NMJ diseases Flashcards
Soma lesions
amyotrophic Lateral sclerosis, Poliomyelitis symptoms- muscle atrophy and weakness, hyporeflexia, fasciculations and fibrilations, eventual loss of muscle fibers being replaced by connective tissue
Axon lesions
Neuropathy, toxins, drugx, axotomy
schwann cell lesions
Guillan- barre syndrome, diptheria weakness, wasting, rare fasciculations, decrease in conduction velocity.
nerve ending lesions
botulism, lambert eaton disease
synptic cleft lesions
acetylcholine esterase absent
End plate lesions
myasthenia gravis, nACh-related defects
muscle fiber lesions
myotonias and muscular dystrophy - will show weakness, wasting, no fasciculations, no decrease in conduction velocity, no fluctuating amplitude of EMG or EMG signs of denervation.
Poliomyelitis
viral infection that attacks the ventral spinal grey matter.
an affected limb of polio myelitis shows
affected limb shows acute flaccid paralysis.
destroyed motor neurons of poliomyelitis do not
regenerate but some surviving neurons my reinnervate the muscle.
if polio affects upper cervical spinal cord
then diaphragm paralysis requires ventilator support
Botulinum toxin
toxic protease that reduces the release of ACh by actin on proteins involved in exocytosis- paralyzes all muscles
ways to become infected with botulism
eating food wound infection consuming botulinum spores
alpha latrotoxin
causes massive release of ACh acts on nerve endings casuing tetanus with occasional patchy flaccid paralysis
beta Bungarotoxin
reduces release by actin on proteins in nerve terminals involved in exocytosis, causes AcH depletion
Curare
D-tubocurarine- plant alkaloid non-depolarising muscle relaxant that blocks ACh receptors at the NMJ
Lambert eaton syndrome.
antibodies attack the voltage gated Calcium channel on neuron terminal.
- strength increases with sustained or repeated contraction in otherwise weakend patients.
- insufficient release of ACh initially but with continued attempts then you will get sufficient ACH
lambert eaton syndrome is often associated with
oat cell caricinoma
lambert eaton symptoms
- reduced ACh
- muscel weakness
- reduced amplitude of EPP
- many EPP’s do not attain threshold in muscle fibers
- amplitude of miniEPP is unchanged
signs and tests of lambert eaton
3 Hz stimulation is gone, 20 hz shows a gradual increase
treatment for LES
plasma exchange or Immunoglobin infusion. 4 aminopyridine
Myasthenia gravis- deficiency of ACh esterase in snaptic cleft
- EPP amplitude is larger and longer than normal
- single motor nerve stimuli at low frequence cause singel muscel twitches
- high frequency motor nerve stimuli produce temporal summations of EPP’s and cause depolarization block
Slow channel syndrome
muscle weakness, rapid fatigue, progressive atrophy, ACh binding to nACHr’s causes prolonged opening of ACh receptor channels and a depolariation block
other forms of myasthenia gravis
- binding of ACh to AChR is abnormal -ACh gated channels have very brief opening times
main symptoms of MG is
weakness in voluntary muscle that improves after rest and worsens with muscular activity. -diplopia, ptosis, difficulty swallowing.
Maysthenia gravis autoimmune
antibodies cross link the nAChR’s and it hastens resorption. weakness in ;cranial nerve muscles, limb.
sometimes myasthenia gravis is associated with
tumors of the thymous gland
test for Myasthenia Gravis
waning muscle EMG recordings. Tensilon test, hand clenching test
treatment for myasthenia Gravis
neostigmine, pyridostigmine. Prednisone, thymectomy
myasthenic crisis
breathing difficulty may be life threatening
Chloride channel syndrome
fewer chloride channels are expressed and insereted incell membrane , causes slow muscular relaxation.
- patients show stiffness and hypertrophy
- increased excitability with smaller depolarization is required to evoke an action potential and may cause a train of acton potentials due to potassium accumulation in Traverse tubules.
normally chloride channels
help keep membrane potential close to Ecl during recovery from an action potential.
motor neuron disorder will show
muscle weakness, wasting, and EMG signs of denervation without decrease in conduction velocity or fluctuating amplitude of EMG.
NMJ lesions will show
muscel weakness and fluctuating amplitude of EMG but not wasting, fasciculations, decrease in conduction velocity or EMG signs of denervation.
