Neuron Structure, Resting Membrane Potential and Action Potential Quiz

Neuronal Membrane Potential

• Under resting conditions, the neuronal membrane is highly permeable to K+ ions and has a small permeability to Na+ ions.
• The resting membrane potential of a neuron is approximately -65 to -70mV.

Formation of the Resting Potential

• The concentration of K+ is highest inside the cell, while the concentration of Na+ is highest outside the cell.
• Large negatively charged proteins are also trapped inside the cell.
• Sodium-potassium ATPase pumps use the energy of ATP to maintain the K+ and Na+ gradients across the plasma membrane, producing approximately -5mV of the membrane potential.
• Open potassium channels in the neuronal membrane allow K+ ions to freely move out of the cell, down its concentration gradient.

Modeling the Resting Potential

• The resting potential can be modeled by an artificial membrane that separates two chambers with different concentrations of KCl.
• K+ diffuses down its gradient to the outer chamber, building up a negative charge (Cl-) in the inner chamber.
• At equilibrium, both the electrical and chemical gradients are balanced.

Neuronal Structure and Function

• Neurons form networks, transmitting information from a presynaptic cell to a postsynaptic cell.
• Most neurons are nourished or insulated by cells called glia.
• The resting membrane potential is the basis for electrical excitability in the nervous system.
• Ion pumps and ion channels establish the resting potential of a neuron.
• Changes in membrane potential act as signals, transmitting and processing information.

Ion Distribution and Membrane Potential

• The distribution of ions is fundamental to the membrane potential.
• Extracellular fluid mainly contains sodium and chloride ions, while intracellular fluid contains potassium and non-diffusible molecules (e.g., proteins with negatively charged side chains and phosphate compounds).
• The thin shell of ions on the inside and outside of the neuronal membrane determines the membrane potential.

Action Potential Initiation

• The axon hillock, also known as the initial segment, is where action potentials are initiated.
• The action potential is an all-or-none response, traveling along the axon to the synaptic terminal.

Action Potential

• Na+ enters the cell down its chemical and electrical gradient, causing the cell to depolarize.
• The action potential begins when the sodium channel opens, and sodium enters the cell.
• The peak of the action potential reaches approximately +30mV.
• K+ channels open, and K+ begins to exit the neuron, causing repolarization.
• The action potential is complete after hyperpolarization, and the neuron returns to its resting potential.

Nernst Equation

• The Nernst equation is used to calculate the equilibrium potential for one ion only.
• The equilibrium potential (Eion) is the membrane voltage for a particular ion at equilibrium.
• EK (equilibrium potential for K+) is approximately -90mV, while ENa (equilibrium potential for Na+) is approximately +62mV.
• The resting membrane potential is closer to the equilibrium potential for K+ due to the membrane's high permeability to K+ ions.