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Reflexes

In biology, a reflex is an involuntary and nearly instantaneous movement in response to a stimulus caused by a simple nervous circuit that involves a nerve impulse passing from a sensory nerve cell to a muscle or gland without reaching the level of consciousness. Scientific use of the term "reflex" refers to a behavior that is mediated via the reflex arc, as an anatomical pathway of a reflex, consisting of an afferent (sensory) and an efferent(secreto-motor) nerve.

The word “reflex” (from Latin reflex, “reflection”) was introduced into Biology by a 19^th-centure English neurologist, Marshall Hall. By reflex, Hall meant the automatic response of a muscle or several muscles to a stimulus that excites an afferent nerve. Now the term is used to describe an action that is an inborn central nervous system activity.

There are a lot of reflexes, unconditioned (unlearned) reflexes, such as patellar, plantar, pupillary, rooting reflexes and many others, but the simplest ones include swallowing, salivation, sweating, blinking, scratching, sucking (in infants), and others.

Knee- jerk reflex (patellar, kneecap, kneepan reflex) is a reflex produced by sharply tapping the patellar ligament. To test this reflex, the lower part of the leg should be relaxed (by crossing a leg at the knee) and the examiner taps the ligament below the patella with a small rubber hammer. The normal reaction is contraction of the quadriceps muscle, causing involuntary extension of the lower leg. The absence or decrease of this reflex is problematic, and known as Westphal's (Вестфаль'c) sign. It has a clinical significance used in determining neurodisorders or CNS diseases.

Probably the best-known reflex is the pupillary light reflex. If a light is flashed near one eye, the pupils of both eyes contract. It is a pupillary light reflex that controls the diameter of the pupil, in response to the intensity (luminance) of light that falls on the retina of the eye, thereby assisting in adaptation to various levels of darkness and light. Greater intensity light causes the pupil to become smaller, whereas lower intensity light causes the pupil to become larger.

Another reflex involving the eye is known as the lacrimal reflex. When something irritates the conjunctiva or cornea of the eye, the lacrimal reflex causes nerve impulses to pass along the fifth cranial nerve and reach the mesencephalon (midbrain) stimulating the lacrimal glands.

A plantar reflex is a reflex obtained by drawing a pointed object along the outer border of the sole of the foot from the heel to the little toe. The normal flexor response is a bunching and downward movement of the toes. An upward movement of the great toe is called extensor response or Babinski reflex. The presence of the Babinski sign can identify disease of the spinal cord and brain in adults, and also exists as a primitive reflex in infants.

POST-TEXT ASSIGMENTS

Exercise 7. Answer the following questions to the text:

1. What do we call a reflex in biology?

2. In what cases does a reflex occur?

3. What do we call a simple nervous circuit?

4. What does the reflex arc consist of?

5. Who was the first to introduce the term”reflex’?

6. What reflexes do you know?

7. What is the patellar reflex produced by?

8. In what case is the patellar reflex considered to be normal?

9. What is the main function of the pupillary light reflex?

10. What produces the lacrimal reflex?

11. What disease may the plantar reflex or Babinski reflex indicate?

Exercise 8. Match the words from the column A with those from the column B to form word-combinations as they appeared in the text. Translate these collocations into Ukrainian:

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