructed from 22 bones, 21 of which are locked together by immovable joints, to form a structure of great strength.

The bony framework of the head is called the skull, and it is subdivided into 2 parts, namely;

1. Cranial Bones. The 8 bones of the cranium support, surround and protect the brain within the cranial cavity. The brain is the center of the Nervous system in animals All Vertebrates and the majority of Invertebrates have a brain They form the roof, sides, and back of the cranium, as well as the cranial floor on which the brain rests. The frontal bones and the parietal bones form the roof and sides of the cranium. The frontal bone is a Bone in the Human Skull that resembles a cockleshell in form and consists of two portions a vertical The parietal bones are bones in the Human Skull and form by their union the sides and roof of the Cranium. Two in the temporal bone, the external auditory meatus, directs sounds into the inner part of the ear that is encased within, and which contains three small, linked bones called ossicles. The ear canal ( external auditory meatus, external acoustic meatus) is a tube running from the Outer ear to the Middle ear. The ossicles (also called auditory ossicles) are the three smallest Bones in the human body The occipital bones forms the posterior part of the cranium and much of the cranial floor. The occipital bone has a large opening, the foramen magnum, through which the brain connects to the spinal cord. The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself In Anatomy, in the Occipital bone, the foramen magnum (Latin 'great hole' is one of the several oval or circular apertures in the base of the Skull (the The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected The occipital condyles articulate with the atlas (first cervical vertebra), enabling nodding movements of the head. The ethmoid bone forms part of the cranial floor, the medial walls of the orbits, and the upper parts of the nasal septum, which divides the nasal cavity vertical into left and right sides, The sphenoid bone, which is shaped like a bat's wings, acts as a keystone by articulating with and holding together, all the other cranial bones. The ethmoid bone (from Greek ethmos, "sieve" is a Bone in the Skull that separates the Nasal cavity from the Brain. The sphenoid bone (from Greek sphenoeides, "wedgelike" is a Bone situated at the base of the Skull in front of the Temporals and basilar

2. Facial Bones The 14 facial bones form the framework of the face; provide cavities for the sense organs of smell, taste, and vision; anchor the teeth; form openings for the passage of food, water, and air; and provide attachment points for the muscles that produce facial expressions. Two maxillae form the upper jaw, contain sockets for the 16 upper teeth, and link all other facial bones apart from the mandible (lower jaw). This article is about the Mammal maxilla For Arthropod maxillae see Mouthparts; for Insect maxillae in particular see Insect mouthparts The mandible (from Latin mandibula, "jawbone" or inferior maxillary bone forms the lower Jaw and holds the lower teeth in place Two zygomatic bones (cheekbones), form the prominences of the cheeks and part of the lateral margins of the orbits. Two lacrimal bones form part of the medial wall of each orbit. Two nasal bones form the bridge of the nose. The nasal bones are two small oblong Bones varying in size and form in different individuals they are placed side by side at the middle and upper part of the Face ss Two palatine bones from the posterior side walls of the nasal cavity and posterior part of the hard palate. The palatine bone is a Bone in the Palate (Latin palatum; unrelated to palatium 'palace' from which other senses of Palatine derive Two inferior nasal conchae form part of the lateral wall of the nasal cavity. In Anatomy, a turbinate (or nasal concha) is a long narrow and curled bone shelf (shaped like an elongated sea-shell which protrudes into the breathing passage The nasal cavity (or nasal fossa) is a large air-filled space above and behind the nose in the middle of the face The vomer forms part of the nasal septum. The vomer (from Latin vomer -ĕris, "ploughshare" is one of the unpaired facial Bones of the Skull. The nasal septum separates the left and right airways in the Nose, dividing the two Nostrils. The mandible, the only skull bone that is able to move, articulates with the temporal bone allowing the mouth to open and close, and provides anchorage for the 16 lower teeth. The mandible (from Latin mandibula, "jawbone" or inferior maxillary bone forms the lower Jaw and holds the lower teeth in place

Sinuses

Sinuses are air-filled bubbles found in the frontal, sphenoid, ethmoid, and paired maxillae, clustered around the nasal cavity. Paranasal sinuses are air-filled spaces communicating with the nasal cavity within the bones of the Skull and face These spaces reduce the overall weight of the skull.

Skull development

In the fetus, skull bones are formed by intramembranous ossification. Intramembranous ossification is one of the two processes during Fetal development of the mammalian skeletal system in which Bone tissue is created A fibrous membrane ossifies to form skull bones linked by areas of as yet unossifued areas of membrane called fontanelles. References in Pop Culture The dragon in John Gardner's 1971 novel Grendel makes reference to the fontanele as a mark of the universe's progress At birth, these flexible areas allow the head to be slightly compressed, and permit brain growth during early infancy. These are named the anterior (Frontal) fontanelle, posterior (Occipital) fontanelle, anterolateral (Sphenoidal)fontanelle, and the posterolateral (Mastoid) fontanelle.

Backbone and ribs

Together with the sternum and ribs, the backbones (also known as the vertebral column, spinal column, or spine) forms the skeleton of the trunk. The sternum (from Greek στέρνον sternon, "chest" or breastbone) is a long flat Bone located in the center of the thorax (chest In Vertebrate Anatomy, ribs ( Latin costae) are the long curved Bones which form the ribcage. In Human anatomy, the vertebral column ( backbone or spine) is a column of 34 Vertebrae the Sacrum, Intervertebral A vertebra (plural vertebrae) is an individual Irregular bone in the spinal or Vertebral column ( aka ischis a flexuous and flexible column The backbone consists of a chain of irregular bones called vertebrae that meet at slightly movable joints. A vertebra (plural vertebrae) is an individual Irregular bone in the spinal or Vertebral column ( aka ischis a flexuous and flexible column Each joint permits only limited movement, but collectively the joints give the backbone considerable flexibility enabling it to rotate, and to bend anteriorly, posteriorly, and laterally. The average backbone makes up about 40 percent of body height. It extends from the skull to its anchorage in the pelvic girdle, where it transmits the weight of the head and trunk to the lower limbs. The pelvis (pl pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known It also supports the skull; encloses and protects the delicate spinal cord; and provides an attachment point for the ribs, and for the muscles and ligaments that support the trunk of the body.

Intervertebral discs

Intervertebral discs are found between adjacent vertebrae from the second cervical vertebra (axis) to the sacrum. Intervertebral discs (or intervertebral fibrocartilage) lie between adjacent vertebrae in the spine. The sacrum is a large triangular bone at the base of the spine and at the upper and back part of the Pelvic cavity, where it is inserted like a wedge between Each disc has an inner soft, pulp nucleus coverbrous covering of fibrous cartilage. Each disc forms a strong, slightly movable joint. Collectively, discs cushion vertebrae against vertical shocks, and allow various movements of the backbone.

Vertebral curves

A normal backbone has four curves that give it an S-shape. The cervical and lumbar curves are convex anteriorly, while the thoracic and sacral curves are concave anteriorly. The S-shape allows the backbone to function as a spring rather than a flexible rod, thereby absorbing shock during walking and running; enhancing the strength and flexibility of the backbone; and facilitating balance when upright by placing the trunk directly over the feet.

Regions of the backbone

An adult backbone consists of 26 vertebrae of which two, the sacrum and coccyx, are composites consisting of vertebrae that fuse during childhood. The sacrum is a large triangular bone at the base of the spine and at the upper and back part of the Pelvic cavity, where it is inserted like a wedge between The coccyx (pronounced kok -siks (Latin os coccygis) commonly referred to as the tailbone, is the final segment of the human vertebral column The backbone has five sections. Seven small cervical vertebrae form the neck,which is the most flexible part of the backbone. The uppermost cervical vertebra, the atlas articulates with the occipital condyle of the skull to enable nodding movements of the head; articulation of the atlas with the axis, the second cervical vertebra, produces shaking movement of the head. An atlas is a collection of Maps typically of Earth or a region of Earth but there are atlases of the other planets (and their satellites in the solar system In Anatomy, the second Cervical vertebra (C2 of the spine is named the axis (from Latin axis, "axle" or epistropheus. In Vertebrates cervical vertebrae (singular vertebra) are those vertebrae immediately behind (posterior to the Skull. Twelve thoracic vertebrae each articulate with a pair of ribs. The 12 thoracic vertebrae compose the middle segment of the Vertebral column, between the Cervical vertebrae and the Lumbar vertebrae. Five large lumbar vertebrae form the hollow small of the back and bear most of the weight of the head and trunk. The lumbar vertebrae are the largest segments of the movable part of the Vertebral column, and are characterized by the absence of the Foramen transversarium within The triangular sacrum, made of five fused bones, forms a strong anchorage for the pelvic girdle, with which it forms the pelvis. The sacrum is a large triangular bone at the base of the spine and at the upper and back part of the Pelvic cavity, where it is inserted like a wedge between The pelvis (pl pelvises or pelves) or pelvic girdle is the irregular bony structure located at the base of the spine (properly known The coccyx, or tailbone, consists of four fused vertebrae. The coccyx (pronounced kok -siks (Latin os coccygis) commonly referred to as the tailbone, is the final segment of the human vertebral column

Bony thorax

The cone-shaped bony thorax surrounds the thoracic cavity, and is formed by 12 thoracic vertebrae posteriorly, 24 ribs laterally, and the sternum and costal cartilages anteriorly. The 12 thoracic vertebrae compose the middle segment of the Vertebral column, between the Cervical vertebrae and the Lumbar vertebrae. The sternum (from Greek στέρνον sternon, "chest" or breastbone) is a long flat Bone located in the center of the thorax (chest The costal cartilages are bars of Hyaline Cartilage which serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the Its cage-like structure protects the thoracic and upper abdominal organs, supports the pectoral girdles and upper limbs, and facilitates breathing. The pectoral girdle is the set of bones which connect the upper limb to the axial skeleton on each side

Ribs

The ribs are curved, flat bones with a slightly twisted shaft. In Vertebrate Anatomy, ribs ( Latin costae) are the long curved Bones which form the ribcage. The 12 pairs of ribs form a ribcage that protects the heart, lungs, major blood vessels, stomach, liver, etc. At its posterior end, the head of each rib articulates with the facets on the centra of adjacent vertebrae, and with a facet on a transverse process. These vertebrocostal joints are plane joints that allow gliding movements. At their anterior ends, the upper ten pairs of ribs attach directly or indirectly to the sternum by flexible costal cartilages. . Together, vertebrocostal joints and costal cartilages give the ribcage sufficient flexibility to make movements up and down during breathing. Ribs 1-7 are called "true ribs". Ribs 8-12 are called "false ribs" of which ribs 11 and 12 are "floating" ribs that articulate with the sternum indirectly via the costal cartilage of another rib or not.

References

1. ^ Human Skeleton, EnchantedLearning. com, 2008-05-07. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 558 - In Constantinople, the dome of the Hagia Sophia collapses

See also

• Human skeleton

The human skeleton consists of both fused and individual Bones supported and supplemented by Ligaments Tendons Muscles and Cartilage

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