Nervous System 3 - Synaptic Transmission Flashcards by Adwoa B

What are the sequence of events involved in transmission at a typical chemical synapse?

An action potential invades the presynaptic terminal
Depolarization of the terminal causes opening of voltage gated Ca2+ channels
Ca2+ enters through channels
Ca2+ causes vesicles to fuse with the presynaptic membrane
Transmitter is released into synaptic cleft via exocytosis
Transmitter binds to receptor molecules in the postsynaptic membrane
Transmitter binds to receptor molecules in the postsynaptic membrane
Opening or closing of postsynaptic channels
Postsynaptic current causes excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell
Removal of neurotransmitter by glial uptake or enzymatic degradation
Retrieval of vesicula membrane from plasma membrane

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What happens when an Action Potential invades the Presynaptic terminal?

It causes openings of voltage gated Ca2+ channels

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What does the opening of Voltage gated Ca2+ channels allow for?

The movement of Calcium inside of the cell

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What does the influx of Calcium trigger?

It triggers vesicles containing transmitters to fuse with the presynaptic membrane

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What happens after vesicles fuse with the presynaptic membran?

The transmitter is released in the cleft via exocytosis

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What happens after transmitters are released from the vesicles?

The transmitters bind to receptor molecules in the postsynaptic membrane

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What happens after transmitters bind to to receptor molecules of the postsynaptic membrane?

It causes opening or closing of the postsynaptic channels which cause excitatory or inhibitory postsynaptic potential that changes the excitability of the postsynaptic cell

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How are neurotransmitter removed?

By glial uptake or enzymatic degradation

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What is the main excitatory transmitter?

Glutamate

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What does Glutamate cause?

Sodium channels to open allowing sodium to enter the cell

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What is the main inhibitory neurotransmitter?

GABA

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What does GABA cause?

Cl- channels allowing Cl- to enter the cell causing hyperpolarization

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What happens to the EPSP when Calcium channels are blocked in the presynaptic neuron?

No EPSP occurs

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What does Calcium Chelator do?

It binds to calcium inside a nerve terminal preventing calcium from triggering transmitter release and therefore blocking postsynaptic potentials

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What is an Endplate?

The synapse between nerve and muscle (neuromuscular junction)

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What is an End-Plate potential?

An EPSP at the neuromuscular junction

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What does EPSP stand for?

Excitatory postsynaptic potential

How does distance affect EPSPs?

EPSP decay in size over long distances

What does MEPP stand for?

Miniature endplate potential

What does a MEPP result from?

The release of a very small amount of neurotransmitter contained in a single vesicle

What causes a single vesicle to be released?

Sometimes due to an action potential and sometimes released spontaneously

How do we know that transmitters are released in quantal packets?

Because each packet results in the same amount of depolarization which is a MEPP

How much depolarization will the smallest Quantum produce?

0.4mV of depolarization

What is a Synaptic delay?

The time between onset of presynaptic spike and onset of EPSP

What is the neurotransmitter at the neuromuscular junction?

Acetylcholine (ACh)

What does ACh cause?

It opens channels that conduct both Na+ and K+ ions

What does AChE break down?

ACh for recycling

What happens once ACh binds to receptors?

Receptors at the NMJ open to allow sodium to enter and potassium to leave

What is an example of Transmitter and Voltage gated channels working together?

In the NMJ ACh opens channels that allow sodium to enter and K+ to leave and then voltage gated Na+ channels allow sodium to enter both working to bring the postsynaptic cell to threshold

What occurs in Myasthenia gravis?

The loss of voltage gated Ca2+ channels in presynaptic terminals of motor neurons which results in reduced neurotransmitter release at NMJ and muscle weakness

What occurs in Botulism?

Food poisoning from clostridium bacteria which impairs transmitter release at NMJ causing paralysis of muscle

What is the Reversal Potential?

The membrane potential at which there is zero net current through a transmitter gated channel because ions are flowing in and out

Which channel conducts sodium and potassium?

ACh receptor channels

What does the Reversal Potential depend on?

It depends on the relative conductances of the synaptic channel to ions and also on the equilibrium potentials for these ions

What is the rule surrounding membrane potentials and reversal potentials?

Vm will always move towards the reversal potential of the synaptic channel when its conductance increases (when the channel opens)

What is the difference between Na and K transmission in between ACtion Potential and EPSPs at NMJs?

In Action potentials have separate Na and K channels | In EPSPs acetylcholine channels conduct both Na and K

What is the Erev in EPSP?

0 mV

What are EPSPs at NMJs triggered by?

Acetylcholine

What are action potentials initiated by?

Depolarization

What are channels controlled by in EPSPs?

Transmitters; they are not sensitive to voltage

What are EPSPs blocked by?

Curare