Electrophysiology

Intracellular action potentials (amplitude ~50 mV) recorded from a Manduca Sexta neuron that result from a brief (~1ms duration) and longer (10s duration) electrical stimulus.

Mathematical analysis frequently assists the understanding of how microscopic properties combine to produce the macroscopic properties; this is especially well illustrated in analysis of electrical responses in excitable cells. Intra- and extra-cellular recordings of neuronal responses can reveal the effects of ion channels that contribute to the generation and spread of complex neuronal signals. In this module, students will record synaptic- and action-potentials arising spontaneously, or by electrical or pharmacological stimulation. Students will direct single or trains of electrical stimuli to the cell body (intracellularly, resulting action potentials right) or nerve processes (extracellularly, anatomy below) and observe responses. Selected cells will be pharmacologically manipulated by the application of Tetraethylammonium (TEA).

Stereo microscope view of a Manduca Sexta ganglion showing connectives that contain nerve and airway structures branching from the round central structure, and multiple small neurons visible as shaded circular objects located in the center of the ganglia.

These procedures will provide the opportunity to study changes in the passive (membrane), transitional (spike-production) and active (firing rate) properies of recorded cells.

Morphology
The morphology of recorded cells will be visualized by Lucifer Yellow staining and confocal microscopy imaging. Images obtained by backfilling peripheral nerves provide an understanding of the overall arragement of clusters

Neurons of Manduca Sexta were highlighted by dye injection, imaged by Confocal microscopy. Shown are a collection of neurons and their dendrites and axons, at the confluence of the ganglia and one of its connectives.

of cell bodies, their dendritic arborization and processes (right). Images obtained by intracellularly filling individual cell bodies show their processes in greater detail (left) and allows for more precise measurment of process diameters and segment lengths. Using both elecrophysiological and morphological data they acquire, students will compare their results to existing mathematical models describing the mechanisms underlying potential generation and spread.

A single cell body (round object at top) and axon with nerve branches clearly visible. Image obtained from a Manduca Sexta neuron backfilled by dye injection through a glass microelectrode.