16.9:
Electrochemical Gradient and Channel Proteins: An Overview
Impulse transmission in a neuron depends on— the presence of membrane potential and channel proteins.
Neurons have a small build-up of negative charge inside the cell membrane and a similar accumulation of positive charge on the outside, creating a membrane potential.
The flow of ions across the membrane can change the membrane potential. This flow of ions— or current, generates electrical impulses — making the neurons electrically excitable.
The direction of ion movement is largely determined by their electrochemical gradient. It is a combined effect of a concentration gradient, where the ions flow from an area of higher to lower concentration, and an electrical gradient, where the ions tend to flow towards an area of opposite charge.
Because the cell membrane is impermeable to charged particles, they can only flow through specific proteins called ion channels.
These channels can be non-gated, which opens and closes randomly, or gated, which requires a stimulus to open.
The controlled opening and closing of these channels allow for a unidirectional flow of electrical impulses from one dendrite to the axon terminal in a neuron.
16.9:
Electrochemical Gradient and Channel Proteins: An Overview
An electrochemical gradient is a fundamental concept in biology and chemistry. It regulates the movement of ions across cell membranes. This movement is influenced by two factors:
The electrical gradient: The electrical gradient across cell membranes refers to the difference in electric charge between the inside and outside of a cell. This difference drives the movement of ions towards or away from the cells. For instance, if the inside of the cell is more negatively charged relative to the outside, positively charged ions or cations are attracted to the inside of the cell, while negatively charged ions or anions are repelled.
The chemical gradient: Ions naturally move from areas of high concentration to areas of low concentration, a process called diffusion. This is driven by the principle that things tend to spread out and reach equilibrium.
Together, these gradients create an electrochemical gradient, which influences the movement of ions across cell membranes. It is crucial for various biological processes, like nerve signaling, muscle contraction, and nutrient uptake.
Channel Proteins
Channel proteins are specialized molecules embedded in cell membranes. They act like gates, allowing specific ions to pass through the membrane. These proteins are vital in maintaining the cell's internal environment and regulating processes such as nerve impulse conduction and muscle contractions.
Channel proteins have a specific three-dimensional structure that forms a pore or channel through the cell membrane's lipid bilayer. This channel allows ions to pass through but is selective, meaning it only allows ions of a specific size and charge to traverse. For example, potassium channel proteins are designed to allow only potassium ions (K+) to pass, while sodium channel proteins permit only sodium ions (Na+). This selectivity is determined by the shape and charge of the channel's interior.
Channel proteins can be regulated to control the flow of ions. Some channels open and close in response to changes in voltage (voltage-gated channels), while others respond to chemical signals (ligand-gated channels).