Demyelinating Diseases

Question 1

What is saltatory conduction?

Answer 1

Propogation of action potentials along myelinated axons away from one node of Ranvier to the next node, increasing the conduction velocity of action potentials.

Question 2

At what speeds do signals travel along myelinated and unmyelinated fibers?

Answer 2

Myelinated: 30-60m/s
Unmyelinated: 1m/s

Question 3

Which cells make myelin?

Answer 3

Schwann cells - PNS

Oligodendrocytes - CNS

Question 4

What is a node of Ranvier?

Answer 4

Where two schwann cells meet.
Lots of sodium channels here.
Jumping conduction.

Question 5

What is a neuromuscular junction?

Answer 5

Synapse where neuron meets muscle.

Cholinergic synapse.

Question 6

What is the main clinical feature of Guillain-Barre syndrome (GBS)?

Answer 6

Total paralysis

Question 7

What is GBS normally caused by?

Answer 7

Infection

C. jejuni about 20% of the time.

Question 8

What is acute motor axonal neuropathy characterised by?

Answer 8

Variant of GBS.
Characterised by acute paralysis and loss of reflexes without sensory loss.
Motor axonal degeneration with antibody mediated attacks of motor nerves and nodes of Ranvier.

Question 9

At a molecular level what is happening in acute motor axonal neuropathy?

Answer 9

Infected with campelobacter.
Generate antibody - may target surface of bug.
Molecular shape on surface of c.jejuni is the same as the molecular shape of motor axons - molecular mimicry.
Antibody binds onto nerve.
Activates complement cascade.

Question 10

How long does acute motor axonal neuropathy take to progress?

Answer 10

From initial infection it can take about a week to peak, then a patient can go from being healthy to completely paralysed in a day.

Question 11

Where can campelobacteria come from?

Answer 11

50% of supermarket chickens have campelobacteria

Question 12

What kind of antibody are the axons covered in?

Answer 12

Gangliosides

Question 13

What is the definition of molecular mimicry?

Answer 13

The theoretical possibility that sequence similarity between foreign and self peptides are sufficient to result in the cross activation of autoreactive T or B cells by pathogen derived peptides.

Question 14

How does GBS cause demyelination?

Answer 14

The molecular mimicry is on the myelin, not the axon.
The myelin bubbles and melts.
The macrophage sweeps up and digests the myelin.
The macrophage ignores the axon.

Question 15

Which type of microorganisms does complement kill?

Answer 15

Gram +

Question 16

How does the complement system cause the damage?

Answer 16

Membrane attack complex
Pore
Water etc. floods in.

Question 17

How could membrane attack complex pore formation be stopped?

Answer 17

Inhibit C5.

Question 18

What happens when you let calcium into a nerve?

Answer 18

Big family of calpanes - calcium activated proteases.

Question 19

Is the drug used to treat GBS curative?

Answer 19

No, it won’t reverse damage that has already been done, but it will stop disease progression.

Question 20

What is an astrocytic scar?

Answer 20

An area an astrocyte will wall off if part of the CNS dies.

Question 21

Which cell types are in the brain?

Answer 21

Microglia
Astrocytes
Oligodendrocytes - myelin
Neurons
Fibroblasts
Ependymal cells

Question 22

What does the limbic system control?

Answer 22

Emotion

Question 23

Can the CNS or PNS repair itself after injury?

Answer 23

PNS can, CNS can’t.