Question

1. Describe the chemical and electrical properties of an action potential. In your answer, describe the movement of Na+ ions and K+ ions across the cell membrane and the resulting changes in electrical potential.

2. Compare and contrast EEG and MEG. Highlight their similarities and differences in your answer.

Answer 1

1. Action potential are generated by special type of voltage gated ion channels present in the cell plasma membrane, these channels are shut when membrane potential is at rest, but open up when membrane potential reaches the threshold value. Action potential are caused when diffrent ions cross the neuron membrane, at rest there are more sodium ions outside the cells as compared to inside of the cell, because of which inside of a cell is more negative than outside (roughly around -70 mv), when the threshold value is reached, the channels open up allowing sodium ions to enter the inside of the cell, which produces furthe rise in membrane potential, this can cause more channels to open up producing a greater electric current across the membrane, this process continous until all avilable ion channels are open resulting in the upswing of membrane potential. the entry of sodium ions makes the inside of the cell positive from negative, the increased positive charge within the cell now causes the potassium channels to open up and the potassium ion begin to move out of the cell because of which potential of the cell approaches resting potential again, this process is known as repolarization, the process of repolarization causes an overshoot in the potential of the cell, potassium ions continue to move out of the cell, so that the resting potential is exceeded and the new cell potential becomes more negative than the resting potential, this process is known as hyperpolarization.

2. Electroencephalography (EEG) is physiological method to record electrical activity generated by the brain via the electrode placed on the scalp surface

Magnetoencephalography (MEG) is a neuro physiological technique that measures the magnetic feild generated by the neuronal activity of the brain

EEG and MEG are generated by the same source (electric current in the brain), so EEG and EMG are very close methodologically, since the main source of the signals are same, that is ionic current generated by biochemical process at cellular level.

An important diffrence between EEG and MEG is that skull and the tissue surrounding the brain affect the magnetic feild measured by the MEG much less than they affect the electric impulse measured by the EEG.. EEG detects radial and tangential currents while MEG detects tangential current only.EEG detects electric potential generated by the neural current instead of the corresponding magnetic feild as in MEG.