Farmasevtika instituti farmakologiya va klinik farmatsiya kafedrasi

 
Mechanism of Referred Pain. 
Figure 48-5 shows the probable mechanism by which most 
pain is referred. In the figure, branches of visceral pain fibers are shownto synapse in the spinal cord 
on the same second-order neurons (1 and 2) that receive pain signals from the skin. When the visceral 
pain fibers are stimulated, pain signalsfrom the viscera are conducted through at least some 
of the same neurons that conduct pain signals from the skin, and the person has the feeling that the 
sensationsoriginate in the skin itself. 
Visceral Pain 
Pain from the different viscera of the abdomen and chest isone of the few criteria 
that can be used for diagnosing visceral inflammation, visceral infectious disease, and other 
visceralailments. Often, the viscera have sensory receptors for no other modalities of sensation besides 
pain.
Causes of True Visceral Pain 
Any stimulus that excites pain nerve endings in diffuse areasof the viscera can cause visceral pain. 
Such stimuli includeischemia of visceral tissue, chemical damage to the surfaces of the viscera, spasm 
of the smooth muscle of a hollow viscus,excess distention of a hollow viscus, and stretching of the 
connective tissue surrounding or within the viscus 
 

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Refraction of Light 
Refractive Index of a Transparent Substance. 
Light rays travel through air at a velocity of 
about 300,000 km/sec, but they travel much slower through transparent solids and liquids. The 
refractive index of a transparent substance is the
ratio 
of the velocity of light in air to the velocity in the 
substance. The refractive index of air itself is 1.00. Thus, if light travels through a particular type of 
glass at a velocity of 200,000 km/sec, the refractive index of this glass is 300,000 divided by 200,000, 
or 1.50. 
Refraction of Light Rays at an Interface Between Two Media with Different Refractive 
Indices.