Libris Britannia 4/science library(b).zip/science library(b)/INFO/BKACHE56.ZIP/PART1.EXE/ANAT2.TXT

Text File | 1992-12-04 | 14KB | 236 lines

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                            BASIC ANATOMY PART TWO
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       Everyone has head the term ligament. We think of football or
       basketball players who have "torn a ligament." Likewise most of
       us have head the term tendon.

       A ligament is a tough, dense strand of gristle-like tissue which
       attaches one bone to another while a tendon attaches muscle to
       bone. The two are thus different.

       Ligaments pass between two bones and have some flexibility so
       that motion can occur, but their elasticity is low. They can
       usually be stretched only a short length before a tear occurs.
       Once torn, a ligament does not normally heal itself and is
       repaired surgically. If left unrepaired, the unrestrained
       movement of the joint can cause additional pain, damage and loss
       of joint function.

       Many ligaments connect the spinal vertebrae, sacrum and pelvis
       into a single structure. 1) Interspinous ligaments connect the
       bony transverse spinous processes together and limit motion
       which can happen between two vertebrae. 2) Intertransverse
       ligaments pass between the transverse processes on each side of
       the vertebra. They are largest at the lower lumbar region of the
       spine and prevent you from bending too far from side to side. 3)
       The ligamentum flavum secures the rear section of vertebrae and
       forms the upper encasement of the spinal canal. It protects and
       covers the spinal cord and is a bit more elastic than most
       ligaments of the spine. 4) The annullus fibrosus connects each
       vertebra to its neighbor via a circular band. It contains the
       gel-like pulp of the disc. Curiously, its fibers are oriented in
       a radial ply orientation much like radial ply cords of an
       automobile tire. While it contains the pulp of the disc, its
       primary function is to hold the disc in alignment with its
       vertebral neighbors. 5) The anterior and posterior longitudinal
       ligaments which extend between the top and a bottom of the
       vertebrae in a longitudinal path.

       The muscles of our spine are for the most part under our
       conscious control unlike muscles of the internal organs such as
       the intestine or stomach. This is an important distinction since
       certain exercises which we can perform consciously can help
       alleviate back pain. It is also important to understand that the
       muscles within your back are only PART of the entire story.
       Other muscles outside the back region strongly affect the shape
       and structure of the back, notably the abdominal and buttock
       muscles.

       Four general groups of muscles support and affect your back. 1)
       The all important abdominal muscles which provide frontal
       support and keep internal organs such as the stomach in correct
       alignment. 2) Extensor muscles of the spine which hold the
       rearmost portion of the torso in an upright position 3) Lateral
       muscles which provide side to side support 4) Hip muscles which
       affect the spine by virtue of their attachment to the pelvis.

       Each of these groups of muscles works in concert with the other.
       One or several groups may contract while the others
       cooperatively relax. Just like the young tree with guy wires to
       hold it erect in the wind, several groups of muscles function
       together to add stability to a less than ideal spinal design.

       The abdominal muscles consist of 1) The rectus abdominus 2)
       internal oblique 3) external oblique 4) transverse abdominus. In
       addition to support for internal organs, when contracted and in
       proper tone, these muscles control bending movements of the
       spine and affect proper posture. Some backaches can be relieved
       by strengthening this group of muscles.

       The extensor muscles lie along the length of the spine. They are
       positioned in layered bands and have detailed names which are
       not necessary within this brief discussion. Some of the layers
       are long, usually those lying close to the skin. Other extensor
       muscle layers are short, and are those which are much deeper
       below the skin. The attachment points of this set of muscles is
       complex, with segments connecting to spine, pelvis, ribs and the
       head. They are most frequently used when you arch your back,
       pull a heavy weight or tense your spine rigidly.

       The lateral muscles, are layered into the side regions of the
       spine. Two major groups are apparent: 1) The quadratus lumborum
       and 2) The psoas major. The quadratus helps in bending and is
       used in dancing and gymnastics. The psoas is quite large and
       attaches to the top of the thigh after running along the side
       the spine.

       In addition, four muscle groups of the hips, although not
       directly connected to the spine, can intimately affect its shape
       and performance. These hip group muscles are 1) the hip flexors
       2) hip abductors 3) hip adductors 4) hip extensors. Groups or
       combinations of these muscles can affect the tilt of the pelvis
       and the all important lumbar lordosis or curve of the lower
       back. The hip muscles dramatically control posture and exercise.
       Proper tension and tone of these muscle groups can affect back
       pain.

       The final stop on our anatomical tour of the back is the nervous
       system. Although the bones, muscles, ligaments and tendons form
       the mechanical structure of the back, it is the nerves which
       transmit sensations of pain.

       The tolerance for pain varies from individual to individual. A
       laborer or professional football player can endure one level of
       pain. An office worker or student perhaps a different level. The
       fact the back pain is often more nagging, virulent and
       unrelenting does not necessarily make it different - just more
       noticeable in our modern society.

       It seems most folks might be able to limp through the day with a
       toothache or muscle ache from playing weekend baseball. But back
       pain SEEMS different. It can lay you low and make you want to
       curl up in bed for days on end. The fact the few treatments SEEM
       to alleviate back pain makes it seems a special breed of pain.
       More unrelenting, debilitating and immune from the treatments of
       modern medicine.

       To understand backaches you need to glance at the anatomy of the
       nervous system. In man and most vertebrates the nerves are
       composed of thin fibers of tissue. The largest cluster of these
       fibers are obviously in the brain. The second largest
       concentration is in the spinal cord. Two separate structures
       distinguish the nervous system. 1) The autonomic nervous system
       and 2) the somatic nervous system.

       The autonomic portion of the system controls involuntary actions
       and senses. Functions such as vascular pressure, nutrition,
       heartbeat and digestion fall in this area. The somatic portion
       of the system governs voluntary actions and senses which we can
       consciously control like bending, looking, opening our mouths
       and so forth. At each level of the spinal chord are groups of
       nerves which receive impulses from transmission points like the
       skin and muscles. These are afferent nerves. Other groups of
       nerves transmit impulses from the brain and spinal cord back to
       the skin, muscle or site of origin. These are efferent nerves or
       motor nerves.

       Approximately 30 pairs of mixed spinal nerves emerge from
       openings in the vertebrae along the length of the spinal cord.
       The small holes which permit passage of nerve tissues through
       the vertebrae are known as foramens. The central spinal canal
       within each vertebra of course houses the spinal cord itself.

       Curiously the main spinal cord is housed in ONLY the upper two
       thirds of the spinal column. The spinal cord terminates and does
       not travel within the spinal canal lower than the first lumbar
       vertebra. In an infant the spinal cord does run the length of
       the bony spinal structure, but differential growth allows the
       spine to become longer while the growth of the spinal cord lags
       behind and thus occupies less than the full spinal column length
       in a mature individual.

       The nerves of the spinal cord continue their downward trip
       towards the legs and lower pelvis OUTSIDE the bony spinal
       structure once they have reached the level of the first lumbar
       vertebra. However the lumbar nerve roots do extend downward and
       emerge on the sides of the lower 5 vertebrae and sacrum. These
       lower lumbar nerve roots are extremely important in the
       production of pain from the classic "slipped disc" which we will
       discuss in a later chapter.

       From a practical standpoint what does this discussion of the
       nervous structure have to do with back pain? In simplest terms,
       this vast collection of nerves MONITORS a variety of locations
       which can cause pain: weak muscles, torn ligaments, torn discs,
       fractured bones and so forth. In some cases, efferent nerves can
       cause a specific muscle group to become overly tense and
       contract into painful spasm. This may be due to a torn disc,
       simple fatigue or poor posture. However this secondary muscle
       contraction in response to an initial pain can make a bad pain
       seem worse.

       We have looked at muscles, bones, tendons and nerves, but until
       this point we have not tied them together with a key word:
       SHAPE.

       Held together by the overlapping forces of various muscles, the
       spinal column assumes a precise S shape when viewed from the
       side. The reason why the spine is not normally straight is that
       varying forces and demands are present along its length. The S
       shape acts as an elegant "counterbalance" to these opposing
       forces. In fact, it has been calculated that the spine is 15
       times stronger due to its natural S curvature than if it were
       straight!

       This S-shaped curve is formed from four separate curves. Two
       curves bend towards the front of the body and two curves arch
       toward the back. The rearward bends are produced by the precise
       wedging of the vertebrae and are called primary spinal curves
       while the forward arches are produced by the wedging of the
       intervertebral discs and are called secondary spinal curves.

       The primary curves probably arose as a mechanical strengthening
       design during our existence as four legged quadrupeds. The two
       primary curves are in a sense genetically "ancient." They have
       been with us and all four legged quadrupeds for a long time.

       The secondary curves of the spine arose much later during
       evolution and were necessary when our upright posture was
       assumed. In a sense, nature had to counteract the primary curves
       when we began to walk in an erect position. And the only way to
       do this was to add rearward secondary curves.

       Only man has these unique secondary curves which are located in
       the cervical region, near the top of the spine, and the
       troublesome and pain-prone lumbar region in the lower spine. As
       we age, the lumbar curve tends to deteriorate and actually begin
       to reverse its curvature. In women the lumbar curve is also more
       acute or pronounced. The curvature becomes still more pronounced
       with pregnancy to offset the protruding abdomen. This effect can
       also occur in people of either sex who are overweight. We will
       talk more about this in a later chapter, but it is sufficient to
       understand that these curves are unique to man, crucial to
       proper balance of the spinal structure and somewhat adjustable
       depending on age, weight and sex.

       This ends our brief anatomical tour of the back. Obviously both
       structure and function have been simplified, but understanding
       even this basic level of anatomy sets the stage for that which
       comes next: what are the causes of pain and ultimately how do
       you treat them?

       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.