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Module 4: The Transmission of Neural Impluses

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Introduction to the Transmission of Neuron Impulses

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Introduction
The neurons are the functional elements of the human nervous system.

The neurons are aligned in sequences, one neuron after the other, to form circuits.

The transmission of information along the length of a neuron is electrochemical in nature.

Introduction
It is important to note 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.

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
resting potential.

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.

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 ½ meter/second).

The B fibers (thicker than C fibers and thinner than A fibers) are faster than C fibers and slower than A fibers.