Electrophysiologists

1.) Electrophysiologists are able to record neuronal activity in two different ways, intracellular recordings and extracellular recordings. The main difference that separates these two methods is the placement of the electrode, where intracellular recordings have the microelectrode placed in the neuron it self and in extracellular recordings the electrode only needs to be placed in the tissue. Therefore it is intracellular recordings that make it possible to record the activity of a single neuron as the microelectrode is placed in the cell, which means that there is no activity being detected by neighbouring neurons. This method differs from the extracellular recording that we performed in our laboratory classes in a few ways. Firstly extracellular recordings measure the negative change in potential that occurs in the extracellular fluid due to the influx of the sodium ions into the cell, leaving the extracellular fluid with a temporary negative charge. Furthermore the intensity of the action potentials that are recorded due to these voltage changes depends on the proximity of the neuron to the electrode. For example if the electrode were to be placed in between two neurons that were a distance of 3nm and 10nm away form the electrode, you would record a more intense action potential (AP) from the neuron only 3nm away compared to the one at a distance of 10nm.

The amplitude and general shape of AP that are produced from both intracellular and extracellular recordings differ even when they are both recording the changes in potential of the same neuron. This is due to extracellular recordings being influenced by the distance between the electrode and neuron, which impacts on the intensity of the AP, and any voltage changes that are simultaneously occurring in the extracellular space, which impacts on the purity of the AP. Intracellular recordings are not influenced by such factors, which makes them the preferred method when only one neuron is being analysed.  Additionally the amplitude of the AP’s for intracellular and extracellular recordings have the opposite charge as an extracellular AP measures the net negative change in potential due to the absence of sodium in the extracellular space. However in an intracellular recording will measure the positive change in potential due to the influx of sodium into the cell.

References

1. "Introduction To Neurons And Neuronal Networks | Section 1, Intro Chapter | Neuroscience Online: An Electronic Textbook For The Neurosciences | Department Of Neurobiology And Anatomy - The University Of Texas Medical School At Houston". Neuroscience.uth.tmc.edu. N.p., 2016. Web. 7 Oct. 2016.
2. "BIO340 Laboratory 5". Pierce.wesleyancollege.edu. N.p., 2016. Web. 9 Oct. 2016.
3. Buzatu, S. "The Temperature-Induced Changes In Membrane Potential". Riv Biol 102 (2009): n. pag. Web. 9 Oct. 2016.
4. Hodgkin, A. L. and B. Katz. "The Effect Of Sodium Ions On The Electrical Activity Of The Giant Axon Of The Squid". The Journal of Physiology 108.1 (1949): 37-77. Web.

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