Função do sódio no organismo

Estava estudando funções dos elementos nos organismo e me surgiu uma dúvida:
O sódio tem, além da função de regulação hídrica, a função de transmissão do impulso nervoso. Seria por causa da base hidróxido de sódio ser forte e a solução aquosa do cátion sódio ter alta condutividade elétrica (lógico que considerando a molaridade do Na no corpo humano, ela torna-se muito pequena) ?

Nas células, há transporte ativo por bomba de Na+ e K-.. Não me lembro bem, mas é tipo assim a transmissão de um impulso nervoso: Quando o impulso nervoso passa, a membrana despolariza (concentração de carga elétrica invertida), aí a bomba de sódio (Na+) e Potássio (K-) age: o Na+ vai pra fora da célula e o K- para dentro. Quando o impulso passa, novamente há uma inversão e isso se repete intensamente.

Bem, acho que não respondeu a sua dúvida, mas creio que a resposta seja sim (a presença de íons livres é uma das formas de condução de corrente elétrica). Talvez alguém saiba responder melhor..

Gostei !!!

Não pense em base forte ou fraca.

Pense nos próprios íons Na+ em solução aquosa. Estão dissociados, livres, junto com outros íons postivos — K+ e Ca²+ — e o cloreto Cl-.

São eles que formam a "corrente elétrica", e não elétrons, como num fio metálico condutor.

Ainda bem que no nosso cérebro e em outras partes não existem bases fortes !

Ia desminliguir tudo !

A base NaOH é forte por causa da eletropositividade do sódio e não o recíproco.

O elemento sódio é muito eletropositivo, assim como K e Ca , sendo o cloro muito eletronegativo, favorecendo uma ddp e a consequente corrente de íons positivos prum lado e negativos pro outro, as quais somadas (em módulo), formam a "corrente elétrica".

Segue uma boa síntese achada em:

http://biology.stackexchange.com/questions/91/how-do-the-brain-and-nerves-create-electrical-pulses


This is quite a big question! I'll try to outline the basic view.


First, let's review how neurons signal between each other. The
canonical way for a neuron to send a signal to a downstream neuron is by
generating an action potential, the "electrical
impulse" you have heard of. This action potential causes the release of
neurotransmitter at a point where the two cells are very close to each
other called a synapse. The downstream postsynaptic
cell receives the neurotransmitter signal and converts it into a small
electrical signal. If enough of these small electrical signals happen in
a short time, they sum together and are likely to initiate an action
potential in the second cell and the cycle repeats all along the
circuit.


How is the electrical signal generated? The basics of how this works
was worked out most famously by Hodgkin and Huxley in 1952. The short
story is that the plasma membrane is selectively permeable to ions. Let's build the concept from the ground up.


The toolbox

1. Imagine a sphere of plasma membrane that represents a simple
   neuron. For starters, we assume that this membrane is bare lipid with no
   membrane-associated proteins. Because of the hydrophobicity of the
   bilayer, charged particles cannot diffuse through the membrane.
   
2. The cell is bathed, inside and outside, in a solution containing many ions
   (charged atoms), including sodium (Na+), potassium (K+), chloride
   (Cl-), and calcium (Ca2+). As we noted above, these ions cannot go
   through the membrane without "help".
   
3. Now we add an ion pump protein into the membrane which will pump sodium ions out and potassium ions in. This particular pump, the Na-K ATPase, creates an excess of sodium ions outside the cell and an excess of potassium ions inside.
   
4. Now we add a potassium ion channel to the
   membrane. This protein creates a pore in the membrane that only allows
   potassium ions through. This particular protein's pore is always open.
   Now things start getting exciting...
   
5. What do the potassium ions do now that they can go through the membrane? Ions will move based on the forces created by their electrochemical gradients.
   The pump created a chemical gradient by putting excess K+ inside, so
   the K+ ions start to flow out through the ion channels. But K+ ions are
   positively charged, so when they flow out, positive charge starts
   building up outside and negative charge builds up inside. This
   electrical gradient opposes the chemical gradient, tending to pull the
   K+ ions into the cell while the chemical gradients pulls K+ ions out.
   The influx and efflux reach an equilibrium at the Nernst potential,
   where the electrical and chemical forces equal out. For physiological
   concentrations of K+ ions, the K+ equilibrium potential is about -80mV
   or -90mV. This means that K+ ions will flow until the outside of the
   cell is 80-90mV more positive than the inside of the cell. We started at
   0mV, so K+ ions mostly flow out.
   
6. We now have a membrane potential, a difference
   in electrical potential between the inside and the outside of the cell
   at about -80mV (usually closer to -70mV or -60mV in "real life"). In
   particular, this membrane potential is the resting potential
   that exists when the cell is not active. We can simplify for now and
   think of the resting potential as being set by a resting permeability of
   the membrane to potassium ions, but not to sodium ions. We call this
   membrane polarized, and thus depolarization is when the membrane potential becomes more positive, and hyperpolarization is when the membrane potential becomes more negative.
   
7. Now, we add to the membrane a voltage-gated sodium channel,
   an ion channel that passes only sodium ions but is usually closed. The
   voltage-gating means that this ion channel is sensitive to the membrane
   potential. At the resting potential, the pore is closed and the membrane
   is still impermeable to sodium ions. When the membrane potential
   becomes slightly more positive, the channels opens and sodium ions can
   flow. This channel is also inactivating, so that when it opens it only opens for a short period of time, letting in a limited amount of sodium.
   
8. What way will sodium flow when we open this channel? Because of
   the negative resting potential (-70mV) and the excess of sodium ions
   outside due to the pump, both the electrical and chemical gradient will
   drive sodium ions into the cell. The sodium equilibrium potential is
   usually around +60mV.
   
9. To complete the machinery for generating an action potential, we also add a voltage-gated potassium channel
   to the membrane. It works just like the voltage-gated sodium channel
   that is also closed at rest and opens when the membrane potential
   becomes more positive. This channel opens a bit more slowly than the
   sodium channel does, but it does not inactivate.
   

Generating an action potential



Ok, so how do these parts come together to create an electrical impulse?

1. The cell sits at its resting membrane potential, with all of its
   voltage-gated channels closed. It receives a signal from an upstream
   cell that causes a slight depolarization. The action potential will
   initiate when the membrane potential hits the threshold potential.
   
2. At the threshold potential, the voltage-gated sodium channels
   open letting sodium ions flow into the cell. The sodium flux pulls the
   membrane from the resting potential (-70mV) towards the sodium
   equilibrium potential (+60mV). These values are far apart, so the
   driving force is large and the membrane depolarizes rapidly. This is the
   action potential upstroke.
   
3. The depolarization also activates the (slightly slower)
   voltage-gated potassium channels. The potassium ions flow out and drive
   the depolarized membrane (about +20mV at the action potential peak) back
   towards the potassium equilibrium potential (-80mV). At the same time,
   the sodium channels are inactivating so that sodium is no longer
   depolarizing the membrane. The repolarization rate is usually slower
   than the depolarization rate. This is the action potential downstroke.
   
4. The whole process of the action potential
   depolarization/repolarization cycle takes about 2-3 milliseconds in an
   "average" neuron. Once the cell reaches resting potentials again, the
   membrane is basically reset. The voltage-gated channels are turned off.
   The ion pump moves the potassium ions that flowed out and the sodium
   ions that flowed in. That patch of membrane is ready to fire another
   action potential!
   

As a final note, I'll mention that the voltage-gated sodium channel provides a mechanism for the action potential to propagate
down the axon. The action potential is initiated in one location of the
cell, and creates a depolarization. This depolarization causes the
voltage-gated sodium channels in neighbouring regions of the membrane to
open and generate an action potential cycle of their own. This is how
an action potential travel down axons (and sometimes dendrites too).



Saudações sinápticas !

Ramon, quanto a bomba de sódio e potássio eu já conhecia.. Acho que o que mais responde a pergunta é o fim de sua mensagem e a do Rihan (aliás, obrigado meu caro), que consiste no fato da condutividade elétrica das soluções de Na+ e outros íons serem altas.

muito obrigado Rihan e Ramon