Glial Cells

Question 1

What are the different types of glial cells?

Answer 1

Astrocytes

Oligodendrocytes

Microglia

Question 2

What is the most common type of glial cell?

Answer 2

Astrocytes

Question 3

What are the functions of astrocytes?

Answer 3

Give structural support to neurones

Contribute to nutrition of neurones

Remove neurotransmitters

Maintain ionic environment

Contribute to blood brain barrier

Question 4

What do neurones metabolise?

Answer 4

Glucose

Question 5

How is glucose transported into neurones?

Answer 5

Diffuses from the blood into the interstitial space in the brain through a GLUT transporter
Diffuses from the interstitial space into the neurone through another GLUT transporter

Question 6

How do astrocytes contribute to nutrition of neurones?

Answer 6

Astrocytes store glucose as glycogen

Glucose-lactate shuttle

Question 7

What is the glucose-lactate shuttle?

Answer 7

In times of increased neuronal metabolism, astrocytes produce lactate from glycogen
Lactate is transported from the astrocyte into the interstitial fluid and then into the neurone using transporters
In neurones, lactate is converted into pyruvate and then metabolised as normal

Question 8

Why do astrocytes remove neurotransmitters?

Answer 8

To end the response

To prevent spread of neurotransmitter and stimulation of other post-synaptic neurones

Because some neurotransmitters e.g. glutamate are toxic to neurones at high concentrations

Question 9

What do astrocytes do with glutamate?

Answer 9

Convert it into glutamine

Question 10

What happens to glutamine in astrocytes?

Answer 10

Transported back to pre-synaptic neurone

Converted back into glutamate

Question 11

How do astrocytes maintain the ionic environment?

Answer 11

Na+ K+ ATPase on astrocyte membranes moves potassium ions into astrocytes

Also they have a very negative resting membrane potential
So potassium ions move down their electrical gradient into astrocytes

Question 12

Why is it important that astrocytes maintain the ionic environment?

Answer 12

Highly active neurones may result in an increase in extracellular potassium ion concentration
This results in depolarisation of neurone membranes, action potentials etc.

Question 13

What is the function of oligodendrocytes?

Answer 13

Myelinate neurone axons in the CNS

One oligodendrocytes can myelinate multiple neurone axons

Question 14

What is the structure of a microglial cell?

Answer 14

Small cell body
Many fine processes

When activated, have a more rounded shape

Question 15

What is the function of microglial cells?

Answer 15

Recognise foreign material or debris

Become activated and phagocytose the substance

Question 16

What is the blood-brain barrier made up of?

Answer 16

Continuous capillaries

Surrounded by end feet of astrocyte processes

Question 17

What are continuous capillaries made up of?

Answer 17

Endothelial cells with tight junctions in between them

Complete basement membrane around them

Question 19

How do astrocytes contribute to the blood-brain barrier?

Answer 19

Promote formation of tight junctions between endothelial cells

Question 20

What is the function of the blood-brain barrier?

Answer 20

Controls passage of substances from the blood to the extracellular fluid to the brain

Allows for maintaining the correct environment for neurones

Question 21

What substances can pass across the blood-brain barrier themselves?

Answer 21

Lipophilic substances passively diffuse across the blood-brain barrier e.g. oxygen, carbon dioxide, water

Question 22

What substances cannot pass across the blood-brain barrier themselves? How do they pass across it then?

Answer 22

Large and hydrophilic substances e.g. glucose, amino acids, ions
Have to be transported across

Question 23

Why is it important to maintain the correct environment for neurones?

Answer 23

Potassium ion concentration affects resting membrane potential of neurones

Amino acid levels affect neurotransmitter function in synapses

Question 24

What is immune privilege?

Answer 24

Refers to a type of immune specialisation

Where antigens can be tolerated by T cells without stimulating an inflammatory response

Question 25

Where does immune privilege occur in the body?

Answer 25

The brain

Question 26

Why does immune privilege occur in the brain?

Answer 26

Brain is enclosed in the skull which is rigid

Swelling due to inflammation would lead to raised intracranial pressure and brain compression or herniation