![]() When an action potential reaches the axon terminal of the presynaptic cell, it opens channels that allow calcium to enter the terminal. As shown in Figure 8.4.3, the presynaptic area contains many tiny spherical vessels called synaptic vesicles that are packed with chemicals called neurotransmitters. ![]() Chemical SynapsesĪt a chemical synapse, both the presynaptic and postsynaptic areas of the cells are full of molecular machinery that is involved in the transmission of nerve impulses. Transmission of nerve impulses across chemical synapses is more complex. Most synapses, however, are chemical synapses. Some synapses are purely electrical and make direct electrical connections between neurons. The cell that sends the nerve impulse is called the presynaptic cell, and the cell that receives the nerve impulse is called the postsynaptic cell. This is where the transmission of a nerve impulse to another cell occurs. The place where an axon terminal meets another cell is called a synapse. These differences in concentration create an electrical gradient across the cell membrane, called resting potential. Tightly controlling membrane resting potential is critical for the transmission of nerve impulses. Sodium is the principal ion in the fluid outside of cells, and potassium is the principal ion in the fluid inside of cells. The video below, “Sodium Potassium Pump” by Amoeba Sisters, describes in greater detail how the sodium-potassium pump works. The sodium-potassium pump moves both ions from areas of lower to higher concentration, using energy in ATP and carrier proteins in the cell membrane. ![]() The sodium-potassium pump is a mechanism of active transport that moves sodium ions (Na+) out of cells and potassium ions (K+) into cells. ![]() During the resting state, the sodium-potassium pump maintains a difference in charge across the cell membrane of the neuron. When a neuron is not actively transmitting a nerve impulse, it is in a resting state, ready to transmit a nerve impulse. How does this difference in electrical charge come about? The answer involves ions, which are electrically-charged atoms or molecules. A nerve impulse occurs because of a difference in electrical charge across the plasma membrane of a neuron. Chapter 1 - Nature and Processes of Scienceġ.1 Case Study: Why Should You Learn About Science?ġ.7 Pseudoscience and Other Misuses of Scienceġ.8 Case Study Conclusion: To Give a Shot or NotĢ.1 Case Study: Why Should You Study Human Biology?Ģ.6 Case Study Conclusion: Our Invisible InhabitantsĤ.14 Case Study Conclusion: More Than Just Tiredĥ.10 Mendel's Experiments and Laws of Inheritanceĥ.12 Sexual Reproduction, Meiosis, and Gametogenesisĥ.18 Case Study Conclusion: Cancer in the FamilyĦ.1 Case Study: Our Similarities and DifferencesĦ.4 Human Responses to Environmental StressĦ.9 Case Study Conclusion: Your Genes May Help You Save a Lifeħ.9 Case Study Conclusion: Under PressureĨ.1 Case Study: The Control Centre of Your Bodyġ0.1 Case Study: Skin, Hair, and Nails - Decorative but Functionalġ0.2 Introduction to the Integumentary Systemġ0.8 Case Study Conclusion: Wearing His Heart on His Sleeveġ1.8 Case Study Conclusion: A Pain in the Footġ2.7 Case Study Conclusion: Needing to Relaxġ3.1 Case Study: Respiratory System and Gas Exchangeġ3.2 Structure and Function of the Respiratory Systemġ3.7 Case Study Conclusion: Cough That Won't Quitġ4.1 Case Study: Your Body's Transportation Systemġ4.2 Introduction to the Cardiovascular Systemġ5.2 Introduction to the Digestive Systemġ5.7 Disorders of the Gastrointestinal Tractġ5.8 Case Study Conclusion: Please Don’t Pass the Breadġ6.5 Ureters, Urinary Bladder, and Urethraġ6.7 Case Study Conclusion: Drink and Flushġ7.7 Case Study Conclusion: Defending Your Defensesġ8.2 Introduction to the Reproductive Systemġ8.3 Structures of the Male Reproductive Systemġ8.4 Functions of the Male Reproductive Systemġ8.5 Disorders of the Male Reproductive Systemġ8.6 Structures of the Female Reproductive Systemġ8.7 Functions of the Female Reproductive Systemġ8.9 Disorders of the Female Reproductive Systemġ8.12 Case Study Conclusion: Trying to ConceiveĬhapter 1 Answers: Nature and Processes of ScienceĬhapter 2 Answers: Biology: The Study of LifeĬhapter 7 Answers: Introduction to the Human BodyĬhapter 14 Answers: Cardiovascular SystemĪ nerve impulse, like a lightning strike, is an electrical phenomenon.
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