Glial cells and Myelin

Question 1

Myelin?

Answer 1

An electrical insulator that increases the conduction velocity of electrical signals transmitted along axons in the nervous system. Formed by oligodendrocytes (central nervous system) and Schwann cells (peripheral nervous system).

Question 2

Which neuroglia cell regulates chemical composition of tissue fluid by absorbing excess neurotransmitters and ions

Answer 2

Astrocytes

Question 3

Which neuroglia cell forms the blood brain barrier

Answer 3

Astrocytes

Question 4

White matter vs gray matter

Answer 4

• White matter - Regions of brain & spinal cord with dense collections of myelinated fibers – usually fiber tracts
• Gray matter - Mostly neuron cell bodies and nonmyelinated fibers

Question 5

Schwann cells MOA

Answer 5

spirals repeatedly around a single nerve fiber • lays down as many as a hundred layers of its own membrane
• no cytoplasm between the membranes
• neurilemma – thick outermost coil of myelin sheath. contains nucleus and most of its cytoplasm
• external to neurilemma is basal lamina and a thin layer of
fibrous connective tissue – endoneurium

Question 6

Oligodendrocytes MOA

Answer 6

reaches out to myelinate several nerve fibers in its immediate vicinity

anchored to multiple nerve fibers
• cannot migrate around any one of them like Schwann cells • must push newer layers of myelin under the older ones
• so myelination spirals inward toward nerve fiber
• nerve fibers in CNS have no neurilemma or endoneurium

Question 7

Types of neuroglia cells

Answer 7

Astrocytes 
Ependymal cells
Microglia
Oligodendrocytes
Satellite cells 
Schwann cells

Question 8

Astrocytes functions

Answer 8

have extensions (perivascular feet) that contact blood capillaries that stimulate them to form the blood-brain barrier

convert blood glucose to lactate and supply it to neurons as energy source

nerve growth factors secreted by astrocytes promote neuron growth and
synapse formation

regulate chemical composition of tissue fluid by absorbing excess neurotransmitters and ions
• astrocytosis or sclerosis – when neuron is damaged, astrocytes form hardened scar tissue and fill space formerly occupied by the neuron

Question 9

Oligodendrocyte function

Answer 9

form myelin sheaths in CNS

Question 10

Microglia?

Answer 10

“macrophages”, wander in search of cellular debris to phagocytize

Question 11

Ependymal cells

Answer 11

lines internal cavities of the brain, cuboidal epithelium with cilia on apical surface

• secretes and circulates cerebrospinal fluid (CSF)

Question 12

Schwann cells

Answer 12

produces a myelin sheath in PNS

Question 13

Satellite cells

Answer 13

surround the neurosomas in ganglia of the PNS

• provide electrical insulation around the soma

Question 14

Myelination

Answer 14

production of the myelin sheath • begins the 14th week of fetal development
• proceeds rapidly during infancy
• completed in late adolescence
• dietary fat is important to nervous system development

Question 15

Myelin sheath gaps / Nodes of Ranvier

Answer 15

Gaps between adjacent Schwann cells

• Sites where axon collaterals can emerge

Question 16

Myelin composition

Answer 16

40% water
Dry mass: about 80% lipids, about 20% proteins

Typical lipid for myelin are cerebroside and sulfatide

Typical proteins for myelin are myelin basic protein (MBP) and
proteolipid protein (PLP)

Other myelin specific proteins are: 2′:3′- cyclic nucleotide 3′- phosphodiesterase (CNP) and myelin-associated glycoprotein (MAG)

Question 17

Cerebrosides?

Answer 17

(group of glycosphingolipids)

a ceramide with a single sugar residue at the 1-hydroxyl moiety

Question 18

Sulfatide

Answer 18

sulfolipids, specifically a class of sulfoglycolipids, which are glycolipids that contain a sulfate group

Question 19

CNS vs PNS myelin protein

Answer 19

CNS myelin is rich in myelin basic protein (MBP) and proteolipid protein (PLP).

PNS: myelin protein 0 and myelin protein 22

Question 20

Myelin-associated glycoprotein (MAG)

Answer 20

• Single transmembrane domain glycoprotein
• Localized in periaxonal Schwann cell and oligodendrocyte membranes
• Involved in myelination during nerve regeneration in the PNS
• In the CNS MAG is one of three main myelin-associated inhibitors of axonal regeneration after injury
• Anti-MAG antibodies result in complement deposits in the myelin sheath and demyelination (neuropathies).

Question 21

MS

Answer 21

Multiple sclerosis
• oligodendrocytes and myelin sheaths in the CNS deteriorate
• myelin replaced by hardened scar tissue
• nerve conduction disrupted (double vision, tremors, numbness, speech defects) • onset between 20 and 40 and fatal from 25 to 30 years after diagnosis
• causemaybeautoimmunetriggeredbyvirus

Question 22

Proteolipid

Protein (PLP)

Answer 22

The major myelin protein in the central nervous system (CNS)

Important for the formation and maintenance of the multilamellar structure of myelin.

Determines membrane spacing