Resting Potential in Neurons (2)

Resting Potential in Neurons

• Neurons are always resting until stimulated.

Membrane Ion Concentrations

• Important Ions involved:

  • Sodium ions ($Na^+$)

  • Potassium ions ($K^+$)

  • Chloride ions ($Cl^-$)

• Concentration gradients for ions:

  • Sodium ($Na^+$): higher outside the cell.

  • Potassium ($K^+$): much lower outside the cell, higher inside the cell.

Na+/K+ Pump

• The sodium-potassium pump operates continuously:

  • Pumps 3 sodium ions ($Na^+$) out of the cell and 2 potassium ions ($K^+$) into the cell.

• This mechanism is ATP-dependent, produced in the mitochondria of cells.

• Energy for the pump is derived from ATP, which is made by the process of degrading ADP + Pi (inorganic phosphate).

Ion Channels

• Types of Channels:

  • Nongated Channels:

  • Allow specific ions to pass without the need for stimulation.

  • More potassium channels than sodium channels in resting neurons.

  • Gated Channels:

  • Open only in response to a specific stimulus (e.g., neurotransmitter binding).

Resting Potential

• The resting potential of a neuron is defined as an electrical charge across the cell membrane when the neuron is not being stimulated.

  • Typically around -70 millivolts (mV) inside the neuron and positive outside.

• This potential represents a store of negative energy on the intracellular side relative to the extracellular side.

Equilibrium of Ions

• Equilibrium is reached when the forces of the concentration gradient are equal and opposite to the voltage gradient:

  • Concentration gradient drives ions in one direction while voltage gradient drives them in the opposite.

• There is no net movement of charge at equilibrium as ions cancel each other out,

  • However, the resting potential is maintained by:

  • Movement of potassium ($K^+$) ions out of the cell through nongated channels.

  • A small number of sodium ($Na^+$) ions moving into the cell, counterbalanced by the functionalities of the $Na^+/K^+$ pump.

Glial Cells

• Support and maintain the resting potential and concentrations of ions, thus contributing to the overall health and functionality of neurons.

Excitatory Postsynaptic Potential (EPSP)

• After neuron stimulation, neurotransmitters (transmitters) bind to the postsynaptic neuron's receptor, leading to:

  • Opening of neurotransmitter-gated ion channels.

  • This process occurs at the presynaptic terminal and takes about 1-2 milliseconds.

• The binding creates an excitatory postsynaptic potential by allowing sodium ions to enter the cell, making the inside of the neuron more positive and potentially triggering an action potential if the threshold is reached.

Key Concepts

• The resting potential is a crucial aspect of neuronal function as it stores energy and prepares neurons for the rapid transmission of electrical signals upon stimulation.

• The reliability of the resting potential relies heavily on sodium-potassium pump function, ion permeability, and glial cell support.