What essentially makes up brain matter?

[einsteinian77]

What essentially makes up brain matter? I mean the very composition of neurons.

 

[Mentat]

Originally posted by einsteinian77
What essentially makes up brain matter? I mean the very composition of neurons.

You mean like, what are dendrites and axions composed of...I really don't know.

 

[Monique]

Good question, I'd actually like to know what is the difference between white and grey matter. We need Zoobyshoe!

The composition of neurons.. basically they are just very long stretched cells with a sheeth of insulating myelin around it.

 

[iansmith]

If i remember my physiology and anatomy course corectly

The gray matter is the actual cell, i.e. the nucleus and most of the organelles

The white matter is the mylenoid fibers, i.e. axion that are coated with some other cell which have a lot fat in them.

 

[einsteinian77]

A couple other questions if you don't mind. Is that myth true that once a brain cell dies it can never grow back? how many connections do neurons have with each other? and do neurons use electricity to communicate through these connections?

 

[Gale]

And i have a few questions too... and no point starting a new thread if it can just be answered here.

How does the whole imprinting thing work? i mean when like a signal is sent through the cells that cell has some sort of memory of it right? er... am i confused, if so straighten me out. And, however that imprinting memory thing works, is theee some limit to it? And do the cells just die from old age, or does headbanging really kill more? how do drugs kill brain cells?

...yeah, that's all... for now.

 

[einsteinian77]

I doubt if anyone will respond to such a large number of questions oh well

 

[Another God]

Thats not true. As long as all of the questions are good questions, if anyone knows the answers, they will reply. I would love to reply, but unfortunately I don't know brain stuff. Dark Wing knows some stuff, but she's busy and won't log on for me ( @ her).

I could make some guesses, but I will wait a little while to see if someone else who actually knows comes in and answers them for you. Otherwise I will do a little bit of looking around online and see what I can find.

I am pretty sure I can answer gales question about cells dying from old age though: taking knowledge from other cells of the body, I can safely guess that brain cells die randomly just like every other cell in the body. Due to gradual DNA damage from chemicals/Radiation/oxidative damage mistakes can build up and the cells last line of defence is to destroy itself (to protect everything else). So yeah, cells do die 'from old age'.

I'm not sure how drugs speed this up (other than to take a guess at the fact that they introduce some foreign chemical into the environment which may be harmful, but you could have guessed that yourself) or how headbanging affects it.

 

[Monique]

Originally posted by einsteinian77
What essentially makes up brain matter? I mean the very composition of neurons.

You might be interested at looking at the following picture, it is a cartoon of a neuron. The myelin sheeths you see are actually specialized cells that wrap themselves around the axon, which insulates it. The impuse will actually jump across these 'Schwann cells', from node of Ranvier to node of Ranvier. Some axons can grow up to a meter long, a single cell!

*edit* I forgot to put in the picture

http://www.botany.uwc.ac.za/sci_ed/grade10/mammal/images/neuron.gif

 

[Monique]

Originally posted by einsteinian77
A couple other questions if you don't mind. Is that myth true that once a brain cell dies it can never grow back? how many connections do neurons have with each other? and do neurons use electricity to communicate through these connections?

We are born with an excess of neurons, during the first 5 years of life most of these neurons will die if they are not used. We still have an excess though, and throughout life more and more will die, since an unused neuron doesn't get the stimulation it needs to survive.

1) It is true we can't grow new neurons, generally. I have heard about research in which blood cells were actually differentiating into neurons and stem cells can be implanted into the brain, which will also can differentiate into neurons. But the research on that is very new, basically, if it dies, it is gone.

BUT: our brain is very adept to taking over functions when damage occurs in the brain.

2) Hard question, I don't know.. many many many I guess.. as you can see in the cartoon I gave before, there are two sides to the neuron. The head = cell body, which has many branches called dentrites. These dentrites connect to the bottom end of other neurons. Many dentrites = many connections. You can also see that the bottom of the neuron has many branches.

3) No, neurons do not use electricity to communicate between connections. Do you understand German? If not, I apologize, but I like the following cartoon: http://gfx.m-ww.de/synapse.jpg What you see is a synapse, the connection between two neurons. The electrical signal moves through one neuron and reaches the end, here it activates channels, which release a neurotransmitter. This neurotransmitter is released into the synaptic cleft, where it binds to receptors of the other neuron. These receptors again stimulate the propagation of an electrical signal.

Now, Gale's questions.. :P

 

[Monique]

Originally posted by Gale17
How does the whole imprinting thing work? i mean when like a signal is sent through the cells that cell has some sort of memory of it right? er... am i confused, if so straighten me out.

Well, I had a whole discussion with Zoobyshoe.. there is a catch phrase: "neurons that fire together wire together". He says the saying is wrong, but it comes down to the following concept:

Neurons can remember past routes taken, since two neurons which cooporate in passing down an electrical signal will actually 'wire' together more tightly. While if two neurons don't pass down an electrical signal, their connection will become more loose. If a neuron is not stimulated at all, it will die.

An excerpt from the textbook Albert et al, Molecular Biology of the Cell (I had posted it in another thread, might as well copy it here)

Synapse modification and its dependence on electrical activity.
Experiments in several systems indicate that synapses are strengthened or weakened by electrical activity according to the rule shown in the diagram. The underlying principle appears to be that each excitation of a target cell tends to weaken any synapse where the presynaptic axon terminal has just been quiet but to strengthen any synapse where the presynaptic axon terminal has just been active. As a result, "neurons that fire together, wire together." A synapse that is repeatedly weakened and rarely strenghened is eventually eliminated altogether.

Hope that helped!

 

[einsteinian77]

Thanks a lot monique that was very educational for a person like me. I'm still a little lost as to how the brain thinks on a large scale but anyway you answered my questions to the fullest, thanks.

 

[Mentat]

I have a question...

Isn't the neurotransmitter mostly composed of sodium ions, which are kept in packets at the end of the axon?

 

[Monique]

Great!

The workings of the brain at a large scale are mainly researched by looking at pathologies, e.g. due to stroke.

If part of the brain dies off due to a blood cloth and that person develops problems in recognizing faces, we know spatially where that region is located in the brain.

Then there are many different structures in the brain itself.. I am not too sure about the processing myself :)

 

[Monique]

Originally posted by Mentat
Isn't the neurotransmitter mostly composed of sodium ions, which are kept in packets at the end of the axon?

Those are actually along the axon at the nodes of Ranvier, for the propagation of the electrical signal. The sodium ions cause a potential to build.. I DO think that the sodium channels are LINKED to the neurotransmittor gates. So when there is a flux of sodium across the membrane, a flux of neurotransmitter is the consequence.

Dopamine is an example of a neurotransmitter, lack of it can cause depression.

 

[Monique]

Actually, more in detail: the action potential that travels along the axon causes the release of Ca2+ into the synapse. This Ca2+ causes vessicles (packets) filled with neurotransmitter to fuse with the membrane and thus be released into the synaptic cleft. The neurotransmitter is rapidly taken up again afterwards.

Some other relatively well known neurotransmitters:

Acetylcholine, Serotonin, Epinepherine (adrenalin).

 

[Mentat]

Thanks for the help, Monique. It's strange, I'm usually not interested in anything between the size of a cell, and the size of a planetary object, but the brain fascinates me.

 

[hypnagogue]

As far as the number of neuron connections...

"The average number of synapses, that is, the average number of neuron connections lies around 10.000, which is to be compared to vaue between to and 3 for the transistors that make up electronic circuits. The number of sysnaptic connections of a human brain is a few times ten thousands of billions."

from http://www.numerisation.net/neurobiologie/Neurone_en.htm

Another good introductory resource:

http://en.wikipedia.org/wiki/Neuron

 

[einsteinian77]

I know this doesn't really fit into this page too well, but since its about the brain i didn't want to start a new thread. Is true that the left hemisphere of Einstein's brain was something like 15 percent larger than normal?