Why does an active potential create an electric impulse?

[scilearner]

I read about it but I don't get it. I can understand how current would flow if one side is positive and other negative but I don't understand what is happening in an axon

 

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I don't understand how current is flowing is it flowing vertically?. What is this electric impulse? Also since at resting potential there is a difference of voltage. Why doesn't this cause electrical impulse. Please help. Thanks

[StrontiDog]

. . .I can understand how current would flow if one side is positive and other negative but I don't understand what is happening in an axon. . .

 

Axons are part of a nerve. Nerve impulses aren't really the same thing as a wire conducting electricity.

 

Basically, the nerve cell is just passing a signal to another nerve cell (through the axon) and the thing physically lets go of a chemical neurotransmitter which tells the next nerve to do the same thing. It is much slower than electricity (~600 mph), it is a one-way only trip, and can be started anywhere along the line.

 

Electric shock can cause a muscle twitch only because it can cause the nerves to fire. We can measure a current off of nerves because they work by a flow of ions through a membrane, but they still arent the same thing as an electrical wire carrying a current. Each nerve cell is like a little power plant and their only function is to tell the next nerve in line to do the same thing that it just did.

 

Help any?

[scilearner]

Axons are part of a nerve. Nerve impulses aren't really the same thing as a wire conducting electricity.

 

Basically, the nerve cell is just passing a signal to another nerve cell (through the axon) and the thing physically lets go of a chemical neurotransmitter which tells the next nerve to do the same thing. It is much slower than electricity (~600 mph), it is a one-way only trip, and can be started anywhere along the line.

 

Electric shock can cause a muscle twitch only because it can cause the nerves to fire. We can measure a current off of nerves because they work by a flow of ions through a membrane, but they still arent the same thing as an electrical wire carrying a current. Each nerve cell is like a little power plant and their only function is to tell the next nerve in line to do the same thing that it just did.

 

Help any?

 

I'm assuming this is like a wire conducting electricty. Where postitive ions flow from negative to positive. Now looking back I think I'm wrong. So what happens. This is my new understanding please tell me if this is right.

 

1. When they say voltage travels across the axon what to they mean?

Do they mean that required ion channels open or close creating depolarization inside the membrane. Is is it the gradual increase of depolarization that makes the voltage travel across.

2. What to they mean when an action potential is fired?

3. How is neurotransmitter released as an action potential?

How does it know depolarization has occured.

4. Why hyperpolarization doesn't create much action potential?

5. In the resting potential -70mv there is still a voltage difference?

Why are ion channels not open at this stage. Is this the norm and ion channels are not designed to open at this potential

6. Apart from neurotranmitter ions can also be released. How does this occur?

7.How does frequency of a signal affect strength of muscle contraction?

Thanks a lot!!

Edited January 7, 2010 by scilearner

[StrontiDog]

 

1. When they say voltage travels across the axon what to they mean?

Do they mean that required ion channels open or close creating depolarization inside the membrane. Is is it the gradual increase of depolarization that makes the voltage travel across.

2. What to they mean when an action potential is fired?

3. How is neurotransmitter released as an action potential?

How does it know depolarization has occured.

4. Why hyperpolarization doesn't create much action potential?

5. In the resting potential -70mv there is still a voltage difference?

Why are ion channels not open at this stage. Is this the norm and ion channels are not designed to open at this potential

6. Apart from neurotranmitter ions can also be released. How does this occur?

7.How does frequency of a signal affect strength of muscle contraction?

Thanks a lot!!

 

Sorry, but you're still thinking along the lines of a wire. This is electrochemistry, not electricity.

 

Try this website, it's the best I've found to explain what you're asking.

 

http://www.bris.ac.uk/synaptic/public/basics_ch1_2.html

 

The other thing to remember is that the nerve cell either fires all the way or it doesn't fire at all. There is no such thing as a stronger or weaker nerve impulse. If you're straining harder or lifting a larger load, it just means that the nerves are firing more often and/or more nerves are firing to trigger the muscle contraction.

 

Number seven is the only question you're asking that even has an answer, but you're not gonna like it.

 

Muscle contractions are like nerve impulses. They get the order and they contract. None are stronger or weaker unless the chemicals needed to make this happen are in short supply. Again, it's all or nothing when it comes to muscle fiber contraction.

 

The difference between picking up a 5 lb or a 50 lb weight is in how many muscle fibers are involved. Each one, however, just does what it's told and either contracts on demand, or not.

 

Hope this helps, a little.

[Mokele]

Again, it's all or nothing when it comes to muscle fiber contraction.

 

Minor technical note: this is only true for vertebrates. Invertebrate muscle fibers can respond in a graded way to levels of neural stimulation (which, in turn, allows them to get away with having very few motor units per muscle, usually less than 10, and often only 3 or so).