electrophysiology BSC Electrophysiology and the NMJ

Question 1

myasthenia grevis

Answer 1

what is it

anti-nicotinic ACh antibodies
block receptor binding of ACh binding

some cases mediate destruction of receptors

Question 2

what effect does a normal presynaptic release of ACh have on the motor end plate ?

Answer 2

the end plate potential would be decreased

likely NOT ABSENT b/c the patient has a normal release of ACh

Question 3

what is the specific mechanism by which ACh release results in an endplate potential?

Answer 3

ACh binds and Na comes into cell causing depolarization

Question 4

what is the normal effect of an EPP on the sarcolemma of a skeletal muscle fiber

Answer 4

voltage gated sodium channels open due t threshold being reaches and this results in muscle action potential

Question 5

what happens if you inhibit acetylcholinesterase

Answer 5

concentration of ACh in the synaptic cleft is increased

Question 6

why does ptosis improve following an ice pack test?

Answer 6

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

Question 7

what is the diagnosis when you have antibodies directed against voltage-gated Ca2+ channels

Answer 7

Lambert Eaton Myasthenic Syndrome

pre-synaptic disorder

loss of Voltage gated calcium channels

Question 8

what is the role of Ca influx in excitation of the NMJ

Answer 8

promotes ACh vesicle fusion and exocytosis

Question 9

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

Answer 9

pt s with lambert eaton

LOOK UP

Question 10

Botulism does what?

Answer 10

impairs acetylcholine vesicle fusion by impairing the function synaptobrevin (v-snare)

causes weakness

Question 11

tetanus toxicity symptoms

Answer 11

spastic rigidity

acts on inhibitory neurons in spinal cord
so when you lose the inhibition of motor neuron

Question 12

muscles spasms after eating bananas and previous case of myotonia, trouble releasing his grip, severe weakness during period of rest after exercise

Answer 12

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

Question 13

what effect does hyperkalemia normally have on resting membrane potential?

Answer 13

depolarization b/c the K wants to stay inside the cell making it more positive inside

Question 14

what are the normal gating kinetics of voltage gated Na channels ?

Answer 14

2 gates (activation and inactivation)

3 states:
RMP
Activation gate M is closed
Inactivation gate H is open

see slide on this

Question 15

what is the impact of mutant Na channels that do not activate

Answer 15

hyperexcitable state
continues to depolarize the membrane

this explains my myotonia and random spasms occurs in patients with hyperkalemic periodic paralysis

Question 16

in a patient with hyperkalemia, weakness and paralysis, what is the effect of elevated serum K+

Answer 16

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

Question 17

what is mild depolarization

Answer 17

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

Question 18

Greater depolarization 20-30 mV

Answer 18

weakness and paralysis
the wild type normal channels are now in an inactivation state due to that constant depolarization

do not reset until depolarization

Question 19

why would carbohydrate diet help individuals with hyperkalemia

Answer 19

promotoes sequestering of postassium into the cell and decrease ECF concentration

Question 20

malignant hyperthermia effect?

Answer 20

rare autosomal dominant

can be triggered by anesthesia

disorder of Ca regulation in skeletal muscle
uncontrolled release of Ca from the SR

Question 21

what receptor is likely defected in Ca 2+ release in malignant hyperthermia

Answer 21

RYR1 gene which is the Ca release channel

Question 22

where is the RyR located?

Answer 22

SR membrane

Question 23

where are the Dihydropyridiine receptors located?

Answer 23

on the t-tubule membrane

these are voltage sensors that release Ca

Question 24

look over last case

Answer 24

do it