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Q: Dog Leg Shaking ( Answered 5 out of 5 stars,   0 Comments )
Subject: Dog Leg Shaking
Category: Family and Home > Pets
Asked by: uedauhes-ga
List Price: $10.00
Posted: 17 Oct 2005 08:35 PDT
Expires: 16 Nov 2005 07:35 PST
Question ID: 581270
Why do dogs shake their legs when you scratch their belly?
Subject: Re: Dog Leg Shaking
Answered By: crabcakes-ga on 17 Oct 2005 10:19 PDT
Rated:5 out of 5 stars
Hello Uedauhes,

    Seeing a dog shake thier hind leg is  indeed a funny looking reflex!

 ?Tickle a dog's tummy, and you could get a knee-jerk reaction.
There is a certain area on a dog's body that is referred to as the
"saddle region." It vaguely consists of the back, sides and flanks of
the pooch. Rubbing or scratching a dog in the saddle region (the exact
spot varies according to the individual pet) will cause the hind leg
to simulate a scratching motion. This is called the "scratch reflex."

The dog's spinal nerves pass all the way to his chest and abdomen, and
stimulation of these nerves will cause a feeling of "itchiness"
(similar to the irritation of a flea) somewhere on his body, causing
the rear leg to involuntarily attempt to scratch it. The leg extends
to different lengths or reaches to varying heights depending upon the
area that is stimulated.
Veterinarians who suspect spinal or neck damage in canines use the
scratch reflex as a diagnostic tool, much like when doctors tap humans
just below the kneecap to test nerve reactions.?

   ?And don't confuse this with an animal's scratch reflex -- that
goofy thing your dog does with his back foot when you tickle his side.
That's an involuntary response controlled by the spinal cord meant to
help rid the skin of insects and irritants. Your dog knows you're
already scratching him (creating the "itch" and getting rid of it
too), but he can't stop waving that leg anyway.?

   ?One of the most interesting discoveries of physiology was the
discovery, made simultaneously in France and Germany fifty years ago,
that nerve currents do not only start muscles into action, but may
check action already going on or keep it from occurring as it
otherwise might. Nerves of arrest were thus distinguished alongside of
motor nerves. The pneumogastric nerve, for example, if stimulated,
arrests the movements of the heart: the splanchnic nerve arrests those
of the intestines, if already begun. But it soon appeared that this
was too narrow a way of looking at the matter, and that arrest is not
so much the specific function of certain nerves as a general function
which any part of the nervous system may exert upon other parts under
the appropriate conditions. The higher centres, for example, seem to
exert a constant inhibitive influence on the excitability of those

 The reflexes of an animal with its hemispheres wholly or in part
removed become exaggerated. You all know that common reflex in dogs,
whereby, if you scratch the animal's side, the corresponding bind leg
will begin to make scratching movements, usually in the air. Now in
dogs with mutilated hemispheres this scratching reflex is so incessant
that, as Goltz first described them, the hair gets all worn off their

?Scratch reflex, a spinal reflex by which an itch or other irritation
of the skin causes a nearby body part to move over and briskly rub the
affected area.?

   ?In front of the tail: Where your dog's tail ends and his pelvis
begins is a sensitive, erogenous zone. By the way, many dogs
reflexively raise their hind legs when rubbed here.?

  ?A standard example is the scratch-reflex: if the insect bites the
dog so as to stimulate a particular centre, the dog's leg is brought
into action so as to scratch the irritated surface.

 This is all very simple and clear, and we begin to hope that it will
be possible to ex-plain all behaviour in the same simple way. Let us
suppose that a stimulus [p. 33]Ěproduces an action on account of the
hereditary structure of the organism. We shall have here a simple
mechanical pattern. But we must be careful not to assume too much.
Though we may select a case in which the process is apparently
invariable, we shall find that it is rarely so fixed as it appears: if
the dog for any reason cannot apply its leg to the right spot, it may
discover another way of removing the nuisance.

 It is also possible to make the action depend on a different
stimulus. If the usual cause of the action is associated with some
other stimulus, in course of time this second stimulus will become
effective by itself; the original reflex response will then follow the
occurrence of this second stimulus. The reflex act is then said to be
"conditioned", and the action as a whole is called a "conditioned

?Still further negative evidence that inhalation anesthesia offers
little or no protection to the brain-cells against trauma is derived
from the following experiment: A dog whose spinal cord had been
divided at the level of the first dorsal segment, and which had then
been kept in good condition for two months, showed a recovery of the
spinal reflexes, such as the scratch reflex, etc. Such an animal is
known as a "spinal dog." Now, in this animal, the abdomen and hind
extremities had no direct nerve connection with the brain. In this
dog, continuous severe trauma of the abdominal viscera and of the hind
extremities lasting for four (p 5-7) hours was accompanied by but
slight change in either the circulation or in the respiration, and by
no microscopic alteration of the brain-cells (Fig. 1). Judging from a
large number of experiments on NORMAL dogs under ether, such an amount
of trauma would have caused not only complete physiologic exhaustion
of the brain, but also morphologic alterations of all of the
brain-cells and the physical destruction of many (Fig. 2). We must,
therefore, conclude that, although ether anesthesia produces
against exhaustion from the trauma of surgical operations; ether is,
so to speak, but a veneer. Under nitrous oxid anesthesia there is
approximately only one-fourth as much exhaustion as is produced by
equal trauma under ether (Fig. 3). We must conclude, therefore, either
that nitrous oxid protects the brain-cells against trauma or that
ether predisposes the brain-cells to exhaustion as a result of trauma.
With these premises let us now inquire into the cause of this
exhaustion of the brain-cells.?

Hope this helps! Please request an Answer Clarification, before
rating, if any part  of my answer is unclear.

Regards, Crabcakes

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