The foot Biology Tid-bit

                                         THE FOOT

Foot – 28 bones – including two tiny sesamoids (shaped like a sesame seed)

• The bones form four arches held together by 112 ligaments and are activated by 20 muscles.  Networks of blood vessels and nerves serve both the skeletal and the muscular structures of the foot.  Sesamoid bones float in the tendon of a small foot muscle and act to protect the tendon as it moves back and forth.
• The 28 bones in each foot divide into 3 groups.  At the front of the foot are the 14 Phalanges that constitute the toes. 
• In the middle of the foot are the 5 metatarsal and 2 sesamoid bones that together make up the instep (metatarsal and 2 sesamoid bones that together make up the instep (metatarsus).
• At the back of the foot are 7 bones that form the heel and ankle (Tarsus).
• The main bone of the foot is the heel bone (Calcaneus).  The ankle bone (Talus) rests directly upon it.
• The weight of the body is transmitted through the anklebone downward to the other bones of the foot.  Part of the weight is distributed downward and forward.
• The toe bones except for those of the big toe, bear almost no weight when you walk.  Their principal function is to give spring to the step.
• When the body is erect, its weight is transmitted through the anklebone to the other bones of the foot and is shared with them.  The 28 bones in the foot are so placed that they catch and bear the entire weight of the body on 4 arches.
• The ankle and toe joints are hinges that allow the ankle and toes to flex and bend up and down and to move forward and backward.
• The other joints of the foot those between the tarsal and metarsal bones can move only slightly.  They are of a gliding nature, one against another (excluding the ankle).
• Your foot cannot function without its 20 muscles and the muscles of the lower leg.  It makes possible the movement of the foot (eg raising foot to tip toe position, rotate the foot; flex the ankle.
• Muscles end in tendons that (fibrous cords of connective tissue that attach muscle to bone.
• The foot’s blood vessels form as extremely fine network of arteries, veins and capillaries to provide the lowest extremity with a rich supply of blood, which carries nutrients to the cells.
• There are nerves that serve the bottom of the foot and nerves that stimulate, the top.
• The skin of the foot is of two types thick and thin.  The sole of the foot is composed entirely of thickened skin up to 5 layers deep.
• Thick skin has no hair follicles or oil glands.  When prolonged pressure or friction is applied to thick skin, the outermost layer grows into a leathery, horny mass that we call a callus.  Thick skin on foot forms a mat tough enough to protect the many structures inside the foot against abrasion, lacerations, and perforations by sharp objects.  The ridges and whorls on the foots’ thick skin, (very much like those of fingerprints) give rise to friction and thus supply a grasping surface for the bare foot.  Thin skin is the normal epidermis covering the whole foot except for the sole and toenails.  It consists of only one layer containing oil glands and follicles.

 TOENAILS – which are protective plates.  

• The part of the nail that is out of sight between the body and the root is known as the matrix.  Injury to the matrix or root interrupts the nail’s natural protective growth pattern; the toenail would then grow either abnormally thick or o one side.