Libris Britannia 4/science library(b).zip/science library(b)/INFO/BKACHE56.ZIP/PART1.EXE/ANAT1.TXT

Text File | 1992-12-04 | 11KB | 187 lines

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                            BASIC ANATOMY PART ONE
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       With over 140 muscles attached to the 24 vertebrae of the spine
       and supporting structures, the human back is a miracle of
       engineering. While the human brain may be more complex in
       design, the human back is more sophisticated in terms of
       mechanical engineering. Consider the mathematics...

       If you bend forward at the waist so you are at about a 65 degree
       angle from vertical, and assuming you weigh about 180 pounds,
       450 pounds of muscle force is needed just to keep you from
       losing your balance and falling over. If you happen to carry a
       50 pound weight in this position, the muscle force rises to 750
       pounds. At the same time over 850 pounds of direct force will be
       exerted on the fifth lumbar vertebra. The fact that the spine
       can be flexible, rigid and twist under varying loads and
       circumstances is a tribute to evolution and engineering on a
       biological scale.

       Despite its impressive performance, the design of our back and
       spinal column is flawed. During our brief evolution from
       quadrupeds or four legged walkers into bipeds or two legged
       walkers nature did not completely finish the job. Quadrupeds
       such as cats, dogs and horses - and presumably four legged
       walking primates from which we evolved - use a spinal column
       which is more evenly supported by four legs which serve as
       support pillars. This conservative engineering system provides a
       stronger design much like a suspension bridge with the spine
       held horizontal and supported by four vertical pillars.

       When man evolved into a bipedal erect walking creature, this
       intrinsically sound design was lost and two of the support
       pillars, our arms, lifted up into the air. To compensate for
       this weaker design, the stomach, hip and back muscles act as
       delicate "guy wires" in much the same manner as you might tie a
       young tree upright with three or four ropes to keep it from
       toppling over in the wind.

       The fact that over 90% of disc and muscle related spinal
       injuries occur in the LOWER spinal area gives testimony to the
       imperfect design which our accelerated primate evolution
       delivered to of our spinal and muscular anatomy. In truth, the
       complicated nature of its design and its slowness to adapt to
       our relatively recent upright posture makes our backs more
       susceptible to injury and pain than most other body organs and
       structures. Your back hurts because its evolution is still
       catching up with the sudden adoption of an upright posture.

       Surprisingly, it was BOTH our brains and backs which played the
       most dramatic role in our evolution since walking erect freed
       our hands which, along with our developing brains, led to new
       skills such as tool making, agriculture and writing. Our brains
       have drawn praise during evolutionary change, but our backs have
       borne the brunt of a shortened and as yet incomplete evolution.

       Let's turn to specifics. A brief course on anatomy...

       The spine has three functions. 1) To support your body, anchor
       your ribs and connect the pelvis and head. 2) To protect and
       house the spinal cord whose nerves connect most major body
       organs to the brain. 3) To provide flexibility, balance and
       mobility.

       The spinal column or backbone, is a series of separate bones
       called vertebrae. Curiously, the vertebrae are not precisely the
       same size nor are they stacked exactly on top of each other.
       Rather, to balance with forces of weight and various organs,
       they are arranged in a precise S curve which is seen when the
       spine is viewed from the side. Each vertebrae, depending on its
       shape and the muscles and ligaments which attach to it rests at
       a slight angle.

       The spine can be divided into four regions, each of which is
       quite unique in form and function. 1) The neck region or
       cervical spine consisting of 7 vertebrae whose function is to
       support the head. These vertebrae permit the extraordinary range
       of motion for our heads, eyes and ears. 2) The middle back or
       thoracic region consisting of 12 vertebrae which are slightly
       less flexible since they provide attachments for the bones of
       the ribs. 3) The lumbar spine or lower back consisting of 5
       large vertebrae which support the substantial mass of our body
       weight and which bear the brunt of many opposing forces. These
       vertebrae are broad and heavy which reflects this task. It is
       this region of the spine which suffers to most wear and tear
       from poor posture, sudden trauma and other injuries. It is also
       this region which displays pain most frequently when people
       visit the doctor for backaches. 4) The coccyx and sacrum region.
       The sacrum is a triangular, broad bone attached to the base of
       the spine which is formed from the fusion of 5 separate bones
       during early pregnancy and gestation of an infant. Finally, we
       arrive at the coccyx which is the lowest bone of the spinal
       column. It is a collection of small bones which are probably all
       that remains of our primitive vestigial primate tails.

       If you were to remove one vertebra from the spine you would see
       that it is a solid cylinder of bone with a hollow canal through
       the middle for the spinal cord. The hole through each vertebra
       is called the vertebral foramen. This hole is the primary
       conduit which houses and protects the spinal cord.

       Three crucial spurs or projections of bone extend from the back
       or side of each vertebra. One spur points straight back and is
       called the spinous process - if you feel your backbone with your
       fingers you can feel the point of each spinous process along the
       length of your back. The two other spurs point to the side and
       are called transverse processes. The single spinous process
       bends down at an angle and overlaps the vertebra below it. This
       overlapping tends to provide additional protection for the
       delicate spinal cord much like shingles on a roof. The two
       sideways-pointing transverse processes serve to act as anchor
       points for muscles.

       Between each vertebra is a tough capsule of ligament which
       encloses an elastic, jelly-like substance called the nucleus
       pulposis. To the average lay person this is the "disc" but in
       fact it is several structures. 1) the outer band of ligament. 2)
       the flexible gel within. 3) on top and bottom of this whole
       affair are a pair of tough cartilaginous plates which are the
       bearing surface upon which the vertebrae rest. Each specific
       region of the disc is designed for a unique function. A single
       disc is a composite of several types of tissue, each with a
       different composition and function.

       If the spine lacked these "shock absorbing" discs, the vertebra
       would rub directly against each other and soon destroy the whole
       structure as well as doing damage to the spinal cord. The clever
       construction of the discs absorbs shock and distributes spinal
       pressures evenly in all directions.

       In early life the disc spaces between vertebrae are wide. As we
       age, changes begin to take place and the disc gap narrows. The
       disc loses flexibility, drying out proceeds and scarring from
       wear and tear can begin. But this can also be a function of use
       as well as aging. A 70 year old man can have good discs if he
       has been active and careful while a 30 year old sedentary office
       worker can have poor discs.

       The discs expand and contract slightly during the day due to the
       effects of gravity and work. When you wake up in the morning you
       are slightly taller than at the end of the day. Astronauts also
       "gain height" in the weightlessness of space where the discs are
       freed from the bonds of gravity.

       The structures of the spine are not the complete bony anatomy of
       the back. Next we come to the pelvis which is a large bony
       structure on which all of the lower soft organs rest. This
       includes the large intestine, uterus, bladder and rectum. At the
       lower end of the spine the backbone rests on a junction of three
       bones: the sacrum, a broad triangular bone mentioned earlier,
       and the right and left and right illium bones.

       Thin, tough ligaments connect the illium bones to the sacrum.
       This ligament is known as the symphysis pubis and it is this
       junction of illium bones and sacrum that gives rise to the
       famous and sometimes painful "sacroiliac" joint.

       Moving to the front of the pelvis are the two large sockets or
       acetabula into which the joints of the upper leg or thigh bones
       fit. Other than the thin joint between the illium bones and the
       sacrum, the remainder of the pelvis is rigid and inflexible
       bone. In the female, the pelvis is wider and broader to allow
       for the demands of childbirth. The coccyx, our vestigial tail,
       is the lowest point of the spinal column and is a fused assembly
       of three or four small bones. The coccyx rarely causes much back
       pain, unless you have had occasion to slip on icy pavement or
       sit on a chair which was suddenly pulled out from under you.

       In a nutshell, this covers the bony structure of the back and
       spinal column. In the next chapter we move on to the soft
       tissues of the back: the muscles and ligaments which give this
       amazing bony foundation its strength, flexibility and tension.

       This tutorial is merely a starting point! For further
       information on back care and back pain, be sure to register this
       software ($25.00) which brings by prompt postal delivery a
       printed, illustrated guide to back pain written by a physician
       plus two software disks. From the main menu select "Print
       Registration Form." Or from the DOS prompt type the command
       ORDER. Mail to Seattle Scientific Photography (Dept. BRN), PO
       Box 1506, Mercer Island, WA 98040. If you cannot print the order
       form, send $25.00 to the above address and a short letter
       requesting these materials. End of chapter.