Lecture 09 - Ion Channels and Electrophysiology

Lecture 09 - Ion Channels and Electrophysiology - Lecture...

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Lecture 09 - ION CHANNELS AND ELECTROPHYSIOLOGY 1. Electrical signaling in excitable cells (neurons, muscles, some endocrine cells) (A409-410, Slide 5 =Fig. 12-31). - Very cell has a membrane and has potential across it - But only endocrine cells are excitable - The dendrites (next to spinal cord) would send out the signal through the axon (down the legs) send the signal down to the nerve terminal (branches off) - Dorsal root ganglion – detects that someone step on your foot --- sensors on the foot that sends it all the way back to the neck o The longest neuron cell we can get (foot to neck) Central conductor jacketed by an imperfect insulator and embedded in a conductive medium. - The axon is very conductive (salted) Electrical signals momentarily injected at one point fade away with time and distance unless re-amplified. - If you pick up a sample and re-amplified it and repeat it again you can carry the signal a long way (digital) - Digital meaning yes or no – you just propagate that YES a came along and you propagate how fast (frequency = strong, slow = weak, silent = none) IT IS NOT BY HOW BIG / STRONG THE SIGNALS ARE Local signals can have any amplitude and shape; long distance signals requiring repeated amplification should be all-or- nothing, yes-no, digital. - Normal 2. Action potentials (APs) are stereotyped, all- or-nothing electrical depolarizing waveform conducted by nerve and skeletal muscle (A410) (Slide 6=Fig. 12-33). - Resting = -60mV - In AP you need a trigger (something that gets the membrane potential at -40) - It will overshoot the resting potential and then return to the resting membrane - This is the base for distance communication for humans o The heart beating also sends signal for uniform contraction Amplitude 70-140 mV depending on cell type. Duration 0.5 - several msec depending on cell type. Speed of propagation <1 meter/sec to > 100 meter/sec. - How fast does this move? - 1 m/sec SLOW you can watch - <100m/sec racing car speend All-or-none; once started, propagate with a standardized shape and properties. - DIGITAL - You will always get a full amplitude if it doesn’t make it will fall and go back to resting Can travel in either direction, though normally the organism sets up propagation in one direction only. - Once you start – it can go either direction - The traditional direction can be altered through experiment (lab) - The axon has no sense of direction - You get the direction because the cell body/dendrite and nerve terminal can only go one direction After each AP, there are brief refractory periods within which the nerve or muscle either cannot fire another AP or requires extra stimulation to fire. -
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This note was uploaded on 09/14/2011 for the course PHARM cs taught by Professor Staff during the Spring '11 term at UCSD.

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Lecture 09 - Ion Channels and Electrophysiology - Lecture...

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