electrophysiology BSC Electrophysiology and the NMJ Flashcards
myasthenia grevis
what is it
anti-nicotinic ACh antibodies
block receptor binding of ACh binding
some cases mediate destruction of receptors
what effect does a normal presynaptic release of ACh have on the motor end plate ?
the end plate potential would be decreased
likely NOT ABSENT b/c the patient has a normal release of ACh
what is the specific mechanism by which ACh release results in an endplate potential?
ACh binds and Na comes into cell causing depolarization
what is the normal effect of an EPP on the sarcolemma of a skeletal muscle fiber
voltage gated sodium channels open due t threshold being reaches and this results in muscle action potential
what happens if you inhibit acetylcholinesterase
concentration of ACh in the synaptic cleft is increased
why does ptosis improve following an ice pack test?
because if you slow down the enzyme ACholinesterase then you would slow down its activity and increase the amount of ACh in the synaptic cleft
what is the diagnosis when you have antibodies directed against voltage-gated Ca2+ channels
Lambert Eaton Myasthenic Syndrome
pre-synaptic disorder
loss of Voltage gated calcium channels
what is the role of Ca influx in excitation of the NMJ
promotes ACh vesicle fusion and exocytosis
why does repetive stimulation result in increased contarctile strength in our patient with Lamber-Eaton vs decreased strenght with repetitive use in patient with myasthenia gravis
pt s with lambert eaton
LOOK UP
Botulism does what?
impairs acetylcholine vesicle fusion by impairing the function synaptobrevin (v-snare)
causes weakness
tetanus toxicity symptoms
spastic rigidity
acts on inhibitory neurons in spinal cord
so when you lose the inhibition of motor neuron
muscles spasms after eating bananas and previous case of myotonia, trouble releasing his grip, severe weakness during period of rest after exercise
this is hyperkalemic periodic paralysis
autosomal dominant trait affecting the skeletal muscle gene SCN 4A located on chromosome 17
has an effect on the inactivation gate (h gate)
the main problem with these indivisual is a voltage gated sodium channel mutation
what effect does hyperkalemia normally have on resting membrane potential?
depolarization b/c the K wants to stay inside the cell making it more positive inside
what are the normal gating kinetics of voltage gated Na channels ?
2 gates (activation and inactivation)
3 states:
RMP
Activation gate M is closed
Inactivation gate H is open
see slide on this
what is the impact of mutant Na channels that do not activate
hyperexcitable state
continues to depolarize the membrane
this explains my myotonia and random spasms occurs in patients with hyperkalemic periodic paralysis
in a patient with hyperkalemia, weakness and paralysis, what is the effect of elevated serum K+
Depolarization of the cell membrane inactivating voltage-gated Na channels
with additional prolonged depolarization, compounds the voltage-gated Na channelopathy
look at these slides
inactivation prevents subsequent AP –> weakness and paralysis
what is mild depolarization
5-10 mV
myotonia stiffness, hyperexcitability
repetitive AP firing
may be caused by increased K ECF or due to influx via mutant Na channels which do not inactivate
Greater depolarization 20-30 mV
weakness and paralysis
the wild type normal channels are now in an inactivation state due to that constant depolarization
do not reset until depolarization
why would carbohydrate diet help individuals with hyperkalemia
promotoes sequestering of postassium into the cell and decrease ECF concentration
malignant hyperthermia effect?
rare autosomal dominant
can be triggered by anesthesia
disorder of Ca regulation in skeletal muscle
uncontrolled release of Ca from the SR
what receptor is likely defected in Ca 2+ release in malignant hyperthermia
RYR1 gene which is the Ca release channel
where is the RyR located?
SR membrane
where are the Dihydropyridiine receptors located?
on the t-tubule membrane
these are voltage sensors that release Ca
look over last case
do it
