Text 3. The nervous system

The nervous system is one of the most complex of all human body systems. More than 10 billion nerve cells are operating constantly all over the boy to coordinate the activities we do consciously and voluntarily, as well as those that occur unconsciously or involuntarily. We speak, we move muscles, we hear, we taste, we see, we think, our glands secrete hormones, we respond to danger, pain, temperature, touch, we have memory, association, discrimination – all of these composing a small number of the many activities controlled by our nervous system.

Nerve cells collected into bundles called nerves carry electrical messages all over the body. External stimuli, as well as internal chemicals such as acetylcholine, activate the cell membranes of nerve cells so as to release stored electrical energy within the cells. This energy when released and passed through the length of the nerve cell is called the nervous impulse. External receptors, like sense organs, as well as internal receptors in muscles and blood vessels receive and transmit impulses to the complex network of nerve cells in the brain and spinal cord. Within this central part of the nervous system, impulses are recognized, interpreted, and finally relayed to other nerve cells which extend out to all parts of the body, such as muscles, glands, and internal organs.

The nervous system can be classified into two major divisions: the central nervous system (CNS) and the peripheral nervous system. The CNS consists of the brain and spinal cord. The peripheral nervous system consists of 12 pairs of cranial nerves, which carry impulses between the brain and the head and neck, and 31 pairs of spinal nerves, which carry messages between the spinal cord and the chest, abdomen, and extremities.

In addition to the spinal and cranial nerves (whose functions are mainly voluntary and involved with sensations of smell, taste, sight, hearing, and muscle movements), the peripheral nervous system consists of a large group of nerves which function involuntarily or automatically without conscious control. These peripheral nerves are those of the autonomic nervous system. This system of nerve fibers carries impulses from the central nervous system to the glands, heart, blood vessels, and the involuntary muscles found in the walls of tubes like the intestines and hollow organs like the stomach and urinary bladder. These nerves are called efferent, since they carry impulses away from the central nervous system.

Some of the autonomic nerves are called sympathetic nerves and others are called parasympathetic nerves. The sympathetic nerves stimulate your body in times of stress and crisis, i.e., increase heart rate and forcefulness, dilate airways so more oxygen can enter, increase blood pressure, stimulate the adrenal glands to secrete epinephrine (adrenalin), and inhibit intestinal contractions so that digestion is slower. The parasympathetic nerves normally act as a balance for the sympathetic nerves. Parasympathetic nerves slow down heart rate, contract the pupils of the eye, lower blood pressure, stimulate peristalsis to clear the rectum, and increase the quantity of secretions like saliva.

Exercise 1. Translate into Russian:

To increase blood pressure; peripheral nerves; spinal cord; nerve cells; nervous impulse; blood vessels; intestines; saliva; involuntary movements; efferent.

Exercise 2. Translate into English:

1) Хребет є низкою нервових тканин, поєднаних у спинному хребті.

2) Гіпоталамус (hypothalamus) містить нейрони, що контролюють температуру тіла, сон, апетит, а також такі емоції, як страх та задоволення.

3) Нейрони та нерви є паренхімальними (parenchymal) тканинами нервової системи, тобто вони виконують основну роботу системи тим, що проводять імпульси по всьому тілу.

4) Мозок – це первинний центр регуляції й координації життєдіяльності усього організму.

5) Всі думки, пам’ять, асоціації знаходяться в головному мозку.