Skeleton and muscle

Skeleton19




4.2 Joints21


4.3 Muscle23





4.1. Skeleton


Cartilage and bone provide mechanical support. Cartilage is more flexible than bone but confers insufficient rigidity to withstand gravity (large cartilaginous creatures are aquatic, where gravity matters less). Some cartilages remain more or less the same throughout life, while others undergo a gradual conversion to bone – ossification – which takes place before birth or during childhood and adolescence.


Bony skeleton (Fig. 4.1)





• Axial skeleton: skull, hyoid, vertebral column (including the sacrum), ribs, and sternum.


• Appendicular skeleton: pectoral and pelvic girdles, limb bones:


– pectoral girdle: clavicle, scapula


– upper limb: humerus, radius, ulna, carpal bones, metacarpals, phalanges


– pelvic girdle: hip bone (ilium, ischium, pubis)


– lower limb: femur, tibia, fibula, tarsal bones, metatarsals, phalanges.








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Fig. 4.1


Sesamoid bones are bones that develop in tendons as they cross joints. The patella is an example, and there are others in the wrist and the feet.


Section through bone (Fig. 4.2)


Important terms are:


• Cortical or compact bone: dense bone around the edges.


• Cancellous, trabecular or spongy bone in which the lines of mechanical stress are evident in the structure of the bone.


• Periosteum: the membranous covering. It has two layers: outer fibrous and inner cellular. The inner layer is vascular and contains stem cells which can when required differentiate into osteoblasts, for example in healing and repair. Damage to periosteum impairs bone healing.


• The medullary (marrow) cavity. This and the spaces in cancellous bone contain haemopoietic (blood-forming) cells; there is therefore a profuse arterial supply.




Arterial supply of a long bone (Fig. 4.3)






• Capsular (retinacular) vessels enter the bone with the attachments of the joint capsule (Fig. 4.3B).


• Many small arteries penetrate the periosteum directly, particularly at the site of muscular attachments and near joints (Fig. 4.3C).


• Bones have a particularly rich blood supply because haemopoiesis (formation of blood components) takes place in the central marrow cavity.

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Jun 16, 2016 | Posted by in ANATOMY | Comments Off on Skeleton and muscle

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