Term
Transmit information between neurons by influencing excitability of postsynaptic neuron.
Delay, diverge, converge, repeat or sustain transmission.
Continuously modify excitability of all central nervous system cells. |
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Definition
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Term
-The gap junctions associated with this synapses provide a pathway for cytoplasmic continuity between the presynaptic and the postsynaptic cells. Gap
junctions appear to be important in the bidirectional transmission of electrical signals, small molecules and ions between neighboring cardiac cells, smooth muscle cells, some nerve cells, and endothelial
cells. |
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Definition
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Term
| The most predominant type of synapse is the ??? . A space called the synaptic cleft separates the presynaptic terminal from the postsynaptic neuron. Always transmit the signals in one direction, from the presynaptic neuron that secretes the transmitter to the postsynaptic neuron on which the transmitter acts. |
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Definition
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Term
| Distance between pre and post-synaptic cell membranes |
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Definition
Electrical Synapse: 3.5 nm
Chemical Synapse: 30-50 nm |
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Term
| Which synapse has cytoplasmic continuity between pre and post-synaptic cell membranes |
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Definition
Electrical Synapse: Yes
Chemical Synapse: No |
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Term
| What type of ultrastructural components do the synapses have? |
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Definition
Electrical Synapse: Gap Junction
Chemical Synapse: Presynaptic active zones and vesicles, postsynaptic neurons |
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Term
| Agent of transmission in synapses are? |
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Definition
Electrical Synapse: Ionic Current
Chemical Synapse: Chemical transmitter |
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Term
| Synaptic delay in synapses |
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Definition
Electrical Synapse: Virtually absent
Chemical Synapse: Significant, at lease 0.3ms |
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Term
| Direction of transmisstion in synapses |
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Definition
Electrical Synapse: Usually Bidirectional
Chemical Synapse: Unidirectional |
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Term
| Synaptic current generated at this site has a stronger signal & greater influence on outcome at trigger zone vs axodendritic contacts. |
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Definition
| Axosomatic synapses (affects cell body) |
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Term
| Proximity of this synapse to trigger zone is important in determining its effectiveness. |
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Definition
| Axodendritic synapses (affects shaft) |
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Term
| Most of these synapses have no direct effect on trigger zone of postsynaptic cell. Affect activity by controlling transmitter release. |
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Definition
| Axo-axonic synapses (affects bouton) |
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Term
| One action potential in the presynaptic cell results in a single action potential in the postsynaptic cell. Example – The neuromuscular junction. What type of synapse is this. |
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Definition
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Term
| A single cell can exert widespread influence by distributing its signal to many target cells. Example – Renshaw cells in the spinal cord. One action potential in the motoneuron induces the Renshaw cell to fire a burst of action potentials. What type of synapse is this? |
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Definition
| One-to-Many Synapse (Divergence) |
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Term
| Neuronal convergence allows a target cell to integrate diverse information from many sources. Example – Most common input-output relation. The motor neurons at the output of the nervous system receive a progressive convergence of connections. What type of synapse is this? |
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Definition
| Many-to-One Synapse (Convergence) |
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Term
General Characteristics of transmission at chemical synapses
AP in Presynaptic cell --> Depolarization of the PM of the presynaptic axon termimal --> Entry of Ca++ into presynaptic terminal --> Release of the transmitter by the presynaptic terminal (exocytosis) --> Chemical combination of the transmitter with specific receptors on the plasma membrane of the postsynaptic cell --> Transient change in the conductance of the postsynaptic PM to specific ions --> Transient change in the membrane potential of the postsynaptic cell |
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Definition
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Term
Chemical Synaptic Transmission
Presynaptic AP --> Increased presynaptic Ca++ permeability, Ca++ inflx --> Release of transmitter by exocytosis of vesicles --> Reaction of transmitter with postsynaptic receptors --> Activation of synaptic channels --> synaptic current produces postsynaptic potential --> Postsynaptic AP |
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Definition
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Term
| The release of transmitter occurs in small packets. |
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Definition
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Term
| Synaptic vesicles release the same amount of transmitter. |
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Definition
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Term
Each quantum of transmitter produces a postsynaptic potential of fixed size. Not enough to produce AP except in example shown below:
NM junction – 300,000 ACh storage vesicles in one synapse. One vesicle contains about 10,000 ACh molecules. About 125 vesicles of ACh released with 1 action potential. |
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Definition
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Term
The release of neurotransmitter at most chemical synapses also occurs in small packets or quanta. Because all of the vesicles are of roughly the same size, they all release about the same amount-that is, a quantum of transmitter. Each quantum of
transmitter produces a postsynaptic potential of fixed size, called the unit synaptic potential. The
total synaptic potential is made up from an integral number of unit potentials. Because of the strong dependence of transmitter release on intracellular Ca concentration, mechanisms within the presynaptic neuron that affect the concentration of free Ca2+ in the presynaptic terminal also affect the amount of transmitter released. |
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Definition
| Quantal Release of Neurotransmitters |
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Term
| After a chemical transmitter is released into the synaptic cleft, it can bind to a receptor located on the postsynaptic cell. The coupling of the transmitter with the receptor causes the receptor to open, permitting the passage of specific ions through the membrane (increase conductance: necessary for depolarization). The receptor can directly activate the ion channel or indirectly activate it through a second messenger such as Gproteins, cAMP, cGMP, or IP3 to alter membrane potential across the postsynaptic membrane. These membrane depolarizations or hyperpolarizations are integrated and can result in activation or inhibition of the postsynaptic cell. |
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Definition
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Term
Postsynaptic potentials that depolarize the
membrane tend to excite the nerve cells to discharge action potentials.
o Opening of sodium channels
o Depressed conduction through chloride or potassium channels, or both.
o Changes in cell metabolism to increase cell excitability, increase in number of excitatory
receptors or decrease in number of inhibitory receptors. |
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Definition
| Excitatory Postsynaptic Potentials (EPSPs) |
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Term
| When a transmitter binds to its postsynaptic receptor, what is the result? |
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Definition
| Membrane potential depolarization |
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Term
Opening of Cl or K channels
Activation of receptor enzymes that inhibit metabolic functions, decrease in # of excitatory receptors or increase in # of inhibitory receptors. |
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Definition
| Inhibitory Postsynaptic Potentials (IPSP) |
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Term
| True or False: Acetylcholine must bind to the cation channels that allow Na+ and K+ ions to move through. This movement cause the opening of the voltage gated Na+ channels. |
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Definition
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Term
Integration of Synaptic Information
Occurs when consecutive synaptic potentials arrive at the postsynaptic cell and add together. |
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Definition
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Term
Integration of Synaptic Information
Occurs when two separate inputs arrive simultaneously at the postsynaptic cell (proximity importnat) and add together. The two
postsynaptic potentials are added so that two simultaneous excitatory inputs will depolarize
the postsynaptic cell about twice as much as either input alone. One EPSP and one IPSP that occur simultaneously will tend to cancel one another. |
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Definition
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Term
Postsynaptic potentials that hyperpolarize the
membrane potential tend to prevent or inhibit the nerve cell from generating an action
potential.
o Opening of chloride channels
o Opening of potassium channels
o Activation of receptor enzymes that inhibit metabolic functions or increase the number
of inhibitory receptors or decrease the number of excitatory receptors. |
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Definition
| Inhibitory Postsynaptic Potentials (IPSPs) |
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Term
Neurons synapse with one another not only on the cell body and dendrites where they can control impulse activity, but also at their terminals (axoaxonic synapses) where they can control transmitter release.
Inhibition if caused by discharge of inhibitory synapses that lie on the presynaptic terminal nerve fibrils before their endings terminate on the
postsynaptic cell is called ??? |
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Definition
Presynaptic inhibition (reduced Ca++ current influx in presynaptic neuron channel)
Ex: Increase gCl in presynaptic membrane
Increase of gK+ in presynaptic membrane
IPSPs cause presynaptic inhibition |
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Term
Neurons synapse with one another not only on the cell body and dendrites where they can control impulse activity, but also at their terminals (axoaxonic synapses) where they can control transmitter release.
Occurs when the discharge of a presynaptic neuron enhances the discharge of transmitter release from another presynaptic neuron that results in an increase in the synaptic potential in the postsynaptic cell. |
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Definition
Presynaptic facilitation (increased Ca++ current influx causing prolong AP)
EPSPs ----> Presynaptic Facilitation |
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Term
Describes a progressive increase in the amount of
transmitter release by successive action potentials during a brief stimulus train lasting up to a few seconds. Dies away rapidly, within tens to hundreds
of milliseconds after the end of stimulation. |
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Definition
| Facilitation or potentiation |
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Term
| Describes an increase in transmitter release by an action potential following repetitive stimulation of a synapse. Requires seconds to develop and lasts tens of seconds to several minutes after cessation of tetanic stimulation. PTP occurs at the neuromuscular junction. PTP might well be a mechanism of “short-term” memory in the CNS. |
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Definition
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Term
Describes a progressive decrease in the amount of transmitter released during a train of action potentials. Often encountered when a synapse is
stimulated at a high rate and, at least in some cases, results from the depletion of
neurotransmitter from the terminal. Important means by which excess excitability during an epileptic seizure is finally subdued so that the seizure ceases. |
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Definition
| Synaptic fatigue or Synaptic depression |
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Term
Ion Channels: Mostly K+ and Cl- channels, some Na+ channels
Ion Channel Mechanism: Channels usually nongated (occasionally gated K+ channels)
Signal Properties: Usualyl steady, ranginf in different cells from -35 to -90 mV |
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Definition
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Term
Ion Channels Type: Separate Na+ and K+ channels
Ion Channels Mechanism: Voltage
Signal Properties: All or none, about 100 mV in amplitude, 1-10 ms in duration |
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Definition
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Term
Ion Channels Type: Single class of channels for both Na+ and K+
Ion Channels Mechanism: Sensory Stimulus
Signal Properties: Graded, fast, several ms in duration, several mV in amplitude |
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Definition
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Term
Ion Channels Type: Gap junctions (permeable) to many ions and small organic molecules)
Ion Channels Mechansim: change in voltage, change in pH, change in Ca++
Signal Properties: Passive spread of presynaptic potential change |
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Definition
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Term
Ion Channels Type: EPSP depends on a single class of channels for Na+ and K+, IPSP depends on channels for Cl- (or K+)
Ion Channels Mechanism: Chemical transmitter
Signal Properties: Graded, fast, several ms to seconds in duration, several mV in amplitude |
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Definition
| INCREASED-CONDUCTANCE PSPs |
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Term
Ion Channels Type: Closure of channels for K+, Na+, or Cl-
Ion Channels Mechanism: Chemical transmitter and intracellular messenger
Signal Properties: Graded; slow, seconds to minutes in duration, one to several mV in amplitude; contributes to the action potentials amplitude and duration |
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Definition
| DECREASE-CONDUCTANCE PSPs |
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Term
| True or False: The unit synaptic potential is the potential change that occurs when a quantum of transmitter is released. The total synaptic potential (EPP) is made up of an integral number of unit synaptic potentials generated from 125 quanta being released. |
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Definition
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