Neuromuscular junction Flashcards
what is the somatic motor division
neuron that originates from CNS and projects its axon to the target tissue - skeletal muscle
the synapse of the somatic motor neuron on a muscle fiber is called what
neuromuscular junction
what do motor neurons stimulate
skeletal muscles
what makes up the motor unit
one motor neuron axon and its branches to multiple muscle fibers
physical elements of NMJ
-presynaptic axon terminal (filled with synaptic vesicles and mitochondria)
-synaptic cleft
-postsynaptic membrane
what neurotransmitters are contained in vesicles in the pre synaptic terminal
acetylcholine
what kind of receptors are on the post synaptic terminal of NMJ
nicotinic ACh receptors
what are the key players in NMJ events
acetylcholine
nicotinic ACh receptor
acetylcholinesterase
what occurs at the end plate potential
sodium ions enter the muscle fiber when acetylcholine gated channels open causes the electron potential inside the fiber at the local area to increase
what is the resting membrane potential in skeletal muscle fibers
-80 to -90mV
how long is the duration of an action potential
1-5 milliseconds
why must the current penetrate deep into the myofibrils
because the fibers are so large that the action potentials cause almost no current deep in the fiber
how is the transmission of the action potential reached deep in the muscle fiber
along T- tubules
voltage gated changes sensed by dihydropyridine receptors are linked to release of what
calcium
calcium release channels are also called what
ryanodine receptor channels
what binds calcium
calsequestrin
calcium binds to what in the cross bridge formation
troponin
steps in initiating muscle contraction
- Ach released binding to receptors
- action potential reaches T tubule
- sarcoplasmic reticulum releases Ca
- active site exposure - cross bridge formation
- contraction begins
steps in muscle relaxation
- Ach broken down by AChE
- sarcoplasmic reticulum recaptures Ca
- active sites covered, no cross bridge interaction
- contraction ends
- passive relaxation occurs - back to normal resting length
botulinum toxin
caused by toxin clostridium botulin (causes botulsim)
when botulinum toxin is consumed what happens
prevents muscles from responding to nerve impulses
what does botulinum toxin block the release of
ACh
botulinum toxin for migraines
injected around pain fibers where the nerve and muscle meet (around affected area of headache)
prevents headaches before they start
how long does one treatment of botox last for headaches
10-12 weeks
what are the risks of botox for headaches
toxin accidentally spreading into the body
what are the side effects of botox
trouble speaking or swallowing, difficulty breathing, muscle weakness
Myasthenia gravis
autoimmune condition
what does the body produce antibodies against in myasthenia gravis
motor end plate Ach receptors
what are symptoms are myasthenia gravis
extreme msucle weakness
is myasthenia gravis inherited
no
what is the cure for myasthenia gravis
none
what is the antagonist that blocks the actions of Ach at the receptor channel
curare
what does curare bind to
Ach receptors
how does curare affect ion permeability
doesn’t alter ion permeability
it is NOT inactivated by AChE
what are organophosphates
group of chemicals that modify the NMJ
what do organophosphates do
irreversibly inhibit AChE
