Neuron Action Potential and Synaptic Transmission Flashcards
Extracellular amounts of what ion blocks sodium (Na+) channels in the neuron?
extracellular Ca2+
Relate how cell diameter and velocity are related?
the greater the cell diameter the greater the conduction velocity
Relate myelination and conduction velocity.
myelin provides greater electrical resistance across cell membrane thereby reducing current leaks through the membrane the Na+ channels cluster at nodes of Ranvier and create a greater speed. (salutatory conduction)
MS and Guillain Barre Syndrome are both demyelinating diseases. Explain the different presentations.
Loss of myelin result in current leakage across the membrane. The magnitude of current reaching the cluster of fast Na+ channels is unable to cause threshold depolarization, resulting in conduction block.
MS preferentially demyelinates neurons in the CNS while GBS in the periphery and that’s why MS patients present with hyperreflexia and GBS with hyporeflexia.
Latrotoxin is found from what?
venom of a black widow spider?
How does latrotoxin work?
opens presynaptic Ca2+ channels resulting in excess ACh release and hyperreflexia
What is the difference beteween myasthenia gravis and Lambert Eaton syndrome?
MG is an autoimmune condition in which ab are created that block the Nm receptor
Lambert Eaton is also an autoimmune condition but the ab block the presynaptic voltage-gated Ca2+ channels
What are the signs of decreased neuronal excitability/conduction?
weakness, ataxia, hyporeflexia, paralysis, sensory deficit
What are some ionic disturbances that can lead to decreased neuronal excitability?
hypokalemia
chronic hyperkalemia
hypercalcemia
What are some conditions in which there are loss of neurons/ demyelination of neurons leading to decreased neuronal excitability?
Guillain-Barre
ALS (amyotrophic lateral sclerosis),
aging
What are some toxins or drugs that can lead to decreased neuronal excitability/ conduction?
local anesthetics (“caine”) drugs
TTX (tetrodotoxin) (pufferfish)
STX (saxitoxin) (consumption of shellfish during algal blooms)
What are drugs or conditions affecting the NMJ that can lead to decreased neuronal excitablility?
depolarizing Nm blockers
non- depolarizing Nm blockers
Lambert Eaton
Myasthenia Gravis
Botulinum toxin
What are some ion disturbance that lead to increased neuronal excitability?
actue hyperkalemia
hypocalcemia
What are some conditions where there are loss of neurons/ demyelination leading to increased neuronal excitability?
MS
What are some toxins that can lead to increased neuronal excitability?
- CTX ciguatoxin (fish)
- BTX batrachotoxin (frogs)
- Latrotoxin
