THE STRUCTURE OF THE NERVOUS SYSTEM
The nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory.
Through its receptors, the nervous system keeps us in touch with our environment, both external and internal.
Like other system in the body, the nervous system is composed of organs, principally the brain, spinal cord,nerves, and ganglia. These, in turn, consist of various tissues, including nerve, blood, and connective tissue. Together
these carry out the complex activities of the nervous system.
The system is composed of specialized cells, termed nerve cells or neurons, that communicate with each other and with other cells in the body. A neuron has three parts:
1) the cell body, containing the nucleus;
2) dendrites, hair-like structures surrounding the cell body, which conduct incoming signals;
3) the axon (or nerve fiber), varying in length from a millimeter to a meter, which conduct outgoing signals emitted by the neuron. Axons are encased in a fatlike sheath, called myelin, which acts like an insulator and speeds impulse transmission.
Typically a given neuron is connected to many thousands of neurons. The specific point of contact between the axon of one cell and a dendrite of another is called a synapse. Messages passed to and from the brain take the form of electrical impulses, produced by a chemical change that progresses along the axon. At the synapse, the release of neurotransmitters and this, in turn, drives the impulse to the next neuron. These impulses travel very fast along these chain of neurons up to 250 miles per hour. This contrasts with other system, such as the endocrine system, which may take many hours to respond with hormones.
The nerve cell bodies are generally located in groups. Within the brain and spinal cord, the collections of neurons are called nuclei and constitute the gray matter, so-called because of their colour. Outside the brain and spinal cord the groups are called ganglia. The remaining areas of the nervous system are tracts of axons, the white matter, so-called because of white myelin sheath.
The nerves of the body are organized into two major systems:
- the central nervous system (CNS), consisting of the brain and spinal cord;
- the peripheral nervous system (PNS), the vast network of spinal and cranial nerves linking the body to the brain and spinal cord. The PNS is subdivided into:
1) the autonomic nervous system (involuntary control of internal organs, blood vessles, smooth and cardiac muscles), consisting of the sympathetic NS and parasympathetic NS;
2) the somatic nervous system (voluntary control of skin, bones, joints, and skeletal muscle).
The two systems function together, with nerves from the periphery entering and becoming part of the central nervous system, and vice versa.
The brain, the body's "control center", is one of the largest of adult organs, consisting of over 100 billion neurons and weighing about 3 pounds. It is typically divided into four parts:
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1) the cerebrum;
2) the cerebellum;
3) the diencephalon (thalamus, hypothalamus, sometimes classed as cerebral
structures);
4) the brain stem (medulla oblongata, pons, midbrain), which is an extension of the spinal cord.
The largest division of the brain, the cerebrum, consists of two sides, the right and left cerebral hemispheres, which are interconnected by the corpus callosum. The two hemispheres are "twins", each with centres for receiving sensory (afferent) information and for intiating motor (efferent) responses. The left side sends and receives information to/from the right side of the body, and vice versa. The hemispheres are covered by a thin layer of gray matter known as the cerebral cortex.The interior portion consists of white matter, tracts, and nuclei (gray matter) where synapses occur. Each hemisphere of the cerebral cortex is divided into four "lobes" by various sulci and gyri. The sulci (or fissures) are the grooves and the gyri are the "bumps" on the brain's surface.
The cerebellum, the second largest brain structure, sits below the cerebrum. Like the cerebellum has an outer cortex of gray matter and two hemispheres. It receives/ relays information via the brain stem. The cerebellum performs 3 major functions, all of which have to do with skeletal-muscle control: Balance of the trunk.
Muscle tension, spinal nerve reflexes, posture and balance of the limbs. *" Fine motor control, eye movement.
The diencephalons, located between the cerebrum and the midbrain, consists of several important structures, two of which are the:
- Thalamus: large, bilateral (right thalamus/left thalamus) egg-shaped mass of gray matter serving as the main synaptic relay center. Receives/relays sensory information to/from the cerebral cortex, including pain/pleasure centers.
- Hypothalamus: a collection of ganglia located below the thalamus and intimatetly associated with the pituitary gland. It has a variety of functions: senses changes in body temperature; controls autonomic activites and hence regulates the sympathetic and parasympathetic nervous systems; links to the endocrine system/ controls the pituitary gland; regulates appetite; functions as part of the arousal or alerting mechanism; and links the mid (emotions) to the body sometimes, unfortunately, to the degree of producing "psychosomatic disease'.
The medulla oblongata, pons and midbrain often referred to collectively as the brain stem control the most basic life functions. Of these three, the medulla is the most important. In fact, so vital is the medulla to survival that diseases or injuries affecting it often prove fatal. All functions of the brain stem are associated with cranial nerves IIIXII. Functions:
- Breathing/respiration (pons, medulla)
- Heart rate/action (medulla)
Blood pressure / blood vessel diameter (medulla)
- Reflex centers for papillary reflexes and eye movements (midbrain, pons); and for vomiting, coughing, sneezing, swallowing, and hiccupping (medulla).
The spinal cord lies within the spinal cavity, consisting of the vertebral column, the meninges, spinal nerves, spinal fluid, blood vessels, and a cushion of adipose/fat tissue. The spinal cord has two general functions: 1) It provides the two-way conduction routes to/from (afferent/efferent) the brain; and 2) it serves as the reflex center for all spinal reflexes.
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III. Post-reading activities.
1. Answer the following questions.
1. What organs is the nervous system composed of?
2. How do we call the cells the nervous system is composed of?
3. How many parts has a neuron? What are they?
4. What is synapse?
5. How fast do the impulses travel along the chain of neurons?
6. How do we call the collections of neurons within the brain and spinal cord?
7. What is ganglia?
8. In what two major systems are the nerves of the body organized?
9. What is the PNS subdivided into?
10.What is the main organ of the nervous system?
11.What is the largest division of the brain?
12.How many sides does it consist of?
13.What are the functions of the cerebellum?
14.What is thalamus?
15.What are the functions of hypothalamus?
16.What does the brain stem consist of?
17.What is the spinal cord composed of?
18.What are the general functions of the spinal cord?
2. Say whether the following sentences are true or false.
1. Dendrites conduct outcoming signals.
2. Messages passed to and from the brain take the form of electrical impulses.
3. The white matter, so-called because of white myelin sheath.
4. The central nervous system consists of the brain.
5. The brain typically divided into two parts.
6. The hemispheres are covered by a thin layer of white matter.
7. The cerebellum performs functions, all of which have to do with skeletal muscle control.
8. Diseases or injuries affecting the medulla often prove fatal.
9. The spinal cord lies within the spinal cavity.
3. Write out of the text all anatomical terms with definitions.
IV. Speaking.
Make up a dialogue between a neurologist and a patient. Here is vocabulary for you to speak about nervous system problems.
| QUESTIONS Could you please frown? Can you whistle for me, please? (...always look on the bright side...) Could you open your mouth and show me/ stick out your tongue? Do you often have headaches? | INSTRUCTIONS You should just try to relax, I am going to test your reflexes, now. This hammer looks more dangerous than it actually is: so, do not be afraid; I won't hurt you. Do you have a sensation of pulsation (compression) in the head? Do your hands tremble? Do you fall asleep at once? Do you sleep well? |
V. Supplement.
Text 1
1. Read the information about some pathological conditions of the nervous system. Be ready to answer the questions after the text.
NERVOUS SYSTEM DISORDERS
Epilepsy is a brain disorder that causes people to have recurring seizures1. The seizures happen when clusters2 of nerve cells, or neurons, in the brain send out the wrong signals. People may have strange sensations and emotions or behave strangely. They may have violent muscle spasms or lose consciousness. Epilepsy has many possible causes, including illness, brain injury and abnormal brain development. In many cases, the cause is unknown. Doctors use brain scans and other tests to diagnose epilepsy. It is important to start treatment right away. There is no cure for epilepsy, but medicines can control seizures for most people.
Encephalitis is an inflammation of the brain. The usual cause is a viral infection, but bacteria can also cause it. Cases can range from mild to severe. For mild cases, you could have flu-like symptoms. Serious cases can cause severe headache, sudden fever, drowsiness3, vomiting, confusion, seizures. For mild cases, you may just need rest, plenty of fluids and a pain reliever. For severe cases, you might need to be hospitalized.
Dementia4 is a word for a group of symptoms caused by disorders that affect the brain. People with dementia may not be able to think well enough to do normal activities, such as getting dressed or eating. They may lose their ability to solve problems or control their emotions. Their personalities may change. They may become agitated or see things that are not there. Memory loss is a common symptom of dementia. However, memory loss by itself does not mean you have dementia. People with dementia have serious problems with two or more brain functions, such as memory and language. Many different diseases can cause dementia, including Alzheimer's disease and stroke. Drugs are available to treat some of these diseases. While these drugs cannot cure dementia or repair brain damage, they may improve symptoms or slow down the disease.
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Alzheimer's disease (AD) is the most common form of dementia among older people. Dementia is a brain disorder that seriously affects a person's ability to carry out daily activities. AD begins slowly. It first involves the parts of the brain that control thought, memory and language. People with AD may have trouble remembering things that happened recently or names of people they know. Over time, symptoms get worse. People may not recognize family members or have trouble speaking, reading or writing. They may forget how to brush their teeth or comb their hair. Later on, they may become anxious or aggressive, or wander away from home. Eventually, they need total care. AD usually begins after age 60. The risk goes up as you get older. Your risk is also higher if a family member has had the disease. No treatment can stop the disease. However, some drugs may help keep symptoms from getting worse for a limited time.
Parkinson's disease is a disorder that affects nerve cells, or neurons, in a part of the brain that controls muscle movement. In Parkinson's, neurons that make a chemical called dopamine die or do not work properly. Dopamine normally sends signals that help coordinate your movements. No one knows what damages these cells. Symptoms of Parkinson's disease may include:
Trembling of hands, arms, legs, jaw and face.
Stiffness of the arms, legs and trunk.
Slowness of movement.
Poor balance and coordination.
As symptoms get worse, people with the disease may have trouble walking, talking or doing simple tasks. They may also have problems such as depression, sleep problems or trouble chewing, swallowing or speaking. Parkinson's usually begins around age 60, but it can start earlier. It is more common in men than in women. There is no cure for Parkinson's disease. A variety of medicines sometimes help symptoms dramatically.
Brain Cancer
There are two main types of brain cancer. Primary brain cancer starts in the brain. Metastatic brain cancer starts somewhere else in the body and moves to the brain. Brain tumors can be benign, with no cancer cells, or malignant, with cancer cells that grow quickly. Brain tumors can cause many symptoms. Some of the most common are:
Headaches, usually worse in the morning.
Nausea and vomiting.
Changes in your ability to talk, hear or see
Problems with balance or walking
Problems with thinking or memory
Muscle jerking or twitching
Numbness or tingling in arms or legs
No one knows the exact causes of brain tumors. Doctors can seldom explain why one person develops a brain tumor and another does not.
Notes:
1seizure ,
2cluster ,
3drowsiness , '
4dementia
5stiffness
6jerking
2. Answer the following questions.
1. What is epilepsy?
2. When do seizures happen?
3. What is the cause of epilepsy?
4. Can medicines control seizures?
5. What is the cause of encephalitis?
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6. What are the symptoms of encephalitis?
7. What's the treatment of encephalitis?
8. What is dementia?
9. What are the symptoms of dementia?
10.What diseases can cause dementia?
11.Is there any cure for Parkinson's disease? What do you know about this disorder?
12.What is the most common form of dementia among older people?
13.Name the main symptoms of Alzheimer's disease.
14.When does Alzheimer's disease usually begin?
15.Can treatment stop the disease (AD)?
16.What are the two main types of brain cancer?
17.What symptoms can brain tumors cause?
3. Fill in the blanks.
1. People with epilepsy may have violent muscle spasms or lose....
2. Doctors use... and other tests to diagnose epilepsy.
3. Encephalitis is an... of the brain.
4. People with dementia may lose their ability to solve... or control their....
5.... is a common symptom of dementia.
6. Alzheimer's disease begins....
7. People with AD need total....
8. Parkinson's disease is more common in men than in....
9. A variety of... sometimes help symptoms of Parkinson's disease dramatically
10. No one knows the exact... of brain tumors.
a) memory loss; b) cause; c) emotions; d) medicines; e) consiousness;
f) slowly; g) brain scans; h) problems; i) women; j) inflammation; k) care
The Endocrine System.
.
I. Vocabulary.
1. Read and learn the topical vocabulary.
pituitary gland ();
thyroid gland ;
parathyroid gland ;
adrenal gland ;
gonads ( );
ovaries ;
testes ;
pineal gland ;
mammary gland ;
mucous gland ;
salivary gland ;
lacrimal gland ;
sweat glands .
2. Match the following English word combinations and the Ukrainian ones.
| 1. exocrine glands 2. endocrine glands 3. hormone secretion 4. sex hormones 5. chemical reactions | a. b. ( ) c. d. e. ( ) |
3. Analyze the structure of the following terms. Memorize the meaning of the term elements from the first column.
| para- | near, beside | parathyroid = beside the thyroid |
| poly- | much, many | polyadenitis = inflammation of many glands |
| thyro- | thyroid | thyroaplasia = defective growth of the thyroid |
| -crine | to secrete | endocrine = endo(within)crine (secrete) |
| -trophy | growth | hypertrophy = excessive growth of an organ or part |
| -megaly | enlargement | hepatomegaly = enlarged liver with hepatitis |
| -physis | growth | a growth or outcropping (as opposed to trophy where something is physically growing) |
II. Reading.
