UNIT V. NERVOUS AND HORMONAL COORDINATION
Text 5.1. Nerves And Hormones
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Essential targets:
By the end of this spread you should be able to:
explain how information is transferred in a multicellular animal
compare nervous systems with endocrine systems.
Pre-reading
■Talk about the following two questions with your partner. Then scan the text to compare your ideas with the author`s.
What do you know about nerves` functions in human body?
In your opinion why is hormonal balance so important for humans?
■ Read the given text and make your essential assignments:
Sensitivity: responding to stimuli
All living organisms must be able to detect changes in their environment and respond appropriately. Changes in the environment are called stimuli (singular: stimulus). A stimulus may be in either the external environment (outside the organism) or the internal environment (inside the organism). Sensitivity, the ability to respond appropriately to stimuli, is one of the characteristic features of life. Each organism has its own specific type of sensitivity that improves its chances of survival. A single-celled amoeba, for example, can move away from a harmful stimulus such as very bright light, and move towards a favourable stimulus such as food molecules, but it can only distinguish between a limited number of different stimuli.
In an amoeba, the detection of the stimulus and the response to the stimulus must both take place in a single cell. However, in large multicellular animals such as mammals, stimuli are detected in sense organs, and organs that respond are called effectors. The sense organs and effectors may be in quite different parts of the body. In addition, responses usually involve the coordinated actions of many different parts of the body. To achieve this coordination, one part of the body must be able to pass information to another part. In mammals, there are two major systems that convey information: the nervous system and the endocrine (hormonal) system.
The nervous system
Nervous systems range from the simple nerve nets of jellyfish and sea anemones, which have no brain and relatively few interconnections, to the nervous system of humans, with brains of staggering complexity. The human brain contains many millions of cells, each of which may communicate with thousands of other nerve cells. Their interconnections form circuits which enable us to control our muscles, think, remember, and even study our own brains.
All the various animal nervous systems are fast-acting communication systems containing nerve cells, neurones, which convey information in the form of nerve impulses (electrochemical changes). Neurones take various forms but each has a cell body, containing a nucleus, and nerve fibres, long extensions that transmit nerve impulses rapidly from one part of the body to another. Fibres carrying impulses away from the cell body are called axons; those carrying impulses towards the cell body are called dendrons. Apart from the main nerve fibre, there may be small dendrons (dendrites) extending from the cell body.
In mammals, sensory neurones carry messages from peripheral sense organs to a central nervous system (CNS) consisting of the brain and spinal cord. The CNS acts as an integration centre and processes information from many sources. Motor neurones convey instructions from the CNS to effector organs (mainly muscles and glands).
A mammalian motor neurone can convey information rapidly over considerable distances; for example, a single nerve impulse may be transmitted from the spinal cord to the feet in a few milliseconds. These fast-conducting neurones are enclosed along most of their length by a thick insulating material called the myelin sheath. The myelin sheath is produced by special supporting cells called Schwann cells. The sheath is essentially a series of cell membranes, each produced by a Schwann cell and wrapped many times around the axon. Gaps between the membranes of each Schwann cell, called the nodes of Ranvier, are the key to the fast transmission of nerve impulses.
Fast transmission enables mammals to respond almost instantaneously to stimuli. Nerve impulses can be directed along the nerve fibres to specific points in the body so that responses can be very localised.
The endocrine system
Typically, the nervous system is adapted to convey messages rapidly between specific locations so that quick responses can be made. In contrast, the endocrine system is adapted to carry information from one source to many destinations to bring about long-lasting responses.
The endocrine system consists of a number of glands that secrete hormones (organic chemicals, usually proteins or steroids). The glands of the endocrine system are called endocrine glands or ductless glands because they secrete their hormones directly into the bloodstream. Once inside a blood vessel, a hormone is carried in the bloodstream so that it can reach almost any cell in the body. However, each hormone has its own target cells on which it acts. Therefore, although all the hormones are transported together in the bloodstream, each has its own specific effect on the body. In some cases, a target cell has specific receptor molecules on its cell surface membrane which bind the hormone molecule. Once bound onto the membrane, the hormone brings about its response.
Endocrine glands occur at strategic points around the body. Their hormones regulate a wide range of activities, including blood glucose concentration, gastric secretion, heart rate, metabolism, growth rate, reproduction, and water balance.
■ Glossary of essential terms for you to know
N
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English term
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Russian equivalent
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1.
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stimulus
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зд. раздражитель
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2.
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single-celled
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одноклеточный
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3.
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multicellular
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многоклеточный
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4.
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effector
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нервное окончание; эффектор
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5.
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mammals
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млекопитающие
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6.
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favourable
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благоприятный
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7.
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sense organs
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органы чувств
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8.
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relatively
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относительно; довольно
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9.
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spinal cord
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спинной мозг
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10.
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characteristic features
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отличительные признаки; характерные черты
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11.
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to transmit nerve impulses
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передавать нервные импульсы
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12.
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the myelin sheath
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миелиновая оболочка
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13.
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ductless glands
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железы внутренней секреции
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14.
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bloodstream
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кровоток
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15.
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blood vessel
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кровеносный сосуд
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16.
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heart rate
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пульс (частота сердцебиений)
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17.
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to respond to stimuli
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реагировать на раздражители
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18.
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cranial nerve
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черепно-мозговой нерв
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19.
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to process information
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обрабатывать информацию
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20.
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to enclose
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окружать; окаймлять
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21.
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insulating material
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изолирующий материал
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22.
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gastric secretion
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желудочная секреция
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■ Your Essential Assignments
I. Quick check
What is an axon?
In what form is information conveyed in:
a) the nervous system
b) the endocrine system?
II. Using monolingual English dictionary write down what the words below mean:
The nodes of Ranvier, proteins, muscle, reproduction.
III. Match the words with their definitions:
Words
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Definitions
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1. neurones
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a) the ability to respond appropriately to stimuli
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2. stimuli
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b) fibres carrying impulses away from the cell body
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3. axons
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c) nerve cells which convey information in the form of nerve impulses
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4. schwann cells
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d) fibres carrying impulses towards the cell body
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5. dendrons
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f) a thing that produces a reaction in living things
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6. sensitivity
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g) special supporting cells which produce the myelin sheath
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IV. Match words in A with words in B to form word combinations. Make up sentences with them.
A
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B
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1. favourable
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appropriately
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2. nervous
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information
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3. to process
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stimulus
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4. motor
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material
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5. target
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balance
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6. water
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system
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7. to respond
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neurones
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8. considerable
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environment
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9. insulating
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cell
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10. external
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distances
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V. Translate into English using all the active possible:
Железы внутренней секреции выделяют гормоны непосредственно в кровоток.
Эндокринная система состоит из некоторого количества желез, которые выделяют гормоны.
Реакции на раздражители обычно предполагают согласованные действия различных частей тела.
Центральная нервная система играет роль интеграционного центра и обрабатывает информацию из многих источников.
Каждый живой организм имеет свой тип чувствительности.
Гормоны регулируют такие процессы как частота сердцебиений, метаболизм, желудочная секреция и др.
Органы чувств и эффекторы находятся в разных частях тела.
Нервная система млекопитающих сложнее, чем нервная система одноклеточных организмов.
Нейроны передают информацию в форме нервных импульсов.
Концентрация глюкозы в крови регулируется эндокринной системой.
VI. Fill in the gaps with the words and expressions from the text:
Nervous systems ____ ____ the simple nerve nets to the nerve system of humans.
The endocrine system _____ ____ a number of glands.
Endocrine glands ____ ____ strategic points ____ the body.
The CNS ____ ____ an integration centre and processes information from many sources.
In large multicellular animals ____ ____ mammals, stimuli are detected in sense organs.
In mammals, there are two ____ systems that convey information: the nervous system and the endocrine system.
____ ____ the main nerve fibre, there may be small dendrons (dendrites) extending from the cell body.
Sensitivity, the ability to respond appropriately to stimuli, is one of the ____ ____ of life.
All living organisms must be able to ____ changes in their environment and respond ____.
Responses usually ____ the coordinated actions of many different parts of the body.
VII. Answer the following questions. Use all information given before.
What is sensitivity?
What do all animal nervous systems consist of?
Why are ductless glands called so?
What is the difference between sense organs and effectors?
What is CNS? What does it consist of?
What are two major systems that convey information in mammals?
VIII. Find English equivalents to the following word combinations and make up sentences with them:
N
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Russian term
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English equivalent
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1.
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главным образом, в основном
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2.
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передача нервных импульсов
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3.
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состоять из чего-либо
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4.
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находиться где-либо
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5.
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железы внутренней секреции
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6.
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выделять гормоны
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7.
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нервные волокна
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8.
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передавать информацию
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9.
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мозг человека
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10.
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содержать, заключать (в себе)
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11.
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реагировать соответственно, должным образом
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12.
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одноклеточный
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13.
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благоприятный
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14.
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ограниченное число / небольшое количество чего-либо
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IX. Read and translate the short text without any dictionary
Fact of life:
Most nerve fibres are very thin (less than 10 um in diameter), but the giant nerve fibre of a squid may be more than 1 mm across.
X. Food for thought.
Squids can escape from danger because they have giant nerve fibres. These fibres can conduct nerve impulses very rapidly, since speed of conduction is directly related to the diameter of the fibre. Squids have nerve fibres of normal diameter to control their slow cruising movements, but giant nerve fibres control their rapid escape response. When danger threatens, giant nerve fibres carry information from the brain down the body, causing circular muscles to contract and force a jet of water out of the body, enabling the squid to make a quick backward escape.
Suggest why squids have giant nerve fibres only for rapid escape responses. Why do mammals not require giant nerve fibres?
XI. Prepare a short presentation on 2 or 3 glands reflecting the following issues:
Type of gland, its position
Type of hormone, its function
Role of the hormone in human health
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