4A+Midterm+TQs - HUMAN BIOLOGY 4A Review/Thought Questions...

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HUMAN BIOLOGY 4A Review/Thought Questions for the Midterm, 2008 This guide is intended to help you think about, review and integrate the material from the class, problem sets, virtual lab and text books. While we believe this guide will be useful it is neither sufficient or exhaustive. If you master the material in this guide you will be in good shape, but it is not intended as a substitute for attending lectures, reading and engaging with the assigned material. It is often helpful to draw diagrams and graphs as necessary to help your understanding of the material. HOMEOSTASIS Homeostasis is essential at all levels of physiological function. Describe what homeostasis is, what essential elements it requires and how it works. Give a specific example. Homeostasis is the steady state of a system/organism. It is a system’s tendency to resist change and try to maintain constant conditions. One example found in the human body is the process by which axon potential is generated and regulated. The equilibrium membrane potential within an axon is around -50 to -70 mV. When an action potential fires (caused by the binding of ligands/signaling from neurotransmitters), the permeability of the membrane to Na+ changes to allow more Na+ to flow in than usual, which depolarizes the membrane. However, the K+ receptors quickly respond to this sudden change in membrane potential and open up, hyperpolarizing the membrane so it gets back to equilibrium. NEURON STRUCTURE AND FUNCTION For a typical interneuron, describe all the morphological structures beginning at the input. Match each structure to its function in the neuron. As a thought exercise, imagine that you found an interneuron that expressed only ligand gated ion channels. How and why would this neuron look and work differently from other neurons? What about a neuron that had only voltage-gated ion channels? If an interneuron only had ligand gated ion channels, then it would have to be very short, the only channels would be at the beginning and the end of the neuron, and would have to be directly stimulated by neurotransmitters right before it. Action potential would be harder, and there wouldn’t be myelin. If it only had voltage gated channels, then the body would have to figure out ways to open voltage gated channels at the beginning of the axon, so the mechanism that initially stimulates the first neuron would have to dump a lot of Na+ or something in order to stimulate the opening of the channels. Track the origin and propagation of an action potential along an axon. Identify the mechanisms through which action potentials can be identical in size along its many branches. Why do neurons have a maximal firing rate? Compare that propagation of an action potential in detail along a myelinated and unmyelinated axon. Identify the relationship among the following variables: axon diameter, myelination, and action potential speed . What are the important features of action potentials? How and why are these different from graded potentials
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This note was uploaded on 08/01/2009 for the course HUMBIO 4a taught by Professor Various during the Spring '08 term at Stanford.

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4A+Midterm+TQs - HUMAN BIOLOGY 4A Review/Thought Questions...

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