Myelin Flashcards
How does myelin increases conductivity of AP?
- sequestered Na and K channels in nodes of ranvier which increases impulse propagation
- reduction of energy costs associated with regeneration of membrane potential
- compact wiring
- prevents loss of AP as it travels down the axon
what determines the speed of AP
- diameter of axon bigger = faster
- degree of myelination
- internal resistivity
state the main source of schwann cells:
trunk neural crest
what is radial sorting and describe this process
radial sorting is the process by which Schwann cells myelinate larger axons during development
once oligodendrocytes/schwann cells made contact with an axon, it will start to extend its myelin membrane and incorporate myelin protein
membrane will be propagated by a force forward to coat the axon and form paranodal junction
explain the driving force of the inner mesaxon to wrap around the axon
depolymerisation and polymerisation of actin molecules causes the front part of the inner mesaxon to protrudes forward
describe the compaction of myelin
compaction involved the p-zero molecule
- this molecule can interact together to keep myelin sheath stick together
state the mutation in charcot-marie tooth 1A (CMT1A) disorder and what happened in individuals with this disorder how does this disorder affect conduction velocity of AP?
duplication of gene PMP22 on chromosome 17 (indiv. carry 3 genes)
individuals affected: destabilise myelin sheath results in demyelination with attempted re-myelination resulting in structures call onion bulbs
slows down conduction velocity
describe the mutation in CMT1B
mutation in gene that carries instruction for making myelin protein zero
describe the pathology of CMT1A
thickening of the nerve and formation of onion bulb
explain the consequences of demyelination
demyelination causes re-distribution of na and k channels, as a result the density of these channels decreases and the inward current necessary to generate AP become too small
