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Summary Adaptive brain chapter 2-4
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This document contains a summary of the lectures of chapter 2-4 of the course The Adaptive Brain.
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Electrical Signals of Nerve CellsLearning objectives When you would inject a positive current the membrane becomes
• Neurons generate electrical signals to transmit information less negative, which causes depolarization. At a certain level of
• Electrical signals are based on the flow of ions across the membrane potential, called the threshold potential, action
membrane potentials occur. The action potentials of a neuron are an all-or-
• Selective permeability to different ions and the non-uniform none principle, they occur fully or not at all. When the positive
distribution of these ions give rise to electrical signals current gets increased, multiple action potentials occur. So, the
• Know the concepts of resting membrane potential and action intensity of a stimulus is encoded in the frequency of action
potential potentials rather than in their amplitude, this is called summation.
Electrical signals
Neurons generate a variety of electrical signals that transmit and
store information. Because neurons are not very good conductors
of electricity, they have mechanisms that generate electrical
signals based on the flow of ions across their plasma membranes.
Membranes are selectively permeable to different ions and the
non-uniform distribution of these ions gives rise to electrical
signals. Neurons generate a negative potential, called the resting
membrane potential, that can be measured by recording the
voltage between the inside and outside of the cells. The fundamental problem of neurons is that their axons are quite
long, which makes them not a good electrical conductors. You can
Electrical signals can be measured by using intracellular see that when the stimulation is under the threshold that the
microelectrodes that can measure the electrical potential across signal dies out. But when the action potential is reached, the
the neuronal membrane. A typical microelectrode is a piece of signal does not die out and continues constantly over a distance.
glass tubing pulled to a very fine point and filled with a good
electrical conductor, such as a concentrated salt solution. This
conductive core can then be connected to a volt meter (computer)
that records the transmembrane voltage of the nerve cell. After
inserting a microelectrode through the membrane of a neuron, it
reports a negative potential, this is called the resting membrane
potential. Neurons encode information via electrical signals that
result from changes in the resting membrane potential. Receptor
potentials are due to the activation of sensory neurons by
external stimuli, such as light, sound, heat or touch.
Ion movements produce electrical signals
Electrical potentials are generated across the membranes of
neurons because they differ in concentrations of ions across
nerve cell membranes. These membranes are selectively
Another type of electrical signal is associated with communication permeable to some of these ions. The ion concentration gradients
between neurons at synaptic contacts, which generates synaptic are established by proteins known as active transporters that can
potentials. actively move ions in or out of the cell against their concentration
Many neurons generate a special type of electrical signal that gradients. Ion channels are proteins that allow only a certain kind
travels along their axons, these signals are called action of ion to cross the membrane in the direction of their
potentials. Action potentials are responsible for the long-range concentration gradients when the channel is open or closed, this
transmission of information to the target organs. In the happens when there is a change in membrane potential. So,
laboratory, an action potential can be produced by inserting a channels and transporters work against each other, and in doing
micro-electrode into a neuron and then connecting the electrode so they generate the resting membrane potential, action
to a battery. A second microelectrode can be inserted to measure potentials, and the synaptic/receptor potentials that trigger the
the membrane potential changes produced by the applied current. action potentials.
If you would inject a negative current into the membrane, the
membrane potential becomes more negative causing
hyperpolarization.
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