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|Role of oxygen (or energy) in nerve impulse transmission - Author Amit Kulshresth (Nov 22, 2005)|
Nerve cells require oxygen and glucose to transmit impulse, in this article I will discuss what is the role of each constituent into propagation of impulse. A look at the structure and composition of neuron and neuronal transmission mechanism will help in understanding the concept.
What are neurons?
Each nerve cell or neuron has a central portion containing the nucleus ( cell body) and one or more extensions protruding from the cell body called axons and dendrites.
Neurons consume oxygen and glucose for fuel. The more challenging the brain's task is, the more fuel it consumes. This energy is produced in the mitochondria. There are hundreds or thousands of mitochondria in neurons. They use oxygen to extract energy from glucose and fats and to produce molecules of the energy-storage compound adenosine triphosphate (ATP). These ATP molecules are then used to fuel the various chemical reactions that take place within the neuron.
Proof of energy consumption : Using fMRI (functional
Magnetic Resonance Imaging), it can be detected that active neurons
consume oxygen . The blood supply of the brain is regulated to give
active neural assemblies more energy whilst inactive assemblies receive
less energy. This dynamic regulation of the blood flow (called haemodynamic)
is the principal on which fMRI is based.
When a neuron is not sending a signal, it is at 'rest'. Its membrane is responsible for the different events that occur in a neuron. A strong stimulus like touch, pressure, stretching, sound waves, motion to the dendrite of a neuron initiates a nerve impulse. The impulse begins as an exchange of ions across a localized area of the plasma membrane.
The stimulus makes the nerve cell secrete a hormone, changing the permeability of outer cell membrane of the axon to positive ions that allow electrically-charged ions to move in and out of the cell . The influx of positive ions reduces the electrical potential across one segment of the membrane (depolarization). This reversal of polarity causes the same change in the neighboring area of the membrane, which causes a reversal of polarity further along, and so on. This impulse travels along the axon as a self-generating chain reaction. This is what really occurs when a nerve is described as "firing." Nerves do not conduct electricity or any other form of energy.
The impulse propagates along the length of the neuron
as a cascade of ionic exchanges. It does not lose energy as it travels
because it is continually regenerated at each new site along the membrane.
Maintaining these ionic gradients is an energy-consuming process that
requires a constant supply of glucose and oxygen to the neuron. Lack
of glucose and oxygen deplete the cellular energy stores required to
maintain electrical potentials and ion gradients. The
energy of a nerve Impulse has been calculated to be 5 x 10-15 joules
on an average, it may vary because of nature of sheath. As the supply
of oxygen decreases the energy of the impulse also decreases. Lack of
glucose and oxygen deplete the cellular energy stores required to maintain
electrical potentials and ion gradients. The oxygen or energy requirement
can be judged from an experiment performed at University of Rochester
For understanding more about
neuronal transmission, view our animation, click
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