Nerve Science: Using Gelatin Circuits to Understand how Neurons Work through Physics and Biology Student Worksheet Purpose: Determine the volume of helium gas in an irregularly-shaped Mylar balloon.
Background (from “Bridging Physics and Biology Using Resistance and Axons” by Joshua M. Dyer):
Neurons are nerve cells that are composed of three major sections, as shown in Fig. 1: the dendrites, the cell body, and the axon. These nerves cells transmit electro-chemical signals to cells such as other neurons, muscles, and endocrine cells. This signal transmission is, for example, how the brain tells muscles to contract. Multiple signals enter the neuron through the dendrites. The separate electrical impulses through these dendrites combine at the cell body. This signal then becomes attenuated as it travels through the cell body toward the axon hillock and is known at this point as the graded potential. This signal reduction is natural since the cell body is composed of cytoplasm, which has electrical resistance. An electrical threshold exists at the axon hillock, determining if an action potential will occur and the signal will continue to pass down the neuron. If the graded potential is smaller than the threshold, then an action potential will not occur and the signal will be stopped. Now, as the signal travels through the axon, it will attenuate further.
At each node of Ranvier including the axon hillock, the signal, assuming it stays above threshold, is reconstructed by a sodium ion channel located at the node, thus boosting the signal voltage up and mitigating the natural signal degradation. To aid in transmitting this signal, some animals, including humans, produce a fatty tissue called myelin, which insulates the axon from surrounding materials and minimizes signal leakage from the axon. The myelin also contributes to the capacitive properties of the axon and affects the speed that electrical impulses are transmitted through nerves. In humans, however, certain congenital problems can cause demyelination, allowing the signal to leak out of the axon between the nodes of Ranvier and fall below threshold, resulting in overall loss of the signal. Demyelination is believed to be the underlying cause of the disease multiple sclerosis.