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Active vocabulary
ability [q'bIlIt] здатність, можливість (зробити щось)
to be аblе, (to do smth.) бути здатним (щось зробити)
amount кількість
amount (to) нараховувати, становити
area область, зона
at least у крайньому разі
brain мозок
cognition [kPg'nIS(q)n] знання; пізнання; пізнавальна здатність
cognize ['kPgnaIz] пізнавати, осягати
distinguish [dIs'tINgwIS] відрізняти, розрізняти
distinction [dIs'tIN(k)S(q)n] розрізнення, розпізнавання
distinctive відмітний, характерний
filter out відфільтровувати
hearing слух
impression враження
impress вражати
impressive виразний; хвилюючий
message повідомлення
quality якість
quantity ['kwPntIti] кількість
sights зір, вид
smell нюхати ; пахнути
supply (with) постачати
taste смак
taste пробувати на смак
touch дотик
touch доторкатися
transmit [trxnz'mIt] передати
transmission передача
neuron, neurone ['nj(q)|rPn, -rqVn] нейрон, нервова клітина
glial ['glaIql, glIql] глиальный
the glial cells of the brain - нервові клітини головного мозку
nerve [nE:v] нерв
nerve plexus - нервове сплетіння
axon, axone ['xksPn, 'xksqVn] аксон, відросток осьового циліндра (нервової клітини)
interneural ["Intq'nj(q)rql] міжневральний
sodium ['sqVdIqm] натрій
multicentric ["mAltI'sentrIk] багатоцентровий
neurotransmitter ["nj(q)rq(V)trxnz'mItq] медіатор, трансмітер
tetanus ['tet(q)nqs] судома; спазм(а)
botulinus ["bPtjV'l(a)Inqs] бакт. збудник ботулізму
cephalized ['sefqlaIzd] що має голову
pons [pPnz] (pl pontes) (варолієв) міст
mammal ['mxm(q)l] ссавець
visceral ['vIs(q)rql] organs внутрішні органи
secretion виділення
smooth muscles гладкі м'язи
sympathetic ["sImpq'TetIk] симпатичний
parasympathetic ["pxrqsImpq'TetIk] парасимпатичний
afferent доцентровий
efferent відцентровий
thoracic portions грудний відділ
thorax грудна клітина
lumbar поперековий
spinal cord спинний мозок
to originate брати початок, відбуватися, виникати
sacral division of the cord крижовий відділ спинного мозку
brainstem стовбур мозку
next to or surrounding сусідні або навколишні
lateral бічний
gray matter сіра речовина
striated muscles смугасті м'язи
ramus галузь, відгалуження
ganglionic гангліозний
fiber тканина
hence звідси
innervate іннервувати
sweat glands потові залози
restful periods періоди спокою
hypothalamus гіпоталамус
rage лють
anterior передній
posterior задній
digestion травлення
pupillary dilation розширення зіниць
Text 1.
The Neuron
Nervous tissue is composed of two main cell types: neurons and glial cells. Neurons transmit nerve messages. Glial cells are in direct contact with neurons and often surround them.
The neuron is the functional unit of the nervous system. Humans have about 100 billion neurons in their brain alone. While variable in size and shape, all neurons have three parts. Dendrites receive information from another cell and transmit the message to the cell body. The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells. The axon conducts messages away from the cell body.
Structure of a typical neuron. Three types of neurons occur. Sensory neurons typically have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system. Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands). Interneurons are found only in the central nervous system where they connect neuron to neuron.
Structure of a neuron and the direction of nerve message transmission. Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells. Schwann cells serve as supportive, nutritive, and service facilities for neurons. The gap between Schwann cells is known as the node of Ranvier, and serves as points along the neuron for generating a signal. Signals jumping from node to node travel hundreds of times faster than signals traveling along the surface of the axon. This allows your brain to communicate with your toes in a few thousandths of a second.
The Nerve Message
The plasma membrane of neurons, like all other cells, has an unequal distribution of ions and electrical charges between the two sides of the membrane. The outside of the membrane has a positive charge, inside has a negative charge. This charge difference is a resting potential and is measured in millivolts. Passage of ions across the cell membrane passes the electrical charge along the cell. The voltage potential is -65mV (millivolts) of a cell at rest (resting potential). Resting potential results from differences between sodium and potassium positively charged ions and negatively charged ions in the cytoplasm. Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane. This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump. The sodium-potassium pump maintains this unequal concentration by actively transporting ions against their concentration gradients.
Changed polarity of the membrane, the action potential, results in propagation of the nerve impulse along the membrane. An action potential is a temporary reversal of the electrical potential along the membrane for a few milliseconds. Sodium gates and potassium gates open in the membrane to allow their respective ions to cross. Sodium and potassium ions reverse positions by passing through membrane protein channel gates that can be opened or closed to control ion passage. Sodium crosses first. At the height of the membrane potential reversal, potassium channels opens to allow potassium ions to pass to the outside of the membrane. Potassium crosses second, resulting in changed ionic distributions, which must be reset by the continuously running sodium-potassium pump. Eventually enough potassium ions pass to the outside to restore the membrane charges to those of the original resting potential. The cell begins then to pump the ions back to their original sides of the membrane.
The action potential begins at one spot on the membrane, but spreads to adjacent areas of the membrane, propagating the message along the length of the cell membrane. After passage of the action potential, there is a brief period, the refractory period, during which the membrane cannot be stimulated. This prevents the message from being transmitted backward along the membrane.
Steps in an Action Potential
1. At rest the outside of the membrane is more positive than the inside.
2. Sodium moves inside the cell causing an action potential, the influx of positive sodium ions makes the inside of the membrane more positive than the outside.
3. Potassium ions flow out of the cell, restoring the resting potential net charges.
4. Sodium ions are pumped out of the cell and potassium ions are pumped into the cell, restoring the original distribution of ions.
Synapses
The junction between a nerve cell and another cell is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neurotransmitters. Neurotransmitters are stored in small synaptic vessicles clustered at the tip of the axon.
Arrival of the action potential causes some of the vesicles to move to the end of the axon and discharge their contents into the synaptic cleft. Released neurotransmitters diffuse across the cleft, and bind to receptors on the other cell's membrane, causing ion channels on that cell to open. Some neurotransmitters cause an action potential, others are inhibitory.
Neurotransmitters tend to be small molecules, some are even hormones. The time for neurotransmitter action is between 0,5 and 1 millisecond. Neurotransmitters are either destroyed by specific enzymes in the synaptic cleft, diffuse out of the cleft, or are reabsorbed by the cell. More than 30 organic molecules are thought to act as neurotransmitters. The neurotransmitters cross the cleft, binding to receptor molecules on the next cell, prompting transmission of the message along that cell's membrane. Acetylcholine is an example of a neurotransmitter, as is nor epinephrine, although each acts in different responses. Once in the cleft, neurotransmitters are active for only a short time. Enzymes in the cleft inactivate the neurotransmitters. Inactivated neurotransmitters are taken back into the axon and recycled.
Diseases that affect the function of signal transmission can have serious consequences. Parkinson's disease has a deficiency of the neurotransmitter dopamine. Progressive death of brain cells increases this deficit, causing tremors, rigidity and unstable posture. L-dopa is a chemical related to dopamine that eases some of the symptoms (by acting as a substitute neurotransmitter) but cannot reverse the progression of the disease.
The bacterium Clostridium tetanus produces a toxin that prevents the release of GABA. GABA is important in control of skeletal muscles. Without this control chemical, regulation of muscle contraction is lost; it can be fatal when it effects the muscles used in breathing.
Clostridium botulinum produces a toxin found in improperly canned foods. This toxin causes the progressive relaxation of muscles, and can be fatal. A wide range of drugs also operate in the synapses: cocaine, LSD, caffeine, and insecticides.
Nervous Systems
Multicellular animals must monitor and maintain a constant internal environment as well as monitor and respond to an external environment. In many animals, these two functions are coordinated by two integrated and coordinated organ systems: the nervous system and the endocrine system.
Three basic functions are performed by nervous systems:
1. Receive sensory input from internal and external environments
2. Integrate the input
3. Respond to stimuli
Sensory Input
Receptors are parts of the nervous system that sense changes in the internal or external environments. Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or hormone levels that are converted to a signal and sent to the brain or spinal cord.
Integration and Output
In the sensory centers of the brain or in the spinal cord, the barrage of input is integrated and a response is generated. The response, a motor output, is a signal transmitted to organs than can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.
Endocrine Systems
Some animals have a second control system, the endocrine system. The nervous system coordinates rapid responses to external stimuli. The endocrine system controls slower, longer lasting responses to internal stimuli. Activity of both systems is integrated.
Divisions of the Nervous System
The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops. The Central Nervous System (CNS) includes the brain and spinal cord. The Peripheral Nervous System (PNS) connects the CNS to other parts of the body, and is composed of nerves (bundles of neurons).
Not all animals have highly specialized nervous systems. Those with simple systems tend to be either small and very mobile or large and immobile. Large, mobile animals have highly developed nervous systems: the evolution of nervous systems must have been an important adaptation in the evolution of body size and mobility.
Coelenterates, cnidarians, and echinoderms have their neurons organized into a nerve net. These creatures have radial symmetry and lack a head. Although lacking a brain or either nervous system (CNS or PNS) nerve nets are capable of some complex behavior.
Bilaterally symmetrical animals have a body plan that includes a defined head and a tail region. Development of bilateral symmetry is associated with cephalization, the development of a head with the accumulation of sensory organs at the front end of the organism. Flatworms have neurons associated into clusters known as ganglia, which in turn form a small brain. Vertebrates have a spinal cord in addition to a more developed brain.
Chordates have a dorsal rather than ventral nervous system. Several evolutionary trends occur in chordates: spinal cord, continuation of cephalization in the form of larger and more complex brains, and development of a more elaborate nervous system. The vertebrate nervous system is divided into a number of parts. The central nervous system includes the brain and spinal cord. The peripheral nervous system consists of all body nerves. Motor neuron pathways are of two types: somatic (skeletal) and autonomic (smooth muscle, cardiac muscle, and glands). The autonomic system is subdivided into the sympathetic and parasympathetic systems.
Peripheral Nervous System
The Peripheral Nervous System (PNS) contains only nerves and connects the brain and spinal cord (CNS) to the rest of the body. The axons and dendrites are surrounded by a white myelin sheath. Cell bodies are in the central nervous system (CNS) or ganglia. Ganglia are collections of nerve cell bodies. Cranial nerves in the PNS take impulses to and from the brain (CNS). Spinal nerves take impulses to and away from the spinal cord. There are two major subdivisions of the PNS motor pathways: the somatic and the autonomic.
Two main components of the PNS:
1. Sensory (afferent) pathways that provide input from the body into the CNS.
2. Motor (efferent) pathways that carry signals to muscles and glands (effectors).
Most sensory input carried in the PNS remains below the level of conscious awareness. Input that does reach the conscious level contributes to perception of our external environment.
Somatic Nervous System
The Somatic Nervous System (SNS) includes all nerves controlling the muscular system and external sensory receptors. External sense organs (including skin) are receptors. Muscle fibers and gland cells are effectors. The reflex arc is an automatic, involuntary reaction to a stimulus. When the doctor taps your knee with the rubber hammer, she/he is testing your reflex (or knee-jerk). The reaction to the stimulus is involuntary, with the CNS being informed but not consciously controlling the response. Examples of reflex arcs include balance, the blinking reflex, and the stretch reflex.
Sensory input from the PNS is processed by the CNS and responses are sent by the PNS from the CNS to the organs of the body.
Motor neurons of the somatic system are distinct from those of the autonomic system. Inhibitory signals cannot be sent through the motor neurons of the somatic system.
Autonomic Nervous System
The Autonomic Nervous System is that part of PNS consisting of motor neurons that control internal organs. It has two subsystems. The autonomic system controls muscles in the heart, the smooth muscle in internal organs such as the intestine, bladder, and uterus. The Sympathetic Nervous System is involved in the fight or flight response. The Parasympathetic Nervous System is involved in relaxation. Each of these subsystems operates in the reverse of the other (antagonism). Both systems innervate the same organs and act in opposition to maintain homeostasis. For example: when you are scared the sympathetic system causes your heart to beat faster; the parasympathetic system reverses this effect.
Motor neurons in this system do not reach their targets directly (as do those in the somatic system) but rather connect to a secondary motor neuron which in turn innervates the target organ.
Central Nervous System
The Central Nervous System (CNS) is composed of the brain and spinal cord. The CNS is surrounded by bone-skull and vertebrae. Fluid and tissue also insulate the brain and spinal cord.
The medulla oblongata is closest to the spinal cord, and is involved with the regulation of heartbeat, breathing, vasoconstriction (blood pressure), and reflex centers for vomiting, coughing, sneezing, swallowing, and hiccupping. The hypothalamus regulates homeostasis. It has regulatory areas for thirst, hunger, body temperature, water balance, and blood pressure, and links the Nervous System to the Endocrine System. The midbrain and pons are also part of the unconscious brain. The thalamus serves as a central relay point for incoming nervous messages.
The cerebellum is the second largest part of the brain, after the cerebrum. It functions for muscle coordination and maintains normal muscle tone and posture. The cerebellum coordinates balance.
The conscious brain includes the cerebral hemispheres, which are separated by the corpus callosum. In reptiles, birds, and mammals, the cerebrum coordinates sensory data and motor functions. The cerebrum governs intelligence and reasoning, learning and memory. While the cause of memory is not yet definitely known, studies on slugs indicate learning is accompanied by a synapse decrease. Within the cell, learning involves change in gene regulation and increased ability to secrete transmitters.
Text 2.
Autonomic Nervous System
The autonomic nervous system is involved in the regulation of the visceral organs and their secretions and in the control of smooth muscles. It consists of two main divisions: the sympathetic and the parasympathetic. Within each of these divisions there are both afferent (sensory) and efferent (motor) components. The sym¬pathetic branch of the autonomic system arises from the thoracic and lumbar portions of the spinal cord. The parasympathetic division originates in the sacral divi¬sion of the cord and in the brainstem. Thus, the term «parasympathetic» literally means next to or surroun¬ding the sympathetic nervous system.
The Sympathetic System. Specifically arising from cell bodies located in the lateral horn of the gray matter of the spinal cord in the thoracic and lumbar regions, the sympathetic system is primarily an efferent or output system. Axons leave the cell bodies and exit through the ventral root of the spinal cord along with somatic fibers destined for striated muscles. The main difference between autonomic and somatic outflow is that in the case of the autonomic outflow there is a ganglion and ganglionic synapse. Thus, fibers exiting in the autonomic nervous system leave the ventral root a short distance from the cord via the white ramus and there enter a ganglionic chain known as the sympathetic paravertebral ganglionic chain. Once these fibers enter the chain they may ascend or descend in the chain and then exit at a difference synapse in the chain.
In some cases a sympathetic fiber, after synapsing in the ganglionic chain, can re-enter the main spinal nerve by means of the gray ramus. The portion of the sympathetic outflow lying between the spinal cord and the ganglionic synapse is termed the preganglionic fiber. The portion beginning at the syn¬apse and traveling toward the target organ is called the postganglionic fiber. All preganglionic fibers utilize ace-tylcholine as a neurotransmitter and hence are called cholinergic fibers. Almost all postganglionic fibers that enter visceral organs utilize noradrenalin as the neu¬rotransmitter at their terminals and are called adrenergic fibers. Postganglionic sympathetic fibers that inner¬vate blood vessels and the sweat glands, however, are cholinergic.
The Parasympathetic Nervous System. In the para¬sympathetic nervous system, fibers from the sacral por¬tion of the spinal cord exit through the ventral roots but do not pass through a specific chain of ganglia. Instead they head directly toward the target organ in the sacral spinal nerves and synapse in parasympathetic ganglia located in its vicinity. Para-sympathetic fibers exit from the brainstem within cranial nerves.
Generally the two divisions of the autonomic nervous system, sympathetic and parasympathetic, act in opposi¬tion to one another. The sympathetic division is primari¬ly active during periods of stress or emergency. The para¬sympathetic system predominates during quiet, restful periods. The latter is involved in homeostatic mechanisms - that is, the normal regulation of organ system.
Text 3.
Sensation and the Nervous System
Of all features that distinguish man from animals, the most striking and the most complex is his ability to make sense to himself and to others of the world around him. He perceives, learns, thinks, remembers and communicates in language and symbol to others. The general term used for the study of these abilities is cognition.
Through the senses we receive information about the world around us. We have at least eleven senses, but the five main ones are taste, touch, smell, hearing and sight. Each of these senses supplies a different quality of information about environment, but they normally work in harmony to give us a complex multi-dimensional impression of the world. The brain is the control centre and the nerves resemble message lines, transmitting information from our senses to our brain.
So far we have named the five basic senses but these are not the only means that man has for receiving information. The sense of touch for example, can be divided into four separate sub-senses of pressure, pain, warmth and cold. Each has its characteristic receptors and varying concentrations of receptors in the body. The ends of the fingers have a large number of pressure receptors, but the back of the hand has very few.
Each sense organ responds to energy (the ear to sound energy, the eye to light waves, etc.) which it transforms into nerve impulses. These nerve impulses are sent along nerve fibres in the nervous system to the brain. The nervous system is an intricate set of fibres. There are differ¬ent pathways for different types of messages. The sensory (afferent) nerve cells and fibres pick up their information from the sense organs and transmit the messages to the spinal cord, which acts as the 'trunk line' for messages to the brain. Messages coming down from the brain are called motor (efferent) impulses and are directed to the muscles which go into action in response to these messages.
Although scientists have been able to discover this specialization of different nerve fibres, they have still a great deal to learn about the nature of nerve 'messages' and how they are coded and dealt with by the brain.
Various areas of the brain specialize in the receipt and translation of the nerve impulses arriving from particular sense organs. The back portion of the cerebrum receives the nerve impulses from the eyes. The top portion takes in the touch senses, and so on.
Apparently, the brain receives and sorts the messages and those that are of little or no use to the person are filtered out. The multitude of noises sounds, smells, that are always around us are banished, pre¬venting our internal message centres from being clogged up with irrel¬evant or distracting information. The messages that are useful or important are sorted and translated.
Imagine yourself driving a car, when suddenly the traffic lights turn red. The red traffic light will be transmitted through the eye, stimulat¬ing nerve impulses to the brain. A return message from the brain makes you stop the car. Other light stimuli, such as the colour of the sky, other cars, people will be also transmitted through your sense of sight, but the brain will filter them out as being irrelevant to your needs at the moment. It is not known how much of this information is stored away in the brain as a permanent record but it is certain that the brain has an enormous capacity for storage. With about ten thousand million interconnected cells the brain can receive, sort and analyze an enormous amount of material for future reference.
Text 4.
Threshold
In order to establish laws about how people sense the external world, psychologists first try to determine how much of a stimulus is necessary for a person to sense it at all. How much energy is required for someone to hear a sound or to see a light? How much of a scent must be in the room before one can smell it? How much pressure must be applied to the skin before a person feels it?
To answer such questions, a psychologist might set up the following experiment.
First, a person (the subject) is placed in a dark room and is instructed to look at the wall. He is asked to say 'I see it' when he is able to detect a light. The psychologist then uses an extremely precise machine that can project a low-intensity beam of light against the wall. The experimenter turns on the machine to its lowest light projection. The subject says nothing. The experimenter increases the light until finally the subject responds, 'I see it'. Then the experimenter begins another test in the opposite direction. He starts with a clearly visible light and decreases its intensity until the light seems to disappear. Many trials are completed and averaged. The absolute threshold — the smallest amount of energy that will produce a sensation — is defined as the amount of energy that a subject can see about half the time.
Interestingly enough, thresholds determined in this way are not as absolute as psychologists first believed. The point at which the person says ‘I see it’ may vary with the instructions he is given (“Say you see it only if you are absolutely certain” versus “If there is any doubt, say you see it”) or even the order in which the stimuli are presented.
Answer the following questions based on the texts
1. In what way does man differ from animals?
2. How do we get information about the world around us?
3. How many senses has man? What are the five main ones?
4. What information do these senses supply us with?
5. What is the control centre of our sensations?
6. What is the function of a sense organ?
7. Where are the nerve impulses sent to?
8. What are the nerve fibres which transmit information from sense organs to the spinal cord called?
9. What are the nerve fibres which transmit impulses from the brain to the muscles called?
10. Do different parts of the brain specialize in the receipt and translation of nerve impulses arriving from particular sense organs?
11. In what part of the brain is the centre of sight situated?
12. In what part of the brain is the centre of touch situated?
13. Does the brain translate all the information it receives?
14. What information is banished?
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