Section V. ELECTROCHEMICAL TRANSMISSION OF NEURON IMPULSES
a. The functional elements of the human nervous system are the neurons. The
neurons are alined in sequences, one neuron after the other, to form circuits. The
transmission of information along the length of a neuron is electrochemical in nature.
b. An important fact is that "connecting" neurons do not actually touch each
other. Instead, there is a space between the end of one and the beginning of the next
("continuity without contact"). A specified chemical, called a neurotransmitter, is
required to cross the gap between one neuron and the next.
12-15. RESTING POTENTIAL
As a part of their life processes, neurons are able to produce a concentration of
negative ions inside and a concentration of positive ions outside of the cell membrane.
The difference in the concentration of ions produces an electrical potential across the
membrane. This condition is often referred to as polarization. When the neuron is not
actually transmitting, this electrical potential across the membrane is known as the
12-16. ACTION POTENTIAL (DEPOLARIZATION AND REPOLARIZATION)
Where a stimulus is applied to the neuron, the polarity of the ions is disrupted at
the same location. Thus, that location is said to be depolarized. The ions in adjacent
areas along the neuron then attempt to restore the original polarity at the location of the
stimulus. However, as repolarization occurs in the area of the stimulus, the adjacent
areas themselves become depolarized. This results in a wavelike progression of
depolarization/repolarization along the length of the neuron. By this means, information
is transferred along the neuron.
12-17. EFFECT OF THE THICKNESS OF THE NEURON PROCESSES
The speed with which an impulse travels is proportional to the thickness of the
neuron process. The thickest processes (A fibers) have the fastest transmission (about
120 meters/second). The thinnest processes (C fibers) are the slowest (as slow as 1/2
meter/second). The B fibers (thicker than C fibers and thinner than A fibers) are faster
than C fibers and slower than A fibers.
12-18. THE SYNAPSE
The gap between successive neurons is wide enough that impulses do not
travel from one neuron to the next in the same way as along a single neuron.
Information travels from one neuron to the next by means of a chemical