6 - MCB 32 Professor Andrew E. Wurmser 09/13/07 Lecture 6...

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These notes are copyrighted by the University of California and are for your personal use only. Sharing or copying these notes is illegal and could end note taking for this course ANNOUNCEMENTS: -No announcements LECTURE: Molecular Functioning of Neural Cells The main purpose of this lecture is to expand on the molecular functioning of neural cells. We’ll build upon how inter- neuronal circuits work to enervate organs. We talked about action potentials last time. It has both positive and negative feedback loops. The resting potential for a neuron is -70mV. The resting potential is disturbed by a depolarization event mediated by an influx of positive ions moving into the cell past voltage gated sodium ion channels. Depolarization occurs in a positive feedback fashion. Depolarization stops when sodium ion channels close and potassium channels open and push positive potassium ions outside of the cell, which helps to repolarize the cell. Potassium functions in a negative feedback loop to regain the resting membrane potential. There are two different refractory periods. The first one occurs because sodium channels are inactivated and no more sodium can come in. This is called the absolute refractory period and it takes about 1 millisecond. The relative refractory period occurs when potassium channels don’t close right away and repolarization overshoots. When this hyperpolarization occurs, it serves as a barrier for a subsequent action potential. Sodium channels contain multiple sub- regions of proteins. One of the proteins acts as a switch to open the channel. Another one inactivates the channel. At -70 mV there are a high amount of positive ions outside the cell and lots of negative ions inside the cell. The sodium channel is closed at this point. When a depolarization event occurs to change the cell to -50 mV, the structure of the sodium protein channel changes and allows sodium into the cell. Sodium-potassium pump gains energy to move ions against their concentration gradient via hydrolysis of ATP. Student : What causes the initial depolarization event? Professor: Neurotransmitters convey the initial depolarization event. We’ll talk more about this later. The ultimate purpose of an action potential is to reach the terminal end of the axon and cause an influx of calcium ions into the button. The calcium channel responds to a depolarization event by allowing calcium ions in. Calcium serves to trigger the fusion of synaptic vesicles with the
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This note was uploaded on 04/02/2008 for the course MCB 32 taught by Professor Wurmser during the Fall '07 term at University of California, Berkeley.

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6 - MCB 32 Professor Andrew E. Wurmser 09/13/07 Lecture 6...

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