Module 3 Lecture 7 - Synapses & Neuronal Integration Flashcards
With excitatory synapses, the post synaptic response to a Neurotransmitter should be what?
Depolarization
When vesicles are released from the pre-synaptic membrane into the receptors at the post synaptic membrane what is happening?
- NT attach to the receptors on the postsynaptic membrane
- Opens up the chemical-gated ion channels (changes ion permeability of the postsynaptic neuron
- Ions (mainly Na+ but other ones too) are able to go down their concentration gradients + electrical gradients
What is an excitatory postsynaptic potential (EPSP)?
A graded potential that decremently spreads from the synapse by local current
Change in postsynaptic potential occuring at an excitatory synapse = EPSP
Are postsynaptic potentials the same as action potentials?
No; instead of being an all or nothing it depends on graded potentials and the magnitude of the graded potentials
Also EPSPs and IPSPs are generated via opening chemically gated channels rather voltage gated channels (depends more on difference in chemical concentration rather than electrical difference like in action potentials)
How is Inhibitory Postsynaptic Potential different from EPSP?
Instead of activating the postsynaptic neuron it inhibits it so it releases less NT & therefore the result is hyperpolarization
What are ligand gated channels?
Channels that respond to chemicals like NT binding to it and causing it to there open
* Synapses use this for their receptors as well as EPSP and IPSP
Different from voltage channels which have inactivation and activation gates and are only used for action potentials
With inhibitory synapses which ions become more permeable and which channels open up?
Since inhibitory is hyperpolarizing the Cl- and K+ ions become more permeable; the Cl- and K+ channels open up
Why does K+ move out and Cl- move in?
K+ follows its concentration gradient outside to Keq which is -90mV and Cl- is following its concentration gradient inside which Cl-eq is -70mV
Some cells have active transport of Cl- into or out of the cell. What does this mean?
Neurons can alter the Cl- to modify membrane potential
* Inhibitory via IPSP (hyperpolarize the cell by importing Cl- via active transport)
* Excitatory via EPSP (Depolarizing the cell by exporting Cl- to ECF via active transport)
Using active transport: disregards equilibrium potential & membrane potential that passive diffusion must take into account
Application: Some tick medications inhibit Cl- transport
If some neurons don’t use active transport for Cl- how does it use passive transport to move it across? What does it need to account for?
Passive diffusion of Cl- depends on equilibrium potential relative to membrane potential
Cl- eq is the same as resting membrane potential (-70mV)
What is a synaptic delay?
The time it takes for an electrical signal from a presynaptic neuron to get to the post synaptic neuron
0.5-1.0ms
What is Total Reaction Time?
The sum of synaptic delays (How much time it takes to respond to a certain event)
Can Neurotransmitters stay on the receptor forever?
No; eventually the NT will have done its job to get the ions needed inside the postsynaptic neuron
What is the equilibrium between the bound NT and the unbound NT?
If unbound receptors are removed from the synaptic cleft, the receptors occupied will decrease
In what ways can NT be removed from the receptors they are bound to?
- Actively transported back into the cell = Reuptake
- Diffuse away from the receptor site and cleft
- Enzymatically transformed into inactive substances (eventually recycled into presynaptic axon terminal)
What is an Excitatory Synapse vs Excitatory Post Synaptic Potential
Excitatory synapse is the physical synapse that causes excitation and the EPSP is the result of the excitatory synapse changing the potential of the membrane
Example: If a NT is released that causes excitatory synapse the EPSP is the result of the E.S. moving from -70mV to -50mV
What does the sum of the IPSPs and EPSPs generate?
The GPSP (Grand Postsynaptic Potential)
Potential being ‘what can happen to the membrane’
Explain how E.S. and EPSP as well as I.S. and IPSP work?
- A and B are excitatory synapses which causes a resultant EPSP (EPSPs are graded potentials that summate on each other)
Excitatory Synapses are action potentials which induce/result in an EPSPs (graded potentials)
Define Temporal, Spatial and Temporospatial Summation?
*Temporal Summation is when one neuron fires and the time fired between each neuron is decreased, the neurons summate (graded potentials summate)
**Spatial Summation is two neurons firing their action potential (E.S. or I.S.) and this results in the EPSP (graded potential) or IPSP (graded potential) either building on top of each other or hyperpolarizing
- Temporospatial Summation is the combination of temporal which is one neuron firing rapidly to increase the likelihood of an action potential occuring and spatial summation which is two neurons firing to summate on top of one another and increase the likelihood of an action potential occuring
Explain how EPSPs and IPSPs are at play here?
- Since the inhibitory synapse is on the excitatory synapse (A); when both fire something will occur
- Excitatory will try to depolarize the membrane and increase the excitability of the membrane (change membrane potential) => EPSP will have to occur (small graded potential change)
- Inhibitory however, will prevent EPSP from occuring and an IPSP counteracting the EPSP will appear so that it looks as though there was no change in membrane potential
