The Nervous System: Action Potentials PDF

# The Nervous System: Action Potentials ## EXS 115 ## Lecture Objectives - Describe the components of the membrane that establish the resting membrane potential. - Describe the changes that occur to the membrane that result in the action potential. - Understand the different forms of channels and h...

# The Nervous System: Action Potentials ## EXS 115 ## Lecture Objectives - Describe the components of the membrane that establish the resting membrane potential. - Describe the changes that occur to the membrane that result in the action potential. - Understand the different forms of channels and how they are active. - Write out the steps of an action potential. ## Neuron to Neuron - **Excitable membrane** - **Synapse:** place where a neuron connects to another neuron or an effector - **Neurotransmitters** ## Synapse - **Presynaptic neurons** - **Synaptic cleft** - **Postsynaptic neuron** ## How does a signal move through the nervous system? The signal travels through a neuron that consists of the following parts: - **Dendrite** - **Cell body** - **Axon** - **Axon terminal** - **Nucleus** - **Myelin sheath** - **Node** - **Collateral** - **Direction of signal movement** ## Neuron at rest - **Resting potential** - **What makes up the cell membrane?** - **Concentration outside of the cell?** - **Concentration inside of the cell?** - **Chemical gradient** A diagram showing the structure of a cell membrane with sodium and potassium ions moving through channels describes these concepts. At rest, all Na+ channels whose opening depends on the voltage and most of the K+ channels whose opening depends on the voltage are closed. Na+/K+ pumps transport K+ ions inside the cell and Na+ ions outside the cell. ## Electrical gradient, Electrochemical gradient, Resting membrane potential A diagram depicts the structure of a cell with a resting membrane potential of -70mV. It shows that the extracellular fluid has a greater concentration of Na+ and the cytosol has a greater concentration of K+ and proteins. The components that contribute to setting the resting potential are: - Na+ leak channel - K+ leak channel - Na+/K+ pump - Microelectrode - Voltmeter ## Active Transport: - **How is RMP maintained at rest?** - **How many Na+ are moved & in which direction?** - **How many K+ are moved and in which direction?** - **What is necessary for the Na+/K+ Pump to work?** A diagram showing the Na+/K+ pump operation helps address these questions. The Na+/K+ pump moves 3 Na+ ions out of the cell for every 2 K+ ions it moves into the cell. This process requires ATP (adenosine triphosphate) to move these ions against their concentration gradients. The sodium ions move from the intracellular fluid to the extracellular fluid and the potassium ions move from the extracellular fluid to the intracellular fluid. ## Concentration Gradients - **Maintained through ion channels** ### Different types of ion channels include: 1. **Leak channels** 2. **Ligand gated: chemical signal** 3. **Voltage gated: open when in voltage** 4. **Mechanically Gated channels** Diagrams show how these channels work. The concentration gradient is the driving force for ions to move. ## Na+ inactive state A diagram shows a channel opening during cell depolarization. ## Goal = Indicate what is happening at each # by drawing & labeling what channels are open & closed at each stage. A diagram showing the action potential illustrates how it is generated. The graph shows five stages: 1. **Stimulus** 2. **Depolarization** 3. **Repolarization** 4. **Hyperpolarization** 5. **Resting State** ## Events of an Action Potential - **The unstimulated axon has a resting membrane potential of -70 mV.** - **Graded potentials reach the initial segment and are added together (-70 mV -55 mV).** - **Depolarization occurs when the threshold (-55 mV) is reached; voltage-gated Na+ channels open and Na+ enters rapidly, reversing the polarity from negative to positive (-55 mV +30 mV).** - **Repolarization occurs due to closure of voltage-gated Na+ channels (inactivation state) and opening of voltage-gated K+ channels. K+ moves out of the cell and polarity is reversed from positive to negative (+30 mV −70 mV).** - **Hyperpolarization occurs when voltage-gated K+ channels stay open longer than the time needed to reach the resting membrane potential; during this time the membrane potential is less than the resting membrane potential (–70 mV -80 mV).** - **Voltage-gated K+ channels are closed, and the plasma membrane has returned to resting conditions by activity of Na+/K+ pumps (–80 mV −70 mV).** A diagram showing the action potential process describes these steps. ## Review Videos A list of YouTube videos are listed on the slide. ## Resting membrane potential to Action Potential A diagram showing the process of depolarization to threshold and activation of sodium ion channels and rapid depolarization illustrates the action potential process. ## Absolute refractory period to Relative refractory period A diagram and several statements illustrate the absolute and relative refractory periods. ## Voltage-gated K+ channels - **No inactivation gate** ## Inactivation of Sodium Ion Channels and Activation of Potassium Ion Channels Starts Repolarization A diagram showing the action potential process emphasizes the role of sodium and potassium channels. ## Time Lag in Closing All Potassium Ion Channels Leads to Temporary Hyperpolarization A diagram again explains the process of action potential generation and shows how the closing of multiple potassium channels leads to a temporary hyperpolarization. ## Goal = Indicate what is happening at each # by drawing & labeling what channels are open & closed at each stage. Another illustration depicts steps 1-5 of the action potential again. ## Nerve Cell conduction - **Direction of signal movement** - **Nodes of Ranvier** - **Myelin sheath** - **Axon** - **Nucleus** - **Collateral** - **Node** - **Cell body** - **Dendrite** - **Axon terminal** ## Continuous vs. Saltatory Conduction Diagrams depict the two modes of signal conduction, showing **Continuous conduction** as the slower process and **Saltatory conduction** as the faster process. ## Neuron at Rest: Gated Channels and Ion Gradients - **Chemically gated cation channel** - **Chemically gated K channel** - **Chemically gated Cl- channel** - **Voltage-gated K+ channel** - **Voltage-gated Na+ channel** - **Voltage-gated Ca^2+ channel** A diagram illustrates the various types of channels and their positions along a neuron, focusing on the concentrations of ions within the cell and outside the cell. - **Receptive segment** - **Initial segment** - **Axon hillock** - **Conductive segment** - **Transmissive segment** - **Synaptic Knob**