Biology Lecture Notes (STEMer’s guide) 2024 Lecture (3) Resting potential – Action potential Mr. Youssef Nagah Biology Lecture Notes Y. Nagah 2 | P a g e Ion pump and ion channels establish the resting potential of a neuron As you know, ions are unequally

Biology Lecture Notes (STEMer’s guide) 2024 Lecture (3) Resting potential – Action potential Mr. Youssef Nagah Biology Lecture Notes Y. Nagah 2 | P a g e Ion pump and ion channels establish the resting potential of a neuron As you know, ions are unequally distributed between the interior of cells and the fluid that surrounds them. As a result, the inside of a cell is negatively charged relative to the outside. Because the attraction of opposite charges across the plasma membrane is a source of potential energy, this charge difference, or voltage, is called the membrane potential. • The membrane potential of a resting neuron—one that is not sending a signal— is its resting potential and is typically between 60 and 80 mV (millivolts). • Inputs from other neurons or specific stimuli cause changes in the neuron’s membrane potential that act as signals, transmitting and processing information. • Rapid changes in membrane potential are what enable us to see a flower, read a book, or climb a tree. Thus, to understand how neurons function, we first need to examine how chemical and electrical forces form, maintain, and alter membrane potentials. Formation of the Resting Potential Potassium ions (K+) and sodium ions (Na+) play an essential role in the formation of the resting potential. Each type of ion has a concentration gradient across the plasma membrane of a neuron, (as shown in the table). • In case of mammalian neurons, the concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside. • These Na+ and K+ gradients are maintained by sodium-potassium pumps in the plasma membrane. These ion pumps use the energy of ATP hydrolysis to actively transport Na+ out of the cell and K + into the cell (as shown in the Figure). • There are also concentration gradients for chloride ions (Cl-) and other anions, but we will ignore these for the moment. Biology Lecture Notes Y. Nagah 3