Action Potential- Electrical Transmissions

Focus on internal communications within the axon part of neurons.
Importance of identity in neuronal signaling.
Ions can sense concentration gradients; they move to equalize concentrations in their environments.

Cells contain various ions and molecules that affect charge dynamics.
The liquid inside a cell (intracellular fluid) differs in ionic concentration from the surrounding extracellular fluid.
Analogy: Think of a water balloon filled with juice inside a pool; the fluids do not mix immediately across the membrane.

High concentration of sodium ions ($Na^+$) is found in extracellular spaces.
Two primary forces driving ionic movement:
- Concentration gradient.
- Electrical gradient.
Sodium ions are highly positively charged, creating a significant difference in potential across the cell membrane.

Resting membrane potential in human neurons is approximately -70 mV.
- The inside of the neuron is more negatively charged compared to the outside.
- This difference in charge needs to be maintained for neuronal function.
Sodium-potassium pump actively works to keep sodium out and potassium ($K^+$) in, which is energy-intensive (uses ATP).

Neurons fire an action potential when a specific threshold is reached, causing sodium channels in the axon membrane to open.
Depolarization Phase:
- A rapid rise in the membrane potential occurs when sodium enters the cell, transitioning from -70 mV to a more positive charge.
- Sodium channels open at a predetermined voltage threshold, allowing a wave of depolarization to travel along the axon.

After depolarization, repolarization occurs, where the membrane potential is reset to -70 mV.
Potassium channels open at higher positive voltages (e.g., +40 mV), allowing potassium to exit the cell, thus dropping the membrane potential back towards resting levels.
This process helps maintain the directional nature of action potentials (unidirectional flow).

Sodium channels are voltage-gated and designed to respond to changes in membrane potential.
Channels can become inactivated for a brief period after opening, preventing immediate reopening (refractory period).
The dual nature of channels means they respond to different voltage stimuli (like different keys for different locks).

Neuron axons can be modeled as continuous tubes with sodium channels along their length; however, they cannot be infinitely long due to size constraints and signaling speed requirements.
Myelination:
- Myelin sheaths act as insulation around axons, enhancing signal speed and efficiency by affecting capacitance.
- Myelin allows for saltatory conduction, where action potentials 'jump' between nodes of Ranvier rather than traveling continuously along the axon. This speeds up signal transmission significantly.

Visualization of action potentials shows more efficient signal jumps with myelination compared to non-myelinated sections.
The functionality of myelinated axons permits rapid response in situations like reflexes (e.g., moving away from potential danger).

Overall neural communication boils down to a yes/no binary system—whether an action potential occurs or not.
Translating these simple signals into complex functions (e.g., speech, movement, feelings) reflects the sophisticated neural architecture of the human brain.

Simplified analogy to binary code (1s and 0s) or Morse code (short and long signals) explains the nature of signal patterns in neurons.
Understanding brain signals through patterns rather than counting individual nodes of activation informs the study of neural responses and behavior (e.g., preference for sugar water in rats).

Revisit video materials and reading materials listed to deepen understanding of these processes, as the information presented is dense and complex.