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PSYC 220 WEEK 2 Notes

by: Lynde Wangler

PSYC 220 WEEK 2 Notes PSYC 220

Lynde Wangler
GPA 3.836

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These are notes from Wednesday only since we didn't have class Monday or Friday.
Meghan Jones
Class Notes
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This 3 page Class Notes was uploaded by Lynde Wangler on Friday January 8, 2016. The Class Notes belongs to PSYC 220 at University of North Carolina - Chapel Hill taught by Meghan Jones in Spring 2016. Since its upload, it has received 19 views. For similar materials see Biopsychology in Psychlogy at University of North Carolina - Chapel Hill.


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Date Created: 01/08/16
PSYC 220 WEEK 2 Notes: Chapter 2 (11 thEd.) Nerve Cells and Nerve Impulses  Electrical versus Chemical Signaling: o Electrical: an action potential is propagated down an axon via salutatory conduction (of an electrical signal); electrical signal can travel anywhere from 1m/s to 100m/s o Chemical: communication between neurons occurs via chemical signaling (using ions and neurotransmitters)  Membrane Potential Review – polarization (aka electrical gradient) is the difference in charge across the membrane (difference between inside and outside charges of a cell); membrane potential change is dependent upon ion movement o Diffusion: passive transport of ions from a high concentration to a low concentration o Electrostatic Pressure: refers to the quality of ions that causes ions of opposite charges to attract and those with like charges to repel one another  For ex., because potassium is more concentrated within a cell at resting potential, the concentration gradient will want to push K+ out of the cell. However, electrostatic forces dictate that since the inside of the cell is more negative, K+ will come into the cell  at resting membrane potential the K+ is approx. at equilibrium (that is, there is no net flow of this ion  Recording Membrane Potential – place one electrode in a solution outside the cell and the other inside the cell; the number recorded in the difference in millivolts between the two o Resting Potential – (for humans) ~-70mV but different people and different neurons vary (ranges from about -60mV to -80mV)  Selectively Permeable Cell Membrane: o Voltage-Gated Ion Channels: open and close in response to electrostatic changes across the membrane  Potassium, Sodium, Chloride, Calcium o Resting Membrane Potential: approx. -70mV; refers to state of neuron membrane before an electrical signal (action potential) is sent  Methods for Recording Activity of a Neuron: place electrodes in and around neuron to measure electrical differences; i.e., occurrence of action potentials can be observed  Sodium-Potassium Pump:  Exchanges internal Na+(3) for external K+(2)  Maintains electrochemical gradient to maintain resting potential  Does NOT cause large changes in membrane potential; works in the background  Equilibrium Potential  ions at resting potential: o Inside the Cell – many K+ ions and Proteins with negative(-) charges o Outside the Cell – many Na+, Ca2+, and Cl- ions  Movement and Forces on Ions: o Sodium is pushed into the cell both by concentration gradient and electrical gradient o The concentration gradient would like to push K+ out of the cell so if the K+ channels were wide open (as they are during the falling phase of an action potential) K+ would flow out o Leaky potassium channels – not voltage-gated; allow a small number of K+ ions to exit the cell at resting potential while the Na+ channels are closed  Action Potential Sequence of Events: o Action potentials originate at the axon hillock (the region on the soma right before the axon begins) strong changes in membrane potential are propagated down the axon regeneration at each node of Ranvier ensures that the signal does not decay the electrical signal communicates to the cell information about how to communicate with the next cell via processes in the axon terminal (coming soon) o Steps: Molecular Basis of the Action Potential  1) Resting Potential – K+ equilibrium, sodium channels are closed, leaky potassium channels are open  2) Depolarization – voltage-gated sodium channels open up allowing Na+ to flood into the cell depolarizing (making the inside of the cell less negative in comparison to the outside) the neuron  3) Reversal of Potential – occurs when the electrostatic potential exceeds 0; the inside of the cell is now positive relative to the outside; called the “overshoot” and this is when Na+ is almost at equilibrium  4) At (shortly after this point) sodium channels are INACTIVATED (absolute refractory period – they cannot open so an action potential CANNOT be generated) they then close; K+ flows in excess out of the cells with the concentration gradient and the charge then becomes more negative again  5) K+ ions continue to flow out causing hyperpolarization of the cell (relative refractory period); aka undershoot; occurs before returning to resting membrane potential when K+ channels close, which is maintained by the sodium-potassium pump  Hyperpolarization – membrane potential moves away from zero; becomes more negative; -80mV; difference between inside and outside of the cell is greater  Depolarization – less difference between inside and outside of cell; membrane potential is closer to zero more positive (but less than zero)  Threshold of Excitation: subthreshold stimulation creates a response that then quickly decays; an action potential occurs only when the stimulation is strong enough to reach threshold of excitation  Reversal Potential/ Reversed Polarity – the peak of the action potential reaches a positive number above zero; the inside of the cell is now positive relative to the outside of the cell  Blocking Action Potential: o Scorpion venom keeps sodium channels open and blocks potassium channels; toxic levels of sodium build up in the neuron  The All-Or-None Law:  Amplitude and velocity of action potential are not dependent on the strength of the stimulus; If threshold of excitation is met, then an action potential will be generated stimulus intensity is coded by the frequency of firing  Action Potentials Travelling in Reverse: they can back-propagate into soma and dendrites (structural changes in dendrites are associated with learning); normally action potentials travel in only one direction toward the axon terminal because of the absolute refractory period where the previously open sodium channels are inactive  Propagation of an Action Potential: saltatory conduction the signal jumps and is regenerated down the axon at each node of Ranvier; speed is influenced by diameter of axon (larger = faster) and degree of myelination  Demyelination Disorders: o Multiple sclerosis – muscle weakness; impaired motor function; impaired speech, vision, and cognition; genetic and environmental causes o Guillain-Barre syndrome – autoimmune disease; muscle weakness starting in legs and travelling upward in time; environmental causes  Dysmyelination Disorders: o Tay-Sachs disease – progressive degeneration of motor and cognitive abilities; causes very young deaths (before age 4); genetic disease o Schizophrenia  Local Neurons and Graded Potentials: o Do not have axons; exchange information with neurons that are very close; produce graded potentials (vary in magnitude and can be inhibitory or excitatory) depolarizes (excitatory)/hyperpolarizes (inhibitory) o Myth – only 10% of neurons are active at any given time……(UHM NOOO)


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