Key Points Exam 3 - Module 17 In this module we will...

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In this module we will explain resting membrane potential in greater depth, and overview the terminology that is used to describe action potentials. Here are 4 points to remember. 1. Sodium and chloride are high outside cells (extracellular fluid) 2. The permeability of a cell for ions depends on the number and type of ion channels in the cell membrane 3. The resting membrane potential in neurons depends on the distribution of sodium as well as potassium across the cell membrane. Resting membrane potentials in neurons are commonly around -70mV 4. The sodium/potassium pump is essential for maintaining the resting membrane potential in neurons. Here are some key concepts. First, there are three types of ion-gated channels: voltage gated, ligand gated and mechanically gated. You are familiar with the first two and you can review these by clicking the appropriate buttons . Mechanically gated channels are a third type and open and close in response to a mechanical force on the membrane. These are usually found in sensory or visceral receptors. All these gated channels are very important to the normal function of the nervous system. If you interfere with gated channels in any way you interfere with the normal function of the nervous system. The -55mV value is the critical level of membrane potential that must be reached for an action potential to be generated. Module 18 Specifically, when you have completed this module you will be able to: Describe how chemical synapses work Compare fast and slow responses at synapses Describe neural integration and the role of the axon hillock in neural integration Describe the major classes of neurotransmitters. Key points then are as follows: Action potentials are triggered when an initial depolarization reaches threshold. This threshold potential varies, but generally is about 15 millivolts above the cell's resting membrane potential, occurring when the inward sodium current exceeds the outward potassium current. The net influx of positive charges carried by sodium ions depolarizes the membrane. But first, here are the key points so far: A stimulus comes into the soma where it moves to the axon hillock This stimulus disturbs voltage gated sodium channels – opening a few that make the membrane at the axon hillock more permeable to sodium. As sodium enters the cell it depolarizes the membrane to -55mV. Once the -55mV level is reached the sodium entering the cell starts a positive feedback loop opening more sodium voltage gated channels. Sodium enters the cell very rapidly. The cell is completely depolarized at +30 mV. Here are some final key points you need to know. The diameter of unmyelinated axons determine how quickly the action potential moves down the axon The larger the diameter the less resistance there is to the current flow. Mylelinated fibers have the fastest speed.
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This note was uploaded on 11/27/2010 for the course APK 2105 taught by Professor Brooks during the Spring '07 term at University of Florida.

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Key Points Exam 3 - Module 17 In this module we will...

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