NEURON
A neuron, or nerve cell (see Figure 5-1), conducts electrical signals (nerve impulses, or action potentials) between different body parts. Other characteristics of neurons are: 1- extreme longevity -- they are capable of full functioning for over 100 years; 2- they do not divide -- which means that they cannot replace themselves if damaged; and 3- they are extremely metabolically active -- that is, they need a large and constant supply of oxygen and glucose.
Neurons are composed of: the Cell Body, Processes, Dendrites, and the Axon.
This is just a hunk of cytoplasm (simply a part of a cell between the plasma membrane and the nucleus (essentially a sock around it)), and containing a number of organelles, or mini-organs. The cell body is irregularly shaped, and looks like it has one big eye (the nucleus).
Processes
The cell bodies have several "arms" (processes) attached to them -- called either "axons" or "dendrites." In discussing processes, a motor neuron will be used as typical, even though there are some other forms.
Dendrites
These critters are similar to tree branches. Their function is to be receptors, and they conduct signals to the cell body. As you might imagine, each neuron has many dendrites to cover the body -- inside and out.
Axon
An axon, roughly like a stem, exists only one per each neuron. In a functional sense, they are impulse generators and conductors that carry nerve impulses away from cell bodies. These impulses are carried to bulb-like axon terminals. From there they cross junctions called synapses, to other neurons in close proximity [Is that redundant?]. So, what is going on is that stimuli is being picked up by receptors, and messages are sent to the brain for a response. (In through dendrites, out through axons.)
Now that we have talked a little about how neurons communicate, lets discuss how they are classified.
Neurons are classified as either structural or functional,
Structural classification is based on how many processes extend from a cell body -- neurons are either multipolar, bipolar, or unipolar.
Most neurons have more than two processes, called multipolar. More than 99% of a body's neurons are multipolar. Bipolar neurons have two processes emanating from opposite sides of a cell body. Unipolar neurons are more-or-less a cell body sitting on a very short process (like a head on a neck), with a right and left branch. (You can look at this as a small head on a short neck, attached to wide shoulders.) The ends of the branches terminate with axon terminals on one end and dendrites on the other. This whole thing looks vaguely like an upside down "T" with a very short upright piece. The structural classifications are more-or-less irrelevant to us, so let's move on to the functional classification.
Functional neuron classification is based on the direction of nerve pulses relative to the CNS. Classifications so defined include: 1) sensory neurons, 2) motor neurons, and 3) interneurons. [Refer back to Figure 4-1 in the April 1998 issue of the Newsletter -- interneurons not shown.]
Sensory (or afferent) neurons send signals toward the CNS (central nervous system -- brain and spinal cord, you will remember) from the PNS (peripheral nervous system -- nerves coming out of the CNS).
Motor (or efferent) neurons carry signals away from the CNS to the effector organs (muscles and glands).
Interneurons (or "association") neurons (not depicted in Figure 5-1) are positioned between motor and sensory neurons, and are exclusively housed in the CNS.
Interneurons are combined into complex neural pathways that facilitate complex information processing.
SUPPORTING CELLS
Neurons all have a working relationship with one of six types of non-nervous system cells. Four types are in the CNS and two are in the PNS. Each type has its own special job, and in addition, supporting cells provide a covering for all neurons not involved with synapses. This insulation of neurons prevents cross-talk (interference) between proximal neurons.
Supporting cells in the CNS are called neuroglia, or glial cells. Neuroglia are similar to neurons, but are significantly smaller. In fact, there are about 50 neuroglia cells in the CNS for each neuron. About half of the brain is made up of these cells. One significant difference between glial cells and neurons is that they can divide themselves, unlike neurons. Important when a cell becomes cancerous -- cell reproduction, or splitting, is how cancer normally spreads. (Or metastasizes, for those of you who like technobabble.)
Glial cells include:
Myelin is a lipoprotein that surrounds the thicker axons, and becomes a segmented myelin sheath. It basically keeps nerve impulses moving along the axon by preventing electrical "leaks."
Myelin in the PNS consists of Schwann cells -- the sheath looks something like a string of beads with a short gap between each. These gaps are called "nodes of Ranvier," and are roughly one millimeter apart. Nerve impulses quickly jump these nodes -- remember that myelin is only in contact with larger, high speed axons.
Myelin in the CNS is formed by oligodendrocytes. The thinnest axons in the CNS , as in the PNS, are unmyelinated, but are still covered -- by glial cells.
Multiple Sclerosis (MS) is an example of what happens when myelin sheaths are eroded. MS is an autoimmune disease characterized by erosion of myelin sheaths (degraded by the body's own immune system), thus allowing leakage. Messages just don't get to their proper destinations, at least not intact. Early symptoms are degraded body functions. In later stages, functions shutdown to a point where death may occur.
Vitamin E is a powerful antioxident that has been a popular subject in the past year or so. According to Bernadine Healy, M.D., dean of the College of Medicine at Ohio State University, studies have indicated that vitamin E may mitigate the following conditions:
Deciphering medical terms -- as promised last month. Here is a more comprehensive list of prefix-root-suffix components of a number of medical terms to help you understand some of your doctor's medspeak.
| a(n) | absence of | hyster(o) | uterus |
| acou, acu | hear | iater(o) | doctor |
| aden(o) | gland | infra | beneath |
| aer(o) | air | inter | among, between |
| alg | pain | intra | inside |
| andr(o) | man | itis | inflammation |
| angi(o) | vessel | lact(o) | milk |
| ankyl(o) | crooked, curved | lepar(o) | flank, abdomen |
| ante | before | latero | side |
| anter(i) | front, forward | leuk(o) | white |
| anti | against | lingu(o) | tongue |
| arteri(o) | artery | lip(o) | fat |
| arthr(o) | joint | lys(is) | dissolve |
| articul | joint | mal | bad, abnormal |
| ather(o) | fatty | malac | soft |
| audi(o) | hearing | mamm(o) | breast |
| aur(i) | ear | mast(o) | breast |
| aut(o) | self | megal(o) | large |
| bi, bis | double, twice, two | melan(o) | black |
| brachy | short | mening(o) | membranes |
| brady | slow | my(o) | muscle |
| bucc(o) | cheek | myc(o) | fungus |
| carcin(o) | cancer | myel(o) | marrow |
| cardi(o) | heart | nas(o) | nose |
| cephal(o) | head | necr(o) | death |
| cerebr(o) | brain | nephr(o) | kidney |
| cervic | neck | neur(o) | nerve |
| chol(e) | bile, or referring to the gall-bladder | nutri | nourish |
| chondr(o) | cartilage | ocul(o) | eye |
| circum | around, about | odyn(o) | pain |
| contra | against, counter | oma | tumor |
| corpor | body | onc(o) | tumor |
| cost(o) | rib | oophor(o) | ovaries |
| crani(o) | skull | opthalm(o) | eye |
| cry(o) | cold | opia | vision |
| cut | skin | opsy | examination |
| cyan(o) | blue | orchi(o) | testes |
| cyst(o) | bladder | osis | condition |
| cyt(o) | cell | osse(o) | bone |
| dactyl(o) | finger or toe | oste(o) | bone |
| dent | tooth | ot(o) | ear |
| derm(ato) | skin | path(o) | disease |
| dipl(o) | double | ped(o) | child |
| dors | back | penia | deficient, deficiency |
| dys | bad, faulty, abnormal | peps, pept | digest |
| ectomy | excision (removal by cutting) | peri | around |
| emia | blood | scope | instrument |
| encephal(o) | brain | scopy | examination |
| end(o) | inside | somat(o) | body |
| enter(o) | intestine | spondyl(o) | vertebra |
| epi | outer, superficial, upon | steat(o) | fat |
| erythr(o) | red | sten(o) | narrow, compressed |
| eu | normal | steth(o) | chest |
| extra | outside | stom | mouth, opening |
| gastr(o) | stomach | supra | above |
| gen | become, originate | tachy | fast, quick |
| gloss(o) | tongue | therap | treatment |
| glyc(o) | sweet, or referring to glucose | therm(o) | heat |
| gram, graph | write, record | thorac(o) | chest |
| gyn | woman | thromb(o) | clot, lump |
| hem(ato) | blood | tomy | incision (operation by cutting) |
| hemi | half | toxi | poison |
| hepat(o) | liver | uria | urine |
| hist(o) | tissue | vas(o) | vessel |
| hydr(o) | water | ven(o) | vein |
| hyper | excessive, high | vesic(o) | bladder |
| hypo | deficient, low | xer(o) | dry |
That's all folks!
(Q) I have had patellar tendonitis, and am sort of getting over it. I have been using ice and rest, and some gentle stretching, but now I would like to start something more vigorous. Any suggestions?
Y.F., Las Vegas, NV
(A) Stationary cycling can be helpful. Try alternating regular two-legged cycling with one-legged cycling (of course using pedal straps). The one-legged mode is done using the recovering leg, since the two-legged technique will allow the uninjured leg to take over more than its share of the load. Try alternating the two techniques, maybe switching every minute for 10 to 15 minutes total, in the beginning.
I like dumbbell exercises for the same reason, each side has to do its full share; where the non-dominant side can be doing less than half the work when using a barbell or many exercise machines, where separate sides are not isolated.
(Q) Should I use cold or heat for sprains or strains. And what is the difference, or are they just two basically interchangeable terms?
T.C., Cupertino, CA
(A) No, they aren't the same. A strain is an overstretched or partially or completely torn muscle, and a sprain is a similar injury to connective tissue -- ligaments and tendons. Initial treatment should be cold -- R(est) I(ce) C(ompression) E(levation) is good. Cold helps reduce swelling. It is usually recommended that heat should not be applied for the first 48 hours, after that it may help the healing process. Alternating heat and cold applications often works effectively.
(Q) I need to buy some new running shoes. Which are the best?
N.F., Las Vegas, NV
(A) There is no best running shoe for everyone. Runner's World magazine typically devotes an issue to this subject every year. Another source of information is the American Orthopaedic Foot and Ankle Society. Send a request for information to: 1216 Pine St., Suite 201, Seattle, WA; and include a self-addressed, stamped, business-sized envelope; and they will send you some information about sports shoes -- sizing, arch suppports, heel pads, etc. Just name your sport.
(Q) I like fish, but I would like to eat the healthiest varieties -- highest in omega-3 fats -- but I'm not sure which are best.
D.B., Bandon, OR
(A) Your list should concentrate on fatty fish that inhabit deep, cold water areas. Mackeral are number one, followed by herring, lake trout, chinook salmon, lake whitefish, tuna, Atlantic salmon, and bluefish. These are all good sources of essential omega-3 fatty acids, but don't worry that they will make you fat, they are similar, ounce-for-ounce, to the leanest cuts of beef.
(Q) A friend suggested that I add jumping rope to my fitness program. Do you think that makes any sense?
G.F., Salt Lake City, UT
(A) It can be a good time-saver when you are in a hurry; or an addition to an existing program; or even an "instead of" activity in your program.
It has been said that five minutes of jumping rope uses up the same number of calories as 15 minutes of brisk walking. It is an aerobic exercise for only about .37 seconds if you haven't done it since the sixth grade, but it can be aerobic with practice; at any rate, it is a calorie burner. And it is something that most people can fit into short time slots in a busy schedule; it will tone and shape calf muscles; it can improve balance and agility; and it can be used as a change in an exercise routine; some people will even find it to be fun. You can be quite creative with your jumping patterns, and can even do it without a rope.
Jumping rope can even be considered a weight-bearing exercise -- a tool in the fight against osteoporosis. And it at least moderately strengthens the muscles that support the knee -- important for active women, who have far more knee injuries than men.
According to Laura Huston, a researcher at the University of Michigan, women usually stabilize their knees with the quads (muscles in the front of the thighs) which pull on the knees at an angle, which can lead to knee ligament strains. Ms Huston contends that jumping rope trains the hamstring muscles (back of thigh) to balance the pull on the knees and reduce stress on them. She says that women should jump rope three to five minutes a day to get these two muscle groups properly coordinated to help protect against knee injury. But whether she is right or not, rope jumping is a good exercise.
(Q) My personal trainer likes me to do power cleans, but I'm not thrilled by them, is there any benefit to doing this exercise?
A.L., Los Altos, CA
(A) A power clean is generally classified as a back exercise, but it also involves the hip, thigh, arm biceps, and forearm muscles. And you may have noticed that it can be a serious grip stressor. Because it uses most major muscle groups, it is considered to be a good warm-up exercise.
_____________________________________
For questions or comments call MAF at (408) 739-0501,
send snail mail to: 965 Ponderosa Ave., 25, Sunnyvale, CA, 94086,
or click here to send an email to the author, Mike Fenner
To see the MAF FITNESS NEWSLETTER archives, go to http://www.dinc.com/maf/