Physiology 2130 Lecture Notes - Minor Places In Middle-Earth (Fictional), Choline, Electrochemical Gradient

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24 Sep 2014
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Physiology 2130 – 4 Nerve Cells
Introduction
Nerve cells and muscle cells are considered “excitable” because they generate an
electrochemical action potential using the resting potential of the membrane
Action potentials necessary for muscle contractions
Structure of a Nerve
The following neuron is called a multipolar neuron
Dendrites
oThin branching processes of cell body which receive signals
Cell Body (Soma)
oControl center of cell which contains nucleus and all other organelles for cellular
activity
Axon
oProjection of cell body that carries out the action potential
oMay or may not be myelinated by a phospholipid myelin sheath that protects the
axon
oMyelin sheath insulates the ionic processes of the axon
oNodes of Ranvier are small notches in the myelin sheath that facilitates the each
action potential and moves from node to node in a high rate
Collaterals
oBranching of the axon at the terminal end which increases the number of
interactions the neuron can have
Terminal Bouton
oSwelling at the end of collateral which contains mitochondria and membrane
bound vesicles carrying various neurocrine molecules
oThe chemicals here facilitate the transfer of the signal to other cells
A Quick Look at the Action Potential
Action potential is a rapid reversal of
the resting potential
During this the membrane potential
changes from (-70mV) to (+35mV)
this is known as depolarization
oAfter this the potential rapidly
changes back to -70 mV
through repolarization
oBecoming -90 mV being in
hyperpolarization
oThe potential returns to
normal to complete one firing
of the signal
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Voltage-Gated Channels
Potassium and sodium voltage-gated channels
oThese are usually found on the axon and are essential for generating the action
potential
oSensitive to changes in the membrane potential and open when the inside of the
cell becomes more positive (-
70 mV to -60 mV) in
depolarization
Voltage-Gated Sodium Channels
Both gates are on the intracellular side of the membrane
The activation gate first opens and the inactivation gate takes a short time longer to react
to depolarization
Steps of the channel
oDepolarization of the membrane occurs as potential becomes more positive
oActivation gates open immediately
oNa+ flow into the cell, down the concentration gradient
oInactivation gate closes and Na+; can no longer flow into the cell; the channel
cannot open
oChannel returns to resting configuration with inactivation gate open
oChannel is now ready to open again
Inactivation of Na+ Voltage-Gated Channel: The Absolute Refractory Period
During the period when the inactivation gate is closed, the channel will not open, no
matter the strength of stimulation; the channel has become inactivated
This time period of inactivation is called the absolute refractory period
Voltage-Gated potassium Channels
These only contain one channel, which doesn’t open immediately at depolarization
They begin to open when the Na+ voltage-gated channel starts to become inactivated
Events of voltage-gated potassium channels
oDepolarization of membrane occurs
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