Neuromuscular Junction (exam 1) Flashcards
What are anchored to the presynaptic membrane and associated with the synaptic vesicles with they are tethered to by short filaments
Dense Bars
In order for acetylcholine-gated ion channels to open, how many Ach molecules are necessary to attach to its alpha subunits
2
The vesicles for acetylcholine are transported to the axon terminal from where
The golgi apparatus
What drugs are used to inactive acetylcholinesterase
Neostigmine, physostigmine, and diisoproyl fluorophophates
What drugs are not broken down by acetylcholinesterase
Methacholine, carbachol, and nicotine
What drugs have the same effect on muscle fibers as acetylcholine but are not broken down by acetylcholinesterase
Methacholine, carbachol, and nicotine
What drugs cause muscle spasms
methacholine, carbachol, nicotine, Neostigmine, physostigmine, and diisopropyl fluorophosphates
What effect does Curare have on muscle contractions
It prevents passage of impulses from nerve endings into muscles
How many mitochondria do a single axon terminal have
Many
How are acetylcholine vesicles release
calcium influx triggers exocytosis
What are dense bars
Anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered to by short filaments
what is the synaptic gutter (trough)
groove or furrow into the surface of the sarcolemma in which the axon terminal makes contact with the sarcolemma
What are sub neural clefts
They are clefts or troughs that are in the bottom of the synaptic trough
about how wide are synaptic clefts
about 20-30nm wide
How many subunits does an acetylcholine-gated ion channel have and what are they
5 subunits,
2 alpha, 1 beta, 1 gamma, and 1 delta
When does the tubular channel of acetylcholine-gated ion channels open
when tow acetylcholine molecules attach to the alpha subunits
What is the function of acetylcholinesterase
It breaks down Acetylcholine to acetate and choline
what is a local potential
potential that is established by the opening of a ligand-gated channel if hits threshold it can depolarize surrounding membranes
where are the 40nm vesicles for Ach formed
in the Golgi apparatus
how are golgi vesicles transported
by axonal transport
where is Ach synthesized
in the cytosol of the nerve axon terminal
when the AP arrives at the terminus of the axon what happens next
Voltage gated calcium channels open and calcium ions enter the axon terminus
What is the purpose of calcium ions in the nerve terminal
It draws synaptic vesicles closer to the neurolemma for exocytosis
about how many vesicle fuse to the neuronal membrane and empty their contents into the synaptic cleft
About 125 vesicles
How many Ach molecules bind to the ligand-gated channel on the sarcolemma. and where do they bind
- one to each alpha subunit
After the ligand-gated channels are open what happens
both potassium and sodium pass through the channel but sodium is more permeable
What does the large amount of sodium influx caused by the opening of the ligand gated channels cause
It leads to a local potential or end-plate potential (50-75mV). This leads to AP on the sarcolemma
what activates the Ryanodine-sensitive calcium ion channels
conformational change caused by the activation of the DHP (dihydropyridine channels) on the T-tubules
What affect does increase calcium have on Ryanodine receptors
It initially activates them thus leading to positive feedback and more release of calcium but at a certain point the concentration makes them close.
what do calcium ions bind to in muscles
Troponin
Where do T-tubules run in skeletal muscles
on both sides of the SR at the boundaries of the A-I bands
How is acetylcholine removed form the synaptic cleft
Acetylcholinesterase
What is acetylcholine degraded to by acetylcholinesterase
choline and acetate
After degradation the reuptake of choline occurs where. and why
Choline is reabsorbed at the axone terminal end. it is recycled because it is expensive
What is meant by excitation-contraction (electro-mechanical) coupling?
the coupling of AP with a mechanical motion such as contraction
After an AP what is formed at the axon terminal and why
Clathrin coated pits. to be refilled as new synaptic vesicles
Calcium concentration increases by how much after SR releases calcium
0.1micromol/liter to 10micromol/liter. about 100x
what is Myasthenia Gravis
Autoimmune disease
antibodies attack acetylcholine receptors on the sarcolemma
end plate potential are too weak to initiate opening of the voltage-gated sodium channels (can’t initiate AP)
Give an example of a drug that can be used to treat myasthenia Gravis
drugs that decrease the activity (inactivate) Acetylcholinesterase
Example in class Neostigmine
-other examples would be physostigmine and diisopropyl fluorophosphates
