The lipid double layer membrane the surrounds a neuron is impermeable to fee molecules or ions. To enter or leave the neuron, ions should pass through special proteins dubbed ion channels that expectancy the membrane. Ion networks have different configurations: open, closed, and also inactive, as shown in number 16.9. Part ion channels need to be activated in order to open and permit ions to pass into or out of the cell. These ion channels are perceptible to the environment and can readjust their shape accordingly. Ion networks that readjust their framework in solution to voltage changes are referred to as voltage-gated ion channels. Voltage-gated ion networks regulate the family member concentrations of different ions inside and also outside the cell. The distinction in full charge in between the inside and also outside the the cabinet is referred to as the membrane potential.

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Figure 16.9. Voltage-gated ion networks open in solution to alters in membrane voltage. After ~ activation, they come to be inactivated because that a brief duration and will no longer open in an answer to a signal.
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Figure 16.10. The (a) resting membrane potential is a an outcome of different concentrations that Na+ and K+ ion inside and also outside the cell. A nerve impulse causes Na+ to enter the cell, leading to (b) depolarization. At the peak activity potential, K+ networks open and the cell becomes (c) hyperpolarized.
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Figure 16.11. The development of an action potential have the right to be split into five steps: (1) A economic stimulation from a sensory cell or another neuron reasons the target cabinet to depolarize towards the threshold potential. (2) If the threshold that excitation is reached, all Na+ channels open and also the membrane depolarizes. (3) in ~ the peak action potential, K+ channels open and also K+ begins to leave the cell. In ~ the very same time, Na+ networks close. (4) The membrane becomes hyperpolarized as K+ ions proceed to leaving the cell. The hyperpolarized membrane is in a refractory duration and cannot fire. (5) The K+ networks close and the Na+/K+ transporter restores the relaxing potential.

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Figure 16.12. The activity potential is carried out down the axon together the axon membrane depolarizes, then repolarizes.