the human endoskeleton
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- The Human Endoskeleton
2. Human endoskeleton
- The skeleton in man refers to the hard, supportive connective tissue around which the organism is built. The skeleton includes all the bones of the body, the joints formed by the attachment of the bones to one another, connective tissues and cartilage which surround the bones and ligaments that connect bone to bone.
3. The Human Skeleton 4.
- As in all other vertebrates, humans have an internal skeleton which is surrounded by muscles and skin. Such an internal skeleton is called an endoskeleton. In human beings the skeleton consists of more than 200 different kinds of bone which are joined together in various ways to form a rigid framework.
- The skeleton can be divided into two main parts, viz. the axial skeleton and the appendicular skeleton. The major components of each are represented in the following table:
5. Skeleton Pectoral (shoulder) girdle and upper limbs Skull Pelvic (hip) girdle and lower limbs Vertebral column, ribs and breastbone APPENDICULAR SKELETON AXIAL SKELETON 6. I.The Axial Skeleton
- The axial skeleton forms the central axis of the body. It consists of theskull, the vertebral column, the ribs and the sternum or breastbone .
7. 1.The Skull
- The skull consists of28 different bones(including the ossicles of the ear). The bones of the skull can be divided into two main groups: thecraniumwhich encloses and protects the brain and thefacial bones .
8. The Cranium
- The cranium consists ofeight flat boneswhich are rigidly attached to each other withdentate sutures (joints with teeth-like protrusions) . They envelop and protect the brain. Thefrontal boneforms the forehead and portions of theeye sockets (or orbits) . Theoccipital bone , at the base of the skull contains a large opening, called theforamen magnum , through which the spinal cord passes. On each side of the opening is theoccipital condyle , - two round protuberances, - by means of which the skull articulates with the first neck (or cervical) vertebra (the atlas). The organs of hearing are situated in thetemporal bone,one on each side. The openings leading into these organs can also be seen on each side.
9. The Facial Bones
- The facial skeleton consists offourteen irregular bones , which are all (with the exception of the lower jawbone) firmly attached to the cranium by means of sutures. They include thenasal bones, the two jawbones and the cheek bones . Thelower jawarticulates with the temporal bone part of the cheek bone, just in front of the ear. This allows for the necessary movement of the lower jaw when food is bitten off and chewed. Bothupper and lower jawshavealveolar pocketsinto which teeth fit.
- The teeth are embedded insocketsin the ridges of the upper and lower jaw bones. Three regions can be distinguished in a tooth: The rootwhich are embedded in the alveolar pocket of the jaw. The root is firmly attached to the jaw by a surrounding layer of cement and strong connective tissue.The neckis the area where the root(s) and crown meet.The crownprojects above the gum. It is covered with a hard, white layer of enamel. The largest part of the tooth consists of dentine which is a harder substance than ordinary bone. The dentine surrounds the cavity which extends from the root to the crown. Blood capillaries and nerves enter the cavity at a small opening in the tip of the root.
11. 2.The Vertebral Column
- The vertebral column forms thecentral partof the skeleton. Itsupports the skullandprotects the spinal cord . It alsoserves as attachment for the ribs, the pectoral and pelvic girdles . The vertebral column consists ofseparate bones, the vertebrae . The different vertebrae are arranged above each other. Because the separate vertebrae are attached to each other by means offibrous cartilaginous discsthey form a flexible column. Each vertebra hasarticular surfaces above and below , which allow articulation movement between them.
- The vertebral column of33 vertebraeis divided intofive regionsaccording to their position and structure. The five regions consist of:Sevencervical (neck) vertebrae,Twelvethoracic (chest) vertebrae,Fivelumbar vertebrae,Fivefused sacral vertebrae, andFourfused vertebrae.
13. 3.The Ribs
- Twelve pairs of ribsarticulate with the 12 vertebrae of the thoracic region. The ribs areflat, narrow boneswith adistinctive bow-shaped curve . Each rib consists of ahead or capitulum , a smalltubercle(which is a short distance back from the head) and theshaft . The head of the rib articulates with the semi-circular articulating facets formed by the centra of two successive thoracic vertebrae. The tubercle fits into and articulates with the articulating facets on the transverse process. The first seven ribs on each side are joined to the breastbone by bars of hyaline cartilage (calledcostal cartilagein this region).
- The first seven pairs of ribs are referred to astrue ribs . The cartilages of the 8th, 9th and 10th ribs are joined to the costal cartilage of the rib immediately above (i.e. to the costal cartilage of the 7th rib). These three pairs of ribs are known asvertebrochondral ribs . The last two pairs of ribs have free ends which are not attached to the sternum at all. They arefloating ribs . The vertebrochondral ribs and the floating ribs are collectively known asfalse ribs . The ribs (together with their muscles) play an important role in thebreathing mechanismof a mammal.
Diagram to illustrate the attachment of the ribs to the thoracic vertebrae and sternum. 15. 4.The Sternum (Breastbone)
- The sternum is along, flat, dagger-shaped bone . It is about15 - 18 cm longand is found in thecenterof the chest region. The broad upper end supports the collar bones. The first seven pairs of ribs are attached to thearticulating facetson the sides of the sternum. The 12 thoracic vertebrae, the 12 pair of ribs and the sternum forms thethoraxwhichprotects the delicate and vital organsof the thorax, viz. the heart and lungs.
16. II.THE APPENDICULAR SKELETON
- The appendicular skeleton consists of thegirdlesand theskeleton of the limbs . Theupper (anterior)limbs are attached to thepectoral (shoulder) girdleand thelower (posterior)limbs are attached to thepelvic (hip) girdle .
17. 1.The Pectoral (Shoulder) Girdle
- The Pectoral girdle consists of two shoulder blades (scapulae) and two collar bones (clavicles). These bones articulate with one another, allowing some degree of movement.
18. 2.Shoulder Blades (Scapulae)
- The shoulder blade is aflat triangular bonewhich stretches from the shoulder to the vertebral column at the back. On the back side it has a bony ridge for the attachment of the muscles. The bony ridge forms a prominent projection,the acromion , above the shoulder joint. Beneath the collar bone and just on the inside of the shoulder joint, is another bony projection of the shoulder blade,the coracoid process , which alsoserves for the attachment of muscles . The upper outer corner of the shoulder blade ends in theglenoid cavityinto which fits the head of the upper arm bone, forming a ball and socket joint.
19. 3.Collar Bones (Clavicles)
- Each collar bone isrod-shaped and roughly S-shaped . It lies horizontally and articulates with the upper end of the breastbone, right in the middle and front, just above the first rib. The lateral end articulates with the acromium.
The Pectoral Girdle. 20.
- Collar bonesserve as a supportfor the shoulder blades in front andkeep the shoulder blades backso that the arms can hang freely at the sides of the body. Theyprevent the pectoral girdles from getting out of joint easilyand ample movement of the shoulders.
21. 4.The Upper Limbs
- The skeleton of the upper limbs or arm may be divided into five main regions: an upper arm bone, the forearm (radius and ulna), the wrist, the palm of the hand and the fingers.
22. 5.The Pelvic (Hip) Girdle
- The pelvic girdle consists oftwo large, sturdy hip bones . Each hip bone consists ofthree fused bonesnamely theilium, ischium and the pubis . Theiliumis the largest of the three and forms the upper part of the hip bones. The sacrum fits like a wedge posteriorly between the two hip bones. The sacrum has a large, flat articular surface on each side for articulation with the ilia. Theischiumforms the inferior part of the hip bone and thepubisthe central in front. The two pubic bones are attached in the middle, on the front side by asymphysiswhich consists offibrocartilageand ligaments, thepubic symphysis . The two hip bones and the sacrum form a completebony ring, the pelvis. On the outer side of the point where the fused bones meet, there is adeep hip socketinto which the head of the femur fits.
- The pelvic girdle forms astrong supportfor the attachment of the limbs. Strong muscles of the back, the legs and the buttocks areattachedto it. Itprotectssome of the internal organs. In females it forms a strong basin-like structure forsupporting and protectingthe developing foetus during child-bearing.
The Pelvic Girdle. 24. 6.The Lower Limbs or Legs
- The skeleton of the lower limb may be divided intofive main regions :the upper leg (thigh), the lower leg, the ankle, the arch of the foot and the toes .
- The Upper Leg or Thigh
- The upper leg has asingle long bone, the femurand is thelongest bonei