Let's get started. So today, as I mentioned, that we are going to cover the electrical part of a neuron. That is to cover the hollow neurons, since, let's put it this way, generate the electrical signals. And then, they can, since the electrical signal propagated to trigger the downstream reactions, most importantly, transmitter release. And this is a very important aspect of neurosystems, because that is how the neurons conveyed the signal from one part of your body or your brain to the downstream targets. The longest neuron in a human may be one meter long from your spinal cord going down to your toe. And how the information is carried from this spinal cord region into the toe is through the electrical signal. The so-called, action potentials. And this is what we are going to discuss. We are going to spend quite some time and then we are going to start with some fundamentals. So this is a typical example of how the information travels in the nervous system. For example, in the peripheral site, the cell signals from the muscles get sensed by the sensory neuron, which a cell body is located close to the spinal column, inside ganglions. And then, this information get transferred to the downstream target neuron, the motor neuron. And why is it a motor neuron get activated? You will subsequently activate the effector target and not a muscle in this case, okay? So, in fact, this is one of the simplest neurocircuit for your reflex, okay? That is, you'll sense the signals without information processing in your central brain. Your immunity cause the muscle contraction and then you will bend your knee, for example. This process illustrates how the information get propagated. Transferred within the same neuron. And then neuronal communications. And then neuron communication with the targets, okay? And more complicated circuits could be a combination of those connections, ways modifications. For example, there will be inhibitory modifications. There will be some learning process to alter the strings of neural communication, or to alter the excitability of the neuron or the targets. With all those countless combinations, that's how our nervous system can do many, many different things. And today, we are going to focus on electrical signaling path of the nervous system. Now, it is during the peripheral site sensing, usually this sensory organ or cells will generate a receptor potential which is not all or none. It's a graded or analog signals that have different amplitudes that reflecting different effectiveness of the sensory. For example, how strong the light intensity might be. But in the neurons, once neuron receiving this graded or analog signals, it will convert this signal into the so-called all or none action potentials or called APs. This is like digital signals. And by the frequency of the APs, the action potentials, the information is encoded and then get transferred to the synapse, the chemical synapse in this case, that the action potential propagate to the nerve terminals will cause transmitter release. Again, the transmitter release will generate the synaptic potential, still graded, analog signals. But, once they reach the action potential, you can get converted into this OO Nam, digital signals get converted back, okay? And we are going to discuss how those electrical potential get generated and how could the action potential have such funny or unique shape, okay? What is the mechanism this action potential can form and can propagate? What is the molecular basis of this action potential? We know, for example, there's special ion channels that mediate the generation of action potential. Those ion channels are with altruistic activity. They can distinguish sodium with potassium. Eventually we're going to discuss what kind of gene or protein that cause for those sodium or potassium tremors. And what is the structural feature that determines this special selectivity for those ion channels? So, that's what we are going to discuss and the logic will be, we are going to start with the mechanism of the action potential and its generation propagation. And historically, this is also the sequence when people understand how you generate and propagate and the development of molecular biology, for example, that lead to the identification or cloning of those ion channels. And the structure studies illustrate at atomical resolutions how those proteins fought and then achieved an ion permeability pathway with increasing sensitivity. Allow sodium to pass in through for voltage-gated sodium channels. Allowed potassium to pass in through for the potassium channels. And there are great heroes that, Make quantum leap for those discoveries and they get Nobel Prize, for example, some of them didn't get Nobel Prize but deserve our honorable mention. So this is, for example, Sir Hodgkin and Sir Huxley. British scientists, originally electronic engineers, but studied neuroscience which illustrate the action potential mechanism, the sodium and potassium channels. And this great Japanese scientist, Shosaku Numa, who unfortunately died around the age of 50, that single-handedly count almost all the ion channels including voltage-gated channels and ligand-gated ion channels. For example, and still common receptors that we're going to discuss in the subsequent lectures. So this is the outline. We have the physics major students, so we are going to illustrate very complicated physics, which is Ohm's law, Ohm invented. We are going to talk about the mechanism of resting membrane potential, Nernst equation, and how the cell membrane can be think of circuit composed of capacitance, resistance and how they are connect. And how the heroes, Hodgkin, Huxley almost single-handedly established the mechanism of action potentials. That is the logic.
