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Afferent signals travel from _____ to _____
receptors to CNS
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Efferent signals travel from _____ to _____ & _____
CNS to muscles & glands
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where do motor neurons going to skeletal muscle originate?
ventral horn of the spinal cord
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Where do sensory neurons going from skeletal muscles terminate?
dorsal horn of the spinal cord
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What type of nerves carry signals to and from skeletal muscles?
somatic
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How many neurons does each muscle fiber have? What is this called?
One. Motor End Plate/ Neuromuscular Junction
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What is a synaptic trough?
invagination in the motor endplate membrane (aka the sarcolemma)
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How deep is the synaptic cleft?
20-30 mm
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The synaptic cleft is plentiful of what enzyme?
acetylcholinesterase
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Explain the positioning of the two different types of receptors on the sub neural cleft
ACh gated channels are at the top, voltage gated Na channels are in the bottom half
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What are two types of receptors located in the lipid bilayer of the pre-synaptic cell?
nicotinic and voltage gated calcium
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Where do the synaptic vesicles that hold ACh come from? how do they get to the junction?
golgi apparatus. arrive via axoplasm streaming
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Where is acetylcholine formed? is it an active or passive process?
cytoplasm. active - it requires ATP
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Through what mechanism is acetylcholine released into the synaptic cleft?
exocytosis
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What is the significance of the dense bar? (i.e. what two things are located near?)
voltage gated calcium channels are located at the ends and this is also where the exocytosis of ACh occurs
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Where does ACh bind post synaptically (specifically)?
binds to the alpha subunit of the nicotinic ACh receptor
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What happens when ACh binds to the alpha component of the nicotinic receptor? how many ACh does it take to cause this response?
nicotinic receptor opens which allows sodium (mostly) and calcium to flow into the cell, potassium flows out of the cell.
two ACh must bind before opening occurs
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What happens to ACh once it has done its job?
acetylcholinesterase metabolizes it, choline enters the pre synaptic cell.
As ACh is metabolized, repolarization occurs
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What are the 5 subunits of the nicotinic receptor?
- 2 alpha
- 1 beta
- 1 gamma
- 1 delta
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What is an extra junctional post synaptic receptor?
a result of damaged skeletal muscle, denervation injury
highly responsive to ACh and succs
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What is the role of the presynaptic nicotinic receptor?
influences the release of neurotransmitter from the nerve ending (positive feedback cycle to increase synthesis of ACh to prevent depletion in the NMJ)
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does chloride flow through the post synaptic nicotinic receptors? why or why not?
no, negative charge at mouth
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What is an end plate potential?
the potential of the membrane after the ACh channels have opened - this may or may not bring the cell to threshold
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What are the two parts of acetylcholine? What is the enzyme that combines them?
choline and acetyle-CoA. Acetyltransferase
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A decrease in calcium will do what to the amount of ACh released?
decrease
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An increase in calcium will do what to the amount of ACh released?
increase
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What does magnesium do to calcium channels on the presynaptic cell?
blocks them
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decrease in magnesium causes ____ ACh to be released
more
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increase in magnesium causes an ____ in ACh release
decrease
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Curariform (D-turbocurarine) works in what way?
competes for ACh binding sites --> reduction in amplitude of the end plate potential which will prevent it from reaching a full action potential
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Botulinum toxin works in what way?
decreases the release of ACh from the nerve terminals --> insufficient stimulus for an action potential
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Methacholine, carbachol, and nicotine do what?
bind and activate nicotinic ACh receptors
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How does myasthenia gravis differ from Lambert-Eaton Myasthenic Syndome?
- MG - degradation of post synaptic ACh receptors
- LEMS - degradation of presynaptic voltage gated calcium channels
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What is the difference in the T tubule for skeletal and cardiac muscle? where do they attach?
- Skeletal = 2 T tubule - attach @ ends of myosin
- Cardiac = 1 T tubule - attaches @ Z disc
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What is the difference in how the Ryanodine receptor is activated in skeletal and cardiac muscle?
- Skeletal - the ryanodine receptor is voltage associated
- Cardiac - the ryanodine receptor is calcium associated
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Does skeletal or cardiac muscle utilize calsequestrin to facilitate the reuptake of calcium ions?
skeletal
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