Lecture 6: Neuromuscular Junction Flashcards
component of an axon that is anchored to the presynaptic membrane, but we do not know it’s true function.
dense bars
axon synaptic vesicles contain…..
ACH
another term for local potential
end plate potential
where is the synaptic gutter located
groove indented in the sarcolemma surface
also called a trough
small clefts in bottom of synaptic trough
Subneural clefts
synaptic cleft
20-30nm wide = very narrow
between axolemma and sarcolemma
where are the ACH ligand gated channels located?
the sarcolemma
how many ACH must attach before the channels can open?
2
enzyme responsible for ACH breakdown
acetylcholinesterase
found on sarcolemma, breaks ACH into —- choline + acetate
ACH binding sites
binds to alpha subunits of the ligand channel
where is ACH synthesized
cytosol of axons
synaptic vesicle creation/transport/filling
formed in golgi (40nm)
carried via axonal transport to terminus
then filled with ACH
how many vesicles fuse to the synaptic membrane?
~125 vesicles
releasing thousands of ACHs
what ions could be responsible for drawing synaptic vesicles closer to the V-gates of the neurolemma?
Ca ions
when an AP reaches an axon terminus, what 2 events follow on the axon?
Ca voltage gates open
Ca enters the axon
a sarcolemma AP is activated by the flux of what ions?
influx of Na ions from the ACH ligand gates
causes Na V-gates to open allowing further influx
calcium’s role in a skeletal muscle contraction
Ca binds to troponin C
conformational change in troponin
tropomyosin then pulls away from active sites on actin
ATP is required for myosin ……?
for myosin heads to release the actin active sites
after each AP ______ appears in the axon terminal
clathrin coated pits
which refill as new synaptic vesicles
how is ACH removed from the synaptic cleft after an AP?
acetylcholinesterase degrades ACH into choline + acetate
clathrin pits re-uptake the choline
acetate diffuses away from site
what is another term for excitation-contraction coupling?
electro-mechanical coupling
what is meant by excitation-contraction coupling?
we are converting electrical energy into mechanical energy
voltage —> induces muscle contraction
methacholine
carbachol
nicotine
drugs that mimic ACH, but are not broken down by ACHase
cause spasms
neostigmine
physostigmine
diisopropyl fluorophosphates
drugs that inactivate ACHase
cause spasms
effect of ‘curare’ on skeletal muscle contraction
prevents passage of impulses from axon to muscle
results = total muscle relaxation
how can total muscle relaxation be dangerous?
too much curare?
relax muscles that we need to be alive
diaphragm, heart
myasthenia gravis
autoimmune disease
antibodies attack ACH receptors
thus no receptor available to accept ACH to induce a muscle contraction ==== very weak contractions
drug that can help alleviate myasthenia gravis and how
neostigmine
can be used to inactivate ACHase, leaving excess ACH in the cleft allowing a relatively normal contraction
