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Chapter 40 Basic Principles of Animal Form and Function PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Diverse Forms, Common Challenges • Anatomy is the study of the biological form of an organism • Physiology is the study of the biological functions an organism performs • The comparative study of animals reveals that form and function are closely correlated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 40.1: Animal form and function are correlated at all levels of organization • Size and shape affect the way an animal interacts with its environment • Many different animal body plans have evolved and are determined by the genome Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Physical Constraints on Animal Size and Shape • The ability to perform certain actions depends on an animal’s shape, size, and environment • Evolutionary convergence reflects different species’ adaptations to a similar environmental challenge • Physical laws impose constraints on animal size and shape – cells as well as animals can only get so big Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-2 (a) Tuna (b) Penguin (c) Seal Exchange with the Environment • An animal’s size and shape directly affect how it exchanges energy and materials with its surroundings • Exchange occurs as substances dissolved in the aqueous medium diffuse and are transported across the cells’ plasma membranes • A single-celled protist living in water has a sufficient surface area of plasma membrane to service its entire volume of cytoplasm Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-3 Mouth Gastrovascular cavity Exchange Exchange Exchange 0.15 mm 1.5 mm (a) Single cell (b) Two layers of cells • Multicellular organisms with a sac body plan have body walls that are only two cells thick, facilitating diffusion of materials Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • More complex organisms have highly folded internal surfaces for exchanging materials Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-4 External environment CO2 Food O2 Mouth Respiratory system 0.5 cm 50 µm Animal body Lung tissue Nutrients Heart Cells Circulatory system 10 µm Interstitial fluid Digestive system Excretory system Lining of small intestine Kidney tubules Anus Unabsorbed matter (feces) Metabolic waste products (nitrogenous waste) • In vertebrates, the space between cells is filled with intercellular (interstitial) fluid, ICF, which allows for the movement of material into and out of cells • Diffusion of materials into and out of cells requires an aqueous environment • A complex body plan helps an animal in a variable environment to maintain a relatively stable internal environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hierarchical Organization of Body Plans • Most animals are composed of specialized cells organized into tissues that have different functions • Tissues make up organs, which together make up organ systems Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 41.3: Organs specialized for sequential stages of food processing form the mammalian digestive system • The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts • Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-10 Tongue Sphincter Salivary glands Oral cavity Salivary glands Mouth Pharynx Esophagus Esophagus Sphincter Liver Stomach Ascending portion of large intestine Gallbladder Gallbladder Duodenum of small intestine Pancreas Liver Small intestine Small intestine Large intestine Rectum Anus Appendix Cecum Pancreas Stomach Small intestine Large intestine Rectum Anus A schematic diagram of the human digestive system Absorption in the Small Intestine • The small intestine has a huge surface area, due to villi and microvilli that are exposed to the intestinal lumen • The enormous microvillar surface greatly increases the rate of nutrient absorption Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-15 Microvilli (brush border) at apical (lumenal) surface Lumen Vein carrying blood to hepatic portal vein Blood capillaries Muscle layers Epithelial cells Basal surface Large circular folds Villi Epithelial cells Lacteal Key Nutrient absorption Intestinal wall Villi Lymph vessel Concept 42.1: Circulatory systems link exchange surfaces with cells throughout the body • In small and/or thin animals, cells can exchange materials directly with the surrounding medium • In most animals, transport systems connect the organs of exchange with the body cells • Most complex animals have internal transport systems that circulate fluid Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Open and Closed Circulatory Systems • More complex animals have either open or closed circulatory systems • Both systems have three basic components: – A circulatory fluid (blood or hemolymph) – A set of tubes (blood vessels) – A muscular pump (the heart) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open circulatory system • In an open circulatory system, there is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid • Closed systems are more efficient at transporting circulatory fluids to tissues and cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-3 Heart Hemolymph in sinuses surrounding organs Pores Heart Blood Interstitial fluid Small branch vessels In each organ Dorsal vessel (main heart) Tubular heart (a) An open circulatory system Auxiliary hearts Ventral vessels (b) A closed circulatory system Concept 42.5: Gas exchange occurs across specialized respiratory surfaces • Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Respiratory Surfaces • Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water • Gas exchange across respiratory surfaces takes place by diffusion • Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mammalian Respiratory Systems: A Closer Look • A system of branching ducts conveys air to the lungs • Air inhaled through the nostrils passes through the pharynx via the larynx, trachea, bronchi, bronchioles, and alveoli, where gas exchange occurs • Exhaled air passes over the vocal cords to create sounds • Secretions called surfactants coat the surface of the alveoli Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-24 Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Terminal bronchiole Nasal cavity Pharynx Larynx Alveoli (Esophagus) Left lung Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM 50 µm Colorized SEM 50 µm Concept 44.3: Diverse excretory systems are variations on a tubular theme • Excretory systems regulate solute movement between internal fluids and the external environment Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Excretory Processes • Most excretory systems produce urine by refining a filtrate derived from body fluids • Key functions of most excretory systems: – Filtration: pressure-filtering of body fluids – Reabsorption: reclaiming valuable solutes – Secretion: adding toxins and other solutes from the body fluids to the filtrate – Excretion: removing the filtrate from the system Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Survey of Excretory Systems • Systems that perform basic excretory functions vary widely among animal groups • They usually involve a complex network of tubules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Kidneys • Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Structure of the Mammalian Excretory System • The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation • Each kidney is supplied with blood by a renal artery and drained by a renal vein • Urine exits each kidney through a duct called the ureter • Both ureters drain into a common urinary bladder, and urine is expelled through a urethra Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-14 Renal medulla Posterior vena cava Renal artery and vein Aorta Renal cortex Kidney Renal pelvis Ureter Urinary bladder Urethra Ureter (a) Excretory organs and major associated blood vessels Juxtamedullary nephron Section of kidney from a rat (b) Kidney structure Cortical nephron 10 µm 4 mm Afferent arteriole Glomerulus from renal artery Bowman’s capsule SEM Proximal tubule Peritubular capillaries Renal cortex Efferent arteriole from glomerulus Collecting duct Renal medulla Branch of renal vein Collecting duct Descending limb To renal pelvis Loop of Henle (c) Nephron types Distal tubule Ascending limb (d) Filtrate and blood flow Vasa recta Concept 40.2: Feedback control loops maintain the internal environment in many animals • Animals manage their internal environment by regulating or conforming to the external environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Regulating and Conforming • A regulator uses internal control mechanisms to moderate internal change in the face of external, environmental fluctuation • A conformer allows its internal condition to vary with certain external changes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-7 40 Body temperature (°C) River otter (temperature regulator) 30 20 Largemouth bass (temperature conformer) 10 0 10 20 30 40 Ambient (environmental) temperature (ºC) Homeostasis • Organisms use homeostasis to maintain a “steady state” or internal balance regardless of external environment • In humans, body temperature, blood pH, and glucose concentration are each maintained at a constant level Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Mechanisms of Homeostasis • Mechanisms of homeostasis moderate changes in the internal environment • For a given variable, fluctuations above or below a set point serve as a stimulus; these are detected by a sensor and trigger a response • The response returns the variable to the set point Animation: Negative Feedback Animation: Positive Feedback Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-8 Response: Heater turned off Room temperature decreases Stimulus: Control center (thermostat) reads too hot Set point: 20ºC Stimulus: Control center (thermostat) reads too cold Room temperature increases Response: Heater turned on Feedback Loops in Homeostasis • The dynamic equilibrium of homeostasis is maintained by negative feedback, which helps to return a variable to either a normal range or a set point • Most homeostatic control systems function by negative feedback, where buildup of the end product shuts the system off • Positive feedback loops occur in animals, but do not usually contribute to homeostasis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Insulin and Glucagon: Control of Blood Glucose • Insulin and glucagon are antagonistic hormones that help maintain glucose homeostasis • The pancreas has clusters of endocrine cells called islets of Langerhans with alpha cells that produce glucagon and beta cells that produce insulin Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 45-12-2 Body cells take up more glucose. Insulin Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Blood glucose level rises. Blood glucose level declines. Homeostasis: Blood glucose level (about 90 mg/100 mL) Fig. 45-12-4 Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Blood glucose level falls. Blood glucose level rises. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Glucagon Fig. 45-12-5 Body cells take up more glucose. Insulin Beta cells of pancreas release insulin into the blood. Liver takes up glucose and stores it as glycogen. STIMULUS: Blood glucose level rises. Blood glucose level declines. Homeostasis: Blood glucose level (about 90 mg/100 mL) STIMULUS: Blood glucose level falls. Blood glucose level rises. Alpha cells of pancreas release glucagon. Liver breaks down glycogen and releases glucose. Glucagon Diabetes Mellitus • Diabetes mellitus is perhaps the best-known endocrine disorder • It is caused by a deficiency of insulin or a decreased response to insulin in target tissues • It is marked by elevated blood glucose levels Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Type I diabetes mellitus (insulin-dependent) is an autoimmune disorder in which the immune system destroys pancreatic beta cells • Type II diabetes mellitus (non-insulindependent) involves insulin deficiency or reduced response of target cells due to change in insulin receptors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Feedback Loops in Homeostasis • Positive feedback loops occur in animals, but do not usually contribute to homeostasis • Some examples are: – Lactation in mammals – Onset of labor in childbirth – Ripening of fruit Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 40.3: Homeostatic processes for thermoregulation involve form, function, and behavior • Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Endothermy and Ectothermy • Endothermic animals generate heat by metabolism; birds and mammals are endotherms • Ectothermic animals gain heat from external sources; ectotherms include most invertebrates, fishes, amphibians, and nonavian reptiles Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Circulatory Adaptations • Regulation of blood flow near the body surface significantly affects thermoregulation • Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin • In vasodilation, blood flow in the skin increases, facilitating heat loss • In vasoconstriction, blood flow in the skin decreases, lowering heat loss Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The arrangement of blood vessels in many marine mammals and birds allows for countercurrent exchange • Countercurrent heat exchangers transfer heat between fluids flowing in opposite directions • Countercurrent heat exchangers are an important mechanism for reducing heat loss Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-12 Canada goose Bottlenose dolphin Blood flow Artery Vein Vein Artery 35ºC 33º 30º 27º 20º 18º 10º 9º • Some bony fishes and sharks also use countercurrent heat exchanges • Many endothermic insects have countercurrent heat exchangers that help maintain a high temperature in the thorax Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cooling by Evaporative Heat Loss • Many types of animals lose heat through evaporation of water in sweat • Panting increases the cooling effect in birds and many mammals • Sweating or bathing moistens the skin, helping to cool an animal down Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Physiological Thermostats and Fever • Thermoregulation is controlled by a region of the brain called the hypothalamus • The hypothalamus triggers heat loss or heat generating mechanisms • Fever is the result of a change to the set point for a biological thermostat Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-16 Sweat glands secrete sweat, which evaporates, cooling the body. Body temperature decreases; thermostat shuts off cooling mechanisms. Thermostat in hypothalamus activates cooling mechanisms. Blood vessels in skin dilate: capillaries fill; heat radiates from skin. Increased body temperature Homeostasis: Internal temperature of 36–38°C Body temperature increases; thermostat shuts off warming mechanisms. Decreased body temperature Blood vessels in skin constrict, reducing heat loss. Skeletal muscles contract; shivering generates heat. Thermostat in hypothalamus activates warming mechanisms. Alterations in Homeostasis • Set points and normal ranges can change with age or show cyclic variation • Acclimatization is the process by which an animal adjusts to changes in its external environment Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Torpor and Energy Conservation • Torpor is a physiological state in which activity is low and metabolism decreases • Torpor enables animals to save energy while avoiding difficult and dangerous conditions • Hibernation is long-term torpor that is an adaptation to winter cold and food scarcity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Metabolic rate (kcal per day) Fig. 40-21 200 Actual metabolism 100 0 35 30 Temperature (°C) Additional metabolism that would be necessary to stay active in winter Arousals Body temperature 25 20 15 10 5 0 –5 Outside temperature Burrow temperature –10 –15 June August October December February April • Estivation, or summer torpor, enables animals to survive long periods of high temperatures and scarce water supplies • Daily torpor is exhibited by many small mammals and birds and seems adapted to feeding patterns Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Digestive Compartments • Most animals process food in specialized compartments • These compartments reduce the risk of an animal digesting its own cells and tissues Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Intracellular Digestion • In intracellular digestion, food particles are engulfed by endocytosis and digested within food vacuoles Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Extracellular Digestion • Extracellular digestion is the breakdown of food particles outside of cells • It occurs in compartments that are continuous with the outside of the animal’s body • This is what people do Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-8 Tentacles Food Mouth Epidermis Gastrodermis Gastrovascular cavity • Animals with simple body plans have a gastrovascular cavity that functions in both digestion and distribution of nutrients Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • More complex animals have a digestive tube with two openings, a mouth and an anus • This digestive tube is called a complete digestive tract or an alimentary canal • It can have specialized regions that carry out digestion and absorption in a stepwise fashion Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 41-9 Crop Esophagus Gizzard Intestine Pharynx Anus Mouth Typhlosole Lumen of intestine (a) Earthworm Foregut Midgut Esophagus Hindgut Rectum Anus Crop Mouth Gastric cecae (b) Grasshopper Stomach Gizzard Intestine Mouth Esophagus Crop Anus (c) Bird Concept 42.5: Gas exchange occurs across specialized respiratory surfaces • Gas exchange supplies oxygen for cellular respiration and disposes of carbon dioxide Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Respiratory Media • Animals can use air or water as a source of O2, or respiratory medium • In a given volume, there is less O2 available in water than in air • Obtaining O2 from water requires greater efficiency than air breathing Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Respiratory Surfaces • Animals require large, moist respiratory surfaces for exchange of gases between their cells and the respiratory medium, either air or water • Gas exchange across respiratory surfaces takes place by diffusion • Respiratory surfaces vary by animal and can include the outer surface, skin, gills, tracheae, and lungs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Gills in Aquatic Animals • Gills are outfoldings of the body that create a large surface area for gas exchange Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-21 Coelom Gills Gills Parapodium (functions as gill) (a) Marine worm Tube foot (b) Crayfish (c) Sea star • Ventilation moves the respiratory medium over the respiratory surface • Aquatic animals move through water or move water over their gills for ventilation • Fish gills use a countercurrent exchange system, where blood flows in the opposite direction to water passing over the gills; blood is always less saturated with O2 than the water it meets Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-22 Fluid flow through gill filament Oxygen-poor blood Anatomy of gills Oxygen-rich blood Gill arch Lamella Gill arch Gill filament organization Blood vessels Water flow Operculum Water flow between lamellae Blood flow through capillaries in lamella Countercurrent exchange PO2 (mm Hg) in water 150 120 90 60 30 Gill filaments Net diffusion of O2 from water to blood 140 110 80 50 20 PO2 (mm Hg) in blood Tracheal Systems in Insects • The tracheal system of insects consists of tiny branching tubes that penetrate the body • The tracheal tubes supply O2 directly to body cells • The respiratory and circulatory systems are separate • Larger insects must ventilate their tracheal system to meet O2 demands Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-23 Air sacs Tracheae External opening Tracheoles Mitochondria Muscle fiber Body cell Air sac Tracheole Trachea Air Body wall 2.5 µm Lungs • Lungs are an infolding of the body surface • The circulatory system (open or closed) transports gases between the lungs and the rest of the body • The size and complexity of lungs correlate with an animal’s metabolic rate Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-24 Branch of pulmonary vein (oxygen-rich blood) Branch of pulmonary artery (oxygen-poor blood) Terminal bronchiole Nasal cavity Pharynx Larynx Alveoli (Esophagus) Left lung Trachea Right lung Bronchus Bronchiole Diaphragm Heart SEM 50 µm Colorized SEM 50 µm Overview: A Balancing Act • Physiological systems of animals operate in a fluid environment • Relative concentrations of water and solutes must be maintained within fairly narrow limits • Osmoregulation regulates solute concentrations and balances the gain and loss of water • Your notes and book discuss examples Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Freshwater animals show adaptations that reduce water uptake and conserve solutes • Desert and marine animals face desiccating environments that can quickly deplete body water • Excretion gets rid of nitrogenous metabolites and other waste products Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 44.2: An animal’s nitrogenous wastes reflect its phylogeny and habitat • The type and quantity of an animal’s waste products may greatly affect its water balance • Among the most important wastes are nitrogenous breakdown products of proteins and nucleic acids • Some animals convert toxic ammonia (NH3) to less toxic compounds prior to excretion Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-9 Proteins Nucleic acids Amino acids Nitrogenous bases Amino groups Most aquatic animals, including most bony fishes Ammonia Mammals, most Many reptiles amphibians, sharks, (including birds), some bony fishes insects, land snails Urea Uric acid Forms of Nitrogenous Wastes • Different animals excrete nitrogenous wastes in different forms: ammonia, urea, or uric acid Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Ammonia • Animals that excrete nitrogenous wastes as ammonia need lots of water • They release ammonia across the whole body surface or through gills Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Urea • The liver of mammals and most adult amphibians converts ammonia to less toxic urea • The circulatory system carries urea to the kidneys, where it is excreted • Conversion of ammonia to urea is energetically expensive; excretion of urea requires less water than ammonia Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Uric Acid • Insects, land snails, and many reptiles, including birds, mainly excrete uric acid • Uric acid is largely insoluble in water and can be secreted as a paste with little water loss • Uric acid is more energetically expensive to produce than urea Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Concept 44.3: Diverse excretory systems are variations on a tubular theme • Excretory systems regulate solute movement between internal fluids and the external environment Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Excretory Processes • Most excretory systems produce urine by refining a filtrate derived from body fluids • Key functions of most excretory systems: – Filtration: pressure-filtering of body fluids – Reabsorption: reclaiming valuable solutes – Secretion: adding toxins and other solutes from the body fluids to the filtrate – Excretion: removing the filtrate from the system Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-10 Filtration Capillary Excretory tubule Reabsorption Secretion Urine Excretion Survey of Excretory Systems • Systems that perform basic excretory functions vary widely among animal groups • They usually involve a complex network of tubules Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Protonephridia • A protonephridium is a network of dead-end tubules connected to external openings • The smallest branches of the network are capped by a cellular unit called a flame bulb • These tubules excrete a dilute fluid and function in osmoregulation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-11 Nucleus of cap cell Cilia Flame bulb Interstitial fluid flow Tubule Tubules of protonephridia Opening in body wall Tubule cell Metanephridia • Each segment of an earthworm has a pair of open-ended metanephridia • Metanephridia consist of tubules that collect coelomic fluid and produce dilute urine for excretion Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-12 Coelom Capillary network Components of a metanephridium: Internal opening Collecting tubule Bladder External opening Kidneys • Kidneys, the excretory organs of vertebrates, function in both excretion and osmoregulation Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Structure of the Mammalian Excretory System • The mammalian excretory system centers on paired kidneys, which are also the principal site of water balance and salt regulation • Each kidney is supplied with blood by a renal artery and drained by a renal vein • Urine exits each kidney through a duct called the ureter • Both ureters drain into a common urinary bladder, and urine is expelled through a urethra Animation: Nephron Introduction Copyright © 2008 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fig. 44-14 Renal medulla Posterior vena cava Renal artery and vein Aorta Renal cortex Kidney Renal pelvis Ureter Urinary bladder Urethra Ureter (a) Excretory organs and major associated blood vessels Juxtamedullary nephron Section of kidney from a rat (b) Kidney structure Cortical nephron 10 µm 4 mm Afferent arteriole Glomerulus from renal artery Bowman’s capsule SEM Proximal tubule Peritubular capillaries Renal cortex Efferent arteriole from glomerulus Collecting duct Renal medulla Branch of renal vein Collecting duct Descending limb To renal pelvis Loop of Henle (c) Nephron types Distal tubule Ascending limb (d) Filtrate and blood flow Vasa recta Fig. 44-14d 10 µm Afferent arteriole from renal artery SEM Glomerulus Bowman’s capsule Proximal tubule Peritubular capillaries Efferent arteriole from glomerulus Distal tubule Branch of renal vein Collecting duct Descending limb Loop of Henle (d) Filtrate and blood flow Ascending limb Vasa recta Open and Closed Circulatory Systems • More complex animals have either open or closed circulatory systems • Both systems have three basic components: – A circulatory fluid (blood or hemolymph) – A set of tubes (blood vessels) – A muscular pump (the heart) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In insects, other arthropods, and most molluscs, blood bathes the organs directly in an open circulatory system • In an open circulatory system, there is no distinction between blood and interstitial fluid, and this general body fluid is more correctly called hemolymph Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In a closed circulatory system, blood is confined to vessels and is distinct from the interstitial fluid • Closed systems are more efficient at transporting circulatory fluids to tissues and cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-3 Heart Hemolymph in sinuses surrounding organs Pores Heart Blood Interstitial fluid Small branch vessels In each organ Dorsal vessel (main heart) Tubular heart (a) An open circulatory system Auxiliary hearts Ventral vessels (b) A closed circulatory system Organization of Vertebrate Circulatory Systems • Humans and other vertebrates have a closed circulatory system, often called the cardiovascular system • The three main types of blood vessels are arteries, veins, and capillaries Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Arteries branch into arterioles and carry blood to capillaries • Networks of capillaries called capillary beds are the sites of chemical exchange between the blood and interstitial fluid • Venules converge into veins and return blood from capillaries to the heart Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Vertebrate hearts contain two or more chambers • Blood enters through an atrium and is pumped out through a ventricle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Single Circulation • Bony fishes, rays, and sharks have single circulation with a two-chambered heart • In single circulation, blood leaving the heart passes through two capillary beds before returning Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-4 Gill capillaries Artery Gill circulation Ventricle Heart Atrium Vein Systemic circulation Systemic capillaries Double Circulation • Amphibian, reptiles, and mammals have double circulation • Oxygen-poor and oxygen-rich blood are pumped separately from the right and left sides of the heart Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 42-5 Amphibians Reptiles (Except Birds) Mammals and Birds Lung and skin capillaries Lung capillaries Lung capillaries Pulmocutaneous circuit Atrium (A) Right systemic aorta Atrium (A) Ventricle (V) Left Right Systemic circuit Systemic capillaries Pulmonary circuit A V Right Pulmonary circuit A A V Left Systemic capillaries Left systemic aorta A V V Right Left Systemic circuit Systemic capillaries Energy Allocation and Use • Animals harvest chemical energy from food • Energy-containing molecules from food are usually used to make ATP, which powers cellular work • After the needs of staying alive are met, remaining food molecules can be used in biosynthesis • Biosynthesis includes body growth and repair, synthesis of storage material such as fat, and production of gametes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 40-17 External environment Animal body Organic molecules in food Digestion and absorption Heat Energy lost in feces Nutrient molecules in body cells Carbon skeletons Cellular respiration Energy lost in nitrogenous waste Heat ATP Biosynthesis Cellular work Heat Heat Quantifying Energy Use • Metabolic rate is the amount of energy an animal uses in a unit of time • One way to measure it is to determine the amount of oxygen consumed or carbon dioxide produced Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Minimum Metabolic Rate and Thermoregulation • Basal metabolic rate (BMR) is the metabolic rate of an endotherm at rest at a “comfortable” temperature • Standard metabolic rate (SMR) is the metabolic rate of an ectotherm at rest at a specific temperature • Both rates assume a nongrowing, fasting, and nonstressed animal • Ectotherms have much lower metabolic rates than endotherms of a comparable size Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Influences on Metabolic Rate • Metabolic rates are affected by many factors besides whether an animal is an endotherm or ectotherm • Two of these factors are size and activity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Size and Metabolic Rate • Metabolic rate per gram is inversely related to body size among similar animals • Researchers continue to search for the causes of this relationship • The higher metabolic rate of smaller animals leads to a higher oxygen delivery rate, breathing rate, heart rate, and greater (relative) blood volume, compared with a larger animal Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chapter 43 The Immune System PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Reconnaissance, Recognition, and Response • Barriers help an animal to defend itself from the many dangerous pathogens it may encounter • The immune system recognizes foreign bodies and responds with the production of immune cells and proteins • Two major kinds of defense have evolved: innate immunity and acquired immunity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Innate immunity is present before any exposure to pathogens and is effective from the time of birth • It involves nonspecific responses to pathogens • Innate immunity consists of external barriers plus internal cellular and chemical defenses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Acquired immunity, or adaptive immunity, develops after exposure to agents such as microbes, toxins, or other foreign substances • It involves a very specific response to pathogens Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-2 Pathogens (microorganisms and viruses) INNATE IMMUNITY • Recognition of traits shared by broad ranges of pathogens, using a small set of receptors • Rapid response ACQUIRED IMMUNITY • Recognition of traits specific to particular pathogens, using a vast array of receptors • Slower response Barrier defenses: Skin Mucous membranes Secretions Internal defenses: Phagocytic cells Antimicrobial proteins Inflammatory response Natural killer cells Humoral response: Antibodies defend against infection in body fluids. Cell-mediated response: Cytotoxic lymphocytes defend against infection in body cells. Concept 43.1: In innate immunity, recognition and response rely on shared traits of pathogens • Both invertebrates and vertebrates depend on innate nonspecific immunity to fight infection Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Innate Immunity of Invertebrates • In insects, an exoskeleton made of chitin forms the first barrier to pathogens • The digestive system is protected by low pH and lysozyme, an enzyme that digests microbial cell walls • Hemocytes circulate within hemolymph and carry out phagocytosis, the ingestion and digestion of foreign substances including bacteria Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Hemocytes also secrete antimicrobial peptides that disrupt the plasma membranes of bacteria • The immune system recognizes bacteria and fungi by structures on their cell walls • An immune response varies with the class of pathogen encountered Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Innate Immunity of Vertebrates • The immune system of mammals is the best understood of the vertebrates • Innate defenses include barrier defenses, phagocytosis, antimicrobial peptides • Additional defenses are unique to vertebrates: the inflammatory response and natural killer cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Barrier Defenses • Barrier defenses include the skin and mucous membranes of the respiratory, urinary, and reproductive tracts • Mucus traps and allows for the removal of microbes • Many body fluids including saliva, mucus, and tears are hostile to microbes • The low pH of skin and the digestive system prevents growth of microbes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cellular Innate Defenses • White blood cells (leukocytes) engulf pathogens in the body • A white blood cell engulfs a microbe, then fuses with a lysosome to destroy the microbe • Peptides and proteins function in innate defense by attacking microbes directly or impeding their reproduction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Inflammatory Responses • Following an injury, mast cells release histamine, which promotes changes in blood vessels; this is part of the inflammatory response • These changes increase local blood supply and allow more phagocytes and antimicrobial proteins to enter tissues. This causes swelling. • Pus, a fluid rich in white blood cells, dead microbes, and cell debris, accumulates at the site of inflammation Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-8-3 Pathogen Splinter Chemical Macrophage signals Mast cell Capillary Red blood cells Phagocytic cell Fluid Phagocytosis • Inflammation can be either local or systemic (throughout the body) • Fever is a systemic inflammatory response triggered by pyrogens released by macrophages, and toxins from pathogens • Septic shock is a life-threatening condition caused by an overwhelming inflammatory response Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Natural Killer Cells • All cells in the body (except red blood cells) have a class 1 MHC protein on their surface • Cancerous or infected cells no longer express this protein; natural killer (NK) cells attack these damaged cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Innate Immune System Evasion by Pathogens • Some pathogens avoid destruction by modifying their surface to prevent recognition or by resisting breakdown following phagocytosis • Tuberculosis (TB) is one such disease and kills more than a million people a year Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 43.2: In acquired immunity, lymphocyte receptors provide pathogen-specific recognition • White blood cells called lymphocytes recognize and respond to antigens, foreign molecules • Lymphocytes that mature in the thymus above the heart are called T cells, and those that mature in bone marrow are called B cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Acquired Immunity: An Overview • B cells and T cells have receptor proteins that can bind to foreign molecules • Each individual lymphocyte is specialized to recognize a specific type of molecule • Lymphocytes contribute to immunological memory, an enhanced response to a foreign molecule encountered previously Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Antigen Recognition by Lymphocytes • An antigen is any foreign molecule to which a lymphocyte responds • A single B cell or T cell has about 100,000 identical antigen receptors Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-9 Antigenbinding site Antigenbinding site Antigenbinding site Disulfide bridge C C Light chain Variable regions V V Constant regions C C Transmembrane region Plasma membrane Heavy chains chain chain Disulfide bridge B cell (a) B cell receptor Cytoplasm of B cell Cytoplasm of T cell (b) T cell receptor T cell • All antigen receptors on a single lymphocyte recognize the same antigen • B cells give rise to plasma cells, which secrete proteins called antibodies or immunoglobulins • Secreted antibodies, or immunoglobulins, are structurally similar to B cell receptors but lack transmembrane regions that anchor receptors in the plasma membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings CELL-MEDIATED RESPONSE • T cells bind to antigen fragments presented on a host cell • These antigen fragments are bound to cellsurface proteins called MHC molecules • MHC molecules are so named because they are encoded by a family of genes called the major histocompatibility complex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Role of the MHC • In infected cells, MHC molecules bind and transport antigen fragments to the cell surface, a process called antigen presentation • A nearby T cell can then detect the antigen fragment displayed on the cell’s surface • Depending on their source, peptide antigens are handled by different classes of MHC molecules Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Class I MHC molecules are found on almost all nucleated cells of the body • They display peptide antigens to cytotoxic T cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-12 Infected cell Microbe Antigenpresenting cell 1 Antigen associates with MHC molecule Antigen fragment Antigen fragment 1 Class I MHC molecule 1 T cell receptor (a) 2 2 Cytotoxic T cell Class II MHC molecule T cell receptor 2 T cell recognizes combination (b) Helper T cell • Class II MHC molecules are located mainly on dendritic cells, macrophages, and B cells • Dendritic cells, macrophages, and B cells are antigen-presenting cells that display antigens to cytotoxic T cells and helper T cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The first exposure to a specific antigen represents the primary immune response • During this time, effector B cells called plasma cells are generated, and T cells are activated to their effector forms • In the secondary immune response, memory cells facilitate a faster, more efficient response Animation: Role of B Cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 43.3: Acquired immunity defends against infection of body cells and fluids • Acquired immunity has two branches: the humoral immune response and the cellmediated immune response • Humoral immune response involves activation and clonal selection of B cells, resulting in production of secreted antibodies • Cell-mediated immune response involves activation and clonal selection of cytotoxic T cells • Helper T cells aid both responses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-16 Humoral (antibody-mediated) immune response Cell-mediated immune response Key Antigen (1st exposure) + Engulfed by Gives rise to Antigenpresenting cell + Stimulates + + B cell Helper T cell + Cytotoxic T cell + Memory Helper T cells + + + Antigen (2nd exposure) Plasma cells Memory B cells + Memory Cytotoxic T cells Active Cytotoxic T cells Secreted antibodies Defend against extracellular pathogens by binding to antigens, thereby neutralizing pathogens or making them better targets for phagocytes and complement proteins. Defend against intracellular pathogens and cancer by binding to and lysing the infected cells or cancer cells. Helper T Cells: A Response to Nearly All Antigens • A surface protein called CD4 binds the class II MHC molecule • This binding keeps the helper T cell joined to the antigen-presenting cell while activation occurs • Activated helper T cells secrete cytokines that stimulate other lymphocytes Animation: Helper T Cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Cytotoxic T Cells: A Response to Infected Cells • Cytotoxic T cells are the effector cells in cellmediated immune response • Cytotoxic T cells make CD8, a surface protein that greatly enhances interaction between a target cell and a cytotoxic T cell • Binding to a class I MHC complex on an infected cell activates a cytotoxic T cell and makes it an active killer • The activated cytotoxic T cell secretes proteins that destroy the infected target cell Animation: Cytotoxic T Cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings B Cells: A Response to Extracellular Pathogens • The humoral response is characterized by secretion of antibodies by B cells • Activation of B cells is aided by cytokines and antigen binding to helper T cells • Clonal selection of B cells generates antibodysecreting plasma cells, the effector cells of humoral immunity Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Active and Passive Immunization • Active immunity develops naturally in response to an infection • It can also develop following immunization, also called vaccination • In immunization, a nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory • This type of immunity is considered permanent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Passive immunity provides immediate, shortterm protection • It is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk • It can be conferred artificially by injecting antibodies into a nonimmune person • This immunity is temporary Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Immune Rejection • Cells transferred from one person to another can be attacked by immune defenses • This complicates blood transfusions or the transplant of tissues or organs Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Blood Groups • Antigens on red blood cells determine whether a person has blood type A (A antigen), B (B antigen), AB (both A and B antigens), or O (neither antigen) See CH 14 pg. 273 • Antibodies to nonself blood types exist in the body • Transfusion with incompatible blood leads to destruction of the transfused cells • Recipient-donor combinations can be fatal or safe Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Tissue and Organ Transplants • MHC molecules are different among genetically nonidentical individuals • Differences in MHC molecules stimulate rejection of tissue grafts and organ transplants Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Chances of successful transplantation increase if donor and recipient MHC tissue types are well matched • Immunosuppressive drugs facilitate transplantation • Lymphocytes in bone marrow transplants may cause the donor tissue to reject the recipient Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 43.4: Disruption in immune system function can elicit or exacerbate disease • Some pathogens have evolved to diminish the effectiveness of host immune responses • If the delicate balance of the immune system is disrupted, effects range from minor to often fatal Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Allergies • Allergies are exaggerated (hypersensitive) responses to antigens called allergens • In localized allergies such as hay fever, IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 43-23 IgE Histamine Allergen Granule Mast cell • The next time the allergen enters the body, it binds to mast cell–associated IgE molecules • Mast cells release histamine and other mediators that cause vascular changes leading to typical allergy symptoms • An acute allergic response can lead to anaphylactic shock, a life-threatening reaction that can occur within seconds of allergen exposure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Autoimmune Diseases • In individuals with autoimmune diseases, the immune system loses tolerance for self and turns against certain molecules of the body • Autoimmune diseases include systemic lupus erythematosus, rheumatoid arthritis, insulindependent diabetes mellitus, and multiple sclerosis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Immunodeficiency Diseases • Inborn immunodeficiency results from hereditary or developmental defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses • Acquired immunodeficiency results from exposure to chemical and biological agents • Acquired immunodeficiency syndrome (AIDS) is caused by a virus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Acquired Immune System Evasion by Pathogens • Pathogens have evolved mechanisms to attack immune responses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Antigenic Variation • Through antigenic variation, some pathogens are able to change epitope expression and prevent recognition • The human influenza virus mutates rapidly, and new flu vaccines must be made each year • Human viruses occasionally exchange genes with the viruses of domesticated animals • This poses a danger as human immune systems are unable to recognize the new viral strain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Latency • Some viruses may remain in a host in an inactive state called latency • Herpes simplex viruses can be present in a human host without causing symptoms Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Attack on the Immune System: HIV • Human immunodeficiency virus (HIV) infects helper T cells • The loss of helper T cells impairs both the humoral and cell-mediated immune responses and leads to AIDS • HIV eludes the immune system because of antigenic variation and an ability to remain latent while integrated into host DNA Animation: HIV Reproductive Cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Chapter 48 Neurons, Synapses, and Signaling PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Overview: Lines of Communication • The cone snail kills prey with venom that disables neurons • Neurons are nerve cells that transfer information within the body • Neurons use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The transmission of information depends on the path of neurons along which a signal travels • Processing of information takes place in simple clusters of neurons called ganglia or a more complex organization of neurons called a brain Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Introduction to Information Processing • Nervous systems process information in three stages: sensory input, integration, and motor output Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neuron Structure and Function • Most of a neuron’s organelles are in the cell body • Most neurons have dendrites, highly branched extensions that receive signals from other neurons • The axon is typically a much longer extension that transmits signals to other cells at synapses • An axon joins the cell body at the axon hillock Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-4 Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic cell Axon Synapse Synaptic terminals Postsynaptic cell Neurotransmitter • A synapse is a junction between an axon and another cell • The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 48.2: Ion pumps and ion channels maintain the resting potential of a neuron • Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential • Messages are transmitted as changes in membrane potential • The resting potential is the membrane potential of a neuron not sending signals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Formation of the Resting Potential • In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell • Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane • These concentration gradients represent chemical potential energy Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The opening of ion channels in the plasma membrane converts chemical potential to electrical potential • A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell • Anions trapped inside the cell contribute to the negative charge within the neuron Animation: Resting Potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-6 Key Na+ K+ OUTSIDE CELL OUTSIDE [K+] CELL 5 mM INSIDE [K+] CELL 140 mM [Na+] [Cl–] 150 mM 120 mM [Na+] 15 mM [Cl–] 10 mM [A–] 100 mM INSIDE CELL (a) (b) Sodiumpotassium pump Potassium channel Sodium channel Concept 48.3: Action potentials are the signals conducted by axons • Neurons contain gated ion channels that open or close in response to stimuli Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Membrane potential changes in response to opening or closing of these channels • When gated K+ channels open, K+ diffuses out, making the inside of the cell more negative • This is hyperpolarization, an increase in magnitude of the membrane potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-9a Stimuli Membrane potential (mV) +50 0 –50 Threshold Resting potential –100 Hyperpolarizations 0 1 2 3 4 5 Time (msec) (a) Graded hyperpolarizations • Other stimuli trigger a depolarization, a reduction in the magnitude of the membrane potential • For example, depolarization occurs if gated Na+ channels open and Na+ diffuses into the cell • Graded potentials are changes in polarization where the magnitude of the change varies with the strength of the stimulus Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-9b Stimuli Membrane potential (mV) +50 0 –50 Threshold Resting potential Depolarizations –100 0 1 2 3 4 5 Time (msec) (b) Graded depolarizations Production of Action Potentials • Voltage-gated Na+ and K+ channels respond to a change in membrane potential • When a stimulus depolarizes the membrane, Na+ channels open, allowing Na+ to diffuse into the cell • The movement of Na+ into the cell increases the depolarization and causes even more Na+ channels to open • A strong stimulus results in a massive change in membrane voltage called an action potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-9c Strong depolarizing stimulus +50 Membrane potential (mV) Action potential 0 –50 Threshold Resting potential –100 0 (c) Action potential 1 2 3 4 5 Time (msec) 6 • An action potential occurs if a stimulus causes the membrane voltage to cross a particular threshold • An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane • Action potentials are the nerve impulses, or signals, that carry information along axons Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-9 Stimuli Stimuli Strong depolarizing stimulus +50 +50 +50 0 –50 Threshold Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Action potential 0 –50 Resting potential Threshold 0 –50 Resting potential Resting potential Depolarizations Hyperpolarizations –100 –100 0 1 2 3 4 5 Time (msec) (a) Graded hyperpolarizations Threshold –100 0 1 2 3 4 Time (msec) (b) Graded depolarizations 5 0 (c) Action potential 1 2 3 4 5 Time (msec) 6 Generation of Action Potentials: A Closer Look • A neuron can produce hundreds of action potentials per second • The frequency of action potentials can reflect the strength of a stimulus • An action potential can be broken down into a series of stages Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-10-5 Key Na+ K+ 3 4 Rising phase of the action potential Falling phase of the action potential Membrane potential (mV) +50 Action potential –50 2 2 4 Threshold 1 1 5 Resting potential Depolarization Extracellular fluid 3 0 –100 Sodium channel Time Potassium channel Plasma membrane Cytosol Inactivation loop 5 1 Resting state Undershoot • During the refractory period after an action potential, a second action potential cannot be initiated • The refractory period is a result of a temporary inactivation of the Na+ channels BioFlix: How Neurons Work Animation: Action Potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Conduction of Action Potentials • An action potential can travel long distances by regenerating itself along the axon • At the site where the action potential is generated, usually the axon hillock, an electrical current depolarizes the neighboring region of the axon membrane Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Inactivated Na+ channels behind the zone of depolarization prevent the action potential from traveling backwards • Action potentials travel in only one direction: toward the synaptic terminals Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-11-3 Axon Plasma membrane Action potential Cytosol Na+ K+ Action potential Na+ K+ K+ Action potential Na+ K+ Conduction Speed • The speed of an action potential increases with the axon’s diameter • In vertebrates, axons are insulated by a myelin sheath, which causes an action potential’s speed to increase • Myelin sheaths are made by glia— oligodendrocytes in the CNS and Schwann cells in the PNS Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-12a Node of Ranvier Layers of myelin Axon Schwann cell Axon Nodes of Myelin sheath Ranvier Schwann cell Nucleus of Schwann cell • Action potentials are formed only at nodes of Ranvier, gaps in the myelin sheath where voltage-gated Na+ channels are found • Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-13 Schwann cell Depolarized region (node of Ranvier) Cell body Myelin sheath Axon Concept 48.4: Neurons communicate with other cells at synapses • At electrical synapses, the electrical current flows from one neuron to another • At chemical synapses, a chemical neurotransmitter carries information across the gap junction • Most synapses are chemical synapses Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The presynaptic neuron synthesizes and packages the neurotransmitter in synaptic vesicles located in the synaptic terminal • The action potential causes the release of the neurotransmitter • The neurotransmitter diffuses across the synaptic cleft and is received by the postsynaptic cell Animation: Synapse Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 48-15 5 Synaptic vesicles containing neurotransmitter Voltage-gated Ca2+ channel Postsynaptic membrane 1 Ca2+ 4 2 Synaptic cleft Presynaptic membrane 3 Ligand-gated ion channels 6 K+ Na+ Generation of Postsynaptic Potentials • Direct synaptic transmission involves binding of neurotransmitters to ligand-gated ion channels in the postsynaptic cell • Neurotransmitter binding causes ion channels to open, generating a postsynaptic potential Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Postsynaptic potentials fall into two categories: – Excitatory postsynaptic potentials (EPSPs) are depolarizations that bring the membrane potential toward threshold – Inhibitory postsynaptic potentials (IPSPs) are hyperpolarizations that move the membrane potential farther from threshold Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • After release, the neurotransmitter – May diffuse out of the synaptic cleft – May be taken up by surrounding cells – May be degraded by enzymes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Neurotransmitters • The same neurotransmitter can produce different effects in different types of cells • There are five major classes of neurotransmitters: acetylcholine, biogenic amines, amino acids, neuropeptides, and gases • Neuropeptides include substance P and endorphins, which both affect our perception of pain • Opiates bind to the same receptors as endorphins and can be used as painkillers Chapter 49 Nervous Systems PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 49.1: Nervous systems consist of circuits of neurons and supporting cells • The simplest animals with nervous systems, the cnidarians, have neurons arranged in nerve nets • A nerve net is a series of interconnected nerve cells • More complex animals have nerves • Nerves are bundles that consist of the axons of multiple nerve cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • In vertebrates – The central nervous system (CNS) is composed of the brain and spinal cord – The peripheral nervous system (PNS) is composed of nerves and ganglia Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Organization of the Vertebrate Nervous System • The spinal cord conveys information from the brain to the PNS • The spinal cord also produces reflexes independently of the brain • A reflex is the body’s automatic response to a stimulus – For example, a doctor uses a mallet to trigger a knee-jerk reflex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The central canal of the spinal cord and the ventricles of the brain are hollow and filled with cerebrospinal fluid • The cerebrospinal fluid is filtered from blood and functions to cushion the brain and spinal cord Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-5 Gray matter White matter Ventricles • The brain and spinal cord contain – Gray matter, which consists of neuron cell bodies, dendrites, and unmyelinated axons – White matter, which consists of bundles of myelinated axons Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Concept 49.2: The vertebrate brain is regionally specialized • All vertebrate brains develop from three embryonic regions: forebrain, midbrain, and hindbrain • By the fifth week of human embryonic development, five brain regions have formed from the three embryonic regions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Brainstem • The brainstem coordinates and conducts information between brain centers • The brainstem has three parts: the midbrain, the pons, and the medulla oblongata Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-UN1 MIDBRAIN PONS MEDULLA OBLONGATA • The midbrain contains centers for receipt and integration of sensory information • The pons regulates breathing centers in the medulla • The medulla oblongata contains centers that control several functions including breathing, cardiovascular activity, swallowing, vomiting, and digestion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings The Cerebellum • The cerebellum is important for coordination and error checking during motor, perceptual, and cognitive functions • It is also involved in learning and remembering motor skills Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-UN2 CEREBELLUM The Cerebrum • The cerebrum develops from the embryonic telencephalon Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-UN4 CEREBRUM Outer part where gray matter is, is called the cortex. • The cerebrum has right and left cerebral hemispheres • Each cerebral hemisphere consists of a cerebral cortex (gray matter) overlying white matter and basal nuclei • In humans, the cerebral cortex is the largest and most complex part of the brain • The basal nuclei are important centers for planning and learning movement sequences Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A thick band of axons called the corpus callosum provides communication between the right and left cerebral cortices • The right half of the cerebral cortex controls the left side of the body, and vice versa Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-13 Left cerebral hemisphere Right cerebral hemisphere Corpus callosum Thalamus Cerebral cortex Basal nuclei Concept 49.3: The cerebral cortex controls voluntary movement and cognitive functions • Each side of the cerebral cortex has four lobes: frontal, temporal, occipital, and parietal • Each lobe contains primary sensory areas and association areas where information is integrated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 49-15 Frontal lobe Parietal lobe Speech Frontal association area Somatosensory association area Taste Reading Speech Hearing Smell Auditory association area Visual association area Vision Temporal lobe Occipital lobe Lateralization of Cortical Function • The corpus callosum transmits information between the two cerebral hemispheres • The left hemisphere is more adept at language, math, logic, and processing of serial sequences • The right hemisphere is stronger at pattern recognition, nonverbal thinking, and emotional processing Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The differences in hemisphere function are called lateralization • Lateralization is linked to handedness Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings