PHYSIOLOGICAL PSYCHOLOGY

**(PSYC 465)**

**Magalis**

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**Neuroscience Project**

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**NAME** ___________________________________

**Directions: ****Please respond to the following problems and questions on a separate sheet. Your responses can either be typed or written. On the due date you will turn in your responses AND this sheet stapled to it with your name included. BEST OF LUCK AND I HOPE YOU LEARN MORE NEW THINGS!! The due date is as indicated on the syllabus**

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PROBLEMS/SHORT ANSWER QUESTIONS:

- A neuron has a particular concentration of potassium in its intracellular and extracellular fluid that is measured in millimolar units (mM). If K+ outside = 10 mM and K+ inside = 400 mM, then what is the value of the Nernst equation for this ion ? (3 pts.)

- A neuron has a particular concentration of sodium in its intracellular and extracellular fluid that is measured in millimolar units (mM). If Na+ outside = 460 mM and Na+ inside = 50 mM, then what is the value of the Nernst equation for this ion ? (3 pts.)

- A neuron has a particular concentration of chloride in its intracellular and extracellular fluid that is measured in millimolar units (mM). If Cl- outside = 540 mM and Cl- inside = 40mM, then what is the value of the Nernst equation for this ion ? (3 pts.)

- A neuron has a particular concentration of calcium in its intracellular and extracellular fluid that is measured in millimolar units (mM). If Ca2+ outside = 2 mM and Ca2+ inside = .0002 mM, then what is the value of the Nernst equation for this ion ? (3 pts.)

- You have calculated various values in the above problems, but they are all telling you a specific bit of information about the neuron. What is the term for the values that you calculated (be specific) ? (1 pt.)

- Give an explanation for this term (i.e. what does it mean and what is it telling you?). (5 pts.)

- There is another famous formula in neuroscience called the Goldman-Hodgkin-Katz correction to the Nernst Equation. It considers multiple ion species AND their relative permeability in a biological system (like a neuron!). Assume for an alpha motor neuron in the mammalian nervous system that the intracellular and extracellular permeability for potassium is 1.0, the intracellular and extracellular permeability for sodium is .03, and that the intracellular and extracellular permeability for chloride is .1. Given the above concentrations for the respective ions in the extracellular and intracellular fluids given in the previous above problems, use the version of the Goldman-Hodgkin-Katz correction to the Nernst equation to compute the value of the voltage Vm. (4 pts)

- What do you notice about the given value you just computed in the above problem? WHY would this value likely be generated using the correction formula whereas the previous values using the Nernst equation would NOT have generated this value?(5 pts.)

- Neuron have, besides voltage, another electrical property termed MEMBRANE CAPACITANCE. Capacitance, in essence, indicates the capacity of charge that can be stored on two charged surfaces. A capacitor, in electro-physics is, is composed of two surfaces that can conduct charge that are separated by an insulator. The neuron membrane has a specific capacitance because the membrane (which can store electric charge in the form of ions) is an insulator, while the extracellular and intracellular fluids can be considered conducting surfaces (ions can have their particular fluxes through the conducting medium of water.

Physicists, biologists, AND psychologists as well, can calculate the specific membrane capacitance per unit area of a neuron. Consider a patch of plasma membrane on the axon of an unmyelinated neuron. Suppose for this particular surface of membrane the intracellular and extracellular surface fluids are separated by a distance of 5 x 10^-9 meters (the ^ symbol indicates an exponent, thus this is scientific notation). If the dielectric constant, ϵ, for this patch of unmyelinated axon is equal to 5 x 10^-11Farads/meters (do not worry about the name of the units!), what will be the capacitance per unit area of the axon ? (3 pts.) (Your units for the numerical answer to this problem will be **Farads/meters squared**-just include this by your answer!)

- NEXT, consider another patch of plasma membrane on the axon of a myelinated neuron. Suppose for this particular surface of membrane the intracellular and extracellular surface fluids are separated by a distance of 1 x 10^-6meters. If the dielectric constant , ϵ, for this patch of myelinated axon is again 5 x 10^-11 Farads/meters, what is the value of the capacitance per unit area of the axon? (3 pts)

- Physicists, biologists AND psychologists can ALSO compute the propagation velocity for an action potential that it would have as it is regenerated down the length of the axon. Consider again the unmyelinated neuron that has an unmyelinated axon in problem 9 for which you computed the capacitance per unit area. Given that the axon radius when considered in cross section is 5x10 ^ -6 meters, specific resistivity of the axoplasm (that is: the cytoplasm inside of the axon) has a value of 2.0 Ohms/meters (an Ohm is simply an electrical measure of resistance), and that the axon has a unit length of 1 x 10^ -3 meters, what would be the propagation velocity of the unmyelinated axon in problem 9? Your units will be meters/second (3 pts).

- NOW, consider the myelinated neuron that has a myelinated axon in problem 10 for which you computed the capacitance per unit area. Given again that the axon radius is 5x10 ^ -6 meters, and that the specific resistivity of the axoplasm for the myelinated axon is also 2.0 Ohms/meters, and that the unit length of the axon is again 1x10^ -3 meters, what is the propagation velocity of the myelinated axon. (3 pts)

- Based on the velocity values that you computed in problems 11 and 12, what do you conclude the relationship is between the particular capacitance per unit area of an axon and propagation velocity(2 pts.)? What propagates the action potential more quickly-unmyelinated axons or myelinated axons?(2pts)?

- Often we do not consider that a small portion of neuron, such as a dentritic branch has a particular electrophysiology. Even dendrites are interesting (in my opinion) in this respect. Dendrites, recall, are one of the first portions of neuron to be electrically altered by EPSPs and IPSPs produced by neurotransmitters. Dendrites are actually like a hose that has many holes punched into it. IN OTHER WORDS, they are VERY poor conductors of electric current (current reflected by EPSPs and IPSP value alterations in the resting membrane potential) and voltage changes decay rapidly over distances along the dendrite of a neuron. WELL, Physicists, biologists, AND YES- Continuing with my theme because this is what ALL OF YOU ARE...PSYCHOLOGISTS can compute the distance at which the voltage change falls off and decreases as a result of the leakiness. This computed value is called the LENGTH CONSTANT (λ), and it is defined as the length at which a voltage change decreases by 1/e, that is 37% of its original value. Suppose that the dendrite of a neuron in the cerebral cortex had a particular radius defined by the variable “a”. For this particular dendrite a =1x10 ^ -4centimeters. The dendrite also has a specific resistance of 5x10 ^ 4 Ohms*cm-squared . Finally, the specific resistivity of the cytoplasm for this dendrite is equal to 200Ohms*cm. With these values compute the value of the length constant for the dendrite. The units I have provided will already set your computed value to the appropriate units, thus simply in your final answer include “micrometers” at the end of your answer(3 pts).

INDEPENDENT RESEARCH:

- Do some research on a particular neuropathology (e.g. Parkinson’s disease, Alzheimer’s etc..). Give a description of the symptomology of the pathology, as well as (as in-depth as you can) the neural systems that are affected and what seems pathological in those systems in association with the pathology. (24ts.)

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The fields of Physiological Psychology and Neuroscience are CONTINULALLY growing! What issue/issues do you think that these scientific disciplines should focus on in the future and why? (5 pts.)

**FORMULAS: **

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**Nernst Equation:**

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** [ion concentration]out**

**E****ion**** = 58 * log ------------------------------------- **

** [ion concentration]in**

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**Nernst Equation: (particularly for calcium given that it is a divalent ion)**

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** [ion concentration]out**

**E = 30.77mV* log -------------------------------**

** ****Ca2+**** [ion concentration]in**

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**Goldman-Hodgkin-Katz Correction to the Nernst Equation:**

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** P****K+****[K+]****out**** + P****Na+****[Na+]****out **** + ****P****cl****-[Cl-]****in**

**Vm = 58 * log ----------------------------------------------------- **

** P****K+****[K+]****in**** + P****Na+****[Na+]****in**** + P****cl-****[Cl-]****out**

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**Where P = the given permeability of an ionic species**

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**CAPACITANCE PER UNIT AREA CALCULATION FORMULA:**

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**C** = **ϵ / d **

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**where** **C = the capacitance per unit area**

** ϵ = a dielectric constant based on the material involved (e.g. plasma **

** membrane**

** d = relative distance between the charged surfaces **

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**THE VELOCITY OF PROPAGATION FOR AN ACTION POTENTAL:**

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**V = r / {(2) (ρ****axon****) (C) (x)} = **

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**Where V = the action potential propagation velocity**

** r = the radius of the axon in cross section**

** ρ****axon**** = the given axoplasm resistivity**

** C = the capacitance per unit area**

** X = the given unit length of the axon **

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**The Length Constant Formula for a Dendrite**

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**Where λ = the length constant for a dendrite**

** Rm = specific membrane resistance for a dendrite**

** Ri = specific membrane resistivity of the cytoplasm of a dendrite**

Subject | Science |

Due By (Pacific Time) | 04/30/2014 05:00 pm |

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