Myelination Flashcards
(10 cards)
What is myelin sheath?
A fatty tube placed around the axon by either an oligodendrocyte or a Schwann cell
What types of cell are wrapped around axons?
Oligogendroglial cells - forms myelin around axons in brain and spinal cord
Schwann cells - wraps around peripheral nerves (arms or legs) to form myelin
What is the difference between myelinated and unmyelinated axons?
There is no ion exchange in the fatty sheath
the action potentials jumps from nodes of ranvier - they happen over and over again
What happens to the depolarisation in myelinated sections?
It decays along the length of the myelinated sections - it is built up at the nodes of ranvier and then decays at through the myelinated sections. When the impulse arrives at the next node of ranvier, there needs to be enough depolarisation to trigger another one
What are the advantages of a myelinated axon?
The action potentials jump and imposes are quicker
Important for coordination
The generation of AP requires energy and time, with myelin, less AP’s are needed to send a nerve impulse along a myelinated neuron - more efficient for the signal to go from the soma to the end
What is multiple sclerosis?
When myelin on neurons are damaged - leads to loss of sensitivity, muscle weakness, difficulty with coordination and balance
What toxins can block action potentials?
Tetrodotoxin (puffer fish)
a-dendrotoxin (green mamba)
What does tetrodotoxin do?
It is found in puffer fish - when you take it, it blocks voltage gated Na+ channels so the action potential won’t occur. This leads to paralysis - can’t move but conscious
cocaine can also do this
What is the zombie ritual?
Gave people a little bit of TTX so they were unconscious, buried them then a few hours they were alive, thought they had come back from the dead
What is a-dendrotoxin
Comes from green mamba snakes if they bite you
Blocks voltage gated K+ channels so potassium can’t leave, inside is too positive
Leads to convulsions
