The Cellular Response to Action Potentials Flashcards
What happens when an action potential arrives at the presynaptic membrane?
It causes the opening of voltage-gated Ca channels
What happens when Ca channels open in the presynaptic membrane?
It causes an influx of Ca ions down their conc gradient
What does an increase in intracellular Ca conc cause?
Release of neurotransmitter
How do voltage gated Ca channels differ from Na channels?
They have structural diversity
What is the result of voltage gated Ca channels having structural diversity?
A blocker that blocks one calcium channel will not necessarily block another
What can be done by selectively blocking one type of Ca channel?
Can produce a localised effect
Why can selectively blocking one type of Ca channel have a localised effect?
Because different Ca channels have different primary locations
What happens in fast synaptic transmission?
The receptor protein is also an ion channel, and the binding of neurotransmitter causes the channel to open
What are many cellular processes dependent on?
A change in intracellular Ca contration
Give an example of where a change in intracellular Ca concentration can be important?
The high density of Ca channels at the nerve terminal provides enough Ca influx during action potential to trigger ACh release
How does Ca influx cause ACh release?
Ca binds to synaptotagmin, leading to the formation of the Snare complex, making a fusion pore leading to ACh release from the bound vesicle
What does the released ACh bind to?
The nicotinic ACH receptor on the post-junctional membrane
What is produced when ACh binds to the post junctional membrane?
It produces an end-plate potential
What is the result of the end-plate potential?
This depolarisation will raise the muscle above threshold so that an action potential is produced
What are the two types of blockers of nicotinic receptors?
Competitive blockers
Depolarising blockers
How do competitive blockers of nicotinic receptors work?
Bind at the molecular recognition site for ACh
Give an example of a competitive blocker of nicotinic receptors?
Tubocurarine
How do depolarising blockers of nicotinic receptors work?
They cause a maintained depolarisation at the post-junctional membrane, so adjacent Na channels will not be activated due to accommodation
Give an example of a depolarising blocker of nicotinic receptor
Succinylcholine
Where is succinylcholine used?
In operations to induce paralysis
What is Myasthenia Gravis?
An autoimmune disease targeting nicotinic ACh receptors
What are the symptoms of Myasthenia Gravis?
Drooping eyelids
Profound weakness, which increases with exercise
What causes Myasthenia Gravis?
Antibodies directed against NAchR’s on the postsynaptic membrane of skeletal muscles. Endplate potentials are reduced in amplitude, leading to muscle weakness and fatigue
How is Myasthenia Gravis treated?
With ACh-esterase inhibitors
Why is Myasthenia Gravis treated with ACh-esterase inhibitors?
To increase the amount of time ACh is in the synaptic cleft
