How does this picture make you feel? Off the bat, most people would say, "Damn, that's crazy." It looks like someone dumped a bunch of trash onto the hills. Is it the end of humanity? Is it a shot from the Inception movie where the surface of the Earth is turning into moving waves? Nope. This is just a part of Naucalpan de Juárez, a large suburb northwest of Mexico City. For perspective, you're only seeing about 2 square miles in this photo. That's all. You're not seeing a city. … [Read more...] about Mexico City Sprawl Porn
Archives for April 2012
We had learned initially that nerve cells exhibit excitability and conductibility. Conductibility is the capacity to conduct the electrical impulse along its pathway. The way the conduction of the action potential occurs along the nerve fiber depends on whether it's myelinated or unmyelinated. Note: All muscle cells are unmyelinated, there is no insulation in muscle cells. Nerve cells could be either. Conduction along an Unmyelinated Nerve Fiber Initially, a threshold stimulus creates an … [Read more...] about Conduction of the Action Potential along the Nerve Fiber
When we talked about the resting cell membrane potential, we mentioned that they figured out the voltage of a neuron by sticking a microelectrode onto the membrane. We could study the generation of AP's in neurons with the information from these probes. Eventually someone thought it would be interesting to stick this into the sensory neuron of an ear so we could understand how the sensory neurons of your ear respond to VOLUME. The problem is there's not a lot of volunteers asking the … [Read more...] about Information and Action Potentials
In this graph to the right, we are shown a neuron and it shows how different intensities of stimuli affect the voltage changes. On the bottom of the graph we see stimuli: starting with a weak stimulus and slowly going to a stronger one. On the top we see our millivolts and when we give a really weak stimulus we have this small little response labeled subthreshold potential. That's not an action potential, it's called a "local response" or "local depolarization" or "subthreshold potential." It … [Read more...] about Subthreshold, Threshold and Suprathreshold Stimuli
Let's use an analogy here. If a guy ejaculates, you gotta wait a little bit before he could do it again. How long does it take to recover from one orgasm before he could do it again? If he's 16 years old, it might take 30 seconds. In a 90 year old it might take several months. This is called the refractory or recovery period between one orgasm to another. Some woman could experience multiple orgasms but that's not really possible with guys. Muscle and nerve cells (excitable cells) need … [Read more...] about Electrical Refractory (Recovery) Period following an Action Potential
Not too long ago we were talking about the resting membrane potential found in every cell of your body. Now it's time to talk about excitable cells (nerve cells and muscle cells) because thery have the ability to generate an action potential. An action potential, or nerve impulse, is a transient (short lasting) reversal in the membrane potential that is conducted down the length of the fiber. This occurs only in excitable cells: nerve and muscle fibers. If you stimulate a liver cell, that … [Read more...] about What is an Action Potential? (Nerve Impulse)
The beauty of the body is the symmetry. Hyperkalemia is simply the reverse of hypokalemia. Normally potassium is 150mEq/L on the inside and 5mEq/L on the outside with a 90mV electric potential on the inside. Let's pretend the potassium levels start to increase in the ECF. That's going to make potassium start to flow inside. What's that going to do to the voltage of the cell? It's going to make it less negative than normal and the term we use for that is depolarized. Why? Because potassium … [Read more...] about What is Hyperkalemia?
Now that we talked about what makes up the resting cell membrane potential, let's talk about the effect of a low potassium ion concentration [K+]ECF on the resting cell membrane potential called hypokalemia. We know as long as the K+ concentration is 150 mEq/L inside and 5 mEq/L outside, everything is in equilibrium and the voltage inside the cell is 90mV and that negativity is preventing anymore positive charges from flowing out. If the potassium levels outside the cell start to drop, … [Read more...] about What is Hypokalemia?
We're going to deal with electricity because we're going to be talking about the electrical properties of cell. So first let's get acquainted with some basic electrical concepts. Basic Electrical Concepts 1) There are positive charges and negative charges. What is the origin of these charges? We have protons and electrons. We know that if there is a difference in either two, there is a polarity. Even in a large molecule like a protein molecule, if the electrons exceed the protons, then … [Read more...] about The Resting Membrane Potential
If any of the structures sound unfamiliar to you, please review the relevant anatomy post: Protection for the Brain: Meninges, CSF, Blood-Brain Barrier Formation of the CSF Cerebrospinal Fluid is produced by the choroid plexus within the ventricles of the brain. Our first thought is, what is the choroid plexus? It's a vascularized membrane, a membrane with a lot of blood vessels. Now where is this membrane? Inside the ventricles (chambers) of the brain. Remember, CSF has a chemical … [Read more...] about Cerebrospinal Fluid (CSF)