Non-Hormone Signaling and Nerve Transmission

by Kevin Ahern, PhD

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    00:01 There are other ways that cells can communicate with each other that don’t involve hormones, and I want to say a few words about those.

    00:07 Well, we all know of course of nerve transmission.

    00:10 Nerve transmission is a way for one part of the body to talk to another part of the body.

    00:15 They have all specialized nerve cells that use ion gradients and neurotransmitter molecules to transmit information like, “Hey dummy, you’ve got your finger in the flame, get the finger out of the flame." That goes from the end of my finger into my brain and happens almost instantaneously.

    00:31 This process can be blocked by ion channel blocking molecules.

    00:34 And these often have medicinal purposes, for example, people who have irregular heartbeats, maybe have part of their ion channels within their heart blocked by ion channel blocking proteins to slow down that arrhythmic process. Another type of non-hormone signaling that happens inside the body is that done by the prostanoids, or more commonly called the prostaglandins. These molecules are derived from arachidonic acid and you can see two of them shown in the figure on the right. They’re derived from arachidonic acid which is a 20 carbon molecule and they exert their effects near where they’re released.

    01:08 They don’t travel very far because they’re fairly unstable.

    01:11 There’s a related group of prostaglandin molecules called the prostacyclins and another more distantly related group of molecules called the thromboxanes.

    01:19 And they all have different effects.

    01:22 The synthesis of all the prostanoids however, can be inhibited by steroids.

    01:26 These steroids include hormones like prednisolone and non-steroidal anti-inflammatories like aspirin and ibuprofen.

    01:34 Now, what are they doing? Well the prostaglandins for example are involved in pain responses, among other effects that they have.

    01:42 So when you think of a pain killer, what they’re doing is they’re inhibiting the production of prostaglandins.

    01:47 Those prostaglandins acting very locally in the area they were released.

    01:53 So for example, if you got stung by a bee, the sting that you feel associated with that arises from release of arachidonic acid at the point of the sting.

    02:02 Painkillers help to kill the effects of prostaglandins.

    02:07 Nerve transmission as I said, is a almost instantaneous process that happens.

    02:12 And I want to spend just a few minutes talking about it.

    02:15 A cell at rest, a nerve cell at rest, has a high concentration of sodium outside of it, and a high concentration of potassium inside.

    02:23 That happens as a result of action of a protein called the sodium potassium ATPase.

    02:29 That’s a cell membrane protein that pops sodium out and potassium in, creating what are called ion gradients.

    02:36 When the nerve cell is stimulated, the sodium gates of the nerve cell open.

    02:42 Well if you open the gates, the flood gates, the flood comes in.

    02:45 And the flood that comes in here is sodium.

    02:48 That change of concentration of sodium from outside the cell to inside the cell causes a voltage change.

    02:55 Why’s that? Well sodium is charged.

    02:57 So when you change the charge difference across the cell, there’s a voltage associated with that.

    03:02 And we can see that process happening in the graph on the right.

    03:06 The graph on the right shows, at the end of point one where we see stimulus, we see an increase in voltage and that increase in voltage is the sodium coming in.

    03:15 That change in voltage is called the action potential.

    03:19 Well that action potential is a stimulus for everything else to happen inside that nerve cell.

    03:24 That action potential actually causes this potassium gates to wake up and say, “Hey, there’s too much sodium coming in, we’ve got too many plus charges coming in.

    03:34 Let’s get rid of some of these plus charges".

    03:36 And since potassium is plus charged, it goes racing out of the cell.

    03:40 Well the voltage falls, so we start letting more positively charged molecules out.

    03:45 The action potential which rose is now falling in the process we call repolarisation.

    03:51 Ultimately, the potassium goes too far and it undershoots, that’s the recovery part.

    03:56 We see when it undershoots that too much potassium went out.

    03:59 Well at that point, the gates all close.

    04:01 And then the sodium potassium ATPase picks up and reestablishes the gradients.

    04:06 But why is that important? Well we started the process at one end of a nerve cell that gets propagated all the way along the nerve cell over and over and over and over, until it reaches the end of the nerve cell where a neurotransmitter continues the same signal from that first nerve cell to a second one.

    04:25 Ultimately that pathway makes its way to the brain.

    04:27 Now what’s remarkable is to think, that happens on the order of less than a second.

    04:32 It’s a pretty phenomenal process.

    04:34 After this recovery phase has happened for a nerve cell, the cell is ready to transmit again.

    04:40 Now we can actually see schematically in this figure what’s happening with this process.

    04:46 We see on the left at the bottom that we see a nerve cell has gotten a stimulus.

    04:50 And when that stimulus happens, we have opening of gates that allow the movement of sodium ions shown in red into the nerve cell.

    04:59 We actually see that happening in the second of power over.

    05:03 We see the sodium gates have opened and we see the movement of the sodium ions in.

    05:07 We also see the movement of potassium ions out because potassium is countering that effect.

    05:14 Well the result of that mixing of the two is where we started with a gradient, more sodium out and more potassium in. We now have a pretty even mix of the two. When we take that gradient, what happens is those ions actually start moving through the nerve cell. And they move through the nerve cell, and we can actually see that process happening in the third process over.

    05:34 We’re now in the middle of the nerve cell, we see a more even mixture of the green and the blue dots; the potassium and the sodium ions.

    05:41 That nerve potential has moved from the end of the nerve cell up to the end of that nerve cell.

    05:46 And when it gets to the end of that nerve cell, a neurotransmitter is released that now leaves the first cell, goes to the second cell and starts the whole process over again.

    05:57 So this sequential process of letting ions in and allowing them to move through a nerve cell is how nerve signals actually move through our body.

    06:05 Pretty amazing.

    About the Lecture

    The lecture Non-Hormone Signaling and Nerve Transmission by Kevin Ahern, PhD is from the course Hormones and Signal Transduction. It contains the following chapters:

    • Non-Homone Signaling
    • Nerve Transmission

    Included Quiz Questions

    1. They can be much more rapid than hormone signaling methods.
    2. They include nerve transmission and protein degradation.
    3. They require cells to expand.
    4. They are not as rapid as hormone signaling methods.
    1. It involves changes in ion gradients.
    2. It starts with potassium gates opening.
    3. It has a cell with low sodium outside to start.
    4. It is initiated by ion channel blocking molecules.
    1. The movement of ions across the cell membrane.
    2. The movement of proteins across the cell membrane.
    3. The movement of cAMP molecules across the cell membrane.
    4. The movement of GTP molecules across the cell membrane.
    5. The movement of prostaglandins across the cell membrane.
    1. To move Na+ ions out of the cell and pump K+ ions back into the cell to recover the resting membrane potential.
    2. To move K+ ions out of the cell and pump Na+ ions back into the cell to recover the resting membrane potential.
    3. To move K+ ions out of the cell and pump Na+ ions back into the cell to set the action potential.
    4. To move Na+ ions out of the cell and pump K+ ions back into the cell to set the action potential.
    5. To move Na+ and K+ ions out of the cell to recover the resting membrane potential.

    Author of lecture Non-Hormone Signaling and Nerve Transmission

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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