This virtual lab allows students to explore the neural basis of behavior by using a leech ganglion attached to the skin via nerves. The leech is a classic model system for studying how neurons respond in behaviorally relevant situations, such as tactile sensation. Simpler animals like leeches, including locusts, lobsters, and marine snails, often have fewer, larger neurons that can be individually identified. As a result, their nervous systems are easier to study and have helped make great contributions to research. Many fundamental principles of neuroscience first learned in these simpler animals also apply to animals with more sophisticated nervous systems, such as mice and humans.

In this lab, students can explore background materials to learn about the ionic basis of the resting potential and the action potential, which are fundamentally important concepts in neuroscience and cell biology. The main lab explores the principle of stimulus encoding (how an individual neuron responds to different stimuli by firing different patterns of action potentials), and the principle of labeled lines (the idea that each neuron has a specific identity and the activity patterns of individually identified neurons are integrated by the brain to perceive the environment).

Curriculum Connections:

Key Concepts:

• The membrane voltage of a neuron depends on the concentration gradients of different ions and their membrane permeabilities.
• An action potential is generated by rapid changes in membrane permeabilities of different ions.
• Individual neurons may differ in how they respond to the same stimuli.
• Individual neurons may respond differently to different stimuli.
• The nature of a stimulus can be reconstructed by monitoring the activity of an ensemble of identified neurons.

References:

Nicholls, John G., A. Robert Martin, and Bruce G. Wallace. "Chapter Thirteen" in From Neuron to Brain. 3rd ed. Sunderland, MA: Sinauer Associates, 1992. [Newer editions exist, but may not cover the nervous systems of simpler animals like leeches as well as this older edition.]

Nicholls, John G. and D. A. Baylor. "Specific modalities and receptive fields of sensory neurons in CNS of the leech." J. Neurophysiol 31 (1968): 740–756.

Blackshaw, Susanna E. "Sensory cells and motor neurons." In Neurobiology of the Leech, edited by Kenneth J. Muller, John G. Nicholls, and Gunther S. Stent, 51–78. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory, 1981.

Muller, Kenneth J., and U. J. McMahan. "The shapes of sensory and motor neurons and the distribution of their synapses in ganglia of the leech: A study using intracellular injection of horseradish peroxidase." Proc. R. Soc. Lond. B 194, 1117 (1976): 481–499.