Review Answers

1. Different concentrations of ionic species across the neuronal membrane and differential permeability to ionic flow across the membrane are the determinants of the membrane potential. The Goldmann equation represents this relationship mathematically.

2. Two forces govern ionic flow across channels, a chemical driving force defined by concentration gradients, and an electrical driving force determined by the membrane potential.

3. The resting membrane potential is principally influenced by the reversal potential for K+. It has the highest permeability at resting conditions and, therefore, contributes the most in the Goldmann equation to the determination of the resting membrane potential.

4. Ligand-gated and voltage-gated channels represent two mechanisms for controlling the opening of gated channels.

5. The voltage-gated Na+ channel is the principal ionic conductance that underlies the upstroke of the action potential. The K+ ion facilitates repolarization.

6. As neuronal size grows, more current is required to achieve a similar level of depolarization, because the larger neuron has larger membrane surface area, which leads to higher capacitance.

7. The two main types of subthreshold stimuli are EPSPs and IPSPs.

8. AMPA, KA, and NMDA receptors are three distinct subtypes of glutamate receptors. AMPA and KA receptors are ligand-gated ionic channels, permeable to Na+ and K+. KA receptors have slower kinetics and differential binding properties with specific agonists. NMDA receptors have both ionotropic and metabotropic properties and are important in synaptic plasticity. NMDA receptors also affects Ca2+ translocation across the membrane.

9. The two main features of the cortex that permit EEG acquisition are its sheet-like organization parallel to the scalp (in large part), as well as its columnar organization, which leads to the generation of orthogonal electrical dipoles in the cortex, detectable by scalp EEG electrodes.

10. The paroxysmal depolarization shift is the term for the pathological wave of cortical excitation that leads to rapid and synchronized regional spiking detectable by EEG as epileptiform activity.

SUGGESTED READING

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Catterall WA. Structure and function of voltage-sensitive ion channels. Science 1988;242:50-61.

Friedman LK, Sperber EF, Moshe SL, Bennett MV, Zukin RS. Developmental regulation of glutamate and GABAA receptor gene expression in rat hippocampus following kainite-induced status epilepticus. Dev Neurosci 1997;19:529-542.

Furshpan EJ, Potter DD. Transmission at the giant motor synapses of the crayfish. J Physiol 1959;145:289-325.

Goldman DE. Potential, impedance, and rectification in membranes. J Gen Physiol 1943;27:37-60.

Hodgkin AL, Huxley AF. A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol 1952;117:500-544.

Hodgkin AL, Katz B. The effect of sodium ions on the electrical activity of the giant axon of the squid. J Physiol 1949;108:37-77.

Jessell TM, Kandel ER. Synaptic transmission: a bi-directional and a self-modifiable form of cell-cell communication. Cell 1993;72(Suppl):1-30.

Kandel ER, Schwartz JH, Jessell TM. Principles of Neural Science. 4th ed. McGraw-Hill, New York, NY, 2000.

Unwin N. Neurotransmitter action: opening of ligand-gated ion channels. Cell 1993;72(Suppl):31-41.

Woodhull AM. Ionic blockage of sodium channels in nerve. J Gen Physiol 1973;61:687-708.

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