Neuron is an electrical device - really?

Monday and Wednesday

1. Let us first understand the overall structure of a neuron - KhanAcademyVideo-Neuron

Links to an external site.

2. Now let us get an overview from a functional point of view to show how it is an electrical device - 

Neuron has electrical components - Slides

A.  CAPACITOR - View this video to understand the structure of an electrical capacitor inside your computer. View video below:

https://youtu.be/u-jigaMJT10

So, a capacitor has an insulator surrounded by two conducting plates.   The corresponding elements in a neuron are: insulator - phopholipid bilayer, and conducting plates - extra and intraceullar fluids. The video below illustrates the cell membrane which acts as the insulator of the capacitor.

https://youtu.be/fJfTDc3WzQ8

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B. RESISTORS - The standard electrical resistor follows Ohm's Law which is V = I*R.  It permits current (typically electrons) to pass through.

In a neuron, the protein pores are the resistors and they permit ions (if you recall, electrons are moving charge carriers in the wiring in home lighting) to pass through as current. The slide below illustrates how the protein pores embedded in a cell membrane act as resistors

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C. BATTERY -  For standard electrical devices that we use regularly, the power source ttypically is a 5, 9 or 12 volts battery. Note that those batteries are powered by chemical energy

What is the battery or power source that charges a neuron?   The power source of a neuron comes from chemical gradients set up across the cell membrane. Here is a video of how the chemical gradients for various ions that is set up using "ion pumps". The different ion pumps consume energy from the food you eat .....and their sole job is to set up these chemical gradients!

https://youtu.be/hk09AkV5_Kc

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D. EXTERNAL SOURCE OF CURRENT - In standard electrical devices, they don't receive any additional currents.  But in neurons, they receive currents from other neurons via synapses. This 'external' current source is what helps activate a neuron, and the neuron membrane potential is otherwise noted as being at "rest" with a membrane potential Vrest, that is largely constant with ~ 1-2 mV flucutation (noise).

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E. PUTTING IT ALL TOGETHER - Here is how we can put all the components of a neuron together in a composite sketch focusing on the electrical properties of the components.

Friday

HW #5 Assigned:  Peruse all the videos and materials above. Then summarize each item in 1 page max (in itemized/bulleted form): 1, 2, and then 2A-E.  Then reproduce the sketch in part E, labeling each component fully. Make sure you fully understand the equivalence since we will later just be sketching electrical circuit diagrams and writing some basic equations.