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Musculoskeletal > Physiology and Pharmacology of the Skeletal Neuromuscular Junction > Flashcards

Physiology and Pharmacology of the Skeletal Neuromuscular Junction Flashcards

Professor John Peters

1
Q

name the three types of muscle found in the body

A

cardiac
smooth
skeletal

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2
Q

what is skeletal muscle innervated by?

A

motor neurones

with myelinated axons and cell bodies in the spinal cord/brain stem

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3
Q

the neurone and the number of fibres that it innervates are know as what?

A

the motor unit

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4
Q

what chemical transmitter is found in skeletal muscle?

A

acetylcholine (ACh)

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5
Q

presynaptic terminal (bouton) of the alpha motor neurone synapses at what region of skeletal muscle fibres?

A

endplate

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6
Q

name the 4 key features of the skeletal neuromuscular junction

A
  1. terminal bouton with Schwann cells
  2. synaptic vesicles
  3. synaptic cleft
  4. end plate region
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7
Q

what are seen at active zones?

A

vesicles containing ACh

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8
Q

what receptor does ACh act on?

A

Nicotinic ACh receptor

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9
Q

what channels are concerned in he pre-synaptic process?

A

voltage-gated Ca2+ channels

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10
Q

what receptors does ACh activate?

A

nicotinic ACh receptors

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11
Q

when ACh is absent, is the gate open or closed?

A

closed

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12
Q

when does the receptor open?

A

when 2 molecules of ACh bond

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13
Q

Na+ efflux and K+ influx

true or false?

A

false

Na+ influx and K+ efflux

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14
Q

what is greater:

influx of Na+ or efflux of K+?

A

influx of Na+

net result is depolarisation known as end plate potential is generated

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15
Q

where is ACh stored and concentrated?

A

vesicles

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16
Q

what is one vesicle worth ACh known as?

A

a quantum

17
Q

what is the electrical response to one quantum of transmitter known as?

A

miniature endplate potential

multiple m.e.p.p summates to the end plate potential

18
Q

is the e.p.p. is large enough, what does it trigger the opening of?

A

voltage-activated Na+ channels - all or nothing response

19
Q

where does the action potential enter in muscle?

A

transverse (T) tubules

releases Ca2+ which interacts with troponin causing contraction

20
Q

what are the symptoms of neuromyotonia/NMT/Isaac’s syndrome?

A

muscle cramps, stiffness and twitches

21
Q

what is the cause of neuromyotonia/NMT/Isaac’s syndrome?

A

autoimmune origin - antibodies against voltage gated K+ channels

22
Q

what is the drug treatment in neuromyotonia/NMT/Isaac’s syndrome?

A

carbamazepine and phenytoin

23
Q

what are the symptoms in Lambert-Eaton Myasthenic Syndrome (LEMS)?

A

muscle weakness - rare

24
Q

what is Lambert-Eaton Myasthenic Syndrome (LEMS)

associated with?

A

small cell carcinoma of the lung

25
Q

what is the cause of Lambert-Eaton Myasthenic Syndrome (LEMS)?

A

autoimmune origin - antibodies against voltage gated Ca2+ channels so reduced release of ACh

26
Q

what is the drug treatment in Lambert-Eaton Myasthenic Syndrome (LEMS)?

A

anticholinesterases - pyridostigmine

potassium channel blockers - 3,4-diaminopyridine

27
Q

what are the symptoms of Myasthenia Gravis (MG)?

A

progressively increasing muscle weakness during activity - eye and eyelid muscle

28
Q

what is the cause of Myasthenia Gravis (MG)?

A

autoimmune origin - antibodies against nicotinic ACh receptors

29
Q

what is the drug treatment in Myasthenia Gravis (MG)?

A

anticholinesterases - edrophonium for diagnosis, pyridostigmine for long term treatment

immunosuppressant agents - azathioprine

30
Q

what is the botulinum toxin related to?

A

tetanus

31
Q

what is the other name for botulinum toxin?

A

botox

32
Q

what drugs Reduce the amplitude of the endplate potential (e.p.p.) to below the threshold for muscle fibre action potential generation?

A

curare-like compounds - competitive antagonists of nicotinic ACh receptors

vecuronium and atracurium

33
Q

alpha-motor neurone and all the skeletal muscle fibres that it innervates is the…

A

motor unit

34
Q

The action of ACh is terminated its hydrolysis of what?

A

acetylcholinesterase (AChE)

35
Q

Botulism is caused by botulinum toxic which causes…

A

failure of ACh release - paralysis

Musculoskeletal (37 decks)

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