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AP Biology Human Body Systems Project

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1 AP Biology Human Body Systems Project
Jeff Zhang

2 Table of Contents Digestive System Circulatory System Respiratory System Immune System Excretory System Muscular System Skeletal System Senses System Endocrine System Reproductive System Nervous System

3 Digestive System The digestive system is responsible for breaking down and converting food into energy.

4 Mouth Beginning of the digestive system
Chewing breaks food into pieces that are easier to digest

5 Pharynx Receives food after it’s swallowed Passageway for food and air
Opens and closes trachea Average: 5 inches long (

6 Esophagus “Channel” that food travels from the mouth to the rest of the digestive system Peristalsis – Muscular contractions that move food down

7 Stomach “Container” that stores and breaks down food with enzymes and hydrochloric acid Processed food becomes “usable” and absorbed into the body

8 Small Intestine Duodenum – Mixes enzymes produced by the pancreas and liver to break down food Jejunum and Ileum - Absorb nutrients into the bloodstream Average: 22 feet long (

9 Large Intestine Also called the “colon”
Average: 6 feet long ( Divided into Ascending (right) colon, Transverse (across) colon, and Descending (left) colon Responsible for processing waste to be removed from the body

10 Rectum Connects large intestine to the anus Holds stool until released
Average: 8 inches long (

11 Anus Final part of digestive system
Internal and External Anal Sphincters Releases stool Average: 2 inches long (

12 Salivary Glands First part of chemical digestion
First part of chemical digestion Produces saliva to help form the bolus (“ball” of chewed food) and begin digestion of food

13 Liver Main function is to process nutrients absorbed in the small intestine Produces certain blood plasma proteins Detoxifies alcohol and ammonia Breaks down drugs Process hemoglobin and stores iron Produces biliverden and biliruben Regulates blood clotting (

14 Pancreas Breaks down proteins, carbohydrates, and fats
Secretes insulin Produces chemicals that help neutralize stomach acids Average: 6 inches long (

15 Gallbladder Stores and releases biliverden and biliruben into the duodenum to help digest fats (

16 Sphincters Controls the release of food from one organ to another
Includes: Pyloric Sphincter, Ileocecal Sphincter, Urethral Sphincter, Glisson’s Sphincter, and the Internal and External Anal Sphincters ( AAZavwQ)

17 Organs Food Passes Through Mouth Pharynx Esophagus Stomach
Pyloric Sphincter Small Intestine Large Intestine Anal Sphincters Rectum Anus Accessory Organs Salivary Glands Liver Gallbladder Pancreas

18 Digestion of Large Molecules
Large food molecules have to be broken down into smaller parts to be able to be digested Food is broken down and “rearranged” into a form that humans can use – The parts we can’t use are excreted as waste Enzymes play a crucial role in the digestion of large food molecules Only food small enough to be absorbed by the villi of the small intestine is used as nutrition by the human body (

19 Role of Enzymes Enzymes dramatically increase the rate at which food is broken down Amylase breaks down carbohydrates Protease breaks down proteins Lipase breaks down fats (lipids) (

20 Physical, mechanical digestion of food through movement
Physical Digestion Physical, mechanical digestion of food through movement Beginning digestion Substances stay the same, just smaller pieces Chemical Digestion Chemical digestion of food through acids and enzymes Necessary to further digest food into finer parts “Transforms” substances into different proteins and sugars Both break down larger food molecules into smaller pieces that can be digested by the body

21 Digestion of Carbohydrates, Proteins, and Lipids
Carbohydrates and proteins are digested in the stomach by amylase and protease, respectively, produced by the pancreas and small intestine Lipids can’t be digested by the stomach alone – Primarily broken down in the duodenum by lipase produced by the small intestine and liver (

22 Ulcers A weakening in the lining of the stomach or small intestine.
Pain in the abdominal region is caused by stomach acid eroding nerve endings. Up to 10% of Americans will develop ulcers sometime in their lives. Treatment is with antacids and/or antibiotics if caused by bacteria. (

23 Gallstones Excessive amounts of cholesterol in the bile ducts can crystallize and form gallstones. Inflammation in the small intestine and severe abdominal pain are common symptoms. About 10% of the population has gallstones, but only 1-2% of the population exhibits symptoms that require medical care Treatment: Extracorporeal shockwave lithotripsy can generate shockwaves that break gallstones apart into small pieces that pass easily though the bile system (

24 Circulatory System Consists of blood, the heart, and blood vessels
The Circulatory System transports nutrients to cells, removes waste from cells, and transports gasses to and from the lungs.

25 Structure and function of blood vessels
Arteries carry blood from the heart to the rest of the body Capillaries connect arteries and veins Veins return blood back to the heart Blood vessels have three layers of tissue: Innermost – Tunica Interna: smooth surface that provides a low-friction channel for blood flow Middle – Tunica Media: smooth muscle tissue that controls contraction and relaxation of blood vessels Outermost – Tunica Adventia: connective tissue that creates a barrier to prevent blood from diffusing into other parts of the body and keep oxygen and nutrients in (

26 Route of Blood Left ventricle, aortic valve, aorta, peripheral arteries, arterioles, capillaries, venules, peripheral veins, vena cava, right atrium, tricuspid valve, right ventricle, pulmonary valve, pulmonary artery, pulmonary capillaries, pulmonary veins, left atrium, mitral valve, and left ventricle. Blood valves ensure the flow of blood goes the intended (one-way) direction. Tricuspid valve allows flow into the Right Ventricle from the Right Atrium Mitral valve allows flow into the Left Ventricle from the Left Atrium Aortic valve allows flow into the Aorta from the Left Ventricle Pulmonary valve allows flow into the Pulmonary Artery from the Right Ventricle (

27 Composition of blood Blood is composed of plasma, erythrocytes, leukocytes, and platelets Plasma is the fluid that carries blood cells, gases, and nutrients to and from cells Erythrocytes (red blood cells) carry oxygen to body cells Leukocytes (white blood cells) protect the body from invading pathogens Platelets clot blood and reduce the amount of blood lost when the body is cut or wounded (

28 Erythrocytes The primary function of erythrocytes is to deliver oxygen from the lungs to other cells in the body They demonstrate how structure influences function because the shape of the cell includes “indents” that allow it to carry and transport oxygen molecules (

29 Open and closed circulatory systems
All vertebrates, and a few invertebrates, have closed circulatory systems – Example: Humans Most invertebrates have open circulatory systems – Example: crabs Closed: Blood is closed at all times within blood vessels and pumped by the heart through vessels not filling body cavities Open: Blood is pumped by the heart into body cavities where tissues are surrounded by blood (

30 Fish circulatory system
2-chambered heart that completely separates oxygen-rich and oxygen-depleted blood Single loop path that takes blood from the heart to the gills and then to the body

31 Amphibian circulatory system
3-chambered heart with two atria and one ventricle Blood moves from the heart to the pulmonary capillaries where gas is exchanged and then returned to the heart Some of the blood returned to the heart goes to the pulmonary circuit, some to the systemic circuit Mixes oxygen-rich and oxygen-depleted blood

32 Reptile circulatory system
3-chambered heart One ventricle, two aortas Some have partial separation of systemic and pulmonary circuits, others complete separation Variations in blood flow allow deoxygenated blood to be returned to the body or oxygenated blood to be returned to the lungs, if needed

33 Mammal circulatory system
4-chambered heart Two atriums, two ventricles Separation of systemic and pulmonary circuits Mammalian red blood cells lack a nucleus to maximize oxygen transport

34 Bird circulatory system
4-chambered heart Separation of systemic and pulmonary circuits Arranged for optimal blood transport – Birds have hearts that are proportionally 3 times larger than mammals and beat 5 to 6 times as fast

35 Atherosclerosis Atherosclerosis is the hardening of the arterial wall due to the build up of plaque. Symptoms include decreased or stopped blood flow and sharp pain. Sometimes the first sign is a heart attack. About 11.5% of the population has some coronary artery disease Treatment: Statins drugs to lower cholesterol reduce build-up of plaque ( /)

36 Hypertension Commonly known as high blood pressure
Most people show no signs, though headaches and dizziness may be a result High blood pressure increases the chances for heart attacks The incidence in US adults is about 30% Treatment: Exercise and a diet low in sodium and fats reduce the risk of heart disease ( /)

37 Respiratory System The respiratory system is in charge of supplying blood with oxygen to deliver to body cells

38 Alveoli Alveoli are at the ends of each pulmonary vein and are the places where gases are exchanged. The total surface area they provide is about 100 square meters. Alveolar tissue is made of elastic fibers and allows the alveoli to stretch and compress. Capillaries cover 70% of the area and gases readily pass through the thin membranes. (

39 Carbon Dioxide and Oxygen
Red blood cells contain hemoglobin which binds to oxygen molecules. They carry the oxygen to other cells in the body and trade it for carbon dioxide molecules, which they bring back to the lungs. ( One red blood cell can carry four oxygen molecules at a time. Path of oxygen: Air > mouth/nose > pharynx > larynx > trachea > lung > bronchi > bronchioles > alveoli > pulmonary capillaries > hemoglobin (

40 Inhalation and Exhalation
Inhalation is the process of taking air into the lungs. The diaphragm contracts to expand the thoracic cavity and increase the volume. This causes the air pressure inside the lungs to be lower than the air pressure outside, so air moves into the body. Exhalation is the process of expelling air from the lungs. The diaphragm relaxes and decreases the volume of the thoracic cavity. The air pressure inside the lungs is now greater than that of the outside of the lungs, and air leaves the body.

41 Asthma Bronchial airways are too narrow
Coughing, wheezing, and difficulty breathing For adults, the incidence of asthma is about 16% Treatment: Bronchodilators relax airway passages ( /)

42 Tuberculosis Tuberculosis is an infectious disease caused by the bacteria Mycobacterium tuberculosis The bacteria causes lesions to form on the lymph nodes Prevalence in the United States is about 3.6 cases per 100,000 individuals, though the incidence rate is far higher for areas of Africa and Asia Treatment: Combinations of antibiotics are usually successful in curing the disease ( /)

43 Immune System The function of the immune system is to protect the body from disease.

44 Major Organs Bone marrow – Creates B cells, granulocytes, T cells and thymocytes for the immune system through hematopoiesis Thymus – Produces lymphocytes and mature T cells Spleen – Filters blood and traps foreign microorganisms for destruction Lymph nodes – Filter interstitial fluid between body cells to destroy antigens (

45 Recognition of Pathogens
All cells have specific markers on their surface that the immune system can recognize as “self” or “non-self.” Antigens are certain markers that cause an immune response. The immune system produces antibodies that bind to antigens and signal for immune system cells to destroy the foreign microbe. (

46 Specific defense adaptations
Innate Immunity Nonspecific defense Includes physical barriers to infection such as skin, blood chemicals, and immune system cells Acquired Immunity Specific defense adaptations New antigens are recognized and new antibodies are created to mark harmful microbes to be attacked by immune system cells i.e. Chicken pox immunity Both are ways that the immune system protects the body from infection Immune system cells inevitably are the ones that actively destroy the foreign cells

47 The body forms antibodies in response to antigens
Active Immunity The body forms antibodies in response to antigens The immune system “remembers” antigens and how to respond to them i.e. Vaccinations Passive Immunity Not made by the individual, passed down to them or transferred artificially i.e. mothers’ immune systems protect their developing child in the womb Both are ways that the immune system is able to respond to infection

48 Cell-Mediated Immunity
Humoral Immunity Antigen-specific B cells play the central role Antibody-mediated specific immunity Involves body fluids Cell-Mediated Immunity Antigen-specific T cells play the central role Does not involve antibodies Involves cells Both are responses by the adaptive immune system T cells activate humoral B cells to produce antibodies

49 B and T Lymphocytes B Lymphocytes are produced in bone marrow and are activated by helper T cells T Lymphocytes are produced in the thymus and activated by specific MHC proteins B lymphocytes identify pathogens and produce antibodies to mark them to be attacked by T cells (

50 Antibiotics Bacteria are alive, while viruses are not
Antibiotics are meant to destroy bacteria by rupturing their cell walls; viruses don’t have cell walls and are parasites inside body cells, so antibiotics can’t touch them Viruses are effectively “complicated molecules” that can reproduce themselves – They can’t be “killed” (

51 Autoimmune Disease The immune system attacks “self” tissues in the body that are necessary for proper function of organ systems Various symptoms such as organ failure, fevers, difficulty breathing, etc Incidence is very low, but usually fatal Treatment: Immune suppressants, but leave the body susceptible to disease (

52 HIV/AIDS Acquired Immunodeficiency Syndrome caused by the Human Immunodeficiency Virus HIV attacks T cells and other cells of the immune system, making the body more susceptible to other diseases Incidence is disproportional – African Americans and homosexuals make up more than half of all cases in the United States Currently about 1.5 million people in the US have the virus, with about 56,000 new infections each year Treatment: Reverse transcriptase inhibitors can slow the spread of the virus ( /)

53 Excretory System The function of the excretory system is to remove excess or unwanted waste materials from an organism.

54 Nitrogenous Wastes Ammonia – The most efficient form of nitrogen waste and a gas. Most aquatic animals excrete waste this way because ammonia readily diffuses through membranes into the water. Urea – A liquid with very low toxicity, almost 100,000 times less than Ammonia – Amphibians, mammals, and some fishes Uric Acid – Most energetically expensive form of waste and is a thick “paste” that is largely insoluble in water – Most reptiles, birds, and arthropods (

55 Nephron Renal corpuscle – Collects and moves urine, secretes waste products to form urine Proximal convoluted tubule – Filtration and reabsorption water Loop of Henle – Regulates water and solute balance of urine Distal convoluted tubule – Reabsorbs additional water until the final concentration of urine is approximately equal to that of the other body fluids; responsible for excretion of urine (

56 Proteinuria Urine contains an abnormal amount of protein – Proteins aren’t filtered out of the urine and are excreted as waste Foam urine, swelling in the hands, feet, and face Very rare in healthy individuals; incidence rate is much higher for those with high blood pressure and/or diabetes Treatment may include blood glucose and blood pressure control and a change in diet (

57 Kidney Disease Loss of kidney function either due to injury or organ failure over time Dangerous accumulation of waste in the body, anemia, high blood pressure, and acidosis Approximately 10% of Americans ages 20 years and older develop some form of kidney disease Treatment includes dialysis and changes in diet. Kidney failure, if detected early enough, is usually reversible (

58 Muscular System The function of the muscular system is to allow movement, maintain posture, and circulate blood throughout the body.

59 The Three Types of Muscle Tissue
Skeletal muscle occurs in muscles attached to the skeleton that allow for movement Cardiac muscle is in the heart and under involuntary control as it pumps blood Smooth muscle forms the walls of hollow organs and is also under involuntary control

60 Skeletal Muscle Contraction
The sliding filament theory involves bind-and-release impulses that cause myosin to move along the filament and forcing thick filament to move over thin filament. After an impulse is sent from the brain, calcium channels in the muscular axon open and calcium ions move in to cause the release of acetylcholine. Acetylcholine acts as a transmitter that attaches itself to receptors in the sarcomere. This triggers an action potential that causes the release of calcium ions from the sarcoplasmic reticulum. These ions trigger actin sites and the ions begin binding to troponin. Tropomyosin is released and then blocks the binding of actin which causes the muscle to contract. The troponin that is formed prevents some of the blocking action of tropomyosin and some myosin heads attach to active actin sites. These myosin heads form cross bridges using ATP. The ATP is broken into ADP and phosphates which cause the myosin to detach from the actin sites and hydrolyze ATP. This recharges the myosin to repeat the process. This bind-and-release action causes muscle contraction.

61 Muscular Dystrophy Muscular dystrophy is a series of more than 30 genetic diseases that cause the degeneration of skeletal muscles that control movement Primarily affecting males, by the age of 12 victims usually cannot walk and need respirators to continue breathing The disease is very rare; females carrying the gene have a 50% chance of passing it to their children There is no treatment to stop or reverse muscular dystrophy – There is only physical and speech therapy and respiratory assistance

62 Myasthenia gravis An autoimmune neuromuscular disease, the immune system produces antibodies that block muscle cells from receiving signals from nerve cells Myasthenia gravis causes severe weakness of voluntary muscles and can result in trouble breathing and walking Incidence is about 1 in 500,000 Very little is known about the disease. Current treatment is lifestyle changes such as rest and avoiding stress and heat.

63 Skeletal System The skeletal system has six major functions: Support
Protection Aiding in Movement Storage of Minerals Production of Red Blood Cells Chemical energy storage (

64 Human Movement Bones fit together at joints, which allow pivotal movement Ligaments connect bones together and can stretch to allow movement Muscles move bones by extending or flexing a joint Tendons attach muscles to bones

65 Hydrostatic Skeleton Hydrostatic skeletons consist of fluid under pressure This type of skeleton is common among worms and higher invertebrates such as hydras, planarians, and segmented worms

66 Exoskeleton Most aquatic animals and some terrestrial animals (insects) have rigid skeletons on the outside of their body Usually made from chitin Animal must shed its skeleton and form a new one when it outgrows its old one Example: Beetles

67 Endoskeleton Animal skeletons are endoskeletons
Consists of bone and cartilage made from calcium and grows with the animal Vertebrates have this skeleton, but some invertebrates such as sponges, sea stars, and sea urchins have endoskeleton plates underneath their skin

68 Osteoporosis Osteoporosis is the most common skeletal disease
Bones become weaker from a lack of calcium and break easily 1 in 5 women over the age of 50 develop the disease Treatments include medication, pain therapy, and lifestyle changes that prevent the risk of falls

69 Arthritis Arthritis is the inflammation of one or more joints – There are over 100 different types Symptoms include joint pain, swelling, reduced ability to move a joint, and stiffness. Many Americans face arthritis at some point in their lives, especially the elderly Treatments include pain therapy, physical therapy, pain medication, and lifestyle changes.

70 Senses System The function of the senses system is to give the body the ability to detect the outside world.

71 Sensory Receptors Mechanoreceptors detect changes in pressure, position, and acceleration (nose, skin, ear) Thermoreceptors detect hot or cold temperatures (skin) Chemoreceptors detect ions and molecules (nose) Photoreceptors detect light (eyes) Pain receptors detect severe heat, pressure, and chemicals that harm the body (skin)

72 Rhodopsin Rhodopsin is a biological pigment of the retina that forms photoreceptor cells and perceive light Rhodopsin provides the ability for photoreceptor cells to signal to each other and the brain about light entering the retina

73 Endocrine System The function of the endocrine system is to transmit hormones to regulate mood, growth, development, tissue formation, metabolism, and sexual reproduction.

74 Homeostasis The primary function of the endocrine system is to maintain homeostasis – A state of internal stability in the body such as constant body temperature and constant water content. The hypothalamus causes the endocrine system to sustain homeostasis by ordering the secretion of enzymes

75 Negative Feedback A negative feedback in the body is the process by which a change in the level of a certain chemical leads directly to a reduction in its formation, reduction in its absorption, or increase in its excretion. Cortisol is an example – Too much suppresses the immune system which causes a different chemical to be produced which shuts down production of cortisol temporarily.

76 Endocrine Glands Insulin is one important hormone that endocrine glands produce. Insulin regulates glucose intake by helping it move from the blood into body cells

77 Type I and Type II Diabetes
Both forms of diabetes involve a deficiency in meeting the body’s insulin needs The incidence rates of both forms have increased in the past 30 years Type I diabetes usually occurs in thinner individuals before the age of 20; Type II diabetics are usually overweight and over the age of 35 Type I people can’t produce insulin because autoantibodies destroy glands in the pancreas that produce it; Type II people don’t produce enough insulin to sustain their body

78 Hyperthyroidism The thyroid gland produces too much thyroid hormone.
Symptoms include fatigue, goiter, increased sweating, heat intolerance, weight loss, and restlessness. The incidence of hyperthyroidism is less than 1% Treatment includes antithyroid medication and possible surgery to remove the thyroid gland.

79 Reproductive System The function of the reproductive system is to continue the survival of the species. It is the means by which the body can transfer genes from one individual to another.

80 Sexual Reproduction vs. Asexual Reproduction
Both are ways for organisms to procreate their species. Sexual reproduction involves two organisms while asexual involves one Sexual reproduction produces diversity; asexual reproduction creates “clones” Hydras, sponges, and planarians are animals that exhibit asexual reproduction

81 Spermatogenesis Spermatogenesis occurs in the seminiferous tubules of the testes in males Primary spermatocytes undergo meiosis to form secondary spermatocytes, which also undergo meiosis to form 4 haploid spermatids These spermatids undergo a stage of metamorphosis to become mature spermatozoa

82 Oogenesis Oogenesis occurs in the ovaries in females
Oogenesis begins with a immature primary oocyte that divides into a secondary oocyte and a smaller first polar body The secondary oocyte produces a mature ovum and a small polar body while the first polar body creates two more smaller polar bodies Oogenesis creates one mature egg cell and three small polar bodies that go on to die These three polar bodies “donate” their cytoplasm and nutrients to the mature egg cell

83 Menstrual cycle vs. Estrous cycle
Humans and the great apes follow the menstrual cycle, while the rest of the animal kingdom (the female half) undergoes the estrous cycle Animals with the estrous cycle reabsorb the endometrium if conception doesn’t occur, while animals with the menstrual cycle shed the endometrium through menstruation Animals with the estrous cycle are sexually active only during the estrous phase of the cycle, while animals with the menstrual cycle are sexually active at any time of the cycle

84 Menstrual cycle The menstrual cycle usually occurs over 28 days.
The cycle starts with menstruation (the uterine cycle) where the endometrium is shed as the egg isn’t fertilized and the body prepares the way for a new egg The follicular phase (the ovarian cycle) comes after as a follicle stimulating hormone (FSH) stimulates the lining of the uterus to grow. These follicles also secrete estrogen and initiate the formation of a new endometrium. The luteal phase (part of the ovarian cycle) occurs when the ovaries form the corpus luteum and release progesterone which readies the uterus for the implantation of the blastocyst. If there is no fertilization, menstruation occurs again and the egg is lost. The menstrual cycle is a feedback mechanism that is regulated by the presence of fertilization and the quantity of certain hormones.

85 Development The fertilized ovum forms a “ball of cells” called a morula through the process of cleavage, where the zygote undergoes rapid cell division This ball eventually expands and becomes hollow, called a blastula Gastrulation comes after and divides the body into three layers as outside ectoderm cells move inward to form the endoderm. This final three-layer ball is called the gastrula. Organogenesis is the final stage in early development as cells in each layer differentiate and form the organs of the human body

86 Germ Layers Ectoderm is the outermost layer and forms the skin, nails, hair, sweat glands, facial muscles, and the brain and the spinal cord. The mesoderm is the middle layer and forms the heart, kidneys, bones, muscles, and blood vessels. Endoderm is the innermost layer and gives rise to the respiratory and digestive systems.

87 Gonorrhea Gonorrhea is a sexually transmitted disease that causes severe pain and infertility Symptoms include swollen reproductive tracts, pain when urinating, and fevers Gonorrhea is the most common STD, but the incidence is less than 1% of the general population Treatments include antibiotics and pain medications

88 Syphilis Syphilis is a sexually transmitted disease that can cause infertility and death Symptoms include sores where syphilis entered the body, rashes, mucous discharge, fatigue, and finally damage to the heart, eyes, nerves, and brain. The incidence rate in the US among males 5.7 percent Treatments include antibiotics

89 Nervous System The function of the nervous system is to coordinate and send signals from one cell to another and from one part of the body to others.

90 Central Nervous System and Peripheral Nervous System
The central nervous system is the part of the nervous system that receives information and coordinate responses. It contains the brain and the spinal cord. The peripheral nervous system connects the central nervous system to the limbs and organs. It consists of the nerves and ganglia outside of the central nervous system.

91 Neuron

92 Reflex arc A sensation is felt through the activation of a receptor and the sensory neuron relays signals to the brain This signal is transported from the Peripheral Nervous System to the Central Nervous System and the brain The brain responds by sending a signal from the CNS back to the PNS This signal activates a motor neuron that causes the body to respond to the sensation

93 Major Parts of the Brain
Cerebral Hemispheres perform high level functions such as thought, judgment, motion, interpretation, memory, and recognition. Diencephalon process sensory and motor information and relay it to the cerebrum. This region also contains the hypothalamus, which regulates involuntary functions, and the pituitary gland, which secretes hormones. Brain stem controls reflexes and helps the cerebrum communicate with the cerebellum. It contains the medulla oblongata which controls heart rate, blood pressure, and breathing. Cerebellum coordinates movement, balance, and coordination.

94 Nerve Impulses The neuron begins with a concentration of Na+ ions outside of a neuron’s membrane and K+ ions on the inside. Pumps along the membrane create this polarized membrane potential. This state is known as the resting potential. When a stimulus reaches a resting neuron, the ion channels open along the action potential and Na+ ions rush inside the neuron and the region becomes depolarized. This, however, only occurs if the stimulus is able to exceed a threshold level and cause the channels to open. The ion channels begin allowing K+ ions to go outside to accommodate the Na+ ions inside. This causes the region to become repolarized. The refractory period begins as ion channels pump K+ ions back inside and Na+ ions outside. During this period, the neuron can’t respond to any stimuli and no action potential occurs.

95 Neurotransmitters Neurotransmitters are chemicals that transmit signals from one neuron to the next across synapses. Axon terminals release neurotransmitters from a pump that is received by receptors on the dendrites of another neuron.

96 Huntington’s Disease Huntington’s Disease is a hereditary disease that causes nerve cells to degenerate Symptoms include changes in behavior, irritability, forgetfulness, paranoia, loss of judgment and speech impairments Prevalence is about 1 in 10,000 people There is no cure. Treatment is only to slow the disease. Dopamine blockers and certain drugs control behavior and may slow degeneration of gray tissue.

97 Multiple Sclerosis Multiple sclerosis is an autoimmune disease that affects the brain and spinal cord. Immune system cells attack the myelin sheath that protects nerve cells. As nerve cells are damaged, nerve signals may slow down or stop. Symptoms include spasms, trouble moving, eye problems, pain, and slurred speech. Incidence is about 0.1% in the United States There is no cure. Therapy can help slow the disease and regain speech and coordination.

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