Week 3 Notes
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This 6 page Class Notes was uploaded by Jennifer Fry on Wednesday September 9, 2015. The Class Notes belongs to PHYS 215 at Ball State University taught by Zamlauski-Tucker in Summer 2015. Since its upload, it has received 17 views. For similar materials see Human Physiology in Science at Ball State University.
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Date Created: 09/09/15
Physiology Class: Notes Week 3 9-9-15 Neurophysiology Excitable Tissues o Nerves and muscles o Membrane potential=Vm (membrane voltage) Intracellular Recording o o Measurement of ion charges across the cell membrane. o There are 3 phases to the action potential. o o Phase 1- depolarization- cell becomes more positive inside o Phase 2- repolarization- cell returns to the resting membrane potential o Phase 3- hyperpolarization- the cell becomes more negative inside than the resting membrane potential. What is happening to the neuron? o o Cell receives signals from synapsing neurons. o The signals have to add up enough to reach threshold. o Graded potentials- local changes in membrane potential Excitatory. o Signals that do not reach threshold are termed “subthreshold.” o o At threshold, the signal is passed on by depolarizing the neighboring membrane. o o The 3 phases are due to the changes in permeability to Na+ and K+ ions. o Action Potential Channel Currents o At rest, imbalance of charge across the membrane. o Signal causes the membrane to reach threshold for sodium channel activation. o Sodium channels open o Sodium rushes into the axon (phase 1) o A region of positive charge develops o The region of positive charge causes nearby sodium channels to open o Sodium channels open briefly before closing (spring loaded gate) o K channels open wide (like and old, rusty gate) (responsible for 3 phase) o Continues as a chain reaction along the axon o Influx of sodium depolarizes the axon, and the outflow of K repolarizes the axon Na+/K+ ATPase o The sodium/potassium pump restores the resting concentrations of sodium and potassium ions o 3 Na+ out for 2 K+ in o Voltage gated sodium (Na) channels Excitability in neuronal tissue, skeletal muscle, and cardiac muscle o At rest all Na+ channels are closed (Vm = -70 mV) o Na channels assum an open configuration when the neuron depolarizes (Vm= -50 mV) o After 1 msec, Na channels shut (inactivate) o o Channels accumulated in the inactive state o They cannot be reopened, this is the absolute refractory period. o As the resting membrane potential returns, a greater amount of stimulus is needed to generate an action potential; relative refractory period. o Channels and AP Stages o Depolarization Membrane became more positive Na+ channel opened, then K+ o Repolarization Na+ channels shut K+ channels stayed open o Hyperpolarization Only K+ channels open Membrane potential dips below resting potential ***Need to know which phases have which channels open Channel Blockers o TTX (tetodotoxin)- the name is derived from the order of fish, tetraodontindae, which means “four-toothed.” This family includes the puffer fish from which the poison was first obtained Poison blocks voltage dependent sodium channels o TEA (tetraethylamonium)- blocks voltage dependent potassium channels Neuronal Structure o Nerve cell Neuron o Nucleus & organelles Cell body o Cell body projections Dendrites Main site for chemical o Axon Hillock Generation of action potential o Axon Nerve fiber Collaterals Axon terminal Conduction o Contiguous conduction Spread of action potential down membrane (example we used earlier) o Saltatory conduction Hopping of the action potential down the Nodes of Ranvier Myelin is important for proper nerve salutatory conduction.
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