are various pump systems in the cell, and they are located in the wall (cell membrane) surrounding each cell.
So, what actually causes the creation of the electrical currents? It is the movement of certain ions (such as sodium, potassium, calcium, magnesium) that are pumped through the gated channels in the cell membrane. This pump system utilizes the energy created by the mitochondria and extracts this energy stored in ATP.
| Image # 14 – Sodium Potassium Channel Resting membrane before depolarization |
The ion pump system in the cell wall or membrane – how does it work?
The various pump systems serve to transport certain elements known as ions in and out of the cell through various gated systems.
The cell membrane possesses multiple channels that are gated (have gates). To open and close these “ion gates” to permit certain ions to enter and leave, the gates are fueled by energy from ATP through various pump systems, and thus, ions can pass through the gated channels. Each gated channel can accommodate different ions, and in the mammalian brain approximately 12 ion channels have been identified (Wilson 1999).
Depending on the ion passing through certain types of gated channels, the stimulation or inhibition of electrical impulses can occur to produce less or inhibit the production of electrical impulses in turn. The amount of stimulation or inhibition also depends upon the amount and extent of the movement of certain ions in and out of the cell membrane.
Think of using the energy stored in the ATP battery system to open and close the gate of the channels for ions such as sodium, potassium, calcium, or chloride to pass in and out of the cell.
| Image # 15 – The sodium potassium pump system during depolarization creating an action potential |
For a moment, let us focus on one of the vital gated and pumping systems of the cell. Located in the wall of cells (cell membrane), this is the sodium-potassium pump. This pump is responsible for opening the doors to the sodium-potassium gated channel to allow sodium to enter from the outside, while potassium moves from inside to outside. When this gated channel is open, sodium moves freely into the cell and potassium moves out. With this movement of the two ions (sodium and potassium) across the cell membrane, an electrical gradient or differential is created. An electrical gradient is usually created across the cell membrane when ions move in and out, which implies there is a difference in the electrical charges inside and outside of the cell. This also depends on the concentration of ions inside and outside the cell.
The electrical gradient at a specific point in the membrane will be different from another in the nerve cell, and that creates a current which then prorogates this gradient along the cell, as the next point attempts to have a charge similar to the previous point. When the ions create an electrical gradient that in turn produces a current, a process known as depolarization or activation of the cell membrane is caused electrically. As the current flows to new areas in the cell, it caused more gated channels to open along the path of the current, thus creating more gradients as the current flows.
| Image # 16 – Sodium potassium gate – depolarization action potential to produce electrical current – shows sodium entering the cell |
| Image # 17 – The energy transformation cycle |
| Energy Production Automobile vs the Human Body | ||
| • Categories | Automobile | Human Body |
| • Energy Source | Gasoline | Glucose, Proteins and Fats |
| • Fuel Intake System | Gasoline Tank | GI Track or Intravenous |
| • Oxygen for Combustion | Carburetor/air filter | Respiratory System |
| • Combustion System | Engine | Cell Body – Mitochondria |
| • Energy Production | Electricity/Current | Electricity/Current |
| • Energy Storage | Battery | Adenosine Triphosphate (ATP) |
| • Energy Utilization | Turn on ignition | Turn on Ion Pump System (cell membrane) |
| • Result | Starts Automobile | Open Ion Gates (sodium, calcium, chloride, etc.) |
| • First Message | Electrical/Current | Electrical/current |
| • Energy Transformation | Convert to Mechanical | Electrical to Chemical to Mechanical |
| • Mechanical end point | Movement of Gears | Movement of a body or perform body function |
This electrical gradient is then propagated down along the second part of the nerve cell called the axon.
I know this is getting challenging, but stay with me…
The Axon
The second major part of the nerve cell is the axon, which extends from the cell body (like electrical wires) and end in branches called nerve terminals. The axon has 360-degree insulation along its length like in electrical wires. The insulation system around nerve cells is called the myelin sheath. In the brain, the myelin sheath is created by a supporting cell called the oligodendrocyte. The myelin sheath is divided into small regions, and the junction between each region is known as the node of Ranvier.
In the spinal cord, the myelin sheath is produced by a cell called the Schwann cell, and each Schwann cell serves one region of individual axon insulation. Electrical currents created by the process of depolarization jump or travel the axon from one node of Ranvier to another. This form of jumping electrical currents (messenger) along the axon is called “salutatory conduction” and allows nerves to conduct currents at a faster rate than if the current had flown directly through the axon. Current flowing directly through the axon will experience more resistance, causing the current or electrical messages to decay and slow down. In conditions such as multiple sclerosis, the myelin sheath is damaged, and this causes a slowing of electrical conduction.
| Image # 18 – Saltatory Conduction with node of Ranvier and Schwann cell |
So, let us summarize this first messenger system that the cell utilizes to send messages.
It all starts in the cell body with the utilization of an energy source.
Table # 12 – Energy and the Messenger System
| Cell Body | Creation and propagation of the first messenger | Description |
| Chemical energy source | Glucose, protein, fats | From nutritional intake (GI and IV) to bloodstream |
| Oxygen source | Respiratory system | Lungs and bloodstream |
| Combustion system | Mitochondria | Energy source and oxygen combust to create energy. |
| Chemical energy storage | Adenosine triphosphate (ATP) | Supply of energy to the cell membrane and pump system |
| Pump system | Open ion gates – sodium-potassium, calcium, chloride, or other systems | Utilize ATP as a chemical energy source |
| Create electrical energy | Ions move in and out of cell membrane, causing an electrical gradient in the internal and external environment of the Cell. | Depolarization of the membrane begins – this is the propagation of electrical impulse or energy from the cell body to the axon. |
| Axon – second part of the cell | Propagation of electrical impulse – the myelin sheath with its node of Ranvier allows for rapid saltatory conduction. | To
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