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40 Cards in this Set

  • Front
  • Back
Gap junctions are formed by what proteins?
Which type of synapses are easily blocked by reagents that affect transmission?
Chemical synapses
Where are electrical synapses usually found, and why?
They are usually found in "fixed action" pathways that must function without delay.
what is the most common synapse type throughout the nervous system?
What does the basal lamina of the synaptic cleft contain?
What are 2 key features of the NMJ?
it's size and density of postsynaptic receptors
What is the most common excitatory neurotransmitter in the brain?
Nerve stimulation that causes release of transmitter produces an
Excitatory postsynaptic potention (EPSP)
What happens when the nerve is stimulated in the absence of Ca?
Either no EPSP is produced or a greatly reduced one.
What occurs with changes in the size of presynaptic depolarizations?
As the size of the depolarizations increases, both the amount of Ca entering the presynaptic terminal and the size of the postsynaptic response increase
How many Ca ions are required for each vesicle released?
What is the normal synaptic delay?
About 0.5 msec
What is most of the delay contributed to?
Due to the time necessary for Ca channels to be activated and to the subsequent reactions triggered by the Ca to promote release.
What contriubtes 10% of the synaptic delay?
Diffusion of the transmitter across the synaptic cleft.
How is neurotransmitter released?
By simultaneous release of a fixed number of acetylcholine molecules
EPSPs are composed of many what?
what is the morphological equivalent of a quantum?
A vesicle
What is the quantal hypothesis?
that synaptic transmitter release takes place by release of small unitary packets of transmitter.
About how many quanta make up a single evoked EPSP at the NMJ
about 100
How does Ca influx affect quanta?
Ca influx increases the probability of release of a single quantum, it does not change quantal size.
Activation of how many Ach receptor molecules is responsible for a single quantal event?
about 2,000
Each vesicle holds how many molecules of Ach?
What is the reversal potential of a neurotransmitter?
The membrane potential at which it causes no net current flow.
What are the three mechanisms used to terminate neurotransmission?
1. diffusion of the neurotransmitter away from the postsynaptic membrane; 2. degradation of the transmitter by enzymes present in the synaptic cleft; 3. reuptake of the transmitter into the presynaptic terminal
How is neurotransmission terminated at the NMJ?
By the action of acetylcholinesterase
What is the result of inhibiting esterase?
The EPSP or MEPP is prolonged (the falling phase only)
What are anti-esterases used for?
used in therapeutically treating cases of muscle weakness
How is postsynaptic inhibition mediated?
By K or Cl ions
What greatly reduces membrane resistance?
Opening of Cl channels
What are the two locations at which inhibitory synapses are efficient?
Presynaptic terminal and the initial segment
Describe facilitation.
several constant stimuli rapidly delivered to a nerve will produce a gradual increase in the size of the successive EPSPs
Describe depression.
Several constant stimuli rapidly delivered to a nerve will often produce a gradual decrease in the sizes of the EPSPs. (habituation)
Give two examples of presynaptic phenomena.
Facilitation and Depression
What are the changes involved in facilitation due to?
An increase in the number of quanta released from the nerve terminal with each successive stimulus, not an increase in the size of each quantum. This is due to the build up Ca in the presynaptic terminal.
What causes the changes involved in depression?
Depletion of presynaptic vesicles
Describe temporal summation
occurs when potentials arise at the same synapse in such quick succession that the effects of one add to the effects of those of the preceding one.
Describe spatial summation
occurs when potentials arising from the activation of different synapses spread through the dendritic tree to produce an effect on the cell that is different than either would produce alone.
What is the net result of summation of synpatic potentials?
The cell either does or does not reach threshold.
Where are most inhibitory synapses located?
At the inital segment
Are all synapses created equal?