PSYC 2410 Lecture Notes - Lecture 5: Golgi Apparatus, Antidromic, Ligand-Gated Ion Channel
27 Jun 2018
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The neuron's resting membrane potential
The membrane potential is the difference in electrical charge between the inside and outside of
a cell
To understand how chemical signals are transmitted it is important to remember this concept of
electrical charge and how this charge is responsible for propagating an action potential
Rest potential
oIs the membrane potential that is found when the neuron is not sending a signal
oThe inside of the neuron has a negative charge relative to the outside of the neuron that
is approx -70mV - this electric differential polarizes the membrane
oThe unequal distribution of positively and negatively charged ions between the inside
and outside of the membrane in neural tissue is responsible for the resting potential
oOutside of the membrane sodium and chloride ions are more highly concentrated while
inside the membrane potassium ions and a variety of negatively charges proteins are more
highly concentrated
Ionic basis of the resting potential
oThere are four factors that act to keep the ratio of negatively to positively charged ions
higher inside the membrane than outside in a resting neuron
oTwo passive factors distribute ions equally across the membrane, then one more passive
factor and one active factor distribute ions unequally across the membrane
oMuch of the understanding for these processes were gained by the ground-breaking
work conducted by Hodgkin and Huxley on the squid axon in the 1950s
Random motion (passive) : ions in solution are in random motion. When there is
an accumulation of a specific class of ions in one are the probability is increased that
the random motion will move ions out of this area and the probability is reduced that
random motion will move more ions into this area
Electrostatic pressure (passive): like charges repel and opposite charges attract.
Therefore, electrostatic pressure disperses any accumulation of positive or negative
charges in an area. The previous two forces are the homogenizing factor. The next two
forces work to distribute the ions unequally across the membrane resulting in the
membrane potential
Differential permeability of the membrane (passive): ions pass through the
membrane at special pores called ion channels. At rest the membrane is totally
resistant to the passage of protein ions, extremely resistant to the passage of Na+
ions, and only slightly resistant to the passage of K+ and Cl- ions
Sodium - potassium pumps (active): these are energy consuming mechanisms
that continually transfer Na+ ions out of the neuron and K+ ions in at a ratio of 3 Na+
ions moved out for every 2 K+ ions moved in
Generation and conduction of postsynaptic potentials
Neurotransmitters released into the synaptic cleft when neurons fire bind with receptor
molecules on the membrane of the next neuron - this action results in one of two events on the
post-synaptic membrane: depolarization or hyperpolarization
oDepolarization of the membrane causes an excitatory post-synaptic potential (EPSP)
which increases the likelihood that the neuron will fire
oHyperpolarization of the membrane causes an inhibitory post-synaptic potential (IPSP)
which decreases the likelihood that the neuron will fire
There are three important characteristics of these post-synaptic potentials:
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Document Summary
The membrane potential is the difference in electrical charge between the inside and outside of a cell. To understand how chemical signals are transmitted it is important to remember this concept of electrical charge and how this charge is responsible for propagating an action potential. Is the membrane potential that is found when the neuron is not sending a signal. The inside of the neuron has a negative charge relative to the outside of the neuron that is approx -70mv - this electric differential polarizes the membrane o. Ionic basis of the resting potential o. There are four factors that act to keep the ratio of negatively to positively charged ions higher inside the membrane than outside in a resting neuron o. Random motion (passive) : ions in solution are in random motion. Electrostatic pressure (passive): like charges repel and opposite charges attract. Therefore, electrostatic pressure disperses any accumulation of positive or negative charges in an area.
