C2.2.10 Oscilloscope traces showing resting potentials and action potentials (HL) Notes

Oscilloscope Traces Visualize Resting and Action Potentials

1. Imagine trying to understand a conversation by only hearing the volume changes.
2. An oscilloscope does something similar for neurons, translating their electrical signals into visual traces.
3. These traces help us understand the resting potential and action potentials that drive neural communication.

How an Oscilloscope Works

1. An oscilloscope displays electrical signals as a graph of voltage (y-axis) against time (x-axis).
2. It provides a continuous trace that allows scientists to visualize the changes in membrane potential as a neuron fires action potentials.

Resting Potential

1. Oscilloscope Trace: When the neuron is at rest, the oscilloscope trace shows a flat line, typically at -70 mV. This is the resting potential, representing the stable state of the neuron before it is stimulated.
2. How It Appears: The flat, horizontal line represents the lack of electrical activity.

Action Potential

1. When a neuron receives a stimulus that reaches the threshold potential, the oscilloscope trace shows a spike. This spike represents the depolarization of the neuron, where the membrane potential rapidly moves from -70 mV to +30 mV as sodium ions enter the axon.
2. How It Appears: The trace starts at the resting potential and then spikes upwards (depolarization), followed by a downward curve (repolarization), returning to the resting potential.

Frequency of Impulses

1. The number of impulses per second can be measured by counting the spikes in the oscilloscope trace.
2. For instance, if there are 10 spikes in one second, this means that the neuron is firing 10 action potentials per second.

Interpreting Oscilloscope Traces

Oscilloscope traces display these phases as a characteristic spike: