BIO 11 Notes IV PDF

BIO 11 BIO 11 Reuben Matteo A. Letaba, BS Psychology Class Number: 13 MODULE 13: Excretion and Osmoregulation I. General Function of Excretion and Osmoregulation ➔ Removes metabolic wastes from the bloodst...

BIO 11 BIO 11 Reuben Matteo A. Letaba, BS Psychology Class Number: 13 MODULE 13: Excretion and Osmoregulation I. General Function of Excretion and Osmoregulation ➔ Removes metabolic wastes from the bloodstream that can disrupt metabolic function ◆ By a filtering process that allows us to keep needed salts and water ➔ Maintenance of proper internal salt and water concentrations in a cell or in the body of a living organism ◆ Osmoregulation II. Getting Rid of Animal Nitrogenous Wastes GETTING RID OF ANIMAL NITROGENOUS WASTES 1  BIO 11 ➔ Majority of anabolic waste comes from the nitrogenous breakdown of protein and nucleic acid ➔ Resulting product is ammonia (NH3) - a toxic compound in the body that can interfere with cellular reactions Ammonia ➔ Aquatic animals, including most bony fishes ➔ Readily diffused throughout the body to surrounding water ➔ Requires large amounts of water for dilution due to its high toxicity. ➔ Advantage: Low energy cost to Proteins ⇒ Amino Acids ⇒ NH2 produce. ⇒ Nitrogenous Waste Urea Nucleic Acids ⇒ Nitrogenous Bases ⇒ NH2 ➔ Mammals, most amphibians, ⇒ Nitrogenous Waste sharks, and some bony fishes ➔ NH3 combines with CO2 in the liver to form urea (a product of an energy consuming metabolic cycle) ➔ Less toxic than ammonia, so it can be concentrated to conserve water. ➔ Requires more energy to synthesize compared to ammonia. Uric Acid ➔ Birds, reptiles, insects, land snails ➔ Synthesized from NH3 using ATP in the process ➔ Non-toxic and excreted as a solid or semi-solid paste to conserve water. ➔ Requires the highest energy investment for synthesis but minimizes water loss. 2  BIO 11 ➔ III. Osmoregulation OSMOREGULATION Active regulation of internal osmolarity levels Hypertonic Isotonic Hypotonic ➔ Water goes out ➔ No net movement ➔ Too much water ➔ Shrivel of water goes in ➔ Ideal ➔ Swell and explode Drastic changes to the osmolality of our bodily fluids will produce negative effects on cellular metabolism Thus, organisms have evolved mechanisms to maintain an osmolarity range that is suited for survival * Sodium is easily absorbed by the body’s circulatory system through rapid uptake, and it also tends to pull water along with it, by action of osmosis IV. Osmoregulation Mechanisms in Aquatic Animals OSMOREGULATION MECHANISM 3  BIO 11 Aquatic Animals Osmotic Regulator: ➔ Controls internal osmolarity independent of that of the external environment Osmotic Conformer: ➔ To be iso-osmotic with its surroundings V. Osmoregulators OSMOREGULATORS Hyperosmotic Animal Hyperosmotic Freshwater animals have internal fluids with an osmolarity (internal salt level) higher than that of their aquatic surroundings ISSUE #1 (WATER OSMOSIS) ➔ Too much WATER INTAKE by OSMOSIS SOLUTION #1 ➔ Fish drinks little to no water ➔ Large amounts of urine, very dilute compared with plasma ISSUE #2 (SALT DIFFUSION) ➔ Too much SALT LOSS by DIFFUSION SOLUTION #2 ➔ Active uptake of Na+ and Cl- ➔ Bodily salts must actively transport salts back inside the organism Hyperosmotic Amphibians Hyperosmotic Freshwater amphibians gain too much water, while losing too 4  BIO 11 much salt SOLUTION: ➔ Frogs excrete excess water as urine ➔ Must compensate for salt loss by actively absorbing salt from the water using their skin Hypoosmotic Animal Hypoosmotic Saltwater animals have internal fluids with an osmolarity (internal salt level) much lower than that of seawater ISSUE #1 (WATER OSMOSIS) ➔ Too much WATER LOSS by OSMOSIS SOLUTION #1 ➔ Fish drinks water ◆ Absorbed in the small intestines through ion absorption ➔ Excretes small amounts of urine, nearly isotonic to plasma ISSUE #2 (SALT DIFFUSION) ➔ Too much SALT INTAKE by DIFFUSION SOLUTION #2 ➔ Active EXCRETION of Na+ and Cl- ➔ Salt tends to diffuse from the water into their bodies ◆ EXCESS SALT ELIMINATED through the gills or kidney VI. Salt and Water Balance in Terrestrial Animals ➔ Terrestrial animals lose water by: ◆ Evaporation from respiratory and body surfaces ◆ Excretion in urine ◆ Elimination in feces 5  BIO 11 ➔ Organisms must maintain internal salt concentration and water volume for functional cellular processes - in order to survive FORMATION OF URINE 1) Filtration ➔ Excretory tubule collects a filtrate from the blood ➔ Water and solutes are forced by blood pressure across the selectively permeable membranes of a cluster of capillaries and into the excretory tubule 2) Reabsorption ➔ Transport epithelium reclaims valuable substances from the filtrate and returns them to the body fluids 3) Secretion ➔ Other substances, such as toxins and excess ions, are extracted from the body fluids and added to the contents of the excretory tube 4) Excretion ➔ The altered filtrate (urine) leaves the system and the body VII. Excretory Organs: Invertebrates EXCRETORY ORGANS: INVERTEBRATES PROTONEPHRIDIA ➔ Branching network of dead-end tubules ➔ Closed system ➔ Ex. flatworms, rotifers, some annelids, larval mollusks, and lancelets 6  BIO 11 METANEPHRIDIA ➔ Surrounded by a network of blood vessels that assist in reclamation of water and valuable materials such as salts, sugars, and amino acids ➔ Made of tubules open at both ends ➔ Ex. annelids, mollusks, and other phyla ANTENNAL GLAND ➔ Elaboration of the nephridial organ but lack nephrostomes ➔ Protein-free filtrate is absorbed and secreted throughout the tubule portion of the gland ➔ Ex. crustaceans 7  BIO 11 MALPIGHIAN TUBULES ➔ Cells lining the Malpighian Tubules that are bathed in hemolymph (blood) ➔ Secretion of salts into the tubules ◆ Creates an osmotic pressure that draws water, solutes, and nitrogenous wastes (especially uric acid) into the tubule ➔ Ex. Insects (at the junction of the midgut and hindgut) NASAL SALT GLANDS ➔ Salt secretions in the nasal salt (VERTEBRATE) glands of a marine bird ➔ Transport epithelium moves salt from the blood into secretory tubules ◆ Drain into central ducts leading to the nostrils 8  BIO 11 VIII. Excretory Organs: Vertebrates EXCRETORY ORGANS: VERTEBRATES KIDNEYS 1) Kidneys produce urine 2) Ureters transport urine 3) Urinary bladder stores urine 4) Urethra passes urine to outside 9  BIO 11 NEPHRON Nephron: basic functional unit of the excretory organ in vertebrates 1) Glomerulus 2) Proximal Convoluted Tubule 3) Loop of the Nephron (loop of Henle) a) Descending limb b) Ascending limb 4) Ascending loop of Henle 5) Distal Convoluted Tubule 6) Collecting Duct VIII. Excretory Process - Vertebrates 10  BIO 11 EXCRETORY PROCESS - VERTEBRATES FILTRATION FILTRATE: H2O Salts (NaCl and others) HCO3- H+ Urea Glucose, amino acids Some drugs Occurs in the Glomerulus ABSORPTION OF H2O AND NaCl 11  BIO 11 ➔ At the descending limb of the ➔ At the THIN ascending limb of loop of Henle: the loop of Henle: ◆ H2O passively diffuses out ◆ NaCl passively diffuses into the interstitial fluid of out the Medulla ➔ At the THICK ascending limb of the loop of Henle: ◆ NaCl actively diffuses out GENERATION OF OSMOLARITY GRADIENT 12  BIO 11 1) FIltrate is highly concentrated due to the release of H2O 2) Filtrate becomes dilute of salt, due to the release of NaCl 3) Filtrate becomes concentrated again due to further release of H2O 4) Excretion - highly concentrated urine at collecting duct to urinary bladder NOTE: ➔ Highly concentrated filtrate can become an issue because H2O will naturally want to flow back into the surrounding interstitial space (High to low gradient diffusion) ➔ To resolve this: urea solute is removed from the filtrate and enters the interstitial space ◆ To match the high concentration of urea in the collecting duct to the interstitial space ➔ This is perpetuated by the recycling of urea back into into the ascending limb of Henle, as it enters back into the collecting duct MODULE 14: Circulation 13  BIO 11 I. Body Circulation Functions BODY CIRCULATION FUNCTIONS ➔ Transport ◆ Most organisms have extensively folded or branched internal surfaces specialized for the exchange of material within the body or with the environment ◆ The circulatory system shuttles material among all the exchange surfaces within the animal ➔ Other Functions: ◆ Defense (WBCs, Platelets) ◆ Regulation (RBCs) II. Animals Without Circulatory System ANIMALS WITHOUT CIRCULATORY SYSTEM ➔ Have simple body plans that places many or all cells in direct contact with the environment ➔ Each cell can thus exchange materials directly with the surrounding medium SINGLE CELL TWO CELL LAYERS 14  BIO 11 ➔ Single celled protist living in ➔ The gastrovascular cavity of water has a sufficient surface hydra opens to the exterior, both area of plasma membrane to outer and inner layers of cells service its entire volume are bathed in water CNIDARIANS (Aurelia) FLATWORMS ➔ Products of digestion in the ➔ “Stretched” out flat body gastrovascular cavity are directly ◆ Way to maximize available to the cells of the exposure to the inner layer surrounding medium ➔ Only a short distance to diffuse to the cells of the outer layer III. Two Types of Circulatory System TWO TYPES OF CIRCULATORY SYSTEM OPEN CLOSED 15  BIO 11 ➔ Heart pumps hemolymph into ➔ Heart pumps blood in a network tissue spaces of blood vessels and capillaries ➔ Insects, other arthropods, most ➔ Earthworms, squid, octopuses, mollusks vertebrates IV. Simplified Network Path of Vertebrate Circulatory System SIMPLIFIED NETWORK PATH OF VERTEBRATE CIRCULATORY SYSTEM (Heart Chambers) Heart Chambers Atrium ➔ Atrium ⇓ ◆ Receives blood from Ventricle blood vessels ⇓ ➔ Ventricle ⇓ ◆ Pumps blood to blood (Blood Vessels) vessels Artery ⇓ Blood Vessels Arteriole ➔ Artery ⇓ ◆ Brings blood AWAY Capillaries from the heart ⇓ ➔ Arteriole Venule ◆ Leads to capillaries ⇓ ➔ Capillaries 16  BIO 11 Vein ◆ Where gas exchange ⇓ takes place ⇓ ➔ Venule (back to) ◆ Leads to vein Atrium ➔ Vein ◆ Brings blood TO the heart V. Vertebrate Circulatory System VERTEBRATE CIRCULATORY SYSTEM *Closely intertwined with respiratory organs (i.e., lungs, gills)* 17  BIO 11 SINGLE CIRCULATION: FISH VENTRAL AORTA ➔ Two-chambered heart: ◆ Ventricle ◆ Atrium ➔ Subsidiary chambers: ◆ Conus Arteriosus (CA) Artery (Anterior) ◆ Sinus Venosus (SV) Vein (Posterior) ➔ PARTS ◆Gill Capillaries (in the anterior middle) ◆ Afferent Branchial Artery ◆ Heart Atrium Ventricle ◆ Vein ◆ Venule ◆ Body Capillaries (in the posterior middle) ➔ Oxygen POOR blood going ⬆ DORSAL AORTA ➔ PARTS ◆Gill Capillaries (in the anterior middle) ◆ Efferent Branchial Artery ◆ Artery ◆ Arteriole ◆ Body Capillaries (in the posterior middle) ➔ Oxygen RICH blood going ⬇ DOUBLE CIRCULATION: AMPHIBIAN 18  BIO 11 THREE CHAMBERED HEART Right Atrium Ventricle Left Atrium RIGHT ATRIUM SIDE ➔ PARTS ◆Pulmocutaneous Circuit Lung and Skin Capillaries ◆ Right Atrium (Heart) ◆ Vein ◆ Systemic Circuit Systemic Capillaries ➔ Oxygen POOR blood going ⬆ VENTRICLE ➔ Ventricle (center of the heart) LEFT ATRIUM SIDE ➔ PARTS ◆Pulmocutaneous Circuit Lung and Skin Capillaries ◆ Left Atrium (Heart) ◆ Artery ◆ Systemic Circuit Systemic Capillaries ➔ Oxygen RICH blood going ⬇ SPECIAL NOTES: ➔ Pulmocutaneous Artery divides into: ◆ Cutaneous Artery (Skin) ◆ Pulmonary Artery (Lung) 19  BIO 11 ➔ Ventricle is partially divided ◆ When the amphibian is submerged in water, blood flow to lungs is shut off DOUBLE CIRCULATION: MAMMALS FOUR CHAMBERED HEART Right Atrium Right Ventricle Left Atrium Left Ventricle *Found in Crocodilians, birds, mammals RIGHT ATRIUM SIDE ➔ PARTS ◆Pulmonary Circuit Lung Capillaries ◆ Right Heart Right Atrium Right Ventricle ◆ Vein ◆ Systemic Circuit Systemic Capillaries ➔ Oxygen POOR blood going ⬆ LEFT ATRIUM SIDE ➔ PARTS ◆Pulmonary circuit Lung Capillaries ◆ Left Heart Left Atrium Left Ventricle ◆ Artery ◆ Systemic Circuit Systemic Capillaries ➔ Oxygen RICH blood going ⬇ 20  BIO 11 VI. Human Heart HUMAN HEART 4 CHAMBERS OXYGEN POOR BLOOD 1) Anterior and Posterior Vena Cava (from body) 2) Right Atrium (Receive) 3) Right Ventricle (Pump) 4) Pulmonary Artery (to lungs) OXYGEN RICH BLOOD 1) Pulmonary Vein (from lungs) 2) Left Atrium (Receive) 3) Left Ventricle (Pump) 4) Aorta (to body) EQUIPPED WITH VALVES Both sides of the heart are equipped with Semilunar Valves (SV) and Atrioventricular Valves (AV) Atrioventricular Valves (AV) ➔ Tricuspid Valve ➔ Bicuspid Valve AV and SV prevents backflow and keep blood flowing in the correct direction VII. Coronary System CORONARY SYSTEM 21  BIO 11 ➔ Contraction of the right ventricle pumps blood away to the lungs via the pulmonary arteries *tentative analogy would be a couple leaving the house, going to work (gas exchange), and going back home tired ➔ Blood flows through capillary beds in the left and right lungs, it loads O2 and unloads CO2 22  BIO 11 ➔ Oxygen-RICH blood returns from the lungs via the pulmonary veins to the left atrium of the heart ➔ The oxygen-rich blood flows to the heart’s left ventricle ➔ Left ventricle pumps the oxygen-rich blood out to the body tissues through the systemic circuit 23  BIO 11 ➔ Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading throughout the body ➔ The first branches leading from the aorta are the coronary arteries (not shown) ◆ They supply blood to the heart muscle itself 24  BIO 11 ➔ Branches lead to capillary beds in the head and arms (forelimbs) ➔ The aorta then descends into the abdomen supplying oxygen-rich blood to arteries ➔ Lastly leads to the capillary beds in the abdominal organs and hind limbs ➔ Within the capillaries, there is a net diffusion of O2 from the blood to the tissues and of CO2 (produced by cellular respiration in the blood) ➔ Capillaries rejoin forming venules, which convey blood to veins 25  BIO 11 ➔ Oxygen-POOR blood from the head, neck and forelimbs is channeled into a large vein, the anterior vena cava ➔ Another large vein, the posterior vena cava, drains the blood from the trunk and hindlimbs ➔ The two venae cavae empty their blood into the right atrium, from which the oxygen-poor blood flows into the right ventricle SPECIAL NOTES: ➔ Both Arteries and Veins carry oxygenated blood and de-oxygenated blood ➔ Arteries carry blood AWAY from the heart ➔ Veins carry blood INTO or BACK INTO the heart 26  BIO 11 FLOW OF BLOOD precava and postcava ⇒ right atrium ⇒ tricuspid valve ⇒ right ventricle ⇒ pulmonary artery ⇒ lungs / capillaries (loads O2, unloads CO2) ⇒ pulmonary vein ⇒ left atrium ⇒ bicuspid valve ⇒ left ventricle ⇒ aorta ⇒ rest of body (1. Heart 2. Head and Arms 3. Abs and Legs) VIII. The Cardiac Cycle THE CARDIAC CYCLE ➔ Systole (Contraction) ❖ Atrial Systole ❖ Ventricular Systole ➔ Diastole (Relaxation) ❖ Atrial Diastole ❖ Ventricular Diastole 1) Atrial Diastole and Ventricular Diastole During a relaxation phase, blood returning from the large veins flows into the atria and then into the ventricles through the AV Valves 2) Atrial Systole and Ventricular Diastole A brief period of atrial contraction then forces all blood remaining in the atria into the ventricles 3) Ventricular Systole and Atrial Diastole During the remainder of the cycle, ventricular contraction pumps blood into the large arteries through the Semilunar Valves Cardiac Output (5.25 L/min) ➔ Heart Rate ◆ Rate of contraction or beats per second 27  BIO 11 ➔ Stroke Volume (75mL) ◆ Amount of blood pumped by the left ventricle in each contraction IX. Properties of Blood Flow and Blood Pressure PROPERTIES OF BLOOD FLOW AND BLOOD PRESSURE ➔ Ventricular Systole ◆ Arterial blood pressure is highest when the heart contracts during this ➔ Diastolic Pressure ◆ Lower but still substantial blood pressure when ventricles are relaxed ➔ Capillary (Arterial End) ◆ Blood pressure is higher than osmotic pressure, so fluid tends to diffuse out of the capillary ◆ Opposite happens at the Venous End X. Blood Vessel Structure BLOOD VESSEL STRUCTURE 28  BIO 11 ARTERIES CAPILLARIES VEINS ➔ Thicker to contain ➔ Thin ➔ Have valves high blood ➔ Endothelial cells pressure from surrounded by heart basal lamina ➔ No smooth muscle layer XI. Blood Composition BLOOD COMPOSITION PLASMA (55%) CONSTITUENT MAJOR FUNCTIONS Water ➔ Solvent Ions (blood electrolytes) ➔ Osmotic balance, pH buffering, 29  BIO 11 ❖ Sodium and regulation of membrane ❖ Potassium permeability ❖ Calcium ❖ Magnesium ❖ Chloride ❖ Bicarbonate Plasma Proteins Respectively: ★ Albumin ➔ Osmotic balance, pH buffering ★ Immunoglobulins (antibodies) ➔ Defense ★ Apolipoproteins ➔ Lipid Transport ★ Fibrinogen ➔ Clotting Substances transported by blood ➔ Nutrients (such as glucose, fatty acids, vitamins) ➔ Waste products of metabolism ➔ Respiratory gasses (O2 and CO2) ➔ Hormones CELLULAR ELEMENTS (45%) CELL TYPE NUMBER FUNCTIONS per μL (mm^3) of blood Erythrocytes (RBCs) 5M - 6M Transport of O2 and CO2 Platelets 250,000 - 400,000 Blood Clotting Leukocytes (WBCs) 5,000 - 10,000 Defense and Immunity ❖ Lymphocytes ❖ Monocytes ❖ Neutrophils ❖ Basophils ❖ Eosinophils XII. Blood Clotting BLOOD CLOTTING 30  BIO 11 1) Platelets 2) Damaged Cells 3) Plasma …all produce CLOTTING FACTORS There are 13 clotting factors that facilitate clotting / coagulation The first two are: ❖ Fibrinogen ❖ Prothrombin …both lead to the creation of FIBRIN (Fibrin clots) 31  BIO 11 MODULE 15: Immune System I. Immune System IMMUNE SYSTEM NON-SPECIFIC INNATE DEFENSE SPECIFIC ADAPTIVE (Broad Recognition) DEFENSE General Protection (Recognition of Specific Pathogens) Specialized Protection First Line of Defense Second Line of Third Line of Defense (Kuya Guard) Defense (SWAT) (Police) ➔ Skin ➔ Phagocytic WBCs ➔ Lymphocytes ➔ Mucous ➔ Antimicrobial ➔ Antibodies membranes proteins ➔ Secretions of skin ➔ Inflammatory and mucous response membranes ➔ Humoral Response: ◆ Antibodies Defend against infection of body fluids ➔ Cell-mediated Response ◆ Cytotoxic cells defend against infection in body cells ➔ Innate Immunity (First and Second Line of Defense) is the primary defense in all animals ◆ Sets the stage for Adaptive Immunity (Third Line of Defense) 32  BIO 11 II. First Line of Defense (Non-specific Innate Defense: Broad Recognition) FIRST LINE OF DEFENSE (NON-SPECIFIC INNATE DEFENSE: Broad Recognition) ➔ In humans, secretions from sebaceous and sweat glands give the skin a pH ranging from 3 to 5, which is acidic enough to prevent colonization by many microbes ➔ Microbial colonization is also inhibited by the washing action of saliva, tears, and mucous secretions ◆ Contain antimicrobial proteins Lysozyme - digests the cell walls of many bacteria III. Second Line of Defense (Non-specific Innate Defense: Broad Recognition) SECOND LINE OF DEFENSE (NON-SPECIFIC INNATE DEFENSE: Broad Recognition) ➔ Damage to tissue caused by physical injury or entry of microorganisms triggers a localized inflammatory response 33  BIO 11 1) At the injury site, 2) Capillaries widen 3) Neutrophils digest mast cells release and become more pathogens and cell histamines, which permeable, allowing debris at the site of cause nearby neutrophils and fluid the injury, and the capillaries to dilate. containing tissue heals Macrophages release antimicrobial other signaling peptides to enter molecules that the tissue attract neutrophils WHITE BLOOD CELLS (Leukocytes) MONONUCLEAR PHAGOCYTE ➔ Monocyte ⇒ Macrophage + SYSTEM Dendritic Cell ➔ Monocyte (5% of all WBCs) ◆ Provide an even more effective phagocytic defense ➔ Macrophage ◆ Develop from monocytes ◆ Major component of the vertebrate lymphatic system ◆ Antigen Presenting Cell: Presents major histocompatibility complex (MHC II) with Helper T-cells Secretes cytokines 34  BIO 11 GRANULOCYTES ➔ Neutrophil (60%-70% of all WBCs) ◆ Microbes that penetrate the first line of defense face the second line of defense, which depends mainly on phagocytosis ➔ Eosinophil (1.5% of all WBCs) ◆ For defense against large parasitic invaders, such as the blood fluke ◆ Position themselves against the external wall of a parasite and discharge destructive enzymes from cytoplasmic granules 35  BIO 11 ➔ Basophils ◆ Release histamine and mast cells in connective tissue Histamines: promote acute inflammation LYMPHOCYTE-LIKE CELLS ➔ Do not attack microorganisms (Natural Killer (NK) Cells) directly, but destroy virus-infected body cells or cells that are becoming cancerous ◆ Also attack body cells that could become cancerous ◆ Mount an attack on the cell’s membrane, causing the cell to lyse 36 BIO 11 37  BIO 11 CHEMOKINES: - (CHEMOTACTIC CYTOKINES) secreted by blood vessel endothelial cells and monocytes, attract phagocytes to the area - Chemokines is a group of about 50 different proteins - Chemokines binds to RECEPTORS on many types of leukocytes - Chemokines induce the production of toxic forms of ocygen in phagocyte lysosomes and the release of histamine from basophils - Fever, another systemic response to infection, can be triggered by toxins from pathogens or by PYROGENS released by certain leukocytes - resets the body’s thermostat to a higher temperature - higher temperature contributes to defense by inhibiting growth of some microbes, facilitating phagocytosis and speeding up repair of tissues - other antimicrobial agents include about 20 serum proteins, known collectively as the complement system. - carry out a cascade of steps that lead to lysis of microbes - some complement components work with chemokines to attract phagocytic cells to sites of infection INTERFERONS 38  BIO 11 - PROTEINS secreted by VIRUS-INFECTED CELLS - Diffuse to neighboring cells and induce them to produce other chemicals that inhibit viral reproduction - limits cell-to-cell spread of viruses WBC SIGNALING ➔ Cytokines ◆ Signaling molecules used to stimulate and activate WBCs ➔ Helper T Cells ◆ Activates B Cells and T Cells through cytokines IV. Third Line of Defense (Specific Adaptive Defense: Recognition of Specific Pathogens) THIRD LINE OF DEFENSE - Lymphocytes (SPECIFIC ADAPTIVE DEFENSE: RECOGNITION OF SPECIFIC PATHOGENS) 39  BIO 11 HELPER T CELL ➔ Secretes cytokines with macrophages, through APC with MHC II ➔ Activates B and T Cells ➔ Memory Helper T Cell ◆ For long term immunity B CELL ➔ Phagocytize pathogens ➔ Antigen-presenting cells ➔ Interacts with cells tagged with Class II MHC ➔ Two types: ◆ Memory B Cell For long-term immunity ◆ Plasma Cell Secretes antibodies to neutralize pathogens CYTOTOXIC T CELL ➔ Use toxic proteins to destroy infected cells ➔ Two types: 40  BIO 11 ◆ Memory Cytotoxic T Cell For long-term immunity ◆ Active Cytotoxic T Cell Destroy infected cells tagged Class I MHC LYMPHOCYTES (key cells of the immune system) B CELLS T CELLS ➔ Originate from stem cells in the ➔ Originate from stem cells in the red bone marrow red bone marrow ➔ B Cells are fully formed in the ➔ T Cells are fully formed in the Bone marrow Thymus ➔ Circulate to lymphatic tissues ➔ Circulate to lymphatic tissues such as lymph nodes such as lymph nodes LYMPHOCYTIC RECOGNITION 41  BIO 11 ★ Lymphocytes can recognize Antigens – from a pathogen or foreign molecule that elicits a specific response by lymphocytes ★ Antigen binding receptors and antibodies can be used interchangeably ANTIGEN RECEPTOR ➔ Specific antigen receptors bounded on the plasma membrane of WBCs ANTIBODIES ➔ Free-floating soluble antibodies that are either attached to lymphocytes or are secreted ➔ An antibody binds with a small, accessible portion of the antigen called an epitope or antigenic determinant ANTIGEN RECEPTORS 42  BIO 11 ➔ Antigen receptors on a B Cell and T Cells are transmembrane versions of antibodies and are often referred to as membrane antibodies (or membrane immunoglobins) ➔ Diversity in the number of antibodies due to variable regions ANTIGEN RECEPTOR (OR ANTIBODY) DIVERSITY 43  BIO 11 ➔ There is an enormous variety of B Cells and T Cells in the body, each bearing antigen receptors of specificity ➔ This allows the immune system to respond to millions of antigens, and this millions of potential pathogens ◆ 1 million different B Cell antigen receptors ◆ 10 million different T Cell antigen receptors ➔ Alternative splicing (during the process of modifying RNA) and different arrangement of various gene sequences (variable regions) translates to million variations of antigen receptors V. Clonal Selection - Antigen Receptor (Antibody) Diversity CLONAL SELECTION - ANTIGEN RECEPTOR (ANTIBODY) DIVERSITY ★ The diversity of B Cells and T Cells million antibodies, ○ Allows for lymphocytes bearing specific receptors To account for a wide array of specific antigen molecules ★ Clonal Selection of B Cells by one of the microbe’s antigens activates the lymphocyte ○ Stimulated to divide and differentiate ○ Produce two clones of cells: 1) Memory B Cell 2) Plasma Cell 44  BIO 11 STEP 1 ➔ Antigens bind to the antigen receptors of only one of the three B Cells shown ➔ Further activation by Helper T Cells is needed STEP 2 ➔ The selected B cells proliferates, forming a clone of identical cells bearing receptors of the antigen STEP 3 ➔ Some daughter cells develop into long-lived memory memory cells that can respond rapidly upon subsequent exposure to the same antigen STEP 4 ➔ Other daughter cells develop into short-lived plasma cells that secrete antibodies specific for the antigen EXAMPLES OF B CELL ANTIBODY FUNCTIONS (to defend against pathogens) (1)AND/OR OPSONIZATION: another word for enhancing phagocytosis 45  BIO 11 BINDING OF ANTIBODIES TO ANTIGENS Inactivates antigens by… ENHANCES PHAGOCYTOSIS LEADS TO CELL (Macrophage) LYSIS Neutralization Agglutination of Precipitation of Activation of Microbes Dissolved Complement Antigens System ➔ Neutralizes ➔ Clumps ➔ Formation of ➔ Triggered-en the antigen particles insoluble zyme by blocking together precipitate cascade viral binding sites; coating bacteria VI. Major Histocompatibility Complex (MHC) - Class II for T-Cell Recognition HELPER T CELLS ➔ Helper T Cells (TH) have receptors that bind to peptides displayed by the body’s Class II MHC molecules ➔ CD4 accessory proteins binds Helper T Cells to pathogen-infected cells ➔ Helper T Cells send out chemical signals that call on the Cytotoxic T-Cell to fight the pathogen 46  BIO 11 VII. Helper T-Cell Signal Pathway and Cell Activation HELPER T-CELL SIGNAL PATHWAY ➔ An antigen-presenting cell engulfs a pathogen, degrades it, and displays antigen fragments complexes with Class II MHC molecules on the cell surface ➔ A specific Helper T Cell binds to this complex via its antigen receptor and an accessory protein called CD4 HELPER T CELL: Class II MHC + CD4 ➔ Binding of the Helper T Cell promotes the secretion of cytokines by the antigen-presenting cell ➔ These cytokines, along with cytokines from the Helper T Cell itself, activate the Helper T Cell and stimulate its proliferation 47  BIO 11 ➔ Cell proliferation produces a clone of activated Helper T Cells ◆ All cells in the clone have receptors for the same antigen fragment complex with the same antigen specificity ➔ These cells secrete other cytokines, which help activate B Cells and Cytotoxic T Cells B CELL ACTIVATION ➔ After an antigen-presenting cell engulfs and degrades a pathogen, it displays an antigen fragment complexed with a Class II MHC molecule ➔ A Helper T Cell that recognizes the complex is activated with the aid of cytokines secreted from the antigen-presenting cell 48  BIO 11 ➔ When a B Cell with receptors for the same epitope internalizes the antigen, it displays an antigen fragment on the cell surface in a complex with a Class II MHC Molecule ➔ An activated Helper T Cell bearing receptors specific for the displayed fragment binds to and activates the B Cell ➔ The activated B Cell proliferates and differentiates into Memory B Cells and antibody-secreting plasma cells ◆ The secreted antibodies are specific for the same antigen that initiated the response CYTOTOXIC T CELL ACTIVATION 49  BIO 11 ➔ An activated Cytotoxic T Cell binds to a Class I MHC–antigen fragment complex on an infected cell via its antigen receptor and an accessory protein called CD8 CYTOTOXIC T CELL: Class I MHC + CD8 ➔ The Cytotoxic T Cell releases perforin molecules, which form pores in the infected cell membrane, and granzymes, enzymes that breakdown proteins ◆ Granzymes enter the infected cell by endocytosis 50  BIO 11 ➔ The granzymes initiate apoptosis within the infected cell, leading to fragmentation of the nucleus and cytoplasm and eventual cell death ➔ The released Cytotoxic T Cell can attack other infected cells VIII. Major Histocompatibility Complex (MHC) - Class I for T-Cell Recognition HELPER T CELLS 51  BIO 11 ➔ Cytotoxic T Cells (TC) have antigen receptors that bind to protein fragments displayed by the body’s Class I MHC molecules ➔ CD8 accessory proteins bind to Cytotoxic T Cells to Class I MHC ➔ Cytotoxic T Cells respond by killing the infected cells MODULE 16: Regulatory Mechanisms Module 16.1: Intercellular Communication I. Intercellular Communication INTERCELLULAR COMMUNICATION ➔ Cells in an animal body communicate with each other through specific molecules, which elicit specific responses from the cells ➔ Different molecules serve as signals ➔ The type of signaling molecules depends on where they are transported and what their target cells are to elicit a response 52  BIO 11 TYPES OF INTERCELLULAR COMMUNICATION ENDOCRINE ➔ Secreted molecules diffuse into the bloodstream and trigger responses in target cells anywhere in the body PARACRINE ➔ Secreted molecules diffuse locally and trigger a response in neighboring cells AUTOCRINE ➔ Secreted molecules diffuse locally and trigger a response in the cells that secrete them SYNAPTIC ➔ Neurotransmitters diffuses across synapses and trigger responses in cells of target tissues NEUROENDOCRINE ➔ Neurohormones diffuse into the bloodstream and trigger responses anywhere in the body II. Signaling Molecules 53  BIO 11 SIGNALING MOLECULES LOCAL REGULATORS ➔ Growth Factors: ◆ Proteins and polypeptides that stimulate cell proliferation ➔ Cytokines: for immune response ➔ Nitric Oxide (NO) ◆ Acts as a neurotransmitter when secreted by neurons ◆ Kills bacteria and cancer cells when secrete by WBCs ◆ Dilates the walls of blood vessels when secreted by endothelial cells ➔ Prostaglandins (PGs) ◆ Modified fatty acids ◆ Stimulate uterine contractions during childbirth when secreted by the placenta ◆ Promote fever and inflammation and intensify the sensation of pain NEUROTRANSMITTERS ➔ Secreted by neurons at many synapses ➔ Diffuse a very short distance ➔ Bind receptors on target cells NEUROHORMONES ➔ Secreted by neurosecretory cells ➔ Diffuse from nerve cell endings into the bloodstream ➔ ADH (vasopressin) - also called antidiuretic hormone PHEROMONES ➔ Released into the external environment ➔ Functions: ◆ Mark trails leading to food ◆ Defining territories ◆ Warning of predators ◆ Attracting potential mates HORMONES ➔ Chemicals that transfer information and instructions between cells in animals and plants ➔ Different responses include: ◆ Body’s chemical messengers ◆ Regulate growth and development ◆ Control the function of various tissues ◆ Support reproductive functions ◆ Regulate metabolism 54  BIO 11 HORMONES ➔ Hormones can be ◆ Water-soluble (easily dissolved in water) ◆ Lipid-soluble (easily dissolved in fats) ➔ Water-soluble Hormones ◆ Bind to receptors on the cell’s surface ◆ They CANNOT penetrate the lipid bilayer ➔ Polypeptide: Insulin ➔ Amine: Epinephrine ➔ PROTEINS 55  BIO 11 ➔ Lipid-Soluble Hormones ◆ CAN pass through the cell’s lipid bilayer ◆ Binds directly to receptors in the nucleus or cytoplasm ◆ Need the assistance of a transport protein to travel the bloodstream ➔ Steroid: Cortisol ➔ Amine: Thyroxine DIFFERENT ELICITED EFFECTS OF ONE HORMONE 56  BIO 11 LIVER CELL SMOOTH MUSCLE SMOOTH MUSCLE CELL CELL (Wall of Blood Vessel in the (Wall of Blood Vessel in the Skeletal Muscle) Intestines) ★ Epinephrine to B ★ Epinephrine to B ★ Epinephrine to A Receptor Receptor Receptor ❖ Glycogen breaks ❖ Cell relaxes ❖ Cell contracts down and glucose ➔ Blood vessel ➔ Blood vessel is released from dilates, increasing constricts, the cell flow to skeletal decreasing flow to ➔ Blood glucose muscle intestines level increases DIFFERENT RECEPTORS SAME RECEPTORS (Different intracellular proteins) 57  BIO 11 Module 16.2: Endocrine System (Hypothalamus and Pituitary Gland Pathway) I. Endocrine System ENDOCRINE SYSTEM ➔ The Endocrine System is an integrative system (just like the nervous system) that controls an animal’s activities via hormones ➔ Hormones are released into the blood in small amounts and transported by the circulatory system throughout the body to distant target cells where they initiate physiological responses II. Major Endocrine Glands MAJOR ENDOCRINE GLANDS HYPOTHALAMUS ➔ Hypothalamus: ◆ Integrates endocrine and nervous function ➔ Posterior Pituitary Gland: ◆ Hormones by the 58  BIO 11 hypothalamus are stored on this side, ready to be released directly into the bloodstream ➔ Anterior Pituitary Gland ◆ Production of releasing and inhibiting hormones by the hypothalamus ◆ Regulating Endocrine Cells are present here POSTERIOR PITUITARY GLAND ➔ Neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones: ◆ Antidiuretic Hormone (ADH) Kidney Tubules ◆ Oxytocin Mammary glands, uterine muscles ➔ Posterior Pituitary Side; extension of hypothalamus axons ➔ After traveling to the posterior pituitary side (still within the long axons of the neurosecretory cells), these neurohormones are stored ◆ To be released in response to nerve impulses transmitted by the hypothalamus The Hypothalamus regulates anterior pituitary hormones. ❖ Hormones produced by the Hypothalamus’ neurosecretory cells: a) Releasing Hormones ➔ Stimulate the anterior pituitary (adenohypophysis) to secrete hormones b) Inhibiting Hormones ➔ Prevent the anterior pituitary from secreting hormones ANTERIOR PITUITARY GLAND ➔ Each hypothalamic hormone that regulates release of one or 59  BIO 11 more hormones by the anterior pituitary is called either a: ◆ Releasing Hormone ◆ Inhibiting Hormone ➔ Hypothalamus ◆ 1st set of Releasing / Inhibiting Hormones ➔ Endocrine Cells ◆ 2nd Set of Hormones ➔ Tropic Targets ◆ 3rd set of Hormones ENDOCRINE HORMONES TO TROPIC TARGETS FSH and LH TSH ACTH PROLACTIN MSH GH Testes or Thyroid Adrenal Mammary Melanocyte Liver, bones, Ovaries Cortex Glands s and other tissues Estrogen or Thyroid Glucocortic Testostero Hormone oids ne Tropic Effects Only Nontropic Effects Only Tropic and ➔ Act on another endocrine gland ➔ Directly simulate Nontropic that stimulates the release of target cells to Effects another set of hormones induce effects MAJOR VERTEBRATE ENDOCRINE GLANDS AND SOME OF THEIR HORMONES GLAND HORMONE CHEMICAL FUNCTIONS REGULATED CLASS BY Hypothalamu Hormones released by the posterior pituitary and hormones s that regulate the anterior pituitary (see below) Posterior PG Antidiuretic Peptide Promotes Water / Salt Hormone retention of Balance water by kidneys (ADH) 60  BIO 11 Oxytocin Peptide Stimulates Nervous contraction of System uterus and mammary gland cells Anterior PG Adrenocortic Peptide Stimulates Glucocorticoi otropic adrenal cortex to ds; secrete Hormone glucocorticoids hypothalamic (ACTH) hormones Follicle-stimul Glycoprotein Stimulates Hypothalamic ating production of Hormones ova and sperm Hormone (FSH) Luteinizing Glycoprotein Stimulates Hypothalamic Hormone (LH) ovaries and Hormones testes Thyroid-stimu Glycoprotein Stimulates Thyroxine in lating thyroid gland blood; Hormone hypothalamic (TSH) hormones Prolactin Protein Stimulates Milk Hypothalamic (PRL) Production and Hormones secretion Growth Protein Stimulates Hypothalamic Hormone (GH) growth Hormones (especially bones) and metabolic function ➔ Hormones by the hypothalamus are stored on at the posterior side, ready to be released directly into the bloodstream ➔ Production of releasing / inhibiting hormones by the hypothalamus regulates anterior pituitary hormones III. Regulated Release of Hormones 61  BIO 11 REGULATED RELEASE OF HORMONES 1) Thyroid Hormone levels drop below the normal range. Sensory neurons respond by sending nerve impulses to neurosecretory cells in the hypothalamus. 2) Neurosecretory cells secrete Hormone (TRH ⏺ Thryro-tropin Releasing ) into the blood, which carries it to the anterior pituitary. 3) TRH cause the anterior pituitary to secrete Thyroid-Stimulating Hormone (TSH ⟁, aka thyrotropin) into the circulatory system. 62  BIO 11 4) TSH stimulates endocrine cells in the thyroid gland to secrete Thyroid Hormone (T3 and T4 into the circulatory system. ⏹ ) 5) Thyroid hormone levels increase in the blood and body tissues. Thyroid hormone acts on target cells throughout the body to control bioenergetics; help maintain normal blood pressure, heart rate, and muscle tone; and regulate digestive and reproductive functions 6) As levels return to the normal range, thyroid hormone blocks TRH release from the hypothalamus and TSH release from the anterior pituitary, forming a negative-feedback loop that prevents overproduction of thyroid hormone HORMONE CASCADE STIMULUS ⬇ Hypothalamus ⬇ TRH (1st Set) ⬇ Anterior Pituitary ⬇ TSH (2nd Set) ⬇ Thyroid Gland ⬇ Thyroid Hormone (3rd Set) ⬇ RESPONSE ⬇ RESTART (negative-feedback loop) 63  BIO 11 IV. Syndromes Related to Hormones SYNDROMES RELATED TO HORMONES PITUITARY GIGANTISM ➔ Results when GH is hyper-secreted in excess during childhood (before puberty) ACROMEGALY ➔ Results when the pituitary gland produces excess GH throughout adulthood (after epiphyseal plate closure at puberty - which typically marks the end of bone growth) ➔ Affects the face and extremities HYPOPITUITARY DWARFISM ➔ Decreased bodily growth due to decreased levels of GH ➔ End result is a proportionate little person, because the height and growth of all other structures of the individual are decreased Module 16.2: Nervous System Coordination I. Types of Neurons TYPES OF NEURONS 64  BIO 11 Sensory (Afferent) Interneuron (Mingling) Motor (Efferent) ➔ Arriving toward ➔ Local ➔ Signals exiting the brain / CNS connections from the bran / between CNS to muscles neighboring neurons NEURONS (Functional Units of the Nervous System) ➔ Synaptic connections transmits information from one neuron to another 65  BIO 11 TYPES NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM PERIPHERAL NERVOUS SYSTEM ➔ Brain ➔ Cranial and Spinal Nerves ➔ Spinal Cord ➔ Sense Organs II. Nature of Nerve Signals NATURE OF NERVE SIGNALS ➔ Every cell has a voltage or membrane potential across its plasma membranes ◆ A membrane potential is a localized electrical gradient across a membrane ➔ Depending on the cell and the permeability of ions on the cell membrane: ◆ Cations and Anions can be more concentrated within a cell or more concentrated in the extracellular fluid MEASURING MEMBRANE POTENTIALS CATIONS ANIONS ➔ K+ is the principal intracellular ➔ Principal intracellular anions cation ◆ Proteins ◆ Higher gradient inside the ◆ Amino Acids cell ◆ Sulfate ➔ Na+ is the principal extracellular ◆ Phosphate cation ➔ Cl- is the principal extracellular ◆ Higher gradient outside anion the cell 66  BIO 11 ➔ An unstimulated cell usually has a resting potential of -70mV ◆ Range from -60 to -80 mV HOW A CELL MAINTAINS A MEMBRANE POTENTIAL 67  BIO 11 UNGATED ION CHANNELS GATED ION CHANNELS ➔ Allow ions to diffuse across the ➔ Excitable Cells (e.g. neurons and plasma membrane (they are receptors) always open) ◆ Can generate large ➔ However, this diffusion does not changes in their achieve an equilibrium membrane potential ◆ Active Na-K pump ➔ Gated Ion Channels transports these ions ◆ Open or close in response against their to stimuli concentration gradient ◆ Subsequent diffusion of ions leads to a change in the membrane potential Changes in membrane potential of a neuron give rise to nerve impulses III. Types of Gated Ions Channels TYPES OF GATED IONS CHANNELS LIGAND-GATED CHANNELS ➔ Chemically-gated ion channels (requires a ligand) open or close in response to a chemical stimulus at postsynaptic cell 68  BIO 11 VOLTAGE-GATED CHANNELS ➔ Voltage-gated ion channels along axons open or close in response to a change in membrane potential IV. Graded Potentials GRADED POTENTIALS (Changes in Membrane Potential) HYPERPOLARIZATION 1) Ligand-gated K+ channels open 2) K+ diffuses out of the cell 3) The membrane potential becomes more negative 69  BIO 11 DEPOLARIZATION 1) Ligand-gated Na+ channels open 2) Na+ diffuses into the cell 3) The membrane potential becomes more positive V. Action Potential 70  BIO 11 THE ACTION POTENTIAL (All or Nothing Depolarization) ➔ If graded potentials sum to ≈-55mV, a threshold potential is achieved ➔ Voltage-gated channels open in response to the threshold being reached, and triggers an action potential on axons only VOLTAGE-GATED CHANNELS 71  BIO 11 ➔ Voltage-gated K+ Channels ◆ CLOSED at resting state but opens slowly in response to depolarization at the peak of action potential ➔ Voltage-gated Na+ Channels (two gates) ◆ Activation Gate: CLOSED at resting state but open rapidly in response to depolarization ◆ Inactivation Loop: OPEN at resting state but close slowly in response to depolarization THE ACTION POTENTIAL (All or Nothing Depolarization) 72  BIO 11 1) Resting State ➔ The gated Na+ and K+ channels are CLOSED ➔ Ungated channels maintain the resting potential 73  BIO 11 2) Depolarization ➔ A stimulus OPENS some sodium channels ➔ Na+ inflow through those channels depolarizes the membrane ➔ If the depolarization reaches the threshold, it triggers an action potential 3) Rising Phase of the Action Potential ➔ Depolarization OPENS most sodium channels, while the potassium channels remains CLOSED ➔ Na+ influx makes the inside of the membrane positive with respect to the outside 4) Falling Phase of the Action Potential ➔ Most sodium channels become inactivated, blocking Na+ inflow ➔ Most potassium channels OPEN, permitting K+ outflow ➔ This makes the inside of the cell negative again 74  BIO 11 5) Undershoot ➔ The sodium channels CLOSE, but some potassium channels are still OPEN ➔ As K+ channels CLOSE and Na+ channels become unblocked (though still CLOSED), the membrane returns to its resting state CONDUCTION OF ACTION POTENTIAL THROUGHOUT THE AXON ➔ Nerve impulses propagate themselves along an axon in one direction ◆ Due to closing of Na+ channels by the inactivation loop that stays closed for a while ➔ The action potential is repeatedly regenerated along the length of the axon ◆ Action potential makes insides of the membrane positive, though is fleeting (turns back to negative) ◆ Outsides are left positive in its wake by K+ 75  BIO 11 This graph illustrates the changes in the membrane potential of a neuron during an action potential, which is how neurons communicate signals. Here's a simple breakdown of the numbered phases: 1. Resting potential: The neuron is at rest, with a stable membrane potential of about -70 mV. It is not actively sending a signal. 2. Threshold: When a stimulus is strong enough, it causes the membrane potential to reach a critical level (around -50 mV), known as the threshold. This triggers the action potential. 3. Depolarization: Sodium (Na⁺) channels open, allowing Na⁺ ions to rush into the neuron. This causes the membrane potential to rapidly increase (become less negative), moving towards +50 mV. 4. Repolarization: After the peak, potassium (K⁺) channels open, allowing K⁺ ions to leave the neuron. This causes the membrane potential to drop back down (become more negative). 76  BIO 11 5. Hyperpolarization: The membrane potential briefly dips below the resting level due to the continued movement of K⁺ ions out of the cell. This ensures the neuron is ready for the next signal. Finally, the neuron returns to its resting potential (1), ready for another action potential if triggered. This process happens very quickly, enabling neurons to transmit signals rapidly! 77 BIO 11 78  BIO 11 This diagram shows how an action potential travels along the axon of a neuron to transmit a signal. What’s happening in each step? 1. First Action Potential: ○ Sodium ions (Na⁺) rush into the axon, causing the inside of the axon to become more positive (depolarization). ○ This change in charge triggers the next section of the axon to prepare for an action potential. 2. Second Action Potential: ○ In the next axon segment, more sodium channels open, and Na⁺ rushes in, causing another depolarization. ○ Meanwhile, the first segment repolarizes (potassium ions, K⁺, leave the cell) to return to resting state. 3. Third Action Potential: ○ The wave of depolarization continues down the axon as each segment undergoes an action potential. ○ Potassium exits the earlier segments to fully reset the charge. Key Points: Signal propagation is like a domino effect: one action potential triggers the next. This process ensures that the signal moves in one direction (from the cell body to the axon terminal). The movement of Na⁺ and K⁺ ions across the axon membrane is crucial for the signal to be sent. This is how neurons communicate information over long distances! 79  BIO 11 COMPARING MYELINATED AXONS UNMYELINATED AXON A MYELINATED AXON B ➔ Slower action potential ➔ Faster action potential transmission transmission This diagram compares how action potentials travel along two types of axons: unmyelinated (A) and myelinated (B). Here's a simple explanation: (A) Unmyelinated Axon: The action potential moves continuously down the axon, step by step. Each small segment of the axon membrane depolarizes and then repolarizes. This process is slower because the signal doesn't "skip" any parts of the axon. (B) Myelinated Axon: 80  BIO 11 The axon is covered by a fatty insulation called myelin, with gaps called nodes of Ranvier. The action potential "jumps" from one node to the next in a process called saltatory conduction. This makes signal transmission much faster because the electrical impulse doesn't need to activate every part of the axon. Why is myelination important? Speed: Myelin dramatically increases the speed of signal transmission, enabling rapid communication between neurons. Energy efficiency: Fewer ions move across the membrane in myelinated axons, so the neuron uses less energy to reset after an action potential. In summary, myelination helps the nervous system transmit signals faster and more efficiently! VI. Synapses SYNAPSES ELECTRICAL SYNAPSES ➔ Action potential travels directly from the presynaptic to the postsynaptic cells via gap junctions CHEMICAL SYNAPSES ➔ More common than electrical synapses ➔ Postsynaptic chemically-gated channels 81  BIO 11 exist for ions such as: ◆ K+ ◆ Na+ ◆ Cl- ➔ Depending on which gates open the postsynaptic neuron can depolarize or hyperpolarize VII. DIversity in Neurotransmitters DIVERSITY IN NEUROTRANSMITTERS ACETYLCHOLINE ➔ Excitatory to skeletal muscles ➔ Inhibitory to cardiac muscles ➔ Secreted by the CNS, PNS, and at vertebrate neuromuscular