Lecture 05 Neuromuscular Junction Flashcards
What is a motor end plate
The junction between a motor neuron and a skeletal muscle fiber
What is anchored to the presynaptic membrane and associated with synaptic vesicles to which they are tethered by short filaments?
Dense bars
What are three things axon terminals have?
Many mitochondria, synaptic vesicles with acetylcholine and dense bars
How many acetylcholine molecules are in one synaptic vesicle?
300,000
What is a synaptic gutter or trough
A groove in the surface of a sarcolemma in which the axon terminal makes close contact with the sarcolemma
What are subneural clefts?
Smaller clefts than synaptic gutters that are in the bottom of the synaptic gutter
How wide are synaptic clefts?
20-30nm wide.
In order for an acetylcholine-gated ion channel to open, how many Ach molecules are necessary to attach to its alpha subunits?
2
What is the first thing that happens after Ach binds to the ligand gated channels on the sarcolemma?
An end-plate potential is created on the muscle fiber
What are the characteristics of the acetylcholine-gated ion channels of the skeletal muscle?
It has a mw of 275,000. Has 2 alpha proteins and a beta, gamma and delta protein. They are a tubular channel that remains closed until two Ach attach.
What is the function of acetylcholinesterase
Break down Ach to acytal groups and choline
What type of potential is end plate potential?
local. involves ligand-gated channels
The vesicles for acetylcholine are transported to the axon terminal from where?
Golgi
How are the vesicles for Ach carried to the axon terminus where they are filled?
By axonal transport
Where is Ach synthesized?
Cytosol of the nerve axon terminal
Once activated, the Ach ligand-gated channel allows for the passage of what ions?
Sodium and potassium
What else activates ryanodine receptors?
Activated by the calcium released into the cytosol, thus allowing more calcium ion to be released
What promotes ryanodine channels to close?
High cytosolic calcium ion concentrations
What two things are reused after each action potential?
Vesicles - clathrin coated pits appear and separate from the plasmalemma. Refilled as new synaptic vesicles
Choline-Acetylchoinesterase degrades Ach into choline and acetate. Choline is reuptaked by axon end terminal
What are two ways acetylcholine is removed from the synamptic cleft?
Diffusion away from the site or acetylcholinesterase breaking down Ach
What is excitation-contraction coupling?
Action potential down the T-tubules is the excitation
The contraction that occurs once the Ca is released.
What can be used to inactivate acetylchoninesterase?
Neostigmine, physostigmine and diisopropyl flurophosphates
What has the same effect on muscle fibers as acetylcholine but are not broken down by acetylcholinesterase? What symptom do they cause?
Methacholine, carbachol, and nicotine. They cause spasm
What does curare do to neuromuscular junctions?
Prevents passage of impulses from nerve ending into muscle
What is myasthenia gravis? What does it do?
Autoimmune disease. Causes antibodies to attach acetylcholine receptors. This causes end plate potentials to be too weak to initiate action potential.
What is used as treatment for myasthenia gravis and why?
Neostigmine, because it can be used to inactivate acetylcholinesterase and therefore allows Ach to stay around longer in the synaptic cleft to open up more receptor channels and create an action potential. Helpful for early disease development.
