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50 Cards in this Set
- Front
- Back
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How are the signaling mechanisms in the NMJ simpler than in the CNS? |
1) Muscle cells are innervated by only one neuron 2) Muscle fibers receive only excitatory input 3) All connections are mediated by the same neurotransmitter, which activates the same kind of receptor channel 4) NMJ is highly effective - each synaptic potential invariably produces an action potential |
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What provides excitatory and inhibitory input in the spinal stretch reflex? |
Excitatory: sensory neuron Inhibitory: interneuron |
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What role does synaptic inhibition play in the spinal stretch reflex? |
Can counteract the sum of the excitatory actions and prevent the membrane potential from reaching threshold Exert powerful control over spontaneously active nerve cells Can determine the pattern of firing in a cell (sculpturing role of inhibition) |
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What causes EPSPs in spinal motor neurons? |
The opening of channels permeable to both Na+ and K+ |
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What is the best way to study the movement of ions responsible for the EPSP? |
Voltage clamp to obtain the the reversal potential |
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What direction is the current when the membrane potential is made more positive than the reversal potential? |
Outward |
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What happens as the EPSP pushes the membrane potential from its resting state to the reversal potential? |
Threshold is reached |
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What is the excitatory transmitter released from the primary afferent neurons? |
Glutamate |
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What are the four types of glutamate receptors? |
AMPA receptor 1) Kainate, not affected by antagonist NMDA, but affected by AMPA (agonist), named after agonist 2) Quisqualate A, not affected by antagonist NMDA, but affected by AMPA (agonist), named after agonist 3) NMDA receptor 4) Quisqualate B, second-messenger |
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Which glutamate receptor produces the EPSP in the spinal stretch reflex? |
AMPA |
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What are two exceptional properties of NMDA channels? |
1) The receptor controls a cation channel of high conductance permeable to cations 2) Channel is plugged by extracellular Mg2+ at the normal resting membrane potential Requires depolarization as well as glutamate binding Only functions in the presence of glycine |
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What part of the EPSP is due to NMDA receptors? |
The small late component |
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How would you block NMDA receptors? |
APV |
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How would you inhibit NMDA receptors? |
PCP |
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What are three other interesting features of NMDA receptors? |
1) Current flow through the channel is maximal when both glutamate is present and the cell is depolarized 2) Ca2+ entry is thought to activate Ca2+-dependent second-messenger cascades (contributes to certain long-term modifications) 3) An imbalance in excitatory transmitters like glutamate may contribute to disease |
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What is glutamate toxicity? |
Excessive amounts of glutamte, brief exposure will kill neurons |
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What causes glutamate toxicity? |
Excessive inflow of Ca2_ |
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What does glutamate toxicity contribute to? |
Cell death after stroke, persistent seizures, and Huntington's chorea |
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How do inhibitory transmitters act on the neuron? |
Open Cl- channels, mediated by second messengers can involve opening of K+ channels as well |
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Does the IPSP become larger or smaller with increasing depolarization? |
Larger |
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If the resting potential is close to the Cl- equilibrium potential, how do Cl- channels prevent a cell from firing? |
It drives down after a depolarization or holds the cell at a lower potential, increases gm, decreasing VEPSP |
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In what three ways does opening of Cl- (or K+) channels inhibit the postsynaptic cell? |
1) An IPSP can hyperpolarize the membrane and move the membrane potential further away from theshold 2) By increasing the cell's permeability to Cl- stabilizes the membrane near the Cl- equilibrium potential 3) Increases the membrane conductance, reducing the amplitude of an EPSP Short-circuiting or shunting action of inhibition |
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Describe glycine. |
Less common than GABA Used in the spinal cord by interneurons that inhibit antagonist muscles |
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Which GABA-A receptor binds GABA with greatest affinity? |
Alpha |
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What two drug types bind the GABA-A receptors? |
Barbituates and benzodiazepines |
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What effect does drug binding have on the Cl- channel? |
Increases the binding of GABA |
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How do Cl- channels select? |
M2 region contains clusters of basic amino acids which are positively charged at neutral pH |
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What five features do membrane-spanning channels share? |
1) Share an architectural plan in which the segments that span the membrane are arranged around a central axis to form a gated, water-filled pathway for ions 2) Subunits are either identical, very similar, or have similar domains 3) Ion selectivity is roughly related to the number of subunits and resulting diameter of the pore 4) Similar conformation, therefore similar mechanisms 5) Switch from open to closed states thought to involve only a small tilting of subunits, not a radical realignment |
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Describe the ion channels involved in the resting potential. |
Type: Mostly K+ and Cl-, some Na+ Mechanism: Nongated channels Signal Properties: Steady |
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Describe the ion channels involved in the action potential. |
Type: Separate Na+ and K+ channels Mechanism: Voltage Properties: All or none; 100 mV amplitude; 1-10 ms in duration |
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Describe the ion channels involved in the receptor potential. |
Type: Single class of channels for both Na+ and K+ Mechanism: Sensory stimulus Properties: Graded; fast; small amplitude |
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Describe the ion channels involved in the electrical PSP. |
Type: Gap junctions (permeable to many ions and small organic molecules) Mechanism: deltaV, deltapH, deltaCa2+ Properties: Passive spread of presynaptic potential change |
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Describe the ion channels involved in increased-conductance PSPs. |
Type: EPSP depends on a single class of channels for Na+ and K+; IPSP depends on channels for Cl- (or K+) Mechanism: Chemical transmitter Properties: Graded, fast, small amplitude |
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Describe the ion channels involved in decreased-conductance PSPs. |
Type: Closure of channels for K+, Na+, or Cl- Mechanism: Chemical transmitter and intracellular messenger Properties: Graded, slow, small, contributes to the action potential's amplitude and duration |
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How many afferent neurons would have to fire to reach motor neuron threshold? |
75 |
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What determines the relative contribution of the inputs? |
Location Size Shape Proximity Relative strength of other synergistic or antagonistic synapses |
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What is the brain's most fundamental activity? |
Neuronal integration, deciding whether or not to fire |
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What is the role of the axon hillock? |
Decision made here at the initial segment of the axon |
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Why is the decision made at the axon hillock? |
Membrane there has a lower threshold than the membrane of the cell body or dendrites (higher density of voltage-dependent Na+ channels) |
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How many trigger zones are there? |
There can be some in the dendritic tree |
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What two passive membrane properties of the neuron determine neuronal integration? |
1) Time constant determines the time course of the synaptic potential, affects temporal summation 2) Length constant determines the degree to which a depolarizing current decreases as it spreads passively, affects spatial summation |
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What are the three most common types of synaptic contact and two less common types? |
1) Axo-axonic 2) Axo-somatic 3) Axo-dendritic 4) Dendro-dendritic 5) Soma-somatic |
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Which synaptic contact type has the strongest signal? |
Axo-somatic |
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What is the location of inhibitory inputs in relation to excitatory ones? |
Inhibitory inputs are often on the cell body of neurons |
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What are two major sites on each dendritic branch for synaptic inputs? |
The main shaft The spines |
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What is the spine? |
A highly specialized input zone with a thin spine neck and a more bulbous spine head; at least one synapse on its surface; represents a distinct biochemical compartment |
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What is the effect of axo-axonic synapses? |
No effect on trigger zone, but affect the activity of the postsynaptic neuron by controlling the amount of transmitter it releases |
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What are the two morphological types of synaptic connections? |
Gray type I and type II |
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Describe Gray type I synapses. |
Glutamatergic Excitatory Slightly widened cleft Dense projections are prominent Round vesicles Amorphous dense basement membrane |
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Describe Gray type II synapses. |
Often GABAergic Inhibitory Smaller active zone Less obvious projections Little or no basement membrane Vesicles oval or flattened
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