myelinated and unmyelinated axons

Question 1

what is myelination?

Answer 1

• Performed by 2 types of glial cells:
  ○ Schwann Cells (peripheral NS)- lie along the axon.
  § Wrap around the axon
  § Wrap individually around the axon
  ○ Oligodendrocytes (central NS)- myelinating cells
  § Feature of MS (malfunction due to change in function and forming of myelination)
  Service a number of cellulation points

Question 2

what is the difference between Schwann cells and Oliogdendrocytes?

Answer 2

SC= wrap around individual axons
O= wrap around several axons

Question 3

what is the anatomy of a myelinated axon?

Answer 3

• Schwann cells= the production of myelin sheaths
• “naked” axon= called nodes of Ranvier
  
  • Ions can only cross the membrane at Nodes of Ranvier
    ○ Crucial because of the movement of the action potential along the neurons
    ○ Only move due to the node of Ranvier
    ○ All gates are situated here
    § No ion leakage (quicker action potential)
    No ion leakage so influence of AP spreads a further distance in myelinated axons

Question 4

what are the differenences between myelinated and unmyelinated axons?

Answer 4

unmyelinated= AP causes passive spread of current, depolarises adjacent membrane
myelinated= myelin stops leakage of ions across membrance, AP only retriggers at each node, saltatory conduction, faster

Question 5

what are the advantages of myelination?

Answer 5

• Speed
  ○ Faster than unmyelinated
  § More myelination = faster
  § [Diameter can compensate]
• Economy
  ○ Less Na+ enters during AP’s (which need to be removed with ATP)

Question 6

what are the reasons for demyelination?

Answer 6

• Hereditary - Tay-Sachs disease, Niemann-Pick disease, Gaucher disease, and Hurler syndrome
  ○ Usually from the 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 7

which part of the neuron releases the neurotransmitters?

Answer 7

terminal buttons

Question 8

What is responsible of the myelination in the PNS?

Answer 8

schwann cells

Question 9

If a patient has relapsing-remitting multiple sclerosis, which of the following statements relating to treatments is true?

Answer 9

Inferions B and Glatiramer acetate are both effective treatments

Question 10

fill in the balnks: in an unmyelinated axon, an action potential causes ____ spread of current, where ion movement is a continuous process down the ____.

Answer 10

1. passive
2. membrane

Question 11

fill in the blanks: In a myelinated axon, they myelin stops ___ ___ across the membrane and action potentials are only triggered at each ___ __ _____.

Answer 11

1. ion leakage
2. node of Ranvier

Question 12

Multiple sclerosis is a disorder of which part of the nervous system?

Answer 12

CNS

Question 13

True or false: An unmyelinated axon produces a faster speed of conductance than a myelinated axon

Answer 13

False

Question 14

what is significant about the amplitude of the action potential?

Answer 14

it is always the same amplitude and duration in a given cell

Question 15

You feel a tickle on you arm that feels like a spide. You jerk your arm away. What is the typical neural pathway fgo rthis type of action?

Answer 15

Sensory neuron -> interneuron -> motor neuron -> muscle

Question 16

MS is an autoimmune demyelinating disease as scattered location

Answer 16

Myelinated sheath

Question 17

Demyelination from MS leaves being hard patches of debris called:

Answer 17

Sclerotic plaques

Question 18

fill in the blank: Ms usually appears in individuals in their late 20s or 30s, with men diagnosed ____ frequently than women

Answer 18

less

Question 19

fill in the blanks: People who spend their childhood living close to the equator are ____ likely to be diagnosed with the disease than those who ____ ___ _____ ____ ___ ______.

Answer 19

1. less
2. live far away from the equator

Question 20

Fill in the blanks: People who are born during the late winter and early spring are at ____ risk of MS than people born in the summer and autumn

Answer 20

higher

Question 21

Interferon b and glatiramer acetate are effective for what form of MS:

Answer 21

Remitting-relapsing