Lecture 3: The Action Potential

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Taken from lecture 3 of PSY 314
McKenzie Sanders
Flashcards by McKenzie Sanders, updated more than 1 year ago
McKenzie Sanders
Created by McKenzie Sanders almost 8 years ago
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Resource summary

Question Answer
What does the action potential do? Depolarizes membrane abruptly, allowing neuron to communicate over long distances
What is the concentration of sodium ions in a neuron at rest? More sodium ions outside the cell than inside
What is the concentration of potassium ions in a neuron at rest? More potassium ions inside the cell than outside
Are there more sodium or potassium ions in a neuron at rest? Sodium
Is the outside of the neuron more positively or negatively charged than the inside of a neuron at rest? Positive
Why is the inside of a neuron at rest more negative than the outside? Fewer potassium ions inside than sodium ions outside
What does membrane potential measure? Difference in electrical potential inside and outside of the cell Measured with respect to the outside of the cell
What is the approximate potential of a neuron at rest? -70 mV
What is resting potential? Membrane potential of a neuron at rest or when it is not being excited or inhibited by other inputs
In comparison to hyperpolarization, how negative is depolarization? Less negative Towards zero
What is a depolarization? Reduction of the membrane potential from its normal resting potential
In comparison to depolarization, how negative is hyperpolarization? More negative
What is a hyperpolarization? Increase in the membrane potential relative to the normal resting potential
What is the name of the voltage level that triggers an action potential? Threshold of excitation
What is the approximate level of the threshold of excitation? -60 mV
What happens during an AP? (step by step) Neuron at rest: -70 mV Threshold of excitation reached: -60 mV Voltage-gated Na+ channels open; Na+ enters Voltage-gated K+ channels open; K+ exits Depolarizes to +40 mV Na+ channels close; K+ continues to exit Repolarizes to -75mV; after-hyperpolarization Na+/K+ transporters re-establish resting potential; -70 mV
What are the 2 forces that move ions? Diffusion Electrostatic pressure
What is diffusion? Movement of molecules from regions of high concentrations to regions of low concentrations Tend to be distributed evenly throughout the medium over time
What is electrostatic pressure? Force of attraction or repulsion between ions Opposites attract Likes repel
What produces membrane potential? A balance between the forces of diffusion and electrostatic pressure
Which ions are in the extracellular fluid? Cl- Na+
Which ions are in the intracellular fluid? K+ Organic anions (A-)
How do diffusion and electrostatic pressure act on K+ ions? Net movement at rest? Diffusion pushes it out of the cell Electrostatic pressure pushes it into the cell Net movement: none
How do diffusion and electrostatic pressure act on Cl- ions? Net movement at rest? Diffusion pushes it into the cell Electrostatic pressure pushes it out of the cell Net movement: none
How do diffusion and electrostatic pressure act on Na+ ions? Net movement at rest? Diffusion pushes it into the cell Electrostatic pressure pushes it into the cell Net movement: ready for action
What type of ion channels play a role in action potentials? Voltage-dependent or voltage-gated
What do voltage-gated ion channels open in response to? Changes in membrane potential Specific ion
How sensitive are voltage-gated Na+ channels? Do they require a large amount of depolarization? Very sensitive Require minimal depolarization to open
How sensitive are voltage-gated K+ channels? Do they require a large amount of depolarization? Less sensitive Require more depolarization to open
What is the change in membrane potential at the peak of an action potential? 100 mV
What change in membrane potential causes voltage-gated K+ channels to open? Membrane potential becomes less negative/more positive
At what measurement do Na+ channels become refractory? +40 mV
What happens to Na+ channels when they enter the absolute refractory period? Na+ channels are unable to open No more Na+ enters
What returns the membrane back to rest during an action potential? What is this period called? Outflow of K+ Overshoot/afterhyperpolarization
What mechanism returns the neuron to resting potential? Na+/K+ transporter
At what rate do Na+ and K+ move in comparison to the other in an action potential? Na+ enters much faster than K+ K+ enters later than Na+ and over a longer period of time
What does the all-or-none law state? Once an action potential is triggered, it is transmitted without decreasing in size to the end of the neuron AP is always the same size
What does the rate law state about an AP? Variations in the intensity of a stimulus or other information transmitted in an axon are represented by variations in the firing rate
What does the firing frequency of an action potential reflect? Magnitude of the depolarization
What would the firing rate from a strong stimulus elicit in comparison to a weaker stimulus? Higher firing rate from neuron
What is firing rate limited by? Refractory period
What is the firing rate of a neuron during an absolute refractory period? No AP
What is the firing rate during a relative refractory period? AP can be triggered given enough stimulation
What is saltatory conduction? Conduction of APs in myelinated axons AP jumps from one node of Ranvier to the next
Do myelin and the nodes of Ranvier make contact with the extracellular fluid during an AP? Nodes of Ranvier do Myelinated portion of axon does not
What are the advantages of saltatory conduction? Economical; less Na+/K+ transporters that require energy Speedy; transmission between nodes is very fast Allows for faster reaction times/faster thinking
What effect will increasing the size of the axon have on conduction? Increases conduction speed
What is synaptic transmission? Primary means of communication between neurons
What does synaptic transmission produce? Postsynaptic potentials (PSPs)
What is the presynaptic membrane? Membrane of a terminal button that lies adjacent to the postsynaptic membrane
What is the postsynaptic membrane? Membrane on the cell that receives the message that is opposite the terminal button
Which area of the postsynaptic membrane has receptors on it? Thickened areas of the postsynaptic membrane have receptors on them
What are receptors? Protein molecules embedded in the membrane
What do synaptic vesicles contain? Molecules of chemical messenger
What happens at the synapse? Release of a neurotransmitter
What happens during the release of a neurotransmitter? An AP is conducted down an axon to the terminal buttons AP triggers synaptic vesicles to fuse with the presynaptic membrane Fusion of synaptic vesicles and presynaptic membrane causes release of chemical messenger (neurotransmitter) from inside the vesicles into the synaptic cleft NT diffuses across synapse to postsynaptic membrane Interacts with receptors located in postsynaptic membrane
Where are neurotransmitters synthesized? Axon terminal or cell body
Where is the NT packaged while waiting to be released? Vesicles
What type of transport is involved in the NT moving from the cell body to the terminal buttons? Anterograde axoplasmic transport
What can trigger a single vesicle to release its contents into the synaptic cleft? A single AP
What are packets of NT called? Quanta
What causes quantal release? Vesicle storage/release system
What does an AP arriving at the terminal button trigger? Opening of voltage-gated Ca2+ channels
What is the flow of Ca2+ during release of a NT? Inward Down electrostatic gradient and concentration gradient
What does an elevation in Ca2+ levels trigger? What is this process called? A sequence of events that causes vesicles to fuse to presynaptic membrane and release contents Exocytosis
What process allows for the vesicle to be recycled and reused? Endocytosis
What protein is activated by Ca2+ entering the terminal? Calmodulin
What is the function of calmodulin? Activates synapse proteins that allow vesicles to fuse to the membrane
What is the synaptic cleft? Space between presynaptic and postsynaptic neurons
What is a ligand? A chemical (molecule of NT or a drug) that binds to a binding site of a receptor
What does ligand binding form? Ligand-receptor complex
How does formation of the ligand-receptor complex happen? Induces conformation change (physical change in shape) in receptor Conformation change induces a chain of physiological events
What does ligand binding result in? The opening or closing of ion channels Changes in membrane potential in postsynaptic neuron
What does receptor activation do? Can open ion channels, changing membrane potential (PSP) Can have intracellular effects Can affect ion channels by making them more or less likely to open or close Affect gene transcription
What is an excitatory postsynaptic potential (EPSP)? A brief depolarization of the postsynaptic membrane caused by the neurotransmitter release and subsequent receptor activation
What is a graded response? Amplitude of response is proportional to intensity of the signal
What is an inhibitory postsynaptic potential (IPSP)? A brief hyperpolarization of the postsynaptic membrane caused by the neurotransmitter release and subsequent receptor activation
What is neural integration? The interaction of all of the IPSPs and EPSPs a neuron receives
Where does neural integration take place? Initial segment of neuron
In what 2 ways can PSPs be summed? Spatially and temporally
What is spatial summation? Summing of PSPs generated simultaneously at different synapses on a neuron
What is temporal summation? Summing of PSPs that occur at the same synapse in rapid succession
What are the two types of receptors? Ionotropic (ligand-gated) Metabotropic (G-protein coupled-GPCR)
What is an ionotropic receptor? Receptor that is an ion channel and contains a binding site for a neurotransmitter
What is a metabotropic receptor? A receptor that contains a binding site for a neurotransmitter and that is coupled to a G-protein
What are the characteristics of ionotropic receptors? Ligand binding opens ion channel allowing ions to pass through Relatively fast Usually selective for a particular ion
What are the characteristics of metabotropic receptors? Ligand binding results in G-protein which while affect an ion channel or affect an enzyme which controls production of 2nd messenger Relatively slow Suited for slow sustained signaling or for modulating fast transmission
What 2 mechanisms keep PSPs brief? Enzymatic deactivation & reuptake
What is enzymatic deactivation? Enzyme that destroys the neurotransmitter at the synapse
What are the components that a NT is broken down into during enzymatic deactivation? Metabolites
What is enzymatic deactivation especially important for? ACh and neuropeptides
What happens to metabolites during enzymatic deactivation? Recycled presynaptic neuron takes up the precursor and reuses it for NT synthesis Neuroglia take it up for excretion via the bloodstream
What is reuptake? Rapid removal of the neurotransmitter from the synaptic cleft by the terminal button Special transporters actively take NT back into presynaptic cell's terminal button Against concentration gradient; requires ATP Enzymes inside cell can then deactivate NT
What effects reuptake? Drugs
What can neurotransmitters be taken up by? Neurons that release it Other neurons in the vicinity Nearby astrocytes
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