Are neurons in humans different of the ones of other animals?

[fluidistic]

Are neurons in humans different of the ones of other animals like spiders for example? In other words if one shows you a neuron under the microscope, can you identify from which animal it comes from?

 

[Pythagorean]

The first highly-descriptive, successful neuron model was designed from a squid axon (The Hodgkin Huxley model) because they have giant axons that those old electric probes could actually take meaningful measurements from.

We now use the Hodgkin Huxley model on mammals, too. In fact, I've used a genetic algorithm to tune a model designed for mollusks to match a rat neuron.

As far as morphology and form (looking at it under a microscope) I don't know. Given two animals of the same size, they few I have seen all look the same to me, but maybe there's some expert that knows a trick to tell the difference. Certainly, a squid axon is going to be much bigger than any human axon. But for two animal sof the same size, I don't think there's a lot of differences except for maybe in the case of different phylums. Even then, in my brief work on C. elegans, I didn't see much difference, but I'm a laymen as far as molecular biology is concerned.

 

[Monique]

Neurons in a single organism can already look very different, but a clear structural example is that Drosophila neurons don't have a myelin sheath and thus no nodes of Ranvier. Glia do wrap the neurons though:

In the absence of a myelin sheath and nodes of Ranvier, Drosophila axons are wrapped by peripheral (inner) glial cells, which in turn are wrapped by much larger perineurial (outer) glial cells (Bellen et al., 1998). The inner glial cell processes wrap the axons, which in turn are ensheathed by the outer glial membrane. This insulation protects the neural microenvironment from the high potassium levels of the hemolymph (Hoyle, 1952).

..

The fundamental basis of axonal ensheathment in any species is to faithfully transmit neuronal signals along the nerve fibers and optimize desired cellular responses. To maximize the speed of conduction and/or to minimize the loss of nerve signals, many species evolved mechanisms in which axonal lengths remained short (as seen in insects) by increasing the diameter of the axons or by clustering voltage-gated Na+ channels to discrete unmyelinated regions of the axon, the node of Ranvier, as seen in myelinated nerve fibers of vertebrates. Most invertebrate species use some type of glial cells to ensheath their axons without generating a myelin sheath. The insulation is contiguous without any breaks, suggesting that primitive nodal structures or clustering of voltage-gated Na+ channels may not exist in invertebrates.
http://www.jneurosci.org/content/26/12/3319.full

 

[fluidistic]

Ok thanks a lot, that's very interesting.
I also wonder what happens to the ions that are exchenged via synapses between different neurons. Are some of them lost, and if so where do they go? I guess there's some loss, otherwise one could eat some potassium, calcium, etc. at birth and the brain would never need it again.
I also find surprising the fact that all animals require many different type of ions such as sodium, potassium and calcium for their brain to function. I would not have thought that bees, ants for example or snails would have needed them.

 

[Pythagorean]

Neurotransmitters are exchanged via synapses, not ions. And they get taken back up (a process creatively named reuptake). The basis of some pharmaceutical drugs (especially anti-depressants) is that they inhibit reuptake, allowing the neurotransmitter to hang around in the synapse longer to greater effect.

K/Na both leak out of the membrane itself, though, and little protein pumps powered by ATP act to keep up with the leaking. I'm not sure how Na/K leave the brain or body.

 

[Monique]

I also find surprising the fact that all animals require many different type of ions such as sodium, potassium and calcium for their brain to function. I would not have thought that bees, ants for example or snails would have needed them.

It's because our common ancestor had already evolved these systems, you might like to read the following publication: Big ideas for small brains: what can psychiatry learn from worms, flies, bees and fish?

 

[fluidistic]

Neurotransmitters are exchanged via synapses, not ions. And they get taken back up (a process creatively named reuptake). The basis of some pharmaceutical drugs (especially anti-depressants) is that they inhibit reuptake, allowing the neurotransmitter to hang around in the synapse longer to greater effect.

K/Na both leak out of the membrane itself, though, and little protein pumps powered by ATP act to keep up with the leaking. I'm not sure how Na/K leave the brain or body.

Ah ok I see. Now my mental picture of ions for neurons is the following: there are several ions floating around a neuron and they can penetrate via the ions channels of the neuron at particular times, when the channels open up. But how do the ions get to be around the neurons?

It's because our common ancestor had already evolved these systems, you might like to read the following publication: Big ideas for small brains: what can psychiatry learn from worms, flies, bees and fish?

ok thank you.