neuron energy use

Richard Vickery Richard.Vickery at unsw.edu.au
Tue Oct 27 18:41:40 EST 1998


jimmyd at cc.gatech.edu wrote:
> I want to know a few things about Neuron energy use.
> 
> * Neurons get all their energy from glucose, right? (Kolb & Whishaw 1996, p 68)


> * The mitochondria turns glucose into ATP. Does the cell body have a storage of ATP, or does the mitochondria produce it as needed?

I am no expert on the energy side of things, but I believe
that the mitochondria use glucose and fatty acids to make
NADH.  This can be combined with oxygen to make ATP.  So the
NADH is a store.  This answers your later question about the
need for oxygen.  There are many good introductory textbooks
about this sort of thing.

> * How much glucose (turned into ATP) is needed to fire a neuron? If the firing rate of a neuron is 700 per second, what is the rate of glucose use?

700 Hz is unreasonably high except for primary sensory nerve
fibres.
The calculations of the heat generated by an action
potential were done in the 60's, and would let you convert
to an energy expenditure per action potential.

> * This is my conception: The dendrites send a message to the soma indicating the change of firing rate. The soma takes energy from the bloodstream to raise the firing rate. This message is in the form of the chemical state inside the dendrites and soma. What is wrong with this conception?

The problem is that the energy is not used to make the
signal, it is used to recover from generating the signal. 
An action potential is the flow of ions along
electrochemical gradients.  It happens when
voltage-sensitive channels (or ligand-gated at the synapse
for making epsps etc) open.  Energy is not required.  A
poisoned cell can still fire a few hundred action potentials
because the cell is effectively a battery, and each action
potential involves only a few ions crossing the membrane, so
the battery takes a while to run down.  The role of energy
is to "recharge the battery" by pumping ions back to the
appropriate side of the membrane.

-- 
Dr Richard Vickery                  
School of Physiology & Pharmacology, UNSW, Australia, 2052
ph. 61 2 93851676,  fax 61 2 93851059              
http://www.med.unsw.edu.au/Physiology/School/staff/vickery/Welcome.html



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