Communication between nerves and the brain

[canadianpoet]

This is quite a specific question, and I'm not entirely sure how to word it, but I'll try to keep it simple and see if it makes sense!

 

When you touch your finger, the nerves in it tell your brain that it is your finger that you are touching. When you touch your leg, your brain is told that it is your leg. My question is:

 

How are the signals from the nerves transmitted to the brain in such a way so that the signals from your finger are different from the ones from your leg? Does anyone know if they are modulated in some way, with headers and data packets, like computers use? What is the bit-rate and propagation speed of these signals?

 

Any information would be most welcome, and I am a nosey person!

[ecoli]

Well, there are different nerves sending the signal to different parts of the brain.

[canadianpoet]

I'm aware of that!

 

But how does the brain know where the signals have come from? What, within the signal, identifies it as a signal from a specific part of the body?

[Kygron]

But how does the brain know where the signals have come from?

The neuron from the leg has the leg-signals, the neuron from the finger has the finger-signals.

 

What, within the signal, identifies it as a signal from a specific part of the body?

Absolutely nothing.

 

Your brain is a system of learning. When you were just developing the brain had no way of determining where any signal came from. You now know that your finger is touched because when it happens you remember seeing (and using other senses) your finger touched last time.

 

To use your computer analogy, would you even need headers if EVERY SINGLE connection had it's own cable?

[Glider]

The primary somatosensory cortex is topographically representative of the body. Nerve impulses from your finger terminate in the part of the somatosensory cortex that is dedicated to your finger, and signals from your leg go to the area dedicated to your leg.

[husmusen]

I always thought that the spinal cord did a huge amount of

pre-processing before the signal got anywhere near the brain?

And that similarly, a signal leaves the brain as a high level instruction

and by the time it leaves the spinal cord has been translated into

a whole bunh of instructions to a whole bunch of muscles.

 

That's part of the reason why when using basic V2.0 yonks ago I could

type the words 'data' and 'poke' in about 1/10th of a second.

I also thought there were neural clusters at major joints that also

did some processing of the signal. Although I could be wrong on this.

 

But there is some pretty beefy neural hardware in the spine, that's second

only to the brain, I find it hard to believe it's just conducting a simple

signal from A to B.

 

Cheers.

 

Edit: Possibly related issue.

Regarding nerve pulses in the leg, what is a spinal echo?

[Glider]

I always thought that the spinal cord did a huge amount of

pre-processing before the signal got anywhere near the brain?

And that similarly' date=' a signal leaves the brain as a high level instruction

and by the time it leaves the spinal cord has been translated into

a whole bunh of instructions to a whole bunch of muscles.[/quote']

A lot of processing does happen in the spinal cord, but it is the somatosensory cortex that is responsible for localisation. The target for descending signals is determined by which area of the motor cortex they originate in, not the spine.

 

That's part of the reason why when using basic V2.0 yonks ago I could type the words 'data' and 'poke' in about 1/10th of a second.

That's mainly because they were learned series of fine motor actions controlled by the cerebellum.

 

I also thought there were neural clusters at major joints that also

did some processing of the signal. Although I could be wrong on this.

There are clusters of receptors at joints, but these are proprioceptive and provide feedback to the brain concerning the relative positions of the joints.

 

But there is some pretty beefy neural hardware in the spine, that's second only to the brain, I find it hard to believe it's just conducting a simple

signal from A to B.

There isn't really much 'beefy neural hardware' in the spine. Most (though not all) sensory pathways are quite simple 3 neuron pathways: From the receptor to the dorsal horn of the spine, from the dorsal horn to the thalamus, and from the thalamus to the appropriate areas of the somatosensory cortex.

 

Edit: Possibly related issue.

Regarding nerve pulses in the leg, what is a spinal echo?

No idea I'm afraid.

[husmusen]

There are clusters of receptors at joints, but these are proprioceptive and provide feedback to the brain concerning the relative positions of the joints.

 

Ahh, grok.

 

The cortex keep track of internal location, i.e. which limb.

The nerve clusters keep track of angular joint displacement or

in other words, where *that* limb is in space.

 

Thanks.

 

That's mainly because they were learned series of fine motor actions controlled by the cerebellum.

 

This may be getting too detailed, but are the memories stored in

the motor cortex and sent as a stream, or does the cortex send of

a single signal which triggers a burst of chatter from the spinal

cord to the fingers.

 

Cheers

 

P.S.

In answer to one of the first posters questions.

I was told by a neurologist that the normal impulse speed for myelinated nerve fibers from toe to lumbar spine was 6-8 milliseconds if that's any help.

[Glider]

This may be getting too detailed' date=' but are the memories stored in

the motor cortex and sent as a stream, or does the cortex send of

a single signal which triggers a burst of chatter from the spinal

cord to the fingers.

[/quote']

The cerebellum is involved in learned motor skills, i.e. motor actions that are practiced. These, in effect, become 'ballistic' motor actions, insofar as once they are initiated, they tend to run to completion without any higher input. This is why, for example, a practiced pianist can hold a conversation at the same time as playing a piece that s/he knows well. Driving is much the same. We drive automatically, and provide 'higher' cognitive input only to modify the action, not to carry it out.

[j_p]

Your brain is a system of learning. When you were just developing the brain had no way of determining where any signal came from. You now know that your finger is touched because when it happens you remember ...

 

Are you certain about that? I learned in developmental biology:

 

The nerves originate in the developing brain; an excess are produced; those that connect with the appropriate tissue survive and the rest atrophize and are re-absorbed.

 

The evidence was an experiment in which either the sensory nerves or the ennervated tissue from the back and the front of a developing mouse where switched; the resulting mouse scratched its back in response to stimulus on its stomach.

 

Has that been disproven?

[Kygron]

The nerves originate in the developing brain; an excess are produced; those that connect with the appropriate tissue survive and the rest atrophize and are re-absorbed.

 

appropriate tissue? and how do they know that? As far as I heard the brain cannot be hard-wired, so some learning has to take place in development.

[j_p]

appropriate tissue? and how do they know that? ...

 

Are "they" the developing nerves? Haven't a clue, I'm a chemist.

 

Thinking back, the shift toward chemistry probably started in the Developmental Biology class. The experiments we learned about were disquieting to say the least. I found the technical expertise and the design of the experiments fascinating, but envisioned the poor mouse doomed to a life of never being able to scratch an itch.

[The Brind]

What is the bit-rate and propagation speed of these signals?

 

Nerve impulses travel at speeds of up to 120 meters per second.

 

I'm not entirely certain that bit-rate is an appropriate term for the type of information processing that the nervous system is involved in.

 

Remember the "brain is a computer analogy" is just that, an analogy. In reality the brain is not a computer of the sort that you seem to be familar with.

 

For a start it is massively parallel. There is no Pentium bottleneck. Hence, there is no need for signals to be different because they do not terminate in the same place.

 

information flows through the nervous system like water flows down a river bed. It ends up in the place that it needs to because either that is the path that it has always traveled or that is the easiest path for it to flow.

[canadianpoet]

Thank you for all you replies. I have learnt quite a bit. I'm very surprised that the brain is a parallel system! And the neuron speed was also a bit of a surprise.

 

On a related topic, now that I've got interested in this. Is it possible to 'pick up' the nerve impulses from a finger say, as they travels up your arm. Going back to the computer analogy for a second; is it possible to intercept the signals in a computer, and view them on an oscilloscope. I'm aware that you can view brain waves, but is it possible to view the inputs to the brain, before they reach the spinal column? And obviously, if possible view them on an oscilloscope!

[The Brind]

On a related topic, now that I've got interested in this. Is it possible to 'pick up' the nerve impulses from a finger say, as they travels up your arm. Going back to the computer analogy for a second; is it possible to intercept the signals in a computer, and view them on an oscilloscope. I'm aware that you can view brain waves, but is it possible to view the inputs to the brain, before they reach the spinal column? And obviously, if possible view them on an oscilloscope!

 

It is possible to record the activity of single neurons using a technique somewhat appropriately called "single cell recording". The data can be viewed using an oscilloscope but we wouldn't try to measure the response from your finger because it is an invasive technique that can damage neurons.

 

Instead single cell recording is a technique used only on animals. Basically you stick an electrode into the body near but not within the neuron and it measures the action potential (the nerve impulse). Unfortunately sticking electrodes into brains is a rather cumbersome procedure that destroys cell in the process.

 

Don't try this at home kids!

 

Anyway where are the neuroscientists.... I'm winging it here a bit... someone correct me if I'm wrong...

[bascule]

If you'd really like to know how nerve impulses work you would do yourself well to read Hodgkin and Huxley's papers, for which they were awarded the Nobel prize in 1963:

 

http://neuron.duke.edu/niasite/nia2000/neurolab/pdf/h&hk1952.pdf

http://neuron.duke.edu/niasite/nia2000/neurolab/pdf/h&h1952a.pdf

http://neuron.duke.edu/niasite/nia2000/neurolab/pdf/h&h1952b.pdf

http://neuron.duke.edu/niasite/nia2000/neurolab/pdf/h&h1952c.pdf

http://neuron.duke.edu/niasite/nia2000/neurolab/pdf/h&h1952d.pdf