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)
Neurons are cells. There are two cells in the body that are not round. Nerve cells and muscle cells are long and skinny and that's why they are called nerve fibers and muscle fibers. Both of them have the general characteristic of excitability and conductibility (ability to conduct that electrical impulse along that length). Nerve and muscle cells are highly specialized cells in the body. All nerve cells are thinner than a nylon thread and sometimes they are four feet long. The more … [Read more...] about Neurons in the Nervous System
In any physiology book the nervous system takes up a third of the book and it's the most complicated because it controls everything else. Let's review the basic anatomy of the nerves before we jump into the heavy topics. If any of this is new to you, then please review the Anatomy posts about the Nervous System. Central Nervous System and Peripheral Nervous System We divide the nervous system into two parts, the central nervous system and the peripheral nervous system. The central nervous … [Read more...] about Review of the Nervous System
Anatomy versus Physiology, What's the Difference? Here's an analogy that might help: Instead of the human body, imagine you were going to learn how a car works. First you would be taught what all the parts are called, what they look like and where they go. That's Anatomy. After you have been acquainted with what the parts look like, then you could learn what they do and how they function all together with the other parts. That's Physiology. Just like the Anatomy Series, each level … [Read more...] about Human Physiology Series