PHIS 206 Lecture Notes - Lecture 5: Membrane Potential, Sodium-Potassium Alloy, Homeostasis
2 May 2018
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Lecture 5: Synapses, Transduction
Na-K Pump
• In every cell, a protein exists that moves sodium out of the cell, and potassium into the
cell against their concentration gradients
• The result of this
Sodium
Potassium
ECF (outside of cell)
High Na+
Low K+
ICF (inside of cell)
Low Na+
High K+
Excitable Cells
• cells that provides the commands to the rest of the body→ go from being negative, to
positive, back to negative
• Nerve cells, muscle cells, and some cells in glands are “excitable” → these cells can
change their electrical state (their “membrane potential”) (remember: at rest, cells tend to
be negative inside)
• The sequence of events that occurs when excitable cells “excite” is known as the “action
potential”
Action Potential
• ****Understand polarization, repolarization, depolarization***
• Channels
o Opening and Closing in time
o Brief, rapid, large changes in membrane potential (start neg, go pos, back to neg)
o From rest → slightly positive → back to rest
o Caused by opening and closing of sodium and potassium channels in a ordered
sequence with precise timing
o Primary way cells communicate in nervous and muscular systems
Channels
• Channels are designed to open and close with timing and precision. Sodium channels
cycle between closed → open → inactivated → closed
• Channels are like holes punched in the membrane (but they are designed to either only let
potassium (potassium channels) through or sodium (sodium channels) through)
• Both the channels open at the same time, sodium channels open immediately, potassium
channels take some time
• Sodium channels have 2 doors that have to be open → as soon as the sodium channel
(activation) gates open, they also begin to close (inactivation gate closes)
• Analogy: 2 doors in front of house. Tied together with a string. IF u open one door, the
other will close (Sodium channel analogy)
find more resources at oneclass.com
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Document Summary
In every cell, a protein exists that moves sodium out of the cell, and potassium into the cell against their concentration gradients: the result of this. Channels: channels are designed to open and close with timing and precision. Sending the signal: graded potentials in dendrites become aps in axon (something that"s not an action potential) Inactivation prevents an immediate encore: need to allow the sodium channels to return to their starting position (closed, absolute refraction period, relative refraction period. Jumping action potential develop right) lead to paralysis, poor nerve function. Integration: both excitatory and inhibitory signals are integrated on the body/at the hillock. Synaptic transmission: conversion of an electrical signal (ap) into a chemical signal (neurotransmitter, then, chemical signal causes another electrical signal (a distinct and different ap, nerves don"t share action potentials. Lock and key: common theme in physiology is that specific chemical signals drive specific actions.
