NP1C Flashcards
The insulating material is lipid formed by glial cells and is known as:
myelin
the exposed patches of axon membrane are known as nodes of :
Ranvier
When a wave of depolarization reaches a lipid insulator, the ion flux is dampened and voltage gated __________________ in the insulated segment do not open
sodium channels
describes the way an electrical impulse skips from node to node down the full length of an axon
saltatory conduction
Why saltatory conduction?
it is fast, increasing velocity of impulse transmission by 5-50 fold
it conserves energy for the neuron
(true/false) All Axons are myelinated
false
Who makes myelin?
Oligodendrocytes = glial cells responsible for the synthesis of myelin in the central nervous system
axons cannot be regenerated in the ________________
central nervous system
One _____________ forms myelin segments for multiple different axons
oligodendrocytes
___________ is a predominant membrane lipid constituting myelin. It serves as an excellent insulator that decreases ion flow through the axonal membrane approximately 500-fold. This insulation inhibits the continuous propagation of an action potential.
sphingomyelin
supports induction of myelin formation:
Myelin-associated glycoprotein
stabilizes the multilamellar structure:
Myelin basic protein
_______________ are glial cells responsible for the synthesis of myelin in the peripheral nervous system (PNS)
Schwann cells
What is one of the differences between oligodendrocytes and Schwann cells?
Unlike oligodendrocytes, Schwann cells myelinate a single segment of axon
When is regeneration of the axon in the peripheral nervous system successful?
Regeneration of the axon may occur, but rein-nervation is only successful if there is a tract guiding the axon sprout to its destination
What is very important in the process of rein-nervation ?
neurilemmal tract
____________ provide supplemental metabolic support of the axon, highlighted by the fact that non-myelinated fibers are also closely associated with these cells
Schwann Cells
Demyelination can be ____________, reflecting damage to the myelin-producing cell or the myelin sheath. The functional result is loss of saltatory conduction.
primary
Demyelination can be __________.
secondary
What factors from the axon are required for proper myelin maintenance so that if the axon dies (Wallerian degeneration), the myelin sheath will unwind.
Trophic factors
if the axons are intact it is considered?
primary demyelination
If the axons are degenerate it is?
secondary demyelination
What are the causes of primary demyelination?
Viral infection (accompanied by inflammation)
Immune mediated (accompanied by inflammation)
Metabolic damage (no associated inflammation)
Toxins (no associated inflammation)
canine distemper virus can infect oligodendrocytes, eliminating their ability to support myelin formation. This is an example of:
primary demyelination
Some antigens in the CNS are shielded from the immune system during development so that T cells reacting to these antigens are not deleted. Damage or inflammation in the CNS can result in the inappropriate presentation of these antigens to autoreactive T cells, and the result is autoimmune ___________________. An example is multiple sclerosis
primary demyelination
Loss of myelin can result in tissue discoloration and softening that is grossly apparent, the change is known as ______________ (primary demyelination)
malacia
Leukoencephalomalacia denotes malacia that is restricted to :
White matter of the brain
Developmental shunts between the hepatic portal vein and the caudal vena cava can occur, allowing blood from mesenteric veins to bypass processing by the liver. There are increases in blood ammonia and other small molecules that can be damaging to oligodendrocytes. This is an example:
primary demyelination
Bromethalin-based rodenticides are in common use and are often ingested by dogs. Bromethalin causes the layers of myelin to separate and the cytoplasm in these layers to expand. This change is referred to as intramyelinic edema. this is example of:
primary demyelination
Can myelin be replaced?
yes, but it is much more efficient in the PNS than the CNS since one Schwann cell is responsible for myelinating a single axon, whereas loss of a single oligodendrocyte can leave 20-50 axons with unmyelinated segments. Both Schwann cells and oligodendrocytes can proliferate (grow rapidly), although the capacity is much greater for Schwann cells.
Defects in myelin formation:
hypomyelinogenesis
What is the primary function of myelin?
Support saltatory conduction
