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Psychopharm Test 1 Lecture 3
Terms in this set (67)
Where does electrical neurotransmission occur?
within the neuron
Where does chemical neurotransmission occur?
What is the membrane (electric) potential?
the difference between the electrical charge within a neuron and the electrical charge of the environment immediately outside of the neuron
What is the average resting membrane potential?
What is it called when a neuron is at resting potential and why?
polarized, because it is more negative inside
What are the 4 ions responsible for setting the resting membrane potential?
What ions are concentrated inside the neuron at resting potential?
K+ and Protein-
What ions are concentrated outside the neuron at resting potential?
Na+ and Cl-
At resting potential, where is the ratio of negative to positive charges greater?
inside the neuron
What are the four factors affecting ions?
2. electrostatic pressure (attraction)
3. differential membrane permeability
4. sodium-potassium exchange pump
charged particles have a tendency to to move across the membrane down their concentration gradients (from high to low)
-where ever it is crowded, ions will diffuse to where it is less concentrated
particles with similar charges repel each other, particles with different charges attract each other
Differential membrane permeability
the ease with which ions flow across the membrane
Describe the permeability of each of the ions
K+ and Cl- flow easily, Na+ passes with extreme difficulty, proteins cannot move
Sodium potassium exchange pump
-Na+ leaks in, K+ leaks out
-pumps 2 K+ in for every 3 Na+ out to counteract natural progression of Na+ influx and K+ efflux
-active energy expending process
What does the sodium potassium pump maintain?
the negative charge
How do the four factors effect K+?
-diffusion pushes it out of the cell (because it is highly concentrated inside)
-electrostatic pressure keeps it in the negatively charged cell
-high permeability, can flow easily
-diffusion works harder and it leaks out (and from permeability), so the exchange pump actively pumps 2 K+ back into cell
How do the four factors effect Protein-?
-diffusion wants it to go outside (because it is highly concentrated inside)
-electrostatic pressure wants it to go outside
-no permeability, protein- cannot move so it remains inside the cell
How do the four factors effect Na+?
-diffusion pushes it into the cell (highly concentrated outside)
-electrostatic pressure pushes it inside to negative charge
-permeability keeps it outside because it is difficult for Na+ to pass through membrane
-exchange pump actively pumps out 3 Na+
How do the four factors effect Cl-?
-diffusion pushes it inside (highly concentrated outside)
-electrostatic pressure keeps it outside because inside is negative
-has high permeability, can easily flow in and out of cell
-exchange pump does not effect Cl-
It is more important for ___________ to get out of the cell
Postsynaptic (local) potentials
electrical potential on a specific part of the neuron (dendrites) caused by binding of neurotransmitter to receptors
-neurotransmitter attaches to synapse and changes electrical potential (how much it is negative compared to outside)
Possible outcomes of postsynaptic potential
depolarization or hyperpolarization
decreases the resting membrane potential to ~67 mV
increases resting membrane potential to ~73 mV
What increases the liklihood of a neuron firing?
What are postsynaptic depolarizations called?
excitatory postsynaptic potentials (EPSPs)
What are postsynaptic hyperpolarizations called?
inhibitory postsynaptic potentials (IPSPs)
What is an action potential?
a momentary reversal of the membrane potential from negative to positive
-it is an all or none response
Explain how an action potential is generated
-EPSPs and IPSPs are constantly occurring and are in balance at resting potential
-when more EPSPs occur and depolarize the cell from -70 mV to -65 mV then an action potential occurs
Where does the action potential happen?
in the axon hillock
What is the threshold of excitation?
What happens once the action potential is generated?
-when depolarization occurs, sodium ion channels open and sodium rushes in
-reaches peak (repolarization), then sodium closes and potassium slowly comes in
-potassium overshoots and hyperpolarization occurs, from which sodium exchange pump takes over and regulates resting potential again
Absolute refractory period
brief period (1-2 ms) after the initiation of an action potential during which it is impossible to elicit a second one
-second one cannot happen until sodium is closed
Relative refractory period
period following the absolute refractory period where it is possible for the neutron to fire again but only by applying higher than normal levels of stimulation
-has to start at -73 mV so it takes a long time (2-4 ms)
Action potential propagation (saltatory conduction)
series of action potentials occurring in succession down the axon
-regenerates action potential the whole way down axon
Where is action potential regenerated during propagation?
nodes of Ranvier in myelinated axon, jumps across nodes of Ranvier
Why is saltatory conduction efficient?
it doesn't have to open ion channels, can change voltage in jump, happens under myelin
In an action potential, what does conduction velocity depend on?
-whether or not there is myelin, myelin makes it go faster
-diameter of axon, large diameter makes it go faster
What is the firing rate of an action potential and what does it depend on?
-number of action potentials per unit of time (ms)
-depends on absolute refractory period
What is the ultimate goal of an action potential?
to get to terminals at the end of the neuron and release neurotransmitters
signaling chemicals that are synthesized in the neuron, released from the neuron and have effects on other neurons/cells
neurotransmitter molecules are made from precursor molecules either in the soma or terminals
Which neurotransmitters synthesize in the soma?
large molecule NTs
Which neurotransmitters synthesize in the terminals?
small molecule NTs
How are neurotransmitters packaged, stored, and transported?
-packed into vesicles by the golgi apparatus and stored until needed
-if necessary, they are transported down the axon along the microtubules (large NTs)
How does release of neurotransmitters occur?
What is added to action potential during exocytosis?
Explain release through exocytosis
-action potential conduction to terminal results in activation of voltage gated calcium channels in release zone
-causes influx in Ca2+ ions into terminal allowing vesicular fusion and formation of an omega figure with subsequent release of neurotransmitter
-adding 5th ion to action potential which comes into release zone, fuses to membrane and opens omega figure
How is calcium involved in exocytosis?
-calcium channels open, and calcium allows vesicle to fuse to membrane then release NT into next neuron
What happens after NTs travel across the synaptic cleft?
-bind to receptors on the postsynaptic membrane, leading to EPSPs or IPSPs in the next neuron
What are receptors?
proteins located in neuronal membranes that neurotransmitters bind to and/or activate (may or may not activate)
Receptors match ___________ neurotransmitters. What is it referred to as?
a single, ligand
A single neurotransmitter has _________ receptors.
Where can receptors be located?
-postsynaptic membrane (more typical)
What types of receptors are found in the presynaptic membrane?
autoreceptors and heteroceptors
Autoreceptors vs heteroceptors
-autoreceptors are activated by the same NT
-heteroceptors are activated by different NT
-both signal their neuron to stop releasing NTs if there is too much (if there is too much NT it will go to presynaptic receptor)
Ionotropic receptors vs metabotropic receptors
-ionotropic open ion channels directly, effects are fast but short duration
-metabotropic open ion channels indirectly, effects are slow, long lasting, more diffuse and varied
How do ionotropic receptors work?
-associated with ligand-gated ion channels
-direct opening of ion channels when neurotransmitter binds
-receptors have multiple subunits
-when GABA binds, it changes shape of gate (subunits) letting ions flow in
How do metabotropic receptors work?
-rely on G-proteins to convey effects through intermediate molecules called 2nd messengers to indirectly open ion channels
-known as G-protein coupled receptors (GPCRs)
-G-protein is inactive until NT comes along
-then G-protein splits into 3 parts that do other things and ultimately go back to ion channel
-passing work onto other steps that can do the work
Why are metabotropic receptors considered to be neuromodulators?
they do nothing directly, just modulate things around them
*look at slide for metabotropic receptors
How does NT termination happen?
-reuptake and recycling
enzymes breakdown the NT molecule into metabolites
Where does enzymatic degradation occur?
within synapse or glial cells (astrocytes)
Reuptake and recycling
membrane transporters return molecules into the axon terminal (presynaptic) to be repackaged in vesicles for later use
Diffusion of NT
NTs diffuse out of concentrated area
Recommended textbook explanations
Lehninger Principles of Biochemistry
David L Nelson, Michael M. Cox
Lisa A. Urry, Michael L. Cain, Peter V Minorsky, Steven A. Wasserman
Modern Biology: Student Edition
Janet L. Hopson, Postlethwait
Fundamentals of Biochemistry: Life at the Molecular Level
Charlotte W. Pratt, Donald Voet, Judith G. Voet
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