III. Independent Work: Pain

Exercise 1. Read the text.

Pain

There are no adequate stimuli for pain; any form of stimulus evokes pain if it's sufficiently strong. Pain is the most primitive and one of the most important sensations. It is generally held that the free nerve endings of small myelinated fibers which do not end in specialized anatomic structures constitute the receptors for pain. They are the most widely distributed receptors in the body, being found in the skin, cornea, blood vessels, and most viscera. The threshold of irritability is high; consequently the stimulations appearing in them are of such intensity as to threaten health and life. For this reason they are frequently called nociceptors. They elicit protective and defensive reflexes. Because of their vital importance, the impulses from the nociceptors always take precedence in the reflex activity of the nervous system.

Many internal organs are insensitive to what are generally regarded as painful stimuli. Tumors have been removed from the brain of patients, who remained conscious during the entire operation, without causing any pain. Handling, cutting or cauterizing the intestine never gives rise to pain. However, pain can be elicited from most hollow organs by an increase of the tension of their walls: this is brought about by great distension (e.g. accumulation of gas in the intestine, or the passage of a gallstone through the bile ducts) or by excessive contraction of their musculature.

Pain can be relieved by reducing the irritability of the nerve as by compression, cold, drugs or by reducing the sensitivity of the cerebral cells, as in general anesthesia.

Pain can be elicited by stimulating a nerve fiber at any point along its course, but the sensation is always referred, or projected, to the endings of the nerve.

Pain cannot always be definitely localized, especially when it is severe and of long duration, the sensation then seems to spread to neighboring parts.

Pain experienced in internal organs is sometimes referred to another and generally, external part of the body. In diseases of some internal organs, certain cutaneous areas may become hyperalgesic (excessively sensitive to pain), so that the least stimulation, such as a soft touch, or even a breath of air, applied to this part of the skin gives rise to pain.

Exercise 2. Find interpretation of the following words in the dictionary.

To evoke, sufficiently, cornea, viscera, threshold, irritability, to threaten, nociceptor, to elicit.

Exercise 3. Find sentences about receptors in the text.

Exercise 4. Find sentences about reaction of the visceral organs to pain.

Exercise 5. Answer the questions.

1. How can pain be relieved? 2. Can pain be localized? 3. Where are receptors for pain distributed? 4. What are nociceptors? 5. Is pain the most primitive sensation?

UNIT TWENTY-THREE

I	Speaking	Sensory System
II	Grammar	Modal Verbs and Verbs of Modal Meaning
III	Independent Work	Drugs