Workshop 2: When electrical transmission goes wrong

Question 1

Myelination: Performed by 2 types of glial cells

Answer 1

Schwann Cells

Oligodendrocytes

Question 2

Schwann cells (and part of NS)

Answer 2

wrap individual axons

peripheral NS

Question 3

Anatomy of a myelinated axon

Answer 3

▪ Yellow areas show schwann cells and the production of myelin sheaths

▪ Purple areas show “naked” axon – called nodes of Ranvier

▪ Ions can only cross the membrane at Nodes of Ranvier

Question 3

Oligodendrocytes

Answer 3

wrap several axons

central NS

(malfunction due to change in function & forming of myelination)

Service a number of cellulation points

Question 4

Anatomy of a myelinated axon

Answer 4

▪ Yellow areas show schwann cells and the production of myelin sheaths

▪ Purple areas show “naked” axon – called nodes of Ranvier

▪ Ions can only cross the membrane at Nodes of Ranvier

Question 5

Importance of Nodes of Ranvier

Answer 5

• Crucial because of the movement of the action potential along the neurons
  
  • Only move from Nodes of Ranvier (saltatory conduction)
  • All gates are situated here
    • No ion leakage… (quicker AP formation)
      ▪ No ion leakage so influence of AP spreads a further distance in myelinated axons

Question 6

Unmyelinated neuron:

Answer 6

• AP causes passive spread of current
• depolerises adjacent membrane
• Slower

Question 7

Thicker myelination means what?

Answer 7

○ Thicker myelin = more advantageous to the axon
§ Increase in speed of propagation
§ Increased regeneration of axon

Question 8

Reasons for demyelination

Answer 8

• Hereditary - Tay-Sachs disease, Niemann-Pick disease, Gaucher disease, and Hurler syndrome
  
  • (usually from mother)
• Stroke
• Infections
• Immune disorders
• Metabolic disorders
• Nutritional deficiencies (such as a lack of vitamin B12)
• Poisons (such as carbon monoxide)
• Drugs or medications (such as the antibiotic ethambutol)
• Excessive use of alcohol

Question 9

What does less myelination look like on microscope?

Answer 9

• Ratio of diameter of centre to the diameter of the outside (Don’t want to be similar)
  
  • Higher the ratio, less myelination!!!

Optimum ratio: 0.6

Normal ratio: around 0.77

Active disease: around 0.96

Recovery: around 0.85

Question 10

What is progressive MS?

Answer 10

Progressive MS is often characterised by a slow increase in the symptoms of the disease.

Question 10

What is multiple sclerosis?

Answer 10

(MS) is an autoimmune demyelinating disease. At scattered locations within the central nervous system, the person’s immune system attacks MYELIN SHEATHS, leaving behind hard patches of debris called SCLEROTIC PLAQUES.

Question 11

When does MS typically occur and does it affect one gender more?

Answer 11

MS usually occurs in individuals in their late twenties or thirties, with men diagnosed less frequently than women. Moreover, people that spend their childhood living close to the equator are less likely to be diagnosed with the disease than those who live far from the equator