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Neurociência Fundamental (Part 1: The Electrical Properties of the Neuron)…
Neurociência Fundamental
Part 1: The Electrical Properties of the Neuron
The History of Bioelectricity
Galvani was one of the first scientists to show that eletricity is a key to life.
Voltage
Is the difference in electrical potential between two points.
Electrostatic force
describes the attraction or repulsion between charged particles (ions). They obey simple rules: opposite charges (+ and –) attract, while like charges (+ and +, or – and –) repel.
In neuroscience, the relevant points in space are the inside and the outside of a cell, which are separated by a membrane that is impermeable to charged particles. Ions cannot flow across this membrane without the help of channels or pumps.
Ions can move through membrane channels and form a charge difference between these two compartments, resulting in a potential (or voltage) across the membrane. The impermeability of the membrane allows this voltage to be maintained.
Voltage is a relative measurement, and neuroscientists always use the outside of the cell as the ‘ground’ or reference point to measure the voltage across the membrane. For example, if the inside of the cell is 50 mV more negative compared to the outside of the cell, we would report the voltage as –50 mV.
Introducing the Resting Potential
Neurons are able to send signals through the use of electricity. Specifically, the lipid membrane of neurons separates solutions of charged particles, such as K+ and Na+ ions, and this separation creates a difference in potential energy across the lipid membrane
In neurons that are not sending or receiving signals, this potential difference is called the
‘resting potential.
Membrane potential
: this is a general term that describes the voltage across the membrane at any point in time; the membrane potential of a neuron can vary widely, for example from -90 mV to +60 mV
Resting potential:
the membrane potential of a neuron that is specifically "at rest," meaning that it is not sending or receiving signals, generally between -60 mV and -70 mV
Diffusion and Electrostatics
Diffusion and electrostatic pressure work collectively to facilitate electrochemical communication.
Ion movement through membrane channels is guided by diffusive and electrostatic forces, and the movement of these ions can change the membrane potential.
The Nernst Potential
This equation is the Nernst Potential, which calculates the membrane potential at which the diffusion and electrostatic forces for an ion balance out, given particular concentrations inside and outside of the cell.
Different "Potentials"
The
membrane potential
is a general term used to describe the voltage across the membrane at any time.
The
Nernst potential
is the membrane potential at which, given certain conditions (i.e. a given temperature and concentration gradient), a single ion is at an equilibrium
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Ion Concentrations
As you saw in the previous lessons, a membrane potential is established by the flow of ions across the membrane due to concentration gradients.
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Direction of Ion Flow
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Nernst potential represents an equilibrium point where two forces are balanced: diffusion and electrostatic force.
