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6/30 Neuromuscular Junction

Terms in this set (62)

What is the NMJ?
site of regulation of skeletal muscles by the nervous system.
Most skeletal muscles cells have _____ NMJ on the surface membrane.
One
What is the sarcolemma?
membrane of muscle cell
The NMJ comprises how much of the sarcolemma area of the muscle cell?
less than 0.1%
The NMJ has highly specialized membranes between the _________ and the ______________.
motorneuron and muscle cell.
The NMJ is a synapse, a point of contact/communication between 2 __________ cells.
excitable.
The exception to the one NMJ for a muscle is in the __________ region.
craniofacial region, specifically extraocular muscles.
What part of the sarcolemma is considered the post-synaptic site?
The motor end plate.
Why is the motor end plate folded a lot?
To increase the surface area and therefore increase the number of receptors to amplify the activation potential.
What 3 channels are located on the motor neuron pre-synaptic terminal?
Na+, K+, and Ca2+
All the channels on the motor neuron are _________ sensitive channels.
voltage, because the AP has to activate them.
What is present on the post-synaptic motor end plate?
folds,
ACh receptors
Na+ channels
Acetylcholinesterase
What does a NMJ look like in a newborn?
There is still a NMJ but it is less defined and a smaller rounded motor end plate.
At the motor end plate Na+ influx is __________ than K+ eflux.
Greater. If it was the same, there would be not voltage change and therefore not depolarization.
At the motor endplate, there is not an AP but a _______-_______ potential.
end-plate potential.
The end-plate potential remains only at the ________.
NMJ
Surrounding the end-plate are ___________-gated Na+/K+ channels which are activated by this small endplate potential.
Voltage gated. This is where AP happen, not at the motor endplate.
What is used to break down ACh and terminate the depolarization event?
Acetylcholinesterase.
The channels on the post-synaptic muscle cell are _________-regulated.
chemically regulated, aka ligand sensitive.
The endplate potential are graded. What does this mean?
It means that they are not all or none events, the more ACh released, the stronger the amplitude.
What is the normal amplitude of an endplate potential vs an AP?
Around 10mV while an AP on a neuron is about 130mV.
What are miniature endplate potentials?
They are deliberate trickles of ACh from the motor neuron of 1 or 2 mV. Spontaneous. They are confined to the endplate but all the body has to do is ramp up this process that is always going on in the background. They can undergo temporal summation (release of a few vesicles at the same time) or spatial summation (close proximity at slightly different times). We ramp up this process to get more amplification and thus a AP along the sarcolemma.
Biochemical processes at the NMJ include acetylcholinesterase, which breaks down ACh and is located on the motor end plate in the _________.
basal lamina.
ACh breaks down into
choline and acetate (acetic acid)
Acetate then enters the bodies' __________, while choline is taken back up by the presynaptic terminal to react again with _______ by choline acetyltransferase to make ACh again.
circulation
acetyl-CoA
What does Curare do?
binds to ACh receptors while prevents endplate potentials. Used by American Indians
What does Botulinum toxin do?
blocks release of ACh
Organophosphates
blocks acetylcholinesterase. Cannot activate skeletal muscle in it's presence because Na+ channels remain open. Starts off as spastic uncontrolled movement but then flaccid paralysis.
organization of a skeletal muscle
muscle -->fascicle---> muscle fiber(cell) --> myofibril --> myofilaments --> sarcomere--->filaments--->proteins
A muscle cell has _________ of myofibrils.
thousands
The thin filaments is made up of a protein called _______.
actin
What are the 2 other proteins on the backbone of thin filaments?
2 tropomyosin (as dimers) and troponin
Troponin is a tertiary protein made of 3 subunits:
TnT, TnI, TnC
What do each of the subunits do for Troponin?
TnC -binds calcium
TnT- anchors Troponin to tropomyosin

TnI- is an inhibitory protein, this ensure that normally the muscle stays at rest.
What essentially makes up thick filaments?
myosin protein
What is myosin?
A hexameric protein (6 subunit protein) with 2 heavy chains for every myosin molecule.
There are 2 pairs of dissimilar light chains on each heavy chain on the ______ region that are referred to as _________ light chains and _________ light chains.
neck region

regulatory and essential light chains.
The regulatory light chains can be ___________, which enhances muscle force generation.
phosphorylated
The essential light chains are essential for things to __________.
work
Myosin is an __________ because it hydrolyses ATP.
enzyme
The myosin heads have to be opposite on each ends why?
Because they pull on actin that is attached to the z-line. If they weren't, it would only pull in one direction.
Same protein but slightly different amino acid sequence; similar function
isoform
What are the proteins that have isoforms?
pretty much everything. myosin heavy, myosin light chains, actin, troponin, tropomyosin. The head and neck express all the isoforms that the body does but there is an additional layer of isoform complexity on top of that bc functions are much more elaborate.
Functional unit of the contractile apparatus.
sarcomere
What are the components of a sarcomere?
thick and thin filaments, and z-lines. He doesn't list the other sections.
What is the worlds largest protein?
titin
What does titin do?
provides elasticity and stabilizes myosin
What does nebulin do?
Thin filament protein. It spans the entire length of the thin filament. Limits length of thin filament.
While filament do not change length, they do vary between different type of ____________.
muscle fibers. This is do to nebulin difference.
Cardiac muscle has no __________.
nebulin. It has nebulette.
Generally, slow muscle fibers have longer ___________.
thin filaments.
What is excitation-contraction coupling?
mechanism where an action potential in the sarcolemma causes muscle fiber contraction.
____ ions play a pivotal role in activation of muscle.
Ca+
Excitation-contraction coupling induces a __________ and very large increase in the free Ca+.
rapid
Transverse tubules are invaginations in the ___________. These allow the AP to dive into the tubules and open voltage regulated channels.
Sarcolemma
_____________ binds Ca+ ions in the lateral sacs of the sarcoplasmic reticulum.
Calsequestrin
Because the sarcoplasmic reticulum is close to the transverse tubules, it causes a release of __________ from the __________.
Ca+ from the lateral sacs. The free calcium bind to TnC and initiation of contraction.
Calcium is taken back up into the ___________ collar of the sarcoplasmic reticulum.
fenestrated
The re-uptake of Calcium into the sarcoplasmic reticulum is a ____ driven event.
ATP. It forces Calcium back in the fenestrated collar where it binds to Calsequestrin in the lateral sacs.
Why do we need to have something that binds Calcium in the lateral sacs, and not just let Ca+ ATPase pump work against the gradient?
Because the total concentration of Calcium is high and that would be very high gradient for ATPase to work against. By letting it bind to a buffer, it can lower the concentration gradient, which requires less ATP to keep and then we can also release a huge amount when we need to.
What kind of channel is located in the transverse tubule? What does it function as?
DHP, dyhydropurine receptor which is a calcium channel but does not actually function as a channel but functions as a voltage sensor.
The DHP receptor is located in apposition to another receptor called the __________ receptor which is a ___________ channel.
ryanodine receptor
calcium channel.
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