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57 Cards in this Set

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What is the refractory period?
The refractory period is the time when neuron is unable to fire a second AP
What is the absolute refractory period?
The absolute refractory period is the time when a second AP is not possible
When does the absolute refractory period take place? Are Na+ channels open or closed?
The absolute refractory period takes place during depolarization. Na+ channels are either completely open or closed and locked
What does the absolute refractory period ensure?
It ensures that each AP is an all-or-none event
What does the absolute refractory period enforce?
It enforces one-way transmission of nerve impulses
Why is a second AP not possible during the absolute refractory period?
Because the first AP is still occurring
During the relative refractory period, what is occurring?
Hyperpolarization is occurring
During the relative refractory period, which channels are open and which are closed?
Most Na+ channels are closed but ready to open and some K+ channels are still open
During the relative refractory period, what may occur?
If there's a exceptionally strong stimulus opening enough Na+ channels, a second AP may occur
During one AP, what is occurring at time = 2 ms?
AP peak is at the recording electron
During one AP, what is occurring at time = 4 ms?
AP peak has passed and recording electrode is recording hyperpolarization
Why doesn't NA+ travel the other way in AP?
Na+ does go the other way but the channels are closed and locked immediately after AP passes
You only see continuous conduction on what kind of neurons?
Unmyelinated neurons
What is conduction velocity?
Conduction velocity is how fast the axon conducts an AP
Unmyelinated axons propagate by what?
Continuous Conduction
Is the conduction velocity fast or slow with continuous conduction?
Slow: 1 m/s
What does continuous conduction require?
Requires voltage-gated channels all along entire axon
Why is continuous conduction inefficient?
Because it must depolarize and repolarize each patch of membrane
What does myelination of the axon prevent?
Prevents leak of charge
What does myelination of the axon do to the conduction velocity?
Speeds it up
What are the Nodes of Ranvier?
Nodes of Ranvier are bare patches of axon
In myelinated axons, voltage gated channels are located where?
They are only clustered at the nodes of Ranvier
What is saltatory conduction?
Saltatory conduction is where APs appear to jump rapidly from node to node on myelinated axons
In a bare plasma membrane, voltage decays why?
Because current leaks across the membrane
On myelinated axons, conduction velocity with saltatory conduction can propagate APs how fast?
Up to 150 m/sec
What is Multiple Sclerosis?
MS is an autoimmune disease that mainly affects young adults
In MS, what is occurring?
Immune system is destroying myelin in the CNS
What are some symptoms of MS?
Loss of muscular control, disturbances of vision of speech
What does the presynaptic neuron do?
Conducts APs toward the synapse
What does the postsynaptic neuron do?
Transmits APs away from the synapse
Neurons are separated by what?
The synaptic cleft
What is the synaptic cleft?
Fluid-filled space through which NT diffuses
What does the cleft do?
Keeps presynaptic AP from directly reaching postsynaptic neuron
What are the 5 events at the Chemical Synapse?
1. Action potential arrives at axon terminal.
2. Voltage-gated Ca+2 channels open and Ca+2 enters axon terminal
3. Ca+2 entry triggers exocytosis of NT
4. NT diffuses across the synaptic cleft which binds to specific receptors on the postsynaptic neuron
5. Binding of NT opens chemically-gated ion channels which sets of GP
What 3 ways are NT effects terminated?
1. Diffusion away from the synapse
2. Enzymatic degradation
3. Reuptake by transport proteins (NE, or serotonin)
What does EPSP stand for?
Excitatory Post-Synaptic Potentials
What do EPSPs do?
Graded depolarization, excites AP
What does IPSP stand for?
Inhibitory Post-Synaptic Potentials
What do IPSPs do?
Graded hyperpolarizations, inhibits AP
How are post-synaptic potentials graded?
Amount of NT released and how long NT is in the area
The amount of NT released depends on what?
Depends on number of ion channels opened
How long NT is in the area depends on what?
How long channels stay open
Graded potentials may last for how long? How long do APs last?
Seconds to minutes. APs last only 2 msec
A single EPSP cannot do what?
A single EPSP cannot set off an AP
A neuron receives input from one or many other neurons?
Many other neurons
What can EPSPs do to reach threshold?
Summate
When IPSPs and EPSPs summate, what occurs?
They cancel each other out
What are the two types of summation?
Temporal summation and Spatial summation
What is temporal summation?
Temporal summation is when one or more pre-synaptic neurons transmit impulses in rapid fire order
What is spatial summation?
Spatial summation is when the neuron is stimulated by a large number of pre-synaptic neurons at the same time
Most neurons make how many NTs?
2 or more
What does Acetylcholine do?
Excites skeletal muscle to contract and inhibits cardiac muscle and slows heart
What does norepinephrine do/
Excites cardiac muscle (speeds heart up, stronger contractions)
What is Tetrodotoxin?
Tetrodotoxin is a powerful poison that selectively blocks voltage-gated Na+ channels.
What does Tetrodoxin cause?
After it blocks the Na+ channels, APs can't occur and then muscles everywhere can't contract. Death ensues
How far do EPSPs and IPSPs travel?
1-2 mm
On what are EPSPs and IPSPs carried?
Carried by local currents along dendrites