BIOL 1107 Study Guide - Midterm Guide: Insulin, White Blood Cell, Antigen Presentation

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Once the threshold potential is reached, certain channels in the axon membrane open, allowing ions to rush into the axon along their electrochemical gradients. This causes the inside of the membrane to become less negative and then positive with respect to the outside. When the membrane potential reaches about +40 mv, an abrupt change occurs and the repolarization phase begins. The cations move down the membrane until they reach a gap in the myelin sheath, known as a node of ranvier, where there is a dense concentration of voltage-gated channels and new action potentials can be generated. The electrochemical gradient for calcium results in the inflow of calcium ions through the open channels. If acetylcholine is not broken down, it will continue to trigger an action potential in the postsynaptic cell. However, in neuromodulation, neuromodulators bind to receptors that activate enzymes whose action leads to the production of a second messenger in the postsynaptic cell.

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