Question

if you were to model a cell membrane as a circuit what kind of circuit would it be?

a. RC circuit with a battery

b. RC circuit without a battery

c. A circuit with a battery and a capacitor

d. A circuit with a battery and a resistor

Answer 1

if you were to model a cell membrane as a circuit it will be RC circuit with a battery

answer is option (a)

source :

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A neuron is the basic building block of the nervous system. A one-year old human has about 100 billion neurons. The brain is a vastly complicated signalling system, with neurons forming the basis of that system. Electrochemical signals flow in one direction only in neurons, originating at the dendrites or cell body (usually in response to stimulation from other neurons) and propagating along axon branches which terminate on the dendrites or cell bodies of perhaps thousands of other neurons. The basis of neuronal electrochemical signals lies in the neuron membrane. Like all cell membranes, the neuron membrane is a phospholipid bilayer. In other words, the membrane is a "fat sandwich", with fatty acids between two slices of polar (phosphate) "bread". The membrane is pierced with proteins that serve as channels for ions to "flow" though (like straws stuck in a sandwich).

In Neurophysiology lab experiments we explained the basic Physiology and Anatomy of neuron and action potential, for understanding mathemathical modeling of simple HH neuron one may go to Neuron Simulation lab. In this experiment we study the basic electric properties of an electricaly excitable neuron. The electrical properties of neurons can be described in terms of electrical circuits. To understand the behavior of this circuit, we need to know the behavior of the basic components of electrical circuit such as resistor and capacitor.

Resistors: A resistor is a component of a circuit that resists the flow of electrical current. It has two terminals across which current flows and drop the voltage of the current as it flows from one terminal to the other. Resistors are primarily used to create and maintain known currents within electrical component.

We model the neuronal cell membrane as a resistor in series with a capacitor as the diagram below illustrates (Figure 3). The amount of current, i that flows through these resistors, R is given by Ohm's Law:

I = V/R

V= Voltage drop across the resistance

In a neuronal membrane there are ion channels which allows the flow of charged ions across the membrane, which results in the action potential generation and propagation. When there are more open ion channels more currents can flow through these channels to the extracellular medium. With this property each ion channel is act as a small resistor and the number of opened ion channels increased can be represented by more number of resistors are in parallel. So that the net resistance of the circuit is smaller

Capacitor: In a RC (resistor, capacitor) equivalent circuit model for passive neuron membrane, the capacitor represents the fact that cellular membranes are good electrical insulators.

Capacitor is a device useful for storing electric charge. The capacitors only function is to store electric charge. A capacitor is simply two metallic plates separated by a gap, where the gap between the plates is usually filled with a a non-conductive material called a dielectric. A voltage across the plates of the capacitor charges up one plate, pushing charge off the nearby plate. But the plates can only hold so much charge, so current only flows for a short while. The capacitive property of phospholipid bilayer.

http://vlab.amrita.edu/?sub=3&brch=258&sim=1448&cnt=1

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