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Neuroscience > L18 Neuromuscular Transmission > Flashcards

L18 Neuromuscular Transmission Flashcards

1
Q

what happens during a myotatic (myotactic) reflex?

A

a muscle is stretched
1a afferent fibers are excited in sensory endings
innervate motor neurons in ventral horn of spinal cord

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2
Q

what does each excitatory synapse of 1a afferent release?

A

glutamate

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3
Q

what do local interneurons release onto motor neurons?

A

glycine ==> IPSP!

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4
Q

explain reciprocal innervation

A

excitation of motor neurons for an AGONIST muscle + inhibition of motor neurons for an ANTAGONIST mucle

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5
Q

what receptors are excited in excitation of 1a afferents?

A

AMPA receptors

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6
Q

where are EPSPs and IPSPs located?

A

motor neurons + interneurons

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7
Q

where are EPPs located?

A

end plate potential

created in muscle end plates!

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8
Q

what makes up a motor unit?

A
  • cell body
  • axon (myelinated)
  • NMJ
  • skeletal muscle fibers
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9
Q

how many muscle fibers under the control of one motor neuron does fine motor control need?

A

small (about 10) - extraocular muscles, hand muscles etc.

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10
Q

how many muscle fibers under the control of one motor neuron that does not need fine motor control?

A

large (about 2000) - postural muscles

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11
Q

define motor nucleus

A

cell bodies of motor neurons distributed over a few spinal cord segments

axons leave the cord via ventral roots via spinal nerves then join in the peripheral nerve to reach target muscle

collections of motor neurons = forming a continuous column in the spinal cord

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12
Q

where does the axon lose its myelin?

A

presynaptic terminal that end with synaptic boutons

they are covered by Schwann cells without myelin = Remak Fiber

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13
Q

define motor end plate

A

the central region of the muscle fiber that received the synaptic boutons and NTs

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14
Q

how many NMJ (or synpases) do each muscle fiber have?

A

only one!

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15
Q

what happens at the NMJ?

A

ACh is released by Ca2+ dependent exocytosis from storage vesicles and binds to its ionotropic receptors in the end plate

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16
Q

every impulse in a motor neuron will release ___ to __ the muscle

A

ACh

excite!

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17
Q

do any inhibitory synapses exist in muscle fibers?

A

NO - inhibition of muscle fiber contraction is done by synaptic inhibition of the neuron that innervates it, not by the muscle itself (i.e. glycine to antagonist muscle in myotactic reflex)

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18
Q

what does choline acetyltransferase (ChAT) do?

A

ACh synthesis

choline + acetyl CoA —ChAT—> ACh + CoA

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19
Q

where does ChAT make Ach

A

in cytosol of nerve ending

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20
Q

what type of neurons make ChAT?

A

only cholinergic neurons - histochemical marker for these neurons on NS

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21
Q

why is the life cycle of ACh unusual compared to other NTs?

A

because it is degraded rapidly in the cleft

22
Q

what enzyme degrades ACh in the synaptic cleft?

A

acetylcholine esterase! (AChE)

23
Q

where is acetylcholinesterase made?

A

cholinergic neuron

24
Q

where is acetylcholinesterase tethered to?

A

the basal lamina!

25
Q

what transport mechanism is used to absorb choline after AChE breaks ACh down into acetyl + Choline?

A

co-transport with Na+ ions

26
Q

where are metabotropic subtypes M1 - M4 located?

A

abundant in brain and in peripheral tissues

27
Q

where is metabotropic subtype M5 located?

A

exclusively in brain but at low levels

28
Q

what does the fetal form of nicotinic ACh receptor have that is different from adult form?

A

gamma instead of epsilon

29
Q

what is the functional different between adult nAChR and fetal nAChR?

A

adult - permits larger currents but have more frequent opening times with a shorter mean open time

fetal - permit smaller currents but have longer mean open times

30
Q

the properties of adult nAChR are better suited for what?

A

fast activation of skeletal muscle fibers!

31
Q

what are active zones

A

site of ACh releae which are close to Ca 2+ channels

32
Q

where are ACh receptors located in the end plate?

A

junctional folds

33
Q

what happens when you have a prolonged binding of agonist at nAChR?

A

further conformational changes in which the channel closes = desensitization ==> normally doesn’t happen because AChE usually breaks ACh down pretty quickly

34
Q

the EPP spreads ____ with ___ from the end plate

A

passively

decrement - because of length constant!

35
Q

what direction does the depolarizing effect of cation flux the open nAChR spread?

A

in both directions form the end plate

36
Q

the EPP evoked by a nerve impulse is always sufficient to evoke a _____ at the end plate

A

muscle impulse

37
Q

what drugs are responsible for preventing arrival of the impulse at the nerve terminal => flaccid paralysis

A

tetrodotoxin and saxitoxin

38
Q

what drugs interfere with exocytosis in the motor nerve terminal?

A

botulinium, alpha-latrotoxin, w-conotoxin

39
Q

what is the mechanism of action of nerve gases like sarin and tabun?

A

irreversibly reduce AChE activity by covalently binding to the enzyme —> ACh effects are prolonged (depolarization) => death by paralyzing respiratory muscles

40
Q

what drugs have structures that resemble ACh and bind to nAChRs and acts as agonists?

A

carbacol
nicotine
succinylcholine

*none are degraded by AChE in cleft!

41
Q

what acts as a reversible competitive antagonist of ACh at nAChRs?

A

curare
pancuronium
= flaccid paralysis

42
Q

what irreversibly binds to ACh binding sites?

A

alpha bungarotoxin

=flaccid paralysis

43
Q

what is a tx for myesthenia gravis (autoimmune - attack nAChR = small amount)?

A

neostigmine (atropine is often given with it)

44
Q

what is a tx for lambert eaton syndrome (autoimmune - attack voltage gated Ca2+ channels)?

A

4-aminopyridine

neostigmine

45
Q

what are neuromuscular blocking agents commonly used for?

A

muscle relaxants during general anesthesia and surgery

46
Q

what are examples of neuromuscular blocking agents

A

depolarizing agent = succinylcholine

non-depolarizing agent = pancuronium

47
Q

where are voltage gated Na+ channels and what do they do?

A

nodes

AP propagation along axon

48
Q

where are voltage gated Ca2+ channels and what do they do?

A

nerve ending

Ca influx = exocytosis of ACh

49
Q

where are ACh gated channels located and what do they do?

A

junctional folds at end plate

large depolarization at end plate

50
Q

where are Na+ channels located and what do they do?

A

junctional folds

muscle depolarization

51
Q

where are voltage gated Na/K channels and what do they do

A

muscle membrane

muscle AP propagation

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