Posts
Showing posts with label the skeleton. Show all posts
Showing posts with label the skeleton. Show all posts
At the base of the skull, the backbone begins. The skull is supported by the topmost cervical (neck) vertebra. The curious thing about a backbone is that the word has come to suggest something solid, straight, and unbending.
The back, however, just isn't like that: it consists of 26 knobby, hollowed-out bones- vertebrae, rather improbably held together by muscles, ligaments, and tendons. Is is not straight when we stand, but has definite backward and forward curvatures; and even some of its most important structures (the disk between the vertebrae) aren't made of bone, but of cartilage.
All in all, however, the backbone is fairly well designed structure in term of several different functions it serves- but with some built-in weaknesses.
The next post will further explain about The Vertebrae.
The hardest substance in the human body is the enamel that covers the exposed surface of a tooth. Below the gum, the tooth's outside surface is composed of somewhat softer cementum. Beneath enamel and cementum is a bonelike substance, call dentin, which covers the soft interior of the tooth, called pulp. Pulp is serviced by blood vessels and nerves through the root or roots of the tooth. The passageway of nerves and blood vessels that lead up through the tooth from the gum sockets is called a root canal. Tooth and gum are stuck to each other by a tough, adhesive tissue called periodontal (or peridental- "surrounding the tooth") membrane.
The bones of the skull have as their most important function the protection of the brain and sense organs. There are also, of course, the jawbones that support the teeth and gums and which enables us to bite and chew our food.
Most of the skull appears to consist of a single bone- a hard, unbroken dome. Actually, the brain cage or cranium consists of eight individual platelike bones which have fused together in the process of growth. At birth, these bones are separated, causing the soft spots of fontanelles we can readily feel on a baby's head. As the baby's brain enlarges, the bones grows along their edges to fill in the fontanelles, finally knitting together in what are called suture lines, somewhat resembling inexpertly mended clothes seams. Along the suture lines, the skull bones continue to grow until the individual's mature skull size is reached.
Most of the skull appears to consist of a single bone- a hard, unbroken dome. Actually, the brain cage or cranium consists of eight individual platelike bones which have fused together in the process of growth. At birth, these bones are separated, causing the soft spots of fontanelles we can readily feel on a baby's head. As the baby's brain enlarges, the bones grows along their edges to fill in the fontanelles, finally knitting together in what are called suture lines, somewhat resembling inexpertly mended clothes seams. Along the suture lines, the skull bones continue to grow until the individual's mature skull size is reached.
Within the framework of the axial skeleton lie all the most vital organs of the body. People have gone on living with loss of a hand or a leg- indeed, with loss of any or all of their limbs. But nobody can live without a brain, a heart, a liver, lungs, or kidneys- all of which are carried within the framework of axial skeleton. each part of the axial skeleton will be explained in the next post, which includes The Skull and The Backbone.
How the Bones of skeletal System Fit and Work Together
0 comments Posted by Delhi Fashion & Tailors at 10:24 PM
Medical textbooks name a total of 206 bones making up the skeletal system of a normal, adult human being. The word "normal" and "adult" are significant. A newborn baby normally has 33 vertebrae making up its backbones (also called spinal column or simply spine); but by the time a person reaches adulthood, the number of individual vertebrae has shrunk to 26.
The explanation: during the growth process, nine bottom vertebrae fuse naturally into just two. In like fashion, we "lose" some 60 bones as we grow up. Some otherwise perfectly normal adults have "extra" bones or "missing" bones. For example, although the normal number if ribs us 12 pairs, some adults may have 11; others may have 13 pairs.
Even a practicing physician might be hard-pressed to identify each of our 200-plus bones and describe its function. An easier way to gain a general understanding of various functions, capabilities- and weaknesses, too- of our bones is to visualize the skeletal system as a standing coatrack, say, about six feet high.
Call the central pole the backbone. About ten inches down from its top (the top of your skull) is a horizontal crossbar (your shoulders- collarbones and shoulder blades), approximately a foot-and-a-half across. Sixteen or so inches below the bottom of the top crossbar is another, shorter crossbar, broader and thicker- the pelvic girdle. The coatrack with its two crossbar is now a crude model of the bones of the head and trunk, collectively called axial skeleton. Its basics unit is the backbone, to which are attached the skull at the top, then the bones of the shoulder girdle, the ribs, and at the bottom, the bones of the pelvic girdle.
By hanging down (or appending) members from the two ends of the top crossbar, and doing the same at the lower crossbar, we would simulate what is called the appendicular skeleton- arms and hand, legs and feet.
Now, make the coatrack stand on its new legs, cut off the central pole just below the lower bar (if you wish, calling it man's lost tail), and you have the two main components of the skeletal system, joined together before you.
*Lets us look at each more closely in the next posts
The explanation: during the growth process, nine bottom vertebrae fuse naturally into just two. In like fashion, we "lose" some 60 bones as we grow up. Some otherwise perfectly normal adults have "extra" bones or "missing" bones. For example, although the normal number if ribs us 12 pairs, some adults may have 11; others may have 13 pairs.
Even a practicing physician might be hard-pressed to identify each of our 200-plus bones and describe its function. An easier way to gain a general understanding of various functions, capabilities- and weaknesses, too- of our bones is to visualize the skeletal system as a standing coatrack, say, about six feet high.
Call the central pole the backbone. About ten inches down from its top (the top of your skull) is a horizontal crossbar (your shoulders- collarbones and shoulder blades), approximately a foot-and-a-half across. Sixteen or so inches below the bottom of the top crossbar is another, shorter crossbar, broader and thicker- the pelvic girdle. The coatrack with its two crossbar is now a crude model of the bones of the head and trunk, collectively called axial skeleton. Its basics unit is the backbone, to which are attached the skull at the top, then the bones of the shoulder girdle, the ribs, and at the bottom, the bones of the pelvic girdle.
By hanging down (or appending) members from the two ends of the top crossbar, and doing the same at the lower crossbar, we would simulate what is called the appendicular skeleton- arms and hand, legs and feet.
Now, make the coatrack stand on its new legs, cut off the central pole just below the lower bar (if you wish, calling it man's lost tail), and you have the two main components of the skeletal system, joined together before you.
*Lets us look at each more closely in the next posts
Subscribe to:
Posts (Atom)
