Term
| What are the different functions of synapses? |
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Definition
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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Term
| What are the basics of structure and function of an electrical synapse? |
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Definition
Gap junctions
-Adjacent cells (the cells are very close together)
-Cytoplasmic continuity
-Small molecules & ions
-Bidirectional flow of signal
They do not constitute the majority of synapses but are important. ex - epithelial cells |
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Term
| What are the basics of structure and function in a chemical synapse? |
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Definition
Most predominant type of synapse
Not structurally connected - distance between cells is much greater than in electrical synapses
Transmitter released
Unidirectional flow of signal (distinction from electrical synapse) |
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Term
| What are the distinguishing properties of electrical and chemical synapses? |
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Definition
1. distance between pre and post synaptic cell membranes
- 3-5 nm in E, 30-50 in C
2. E has cytoplasmic continuity (gap junction) while C does not
3. ultrastructural components
- E has gap junction channels
- C has pre-synaptic active zones and vesicles, post-synaptic receptors
4. agent of transmission
- E uses ionic current
- C uses chemical transmitter
5. synaptic delay
- E virtually has none
- C has significant, at least 0.3 ms, usu.1-5 ms
6. direction of transmission
- E is usually bi-directional
- C is unidirectional |
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Term
| What are the different type of synaptic contacts and why are the differences important? |
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Definition
Axosomatic synapses
Synaptic current generated at this site has a stronger signal & greater influence on outcome at trigger zone vs axodendritic contacts.
Axodendritic synapses
Proximity of this synapse to trigger zone is important in determining its effectiveness.
Axo-axonic synapses
Most of these synapses have no direct effect on trigger zone of postsynaptic cell. Affect activity by controlling transmitter release
location of the synapses can influence the signal strength and transmitter release |
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Term
| What are the basics behind the one-to-one synapse? |
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Definition
One action potential in the presynaptic cell results in a single action potential in the postsynaptic cell.
This is rare and only known example is in the neuromuscular junction |
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Term
| Explain the one-to-many synapse input-output relation |
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Definition
A single cell can exert widespread influence by distributing its signal to many target cells. this is divergence
Example – Renshaw cells in the spinal cord. One action potential in the motoneuron induces the Renshaw cell to fire a burst of action potentials. |
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Term
| Explain the many-to-one synapse input-output relation |
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Definition
Neuronal convergence allows a target cell to integrate diverse information from many sources.
Ex – Most common input-output relation. The motor neurons at the output of the nervous system receive a progressive convergence of connections. |
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Term
| What is the sequence of transmission in a chemical synapse? |
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Definition
1. action potential in presynaptic cell
2. depolarization of the plasma membrane of the presynaptic axon terminal
3. voltage-gated Ca2+ channels are open and Ca2+ enters the presynaptic terminal
4. exocytosis of the transmitter by the presynaptic terminal
5. chemical combination of the transmitter with specific receptors on the plasma membrane of the postsynaptic cell
6. transient change in the conductance of the postsynaptic plasma membrane to specific ions
7. transient change in the membrane potential of the postsynaptic cell |
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Term
| Explain the quantal release of neurotransmitters |
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Definition
Quanta – The release of transmitter occurs in small packets.
Quantum – Synaptic vesicles release the same amount of transmitter.
Unit Synaptic Potential - Each quantum of transmitter produces a postsynaptic potential of fixed size.
Ex – NM junction – 300,000 ACh storage vesicles (quanta) in one synapse. One vesicle contains about 10,000 ACh molecules. (quantum) About 125 vesicles of ACh released with 1 action potential (unit synaptic potential) |
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Term
| Explain how the synaptic input works |
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Definition
Acetylcholine binds to an ACh receptor channel and opens it causing inflow of Na+ and outflow of K+
This causes a depolarization and the result is an end-plate potential
The potential causes voltage-gated Na+ channels to open and Na+ flows in causing depolarization and action potential firing |
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Term
| Explain how the excitatory postsynaptic potential (EPSP) is generated |
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Definition
Opening of Na or cation channels
Closure of Cl or K channels or both
ACh can bind to Na or cation channels and open them. ACh can bind to K or Cl channels and close them. Both of these events lead to depolarization
Changes in cell metabolism to increase cell excitability, # of excitatory receptors or decrease in # of inhibitory receptors |
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Term
| Explain how the inhibitory postsynaptic potential (IPSP) is generated |
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Definition
Opening of Cl or K channels - this is caused by transmitter binding to ligand gated channels
This opening will cause a hyperpolarization
Activation of receptor enzymes that inhibit metabolic functions, decrease in # of excitatory receptors or increase in # of inhibitory receptors. |
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Term
| Explain the two types of synaptic summation |
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Definition
Temporal summation occurs when consecutive synaptic potentials arrive at the same exact spot on the postsynaptic cell and add together
Spatial summation occurs when two separate inputs arrive simultaneously at different spots on the same postsynaptic cell and add together |
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Term
| How does presynaptic inhibition work? |
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Definition
It is the discharge of inhibitory synapses on presynaptic terminals that results in a decrease in synaptic potential of postsynaptic cell.
The conductance of K and/or Cl is increased on the post-synaptic cell. This causes a hyperpolarization which counter-acts the depolarization. |
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Term
| How does presynaptic facilitation work? |
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Definition
This is where discharge of presynaptic cell enhances discharge of transmitter release from another presynaptic neuron that results in an increase in the synaptic potential of postsynaptic cell.
Here you decrease the conductance of K and Cl and increase the conductance of Na. This causes depolarization which helps facilitate |
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Term
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Definition
| This is where a rapid train of action potentials will cause more transmitter release |
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Term
| What is synaptic fatigue? |
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Definition
This is when the transmitter stores are being depleted. This happens when the transmitters are being used faster than they can be synthesized.
This happens in epileptic seizures. |
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Term
| What are the different types of electrical potentials in neurons? |
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Definition
Resting potential
action potential
receptor potential
electrical PSP
increased conductance PSP
decreased conductance PSP |
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Term
| What are the main features of the resting potential? |
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Definition
Mostly leak K+ channels, some leak Na+
the signal is usually steady and ranges from -35 mV to -90 mV |
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Term
| What are the main features of the action potential? |
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Definition
Separate voltage-gated Na+ and K+ channels
signal is all-or-none, about 100 mV in amplitude, 1-10 ms in duration |
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Term
| What are the main features of the receptor potential? |
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Definition
single class of channels for both Na+ and K+
the sensory stimulus is the mechanism
the signal is graded and fast, several ms in duration, several mV in amplitude |
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Term
| What are the main features of the electrical pre-synaptic potential? |
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Definition
they use gap junctions
the gap junctions are regulated by changes in pH and Ca2+
the signal is passive spread of presynaptic potential change |
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Term
| What are the main features of the increased-conductance PSP's? |
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Definition
EPSP relies on opening of Na+ or cation channels. (depol)
IPSP relies on opening of Cl and K channels (hyperpol)
chemical transmitters are what regulate
the signal is graded and fast, several ms to several seconds, several mV in amplitude |
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Term
| What are the main features of decreased-conductance PSP's? |
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Definition
This is the closure of Na+,K+, and Cl- channels. (decreased conductance)
chemical transmitter and intracellular messenger regulate
the signal is graded and slow, seconds to minutes in duration, one to several mV in amplitude |
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