Neural Action Potential.
Action potentials are electrical signals generated by neurons to transmit information within the nervous system.
Here’s a general overview of the process “neuronal firing” action potentials are generated:
- Resting Membrane Potential: When a neuron is at rest, it maintains a stable electrical charge across its cell membrane. This resting membrane potential is typically around -70 millivolts (mV) and is primarily maintained by the balance of ion concentrations inside and outside the neuron.
2. Threshold Potential: To initiate an action potential, a neuron needs to reach a certain threshold potential. This threshold is typically around -55 mV. If the combined effect of incoming electrical signals (excitatory inputs) from other neurons exceeds this threshold, it triggers the initiation of an action potential.
3. Depolarization: When the threshold potential is reached, voltage-gated ion channels, specifically sodium (Na+) channels, rapidly open in the neuron’s cell membrane. This allows an influx of positively charged sodium ions into the neuron, causing depolarization. The inside of the neuron becomes less negative, and the membrane potential rises.
4. Rising Phase: The influx of sodium ions during depolarization causes a positive feedback loop. As the membrane potential becomes more positive, it triggers the opening of additional voltage-gated sodium channels, leading to a rapid increase in the membrane potential. This results in the rising phase of the action potential.
5. Peak and Repolarization: As the membrane potential reaches its peak, typically around +40 mV, the sodium channels close, and voltage-gated potassium (K+) channels open. Potassium ions move out of the neuron, repolarizing the membrane and restoring the negative charge inside.
6. Hyperpolarization: In some cases, the efflux of potassium ions can cause the membrane potential to briefly become more negative than the resting membrane potential. This phase is known as hyperpolarization and is caused by the delayed closing of potassium channels.
7. Resting State: After hyperpolarization, the membrane potential gradually returns to the resting membrane potential of -70 mV. This is achieved by the activity of ion pumps and ion channels that help restore the ion concentration gradients across the membrane.
When a stimulus is applied to a neuron, such as a sensory input or synaptic input from other neurons, it can cause a change in the membrane potential, leading to the generation of action potentials. The strength or intensity of the stimulus can be encoded by the rate at which action potentials are fired by the neuron. Stronger stimuli tend to elicit a higher frequency of action potentials compared to weaker stimuli.
For example, if a sensory receptor is exposed to a brighter light or a louder sound, the associated neurons will generate action potentials at a higher frequency.
The frequency of action potentials typically ranges from a few hertz (Hz) up to several hundred hertz depending on the stimulus intensity and the specific properties of the neuron.
Brain Waves: different types of brain waves are associated with specific frequency ranges.
- Delta Waves: 0.5 to 4 Hz (Deep sleep)
- Theta Waves: 4 to 8 Hz (Dreaming)
- Alpha Waves: 8 to 12 Hz (Relaxation)
- Beta Waves: 12 to 30 Hz (Cognitive Processing)
- Gamma Waves: 30 to 100+ Hz (Cognitive Processing)
