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Nervous System: Fundamentals 3.23.16

by: Brooke Sullivan

Nervous System: Fundamentals 3.23.16 BSCI 201

Marketplace > University of Maryland > Biological Sciences > BSCI 201 > Nervous System Fundamentals 3 23 16
Brooke Sullivan

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About this Document

Notes from the second part of the Nervous System lecture.
Human Anatomy and Physiology
Dr. Meredith Bohannon
Class Notes
25 ?




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This 4 page Class Notes was uploaded by Brooke Sullivan on Sunday April 10, 2016. The Class Notes belongs to BSCI 201 at University of Maryland taught by Dr. Meredith Bohannon in Spring 2016. Since its upload, it has received 11 views. For similar materials see Human Anatomy and Physiology in Biological Sciences at University of Maryland.

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Date Created: 04/10/16
Nervous System: The Fundamentals Part 2 4/10/16 10:29 PM Resting Membrane Potential • Resting membrane potential lies at around -70mV • Difference in electrical charge across the membrane • Always negative • Inside of the cell is more negative that outside Role of Ion Channels In Membrane Potential • Leaky channels are always open • Gated channels are not always open • Voltage Gated channels only open in response to a voltage change Two Factors Contribute to RMP • Concentration gradient: ions will move down their concentration gradient • Electrical gradient: ions will move down their electrical gradient • Balance between the two is the electrochemical gradient • Ion Concentration in RMP • More sodium on the outside and more potassium on the inside of the cell • Role of Plasma Permeability in RMP • Not permeable to protein anions • Very little Na+ is permeable • Mostly permeable to K+ ions • K+ and Na+ contribute most to RMP • What happens to disrupt RMP? • Graded potentials which occur in dendrites and are incoming signals (vary in strength) • Action potentials occur in axons and are outgoing signals (all or nothing) • Changes in Polarity • Depolarization: membrane potential is more positive • Hyperpolarization: membrane potential is more negative than resting • Repolarization: membrane potential is more negative after depolarization • Graded Potentials • Short and localized • Magnitude and distance are determined by the strength of the stimulus • Two Instances of Graded Potentials • Receptor Potential or Generator Potential: when a sensory neuron fires • Postsynaptic Potential: when an axon meets with the dendrites of another neuron • Axosomatic, axoaxonal, axodendritic synapses • Action Potentials • 1. Resting State: no membrane potential change • 2. Na+ flows into the cell because the voltage gated channels have opened • 3. Repolarization: sodium channels close, and potassium channels open, allowing potassium to flow out of the cell • 4. K+ ions continue to leave the cell causing hyperpolarization • 5. Sodium potassium pump restores resting membrane potential • Threshold • Action potentials do not occur if voltage does not reach -55mV • Not all depolarizations cause action potentials • Propagation of Action Potentials • Local voltage change causes sodium channels to open • Those open channels cause the sodium channels further down the neuron to open • This happens all the way down the neuron • Stronger stimuli result in more action potentials • Refractory Periods • Time when another action potential can’t happen • Absolute: action potential will not occur, regardless of stimulus strength • Relative: action potential will only occur with a super strong stimulus • How Fast Do Action Potentials Travel? • Factors: diameter of axon and amount of myelination • Role of Myelination in Action Potential Velocity • In non-myelinated axons, action potentials have to constantly regenerate, so conduction is slow • In myelinated axons, the myelin sheath houses areas of the axon with no leaky channels, meaning the voltage of the action potential does not decay as it travels. This leads to fast conduction • Multiple Sclerosis • White blood cells attack myelin • Causes poor nerve signaling • Mostly seen in women 4/10/16 10:29 PM 4/10/16 10:29 PM


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