The nerves

Our nervous system is a busy network of nerves. It includes the nerves in our brain and the nerves that stretch throughout our bodies. Our brain is connected to the rest of our body by the spinal cord, a thick cable that runs down the spinal column in our back.

Nerves are made up of thin strands called neurons. There are millions of these throughout the nervous system and each consists of a cell body, which has short branches called dendrites. The long arm of the neuron is called the axon. Some axons are enclosed in a fatty layer called myelin, which helps to speed up the conduction, or passing, of nerve messages along the axon. Nerve cells in our spinal cord cannot be replaced, so spinal injury can be serious.

Nerves carrying sensations, such as pain, are known as sensory nerves. When a wasp stings your leg the sensory impulse travels up the leg and into the spinal cord. It is then transmitted to neurons in the gray matter of the cord, which link up with motor neurons. The impulse travels back down the leg in the motor nerve and the leg muscle tightens, making the leg jerk. The reflex action does not involve the brain.

Nerve impulses link up neurons by jumping across a gap called a synapse. When an impulse reaches the end of an axon, chemicals are released that allow it to pass across the synapse and on to the next neuron.

The axon of a motor neuron meets the muscle at a special junction called the motor end-plate. When the nerve impulse is received at the motor end-plate a substance called acetylcholine is released, which sticks to the outside of the muscle fiber, causing gates in the muscle fiber to open and let in sodium. This activity makes our muscle contract and movement occurs.

The brain and spinal cord compose the central nervous system. The somatic nervous system conducts nervous impulses that have already been processed, away from the central nervous system to the skeletal muscle tissue. The somatic nervous system is under voluntary control. All the parts of the nervous system, excluding the brain and spinal cord are collectively known as the peripheral nervous system.

The autonomic nervous system consists of the nerves that carry nervous impulses from the central system to the heart (cardiac muscles), to the muscles in the digestive system (smooth muscles), and to the glands. All of these muscles and glands contract and function involuntarily. The autonomic nervous system is subdivided into two parts, the sympathetic and parasympathetic systems. These function in opposition to one another; the first inhibits organs, while the latter usually excites organs.

2. COMPREHENSION CHECK.

a) Mark the following statements as true or false:

a) Our nervous system includes the nerves in our brain.

b) Our brain is connected to the rest of our body by the spinal column.

c) Nerves are made up of millions of neurons, each consisting of a cell body, which has short branches called dendrites.

d) Nerve cells in our spinal cord can be replaced.

e) Myelin slows down the conduction of nerve messages.

f) Our muscles contract and movement occurs due to nerve impulses.

g) The central nervous system is composed of the brain and spinal cord.

h) All parts of the nervous system are known as the peripheral nervous system.

i) The peripheral nervous system is subdivided into 2 parts: the sympathetic and parasympathetic.

j) The autonomic nervous system conduct nervous impulses from the central system to the heart.

k) Cardiac muscles, smooth muscles and glands contract and function under voluntary control.

l) The reflex action involves the brain.

b) Prepare extensive answers to these questions:

1) What does the nervous system include?

2) What connects our brain to the rest of our body?

3) What are our nerves made up of?

4) What is the axon?

5) What can the replacement of nerve cells in our spinal cord cause?

6) What happens when a wasp stings your leg?

7) What is the synapse?

8) How does a muscle contract and movement occur?

9) What is the difference between the central and peripheral nervous systems?

10) How do sympathetic and parasympathetic nervous systems function?

c) Find in each paragraph the sentence which conveys the main idea.

3. LANGUAGE FOCUS.

I. Find in the text: a) synonyms and b) antonyms to the following words:

a)	b)
to take place	parasympathetic
to be bound up (with)	peripheral
secret	to relax
to transfer	to break
to contract	to excite
to act, to work	to exclude
to be composed of	the first
to name	thin

II. Change the words in capital letters to fit the context of the sentence:

1. Our …… system is a busy network of nerves (NERVE).

2. The spinal cord ………our brain to the rest of our body (CONNECTION).

3. Myelin speeds up the ……….. of nerve messages along the axon (CONDUCT).

4. Spinal …… can be serious if nerve cells in our spinal cord are ……. (INJURE, REPLACEMENT).

5. ……. nerves are nerves carrying sensations (SENSE).

6. The leg muscle …. and the leg jerks (TIGHT).

7. The …. nervous system includes all the parts of the nervous system except the brain and spinal cord (PERIPHERY).

8. Glands and cardiac and smooth muscles ….. and function …… (CONTRACTION, VOLUNTEER).

3). Translate the sentences into English using the vocabulary of the unit:

I. Спинной мозг связывает мозг человека и его тело.

б) Нейрон – это нервная клетка, состоящая из тела и отходящих от него отростков: дендритов и аксона.

в) Серьезное повреждение спинного мозга может быть вызвано замещением в нем нервных клеток.

г) Головной и спинной мозг составляют центральную нервную систему.

д) В результате воздействия на чувствительные нервные окончания происходит возбуждение нервных тканей, которое делает возможным сокращение мышечных волокон и мышц.

е) Рефлекс – это непроизвольное движение какой-либо части тела в ответ на раздражение.

ж) Автономная нервная система состоит из двух частей, которые выполняют противоположные функции.

4. FOLLOW-UP ACTIVITIES.

a) Name different constituents and types of our nervous system and define their functions.

b) Discuss the following problem in pairs: The nervous system plays the leading role in the regulation of all physiologic processes in a complex organism.

c) Write an essay about our nervous system.

Дата добавления: 2015-09-03