Neuronal Noise - Types

Types

• Ions exist inside and outside of the neuron and are subject to many bodily conditions. One major source of noise arises from ions or molecules in response to the third law of thermodynamics. This law states that the entropy of a system approaches a constant value as the temperature approaches zero. Since the body maintains temperatures above 0° C, the molecules are subjected to increased kinetic energy, or motion. The stochastic, or random, movements give rise to receptor noise produced by the constant bombardment of ions, as described by Brownian motion. Ions are constantly being leaked across the membrane in efforts to equalize the ionic gradient produced by ATPase channels embedded in the membrane. These leaky channels permit the movement of ions across the membrane leading to small fluctuations, or noise, in the membrane potential.

• Synapses are another major source of neural noise. More than often, there is random exocytosis of vesicles containing neurotransmitters, which eventually bind to the postsynaptic membrane, leading to a spontaneous action potential by graded potentials in the postsynaptic neuron. It is considered the largest-amplitude noise source in the cerebral cortex.