Ebook The handy anatomy answer book (2/E): Part 1

(BQ) Part 1 book The handy anatomy answer book has contents: History of anatomy, anatomy and biology basics, integumentary system, skeletal system, levels of organization, muscular system, nervous system,... and other contents.

About the Authors Patricia Barnes-Svarney is a science and science fiction writer Over the past few decades, she has written or coauthored more than 35 books, including When the Earth Moves: Rogue Earthquakes, Tremors, and Aftershocks and the award-winning New York Public Library Science Desk Reference, along with authoring several hundred magazine articles Thomas E Svarney is a scientist who has written extensively about the natural world His books, with Patricia Barnes-Svarney, include Visible Ink Press’ The Handy Dinosaur Answer Book, The Handy Math Answer Book, and The Handy Nutrition Answer Book; in addition, they have written Skies of Fury: Weather Weirdness around the World and The Oryx Guide to Natural History You can read more about their work and writing at www.pattybarnes.net Please visit the “Handy” series website at www.handyanswers.com Also from Visible Ink Press The Handy African American History Answer Book by Jessie Carnie Smith ISBN: 978-1-57859-452-8 The Handy Geology Answer Book by Patricia Barnes-Svarney and Thomas E Svarney ISBN: 978-1-57859-156-5 The Handy Answer Book for Kids (and Parents), 2nd edition by Gina Misiroglu ISBN: 978-1-57859-219-7 The Handy History Answer Book, 3rd edition by David L Hudson, Jr ISBN: 978-1-57859-372-9 The Handy Art History Answer Book by Madelynn Dickerson ISBN: 978-1-57859-417-7 The Handy Hockey Answer Book by Stan Fischler ISBN: 978-1-57859-569-3 The Handy Astronomy Answer Book, 3rd edition by Charles Liu ISBN: 978-1-57859-190-9 The Handy Bible Answer Book by Jennifer Rebecca Prince ISBN: 978-1-57859-478-8 The Handy Biology Answer Book, 2nd edition by Patricia Barnes Svarney and Thomas E Svarney ISBN: 978-1-57859-490-0 The Handy Chemistry Answer Book by Ian C Stewart and Justin P Lamont ISBN: 978-1-57859-374-3 The Handy Civil War Answer Book by Samuel Willard Crompton ISBN: 978-1-57859-476-4 The Handy Investing Answer Book by Paul A Tucci ISBN: 978-1-57859-486-3 The Handy Islam Answer Book by John Renard, Ph.D ISBN: 978-1-57859-510-5 The Handy Law Answer Book by David L Hudson Jr ISBN: 978-1-57859-217-3 The Handy Math Answer Book, 2nd edition by Patricia Barnes-Svarney and Thomas E Svarney ISBN: 978-1-57859-373-6 The Handy Military History Answer Book by Samuel Willard Crompton ISBN: 978-1-57859-509-9 The Handy Mythology Answer Book, by David A Leeming, Ph.D ISBN: 978-1-57859-475-7 The Handy Dinosaur Answer Book, 2nd edition by Patricia Barnes-Svarney and Thomas E Svarney ISBN: 978-1-57859-218-0 The Handy Nutrition Answer Book by Patricia Barnes-Svarney and Thomas E Svarney ISBN: 978-1-57859-484-9 The Handy English Grammar Answer Book by Christine A Hult, Ph.D ISBN: 978-1-57859-520-4 The Handy Ocean Answer Book by Patricia Barnes-Svarney and Thomas E Svarney ISBN: 978-1-57859-063-6 The Handy Geography Answer Book, 2nd edition by Paul A Tucci ISBN: 978-1-57859-215-9 The Handy Personal Finance Answer Book by Paul A Tucci ISBN: 978-1-57859-322-4 The Handy Philosophy Answer Book by Naomi Zack ISBN: 978-1-57859-226-5 The Handy Physics Answer Book, 2nd edition By Paul W Zitzewitz, Ph.D ISBN: 978-1-57859-305-7 The Handy Politics Answer Book by Gina Misiroglu ISBN: 978-1-57859-139-8 The Handy Presidents Answer Book, 2nd edition by David L Hudson ISB N: 978-1-57859-317-0 The Handy Psychology Answer Book by Lisa J Cohen ISBN: 978-1-57859-223-4 The Handy Religion Answer Book, 2nd edition by John Renard ISBN: 978-1-57859-379-8 The Handy Science Answer Book, 4th edition by The Carnegie Library of Pittsburgh ISBN: 978-1-57859-321-7 The Handy Supreme Court Answer Book by David L Hudson, Jr ISBN: 978-1-57859-196-1 The Handy Technology Answer Book by by Naomi Balaban and James Bobick ISBN: 978-1-57859-563-1 The Handy Weather Answer Book, 2nd edition by Kevin S Hile ISBN: 978-1-57859-221-0 Please visit the “Handy” series website at www.handyanswers.com THE HANDY ANATOMY ANSWER BOOK Copyright © 2016 by Visible Ink Press® This publication is a creative work fully protected by all applicable copyright laws, as well as by misappropriation, trade secret, unfair competition, and other applicable laws No part of this book may be reproduced in any form without permission in writing from the publisher, except by a reviewer who wishes to quote brief passages in connection with a review written for inclusion in a magazine, newspaper, or website All rights to this publication will be vigorously defended Visible Ink Press® 43311 Joy Rd., #414 Canton, MI 48187-2075 Visible Ink Press is a registered trademark of Visible Ink Press LLC Most Visible Ink Press books are available at special quantity discounts when purchased in bulk by corporations, organizations, or groups Customized printings, special imprints, messages, and excerpts can be produced to meet your needs For more information, contact Special Markets Director, Visible Ink Press, www.visibleink.com, or 734-6673211 Managing Editor: Kevin S Hile Art Director: Mary Claire Krzewinski Typesetting: Marco DiVita Proofreaders: Larry Baker and Sharon R Gunton Indexer: Shoshana Hurwitz Cover images: Shutterstock Cataloging-in-Publication Data is on file at the Library of Congress Printed in China 10 Contents ACKNOWLEDGMENTS … ix PHOTO C REDITS … x I NTRODUCTION … xi HISTORY OF ANATOMY … INTEGUMENTARY SYSTEM … 67 Defining Anatomy (1) … Studies in Anatomy (2) … Comparing Other Organisms (7) Introduction (67) … Skin Structure (68) … Skin Function (75) … Nails (78) … Hair (79) … Accessory Glands (82) … Comparing Other Organisms (84) ANATOMY AND BIOLOGY BASICS … SKELETAL SYSTEM … 87 Human Anatomical Terminology (9) … Chemistry in Biology and Anatomy (12) … Biological Compounds and the Human Body (15) … Comparing Other Organisms (18) Introduction (87) … Bone Basics (89) … Axial Skeleton (93) … Appendicular Skeleton (98) … Joints (102) … Comparing Other Organisms (107) LEVELS OF ORGANIZATION … 21 MUSCULAR SYSTEM … 109 Defining Levels of Organization in Anatomy (21) … Cells (22) … Tissues (31) … Organs and Organ Systems (38) … Homeostasis (40) … Comparing Other Organisms (41) SENSORY SYSTEM … 43 Smell (46) … Taste (48) … Hearing (50) … Vision (55) … Comparing Other Organisms (63) Introduction (109) … Organization of Muscles (112) … Muscle Structure (116) … Muscle Function (120) … Comparing Other Organisms (126) NERVOUS SYSTEM … 129 Introduction (129) … Neuron Function (131) … Central Nervous System (136) … The Brain (139) … Spinal Cord (145) … Peripheral Nervous System: Somatic vii Nervous System (146) … Peripheral Nervous System: Autonomic Nervous System (150) … Learning and Memory (151) … Sleep and Dreams (154) … Comparing Other Organisms (159) ENDOCRINE SYSTEM … 163 Introduction (163) … Hormones (164) … Pituitary Gland (167) … Thyroid and Parathyroid Glands (171) … (Adrenal Glands (176) … Pancreas (178) … Pineal Gland (182) … Reproductive Organs (182) … Other Sources of Hormones (184) … Comparing Other Organisms (186) CARDIOVASCULAR SYSTEM … 189 Introduction (189) … Blood (190) … The Heart (198) … Blood Vessels (202) … Circulation (205) … Comparing Other Organisms (208) LYMPHATIC SYSTEM … 211 Introduction (211) … Lymphatic Vessels and Organs (214) … Nonspecific Defenses (217) … Specific Defenses (218) … Allergies (226) … Comparing Other Organisms (229) RESPIRATORY SYSTEM … 231 Introduction (231) … Structure and Function (232) … Respiration and Breathing (239) … Sound Production (243) … Comparing Other Organisms (244) viii FURTHER READING … 341 GLOSSARY … 345 I NDEX … 351 DIGESTIVE SYSTEM … 247 Introduction (247) … Upper Gastrointestinal Tract (248) … Lower Gastrointestinal Tract (255) … Accessory Glands (260) … Metabolism and Nutrition (265) … Comparing Other Organisms (272) URINARY SYSTEM … 275 Introduction (275) … Kidneys (276) … Accessory Organs (281) … Urine and Its Formation (282) … Comparing Other Organisms (283) REPRODUCTIVE SYSTEM … 285 Introduction (285) … Male Reproductive System (286) … Female Reproductive System (292) … Conception (298) … Sexually Transmitted Diseases (301) … Comparing Other Organisms (302) HUMAN GROWTH AND DEVELOPMENT … 303 Introduction (303) … Prenatal Development—Embryonic Period (304) … Prenatal Development—Fetal Stage (309) … Birth and Lactation (313) … Postnatal Development (318) … Comparing Other Organisms (322) HELPING HUMAN ANATOMY … 325 Anatomy and Imaging Techniques (325) … Diagnostic Techniques for Various Systems (329) … Operations, Procedures, and Transplants (335) … Comparing Other Organisms (340) Acknowledgements W e are indebted to the authors of The Handy Anatomy Answer Book’s first edition, Naomi Balaban and James Bobick Their knowledge and research for the book made the task of revising that much easier We would also, as always, like to thank Roger Jänecke for all his help, patience, and consideration, and especially for asking us to revise another Handy Answer book Also, thanks to typesetter Marco DiVita, cover and page designer Mary Claire Krzewinski, indexer Shoshana Hurwitz, and proofreaders Larry Baker and Sharon R Gunton Our editor, Kevin Hile, always gets special kudos from us—he’s the best And an extra special thanks to Agnes Birnbaum, who not only helps us with the intricacies of publishing but has been a wonderful friend for many, many years (and we hope many more) We would also like to express our thanks to all the scientists, researchers, and health care professionals who deal with anatomy of the human body We are not all alike, and trying to figure out what is best for “everyone’s internal [some say infernal] configuration” is an immense task We know so much more about human anatomy than we did even five years ago And we have no doubt we will know more in the near and far future thanks to their expertise and efforts ix of cervical nerves (C1–C8), twelve pairs of thoracic nerves (T1–T12), five pairs of lumbar nerves (L1–L5), five pairs of sacral nerves (S1–S5) and one pair of coccygeal nerves (Co1) The longest spinal nerve is the tibial nerve, which averages twenty inches (fifty centimeters) long How does the location of an injury along the spinal cord cause a certain paralysis? Injuries or damage to the spinal cord at or above the fifth cervical vertebra eliminates sensation and motor control of the upper and lower limbs, as well as any part of the body below the level of the injury The paralysis after a high spinal injury is termed quadriplegia, and the person is unable to feel or move both arms and legs Damage that occurs in the thoracic region of the spinal cord effects motor control of the lower limbs only This paralysis is called paraplegia, and the person is unable to move or feel both lower limbs How are spinal nerves attached to the spinal cord? Spinal nerves divide in the vertebral canal into two branches: the dorsal root and the ventral root The dorsal root, which is the posterior branch, contains the axons of sensory neurons that bring information to the spinal cord The ventral root, which is the anterior branch, contains the axons of motor neurons that carry commands to muscles or glands Therefore, each spinal nerve is considered a mixed nerve with both sensory and motor neurons What is a plexus? A plexus (from the Latin plectere, meaning “braid”) is an interwoven network of spinal nerves There are four major plexuses on each side of the body: 1) the cervical plexus innervates the muscles of the neck, the skin of the neck, the back of the head, and the diaphragm muscle; 2) the brachial plexus innervates the shoulder and upper limb; 3) the lumbar plexus innervates the muscles and skin of the abdominal wall; and 4) the sacral plexus innervates the buttocks and lower limbs The nerves then divide into smaller branches What causes sciatica? Sciatica is caused by compression of the sciatic nerve, such as from a herniated disc or even from sitting for extended periods of time with a wallet in the back pocket The pain usually subsides after a few weeks, although over-the-counter pain relievers may be helpful What are dermatomes and what infection affects the skin of a single dermatome? 148 Dermatomes (from the Greek derma, meaning “skin,” and tomos, meaning “cutting”) are areas on the skin surface supplied by an individual spinal nerve Shingles, or herpes zoster, appears as a painful rash on the skin that most often corresponds NERVOUS SYSTEM The lumbar plexus to the sensory nerve in the area of a single dermatome The virus is the same one that causes chicken pox If someone has chicken pox as a child, the virus may lie dormant in the nerve roots of the spinal nerves for decades If reactivated for some reason (usually stress is implicated), the virus will present itself as shingles Which nerve is responsible for carpal tunnel syndrome? The median nerve controls sensations to the palm side of the thumb and fingers (although not the little finger), as well as impulses to some small muscles in the hand that allow the fingers and thumb to move Carpal tunnel syndrome occurs when the median nerve, which runs from the forearm into the hand, becomes pressed or squeezed at the wrist The carpal tunnel, a narrow, rigid passageway of ligament and bones at the base of the hand, houses the median nerve and tendons At times thickening from irritated tendons or other swelling narrows the tunnel and causes the median nerve to be compressed Carpal tunnel syndrome is characterized by pain, weakness, or numbness in the hand and wrist, often radiating up the arm According to the National Institute of Neurological Disorders and Stroke, initial treatment of carpal tunnel syndrome includes resting the affected hand and wrist for a minimum of two weeks Nonsteroidal, anti-inflammatory drugs may be used to ease the pain Ice and corticosteroids may relieve the swelling and pressure on the 149 What is cellphone elbow? ith an estimated one out of two people owning cellphones—around three billion people on the planet—it is no wonder there is an injury the media has labeled “cellphone elbow,” or the scientific name cubital tunnel syndrome It occurs when a person’s arm is bent for long periods of time while talking on a cellphone and involves the compression of the ulnar nerve as it winds around the back of the elbow The symptoms are aching, burning, tingling, and numbness in the forearm and the hand This syndrome is the second most common nerve compression syndrome in the hands and wrist after carpal tunnel syndrome W nerve If symptoms persist, surgery may be required to sever the band of tissue around the wrist and reduce pressure on the median nerve P E R I P H E R A L N E RVO U S SYST E M : A U TO N O M I C N E RVO U S SYST E M What does the autonomic nervous system regulate? The autonomic nervous system regulates “involuntary” activity, which is not controlled on a conscious level Specifically, the autonomic nervous system innervates the activity of smooth muscle, cardiac muscle, and glands of the body What causes the sensation of “pins and needles” when your foot “falls asleep”? Local pressure, such as crossing or sitting on your legs, may temporarily compress a nerve, removing sensory and motor function in your foot When the local pressure is removed, the familiar feeling of “pins and needles” is felt as the nerve endings become reactivated How is the autonomic nervous system organized? The autonomic nervous system consists of two divisions: the sympathetic nervous system and the parasympathetic nervous system The sympathetic division is often called the “fight or flight” system because it usually stimulates tissue metabolism, increases alertness, and generally prepares the body to deal with emergencies The parasympathetic division is considered the “rest and repose” division because it conserves energy and promotes sedentary activities, such as digestion In general, both the sympathetic and parasympathetic divisions innervate the target cells How does the somatic nervous system differ from the autonomic nervous system? 150 The table below explains the main differences between the somatic and autonomic nervous systems: Autonomic Nervous System Effectors Type of control Neural pathway Skeletal muscles Voluntary One motor neuron extends from the central nervous system and synapses directly with a skeletal fiber Neurotransmitter Action of neurotransmitter on effecor Acetylcholine Always excitatory (causing contraction of skeletal muscle) Cardiac muscle, smooth muscle, and glands Involuntary One motor neuron (preganglion neuron) extends from the central nervous system and synapses with another motor neuron in a ganglion; the second motor neuron (postganglion neuron) synapses with a visceral effector Acetylcholine or norephinephrine May be excitatory (causing contraction of smooth muscle, increased heart rate, increased force of heart contraction, or increased secretions from glands) or inhibitory (causing relaxation of smooth muscle, decreased heart rate, or decreased secretions from glands) L E A R N I N G A N D M E M O RY NERVOUS SYSTEM Somatic Nervous System Which parts of the brain are involved in higher order functions, such as learning and memory? Higher order functions, such as learning and memory, involve complex interactions among areas of the cerebral cortex and between the cortex and other areas of the brain Information is processed both consciously and unconsciously Since higher order functions are not part of the programmed “wiring” of the brain, the functions are subject to modification and adjustment over time What are the areas of the cerebral cortex and their functions? The cerebral cortex is divided into three functional areas: 1) sensory areas, 2) motor areas, and 3) association areas The sensory areas receive and interpret sensory impulses The motor areas control muscular movement The association areas are involved in integrative functions such as memory, emotions, reasoning, will, judgment, personality traits, and intelligence Which areas of the brain are responsible for specific functions? Researchers know that certain areas of the brain are responsible for certain general functions In 1909, German physician and researcher Korbinian Brodmann (1868–1918) published Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues This treatise included maps of the localization of functions in the cerebral cortex Brodmann’s maps are still used to depict the areas of cerebral cortex that are responsible for specific functions 151 Who discovered which area of the brain is responsible for speech and language? Broca’s area of the brain is responsible for speech production, while Wernicke’s area allows one to understand and interpret speech French physician Pierre Paul Broca (1824–1880) identified an area of the brain responsible for speech production in 1861 Having observed a patient who could not speak except for the meaningless utterance of “tan, tan,” Broca examined the brain of the individual upon his death Broca determined the patient was missing a section of the frontal lobe from the cerebral hemisphere Broca continued to examine the brains of individuals with a lack of speech and found they all lacked the same area of the brain How Broca’s area and Wernicke’s area differ? Broca’s area and Wernicke’s (named after German physician, anatomist, psychiatrist, and neuropathologist Karl [or Carl] Wernicke, 1848–1905) area are both associated with speech Broca’s area is associated with the production of speech It controls the flow of words from brain to mouth Wernicke’s area is associated with the interpretation and understanding of speech What are the causes of aphasia? Aphasia is a language disorder that results from damage to portions of the brain that are responsible for language Strokes are the most common cause of aphasia, although aphasia can also result from a brain tumor, infection, head injury, or dementia that damages the brain Individuals with aphasia have difficulty speaking—both in producing words and complete sentence structure—or understanding speech, or both Depending on the severity of the aphasia (and the degree of permanent brain damage), What did scientists recently discover about Broca’s area? n 2015, scientists knew that the Broca’s area of the brain is the command center for human speech (and vocalization), but they have now found out that the area switches off when we talk out loud They also believe that the area may remain active during conversation as the person plans future words and full sentences Overall, the researchers hope that this leads to diagnoses and treatments of stroke, epilepsy, and brain injuries that often affect and/or impair language skills of the affected person I 152 some patients regain their speech capabilities with little or no rehabilitation In most cases, however, speech therapy is necessary to regain language capabilities What is intelligence? There is no clear, standard definition of intelligence Psychologists identify intelligence as an individual’s adaptation to the environment as fundamental to understanding what intelligence is and what it does Most researchers agree that intelligence is a person’s ability to comprehend his or her environment, evaluate it rationally, and form appropriate responses Is it possible to measure intelligence? How is IQ calculated? NERVOUS SYSTEM The earliest test created to measure intelligence was developed by French physiologist Alfred Binet (1857–1911) in 1905 The purpose of the test was to measure skills such as judgment, comprehension, and reasoning in order to place children in the appropriate classes in school The test was brought to the United States by Stanford University psychologist Lewis Terman (1877–1956) in 1916 and renamed the Stanford-Binet test Since then, other intelligence tests, such as the Wechsler Adult Intelligence Scale and the Wechsler Intelligence Scale for Children have been developed These tests have produced a score referred to as an intelligence quotient (IQ) IQ, or the intelligence quotient, was originally computed as the ratio of a person’s mental age to his or her chronological age, multiplied by 100 Following this method, a child of ten years old who performed on the test at the level of an average twelve year old (mental age of twelve), was assigned an IQ of 12/10 x 100 = 120 More recently, the concept of “mental age” has fallen into disrepute and IQ is computed on the basis of the statistical percentage of people who are expected to have a certain IQ An IQ of 100 is considered average An IQ of 70 or below indicates mental retardation, and an IQ of 130 or above indicates gifted abilities What is memory? Memory is the ability to recall information and experiences Memory and learning are related because in order to be able to remember something it must first be “learned.” Memories may be facts or skills Memory “traces” have been described traditionally as concrete things Rats have been shown to have very good memories when it comes to finding food sources 153 that are formed during learning and imprinted on the brain when neurons record and store information However, the way that memories are formed and represented in the brain is not well understood How does short-term memory differ from long-term memory? Short-term memory, also called primary memory, refers to small bits of information that can be recalled immediately The recalled information has no permanent importance, such as a name or telephone number that is only used once Long-term memory is the process by which information that for some reason is interpreted as being important is remembered for a much longer period Short-term memories may be converted to long-term memories Which areas of the brain are involved in memory? Several areas of the brain are associated with memory, including the association cortex of the frontal, parietal, occipital, and temporal lobes, the hippocampus, and the diencephalon Damage to the hippocampus results in an inability to convert shortterm memories to long-term memories Memory loss may be the result of trauma or injury, disease, lifestyle choices, such as alcoholism and drug use, and aging What is amnesia? Amnesia refers to the loss of memory from disease or trauma The extent and type of memory loss is dependent on the area of the brain that is damaged Individuals with retrograde amnesia suffer from memory losses of past events This is a common occurrence when head injury is involved Oftentimes, an individual will not be able to recall the events and moments immediately preceding an accident or fall Individuals who suffer from anterograde amnesia are unable to store additional memories, but their earlier memories are intact and accessible They have difficulty creating new long-term memories As a consequence, every experience is a new experience for these individuals, even if they have experienced it earlier, such as meeting a new person or reading a new book S LE E P AN D DREAM S What is consciousness? A conscious individual is alert and attentive to his or her surroundings, while an unconscious individual is not aware of his or her surroundings Conscious states, however, range from normal consciousness to the conscious yet unresponsive state, while unconscious states range from being asleep to being in a coma What is the Glasgow coma scale? 154 The Glasgow coma scale is a system of classifying the severity of head injuries or other neurologic diseases It rates three areas of response, involving eye, verbal, and motor responses, and then tallies a total score It is based on a fifteen-point score and is the most common scoring system used to describe the level of consciousness in a person following a traumatic brain injury What are the stages of sleep? Data collected from EEGs (electroencephalograms) of brain activity during sleep have shown at least four separate stages of sleep During stage 1, heart and breathing rates decrease slightly, the eyes roll slowly from side to side, and an individual experiences a floating sensation • Stage sleep is not usually classified as “true” sleep This stage generally lasts only five minutes Individuals awakened during stage sleep will often insist that they were not sleeping, but merely “resting their eyes.” • Stage sleep is intermediate sleep and is characterized by steady, slow breathing, a slow pulse rate, and a decline in temperature and blood pressure Only a loud noise awakens sleepers in stage sleep • Stage sleep, known as oblivious sleep, is the deepest stage It usually does not begin until about an hour after falling asleep Brain waves become even slower, and heart and breathing rates drop to 20 or 30 percent below those in the waking state The sleeping individual in stage sleep is not awakened by external stimuli, such as noise, although an EEG will indicate that the brain acknowledges such stimuli Stage sleep continues for close to an hour, after which the sleeper will gradually drift back into stage sleep, followed by stages and then 1, before the cycle begins again NERVOUS SYSTEM • Stage sleep is characterized by the appearance of short bursts of waves known as “sleep spindles” along with “K complexes,” which are high-voltage bursts that occur before and after a sleep spindle Eyes are generally still and heart and breathing rates decrease only slightly Sleep is not deep Why people need sleep? Scientists not know exactly why people need sleep, but studies show that sleep is necessary for survival Sleep appears to be necessary for the nervous system to work properly While too little sleep one night may leave us feeling drowsy and unable to concentrate the next day, a prolonged period of too little sleep leads to impaired memory and physical performance Hallucinations and mood swings may develop if sleep deprivation continues What is REM sleep? REM sleep is rapid eye movement sleep It is characterized by faster breathing and heart rates than NREM (nonrapid eye movement) sleep The only people who not have REM sleep are those who have been blind from birth REM sleep usually occurs in four to five periods, varying from five minutes to about an hour, growing progressively longer as sleep continues 155 What is the sleep cycle? Typically, there are several cycles of sleep each night Each cycle begins with a period of REM sleep Earlier in the night there will be periods of stage and stage sleep, but these diminish towards morning, when there are longer periods of REM sleep and less deep sleep When does dreaming occur during the sleep cycle? Almost all dreams occur during REM sleep Scientists not understand why dreaming is important One theory is that the brain is either cataloging the inDreams occur during REM sleep, it has been discovered, yet formation it acquired during the day and still no one understands for certain why we dream discarding the data it does not want or is creating scenarios to work through situations causing emotional distress Regardless of its function, most people who are deprived of sleep or dreams become disoriented, unable to concentrate, and may even have hallucinations Why is it difficult to remember dreams? The average person has three or four dreams each night, with each dream lasting ten minutes or more But it appears that the content of dreams is stored in short-term memory and cannot be transferred into long-term memory unless they are somehow articulated Sleep studies show that when individuals who believe they never dream are awakened when they are in the middle of a dream, they are more likely to recall the dream How much sleep does an individual need? 156 In 2015, the National Sleep Foundation published a study that took more than two years of research to complete It was an update of its most-cited guidelines on how much sleep a person needs depending on his or her age A new range labeled “may be appropriate” has been added to acknowledge the individual variability in appropriate sleep durations The recommendations now define times as either (a) recommended; (b) may be appropriate for some individuals; or (c) not recommended Though the research cannot pinpoint the exact amount of sleep needed by people at different ages, the new chart features minimum and maximum ranges for health as well as “recommended” windows Nevertheless, as most health care professionals point out, it is important for an individual to pay attention to his or her own needs by assessing how he or she feels after different amounts of sleep The following lists the new chart, along with comparisons of the old chart: How much time does a human spend sleeping in life? y the time someone is twenty years old, he or she will have spent approximately eight years of his or her life asleep By the age of sixty, he or she will have spent about twenty years sleeping B • Newborns (0–3 months )—Sleep range narrowed to 14–17 hours each day (previously it was 12–18) • Infants (4–11 months)—Sleep range widened two hours to 12–15 hours (previously it was 14–15) • Toddlers (1–2 years)—Sleep range widened by one hour to 11–14 hours (previously it was 12–14) • School age children (6–13)—Sleep range widened by one hour to 9–11 hours (previously it was 10–11) • Teenagers (14–17)—Sleep range widened by one hour to 8–10 hours (previously it was 8.5–9.5) NERVOUS SYSTEM • Preschoolers (3–5)—Sleep range widened by one hour to 10–13 hours (previously it was 11–13) • Younger adults (18–25)—Sleep range is 7–9 hours (new age category) • Adults (26–64)—Sleep range did not change and remains 7–9 hours • Older adults (65+)—Sleep range is 7–8 hours (new age category) How long can a person survive without sleep? A total lack of sleep will cause death quicker than starvation A person can survive a few weeks without food, but only ten days without sleep Sleep-deprived individuals experience extreme psychological discomfort after a few days, followed by hallucinations and psychotic behavior What are some common sleep disorders? The most common sleep disorder is insomnia Insomnia is ongoing difficulty in falling asleep, staying asleep, or restless sleep Technically, insomnia is a symptom of other sleep disorders Consequently, treatment for insomnia depends on the primary cause of insomnia, which may be stress, depression, or too much caffeine or alcohol Another sleep disorder is hypersomnia, or extreme sleepiness during the day even with adequate sleep the night before Hypersomnia has been mistakenly blamed on depression, laziness, boredom, or other negative personality traits Another is narcolepsy, which is characterized by falling asleep at inappropriate times The sleep may last only a few minutes and is often preceded by a period of muscular weakness Emotional events may trigger an episode of narcolepsy Some individuals with narcolepsy experience a state called sleep paralysis They wake up to find their body is 157 paralyzed except for breathing and eye movement In other words, the brain is awake but the body is still asleep What is sleep apnea and how does it affect sleep? Sleep apnea is a breathing disorder in which an individual briefly wakes up because breathing has been interrupted and may even stop for a brief period of time Obstructive sleep apnea (OSA) is the most common form of sleep apnea It occurs when air cannot flow into or out of the person’s nose or mouth as he or she breathes According to the National Sleep Foundation, sleep apnea often occurs in conjunction with snoring And although snoring may be harmless for most people, it can be an indication of apnea, espe- Snoring is caused when the airway becomes obstructed; cially if it is accompanied by severe day- sleep apnea is a more extreme case when the blockage time sleepiness Men seem to have apnea becomes so bad that breathing can stop, disturbing a person’s sleep more than women, as people who are obese, but it can occur in anyone at any age for various other reasons, such as having a large neck or small airways (in the nose, throat, or mouth) A person who has apnea awakens frequently during the night gasping for breath This pause in breathing can reduce the blood oxygen in the body, putting a strain on the cardiovascular system (including the heart), which is why many people with sleep apnea are considered at risk for cardiovascular disease When does sleepwalking occur during the sleep cycle? Sleepwalking generally occurs during deep sleep but may also be present during periods of NREM (non-rapid eye movement) sleep It is most common in children, although the National Sleep Foundation estimates that percent to 15 percent of the population may be sleepwalkers Sleepwalkers generally remain asleep and not remember leaving their beds Contrary to popular myth, sleepwalkers should be awakened, although they may be confused when awakened What are circadian rhythms? 158 Circadian (from the Latin circa, meaning “about,” and dies, meaning “day”) are the regular, internal body rhythms Circadian rhythm is a roughly twenty-four-hour cycle in the physiological processes of every living organism, including plants, animals, fungi, protists, viruses, and bacteria Depending on the organism, these rhythms can be associated with feeding, hormone secretions, brainwave activity, cell regeneration, and/or sleeping patterns Although human lives revolve around a twenty-four-hour day, researchers have found that normal circadian rhythms are more on a twenty-five-hour cycle Many physiological processes, including the sleep/wake cycle, body temperature, gastric secretion, and kidney function, follow a set pattern For example, body temperature peaks in the late afternoon/early evening and is lowest between 2:00 A.M and 5:00 A.M Blood pressure, heartbeat, and respiration follow rhythmical cycles The production of urine drops at night, allowing for uninterrupted rest Circadian rhythm disturbances occur when sleep/wake cycles are interrupted They often affect shift workers whose biological clocks are disrupted by conflicting sleep and work schedules “Jet lag” is another form of circadian rhythm disturbance Do all animals have a nervous system? No, not all animals have a nervous system like that of humans Instead they have a nerve net, an interconnection of sensory neurons that allow them to respond to physical contact (especially to help find food) and to their surrounding environment For example, hydra are simple animals with nerve nets NERVOUS SYSTEM C O M PA R I N G OT H E R O R GA N I S M S What are some animal brain sizes compared to humans? On the average, the human brain weighs 2.7 pounds (1.2 kilograms), representing about percent of a person’s body weight (although on the average, the male brain is about 0.3 pounds [100 grams] heavier than the average female brain) The largest brain belongs to the sperm whale and measures about 17.5 pounds (7 kilograms) in weight The largest land animal brain belongs to the elephant, weighing an average 10.5 pounds (4.78 kilograms) Mountain gorillas have a brain that is 0.95 pounds (430 grams), while the smallest known primate brain belongs to the mouse lemur (Microcebus murinus) in Madagascar, weighing 0.004 pounds (2 grams) How human and other primate brains differ? The human brain—with an average weight of about three pounds—is very large for body size To compare, humans’ closest relative, the chimpanzee, has relatively the same body size, but its brain is about one-third the size of a human In addition, the human brain’s cortex Apes, such as the gorilla seen here, possess an intelligence that is impressive, but their brains are only about one third the size of a human’s 159 What is a sleep characteristic of most mammals? here is one sleep characteristic that is common with most mammals—both humans and other mammals experience rapid eye movement (REM) In particular, scientists note that mammals all display the same level of brain and heart activity associated with REM sleep For humans, this is when a person dreams at night Because humans relate their dreams, scientists know about the connection between REM sleep and dreams But they will probably never know if animals truly dream during their REM sleep since non-human animals cannot talk T has more neurons and a greater number of fibers connecting certain brain regions, especially those responsible for language, reasoning, and toolmaking What are thought to be the most intelligent invertebrates? Cephalopods (squid, octopi, and nautilus) are unique among the invertebrates because of their intelligence For example, octopi can be taught to associate geometric shapes with either punishment (a mild electric shock) or reward (food) This can then be used to train them to avoid one type of food and reach for another Research has indicated that octopi are also tool users; with their flexible arms and suckers, octopi are able to manipulate their environment, as in building a simple home After an octopus has selected a home site, it will narrow the entrance size by moving small rocks Besides humans, what vertebrates are the most intelligent? The answer to this question is highly debated—even saying “besides humans” is bound to result in a heated discussion Many lists of “the most intelligent” animals exist, and some of them include such vertebrates as rats and sheep But according to the famous American behavioral biologist Edward O Wilson (1929–), the ten most intelligent animals are as follows: 1) chimpanzee (two species); 2) gorilla; 3) orangutan; 4) baboon (seven species, including drill and mandrill); 5) gibbon (seven species); 6) monkey (many species, especially macaques, the patas, and the Celebes black ape); 7) smaller toothed whale (several species, especially killer whale); 8) dolphin (many of the approximately eighty species); 9) elephant (two species); 10) pig Still another list based on a scientific study includes 1) dolphins; 2) chimps and orangutans; 3) elephants; 4) parrots; and 5) crows Like all similar scientific studies, the list of animals not only changes as new information is learned, but also varies depending on the researcher’s criteria for “intelligent.” Do all land animals sleep? 160 All land animals sleep, but some “sleep” in different ways For example giraffes can go without sleep for weeks; rats seem to have the same sleep needs as humans, as they need night sleep to hunt during the day Large land animals sleep less than four hours on the average per day, such as elephants and cows (because they spend so much time during the day grazing and eating) And some birds sleep with one eye open to keep track of predators Do aquatic animals sleep? Certain marine animals have unique sleep habits For example, when most species of marine mammals are asleep, one hemisphere of their brain is still awake Dolphins are known to reach the surface to breathe while “sleeping.” It was once thought that sharks never sleep, but now researchers say that most of these animals either keep their brain active enough to respond to some degree—similar to what happens when a human walks in their sleep—or tend to have periods of inactivity, essentially taking a “rest” on the ocean floor NERVOUS SYSTEM 161 ... 10 0, 10 6, 10 9, 11 1, 11 3, 11 5, 11 7, 11 9, 12 1, 12 3, 12 5, 12 7, 12 9, 13 0, 13 2, 13 3, 13 7, 14 0, 14 2, 14 3, 14 5, 14 6, 14 9, 15 2, 15 3, 15 6, 15 8, 15 9, 16 3, 16 4, 16 7, 16 8, 17 2, 17 4, 17 7, 17 9, 18 1, 18 4, 18 5,... 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