2.1.1 Neurones and Glia

Question 1

What do neurones do?

Answer 1

Sense changes and commnicate with other neurones

Question 2

What do glia do?

Answer 2

Support, nourish and insulate neurones and remove waste

Question 3

What are the different types of glial cells?

Answer 3

Astrocytes
Oligodendrocytes
Microglia

Question 4

What do astrocytes do?

Answer 4

• Structural support
• Help to provide nutrition for neurones (glucose-lactate shuttle)
• Remove neurotransmitters (uptake), controls concentration of neurotransmitters
• Maintain ionic environment, K+ buffering
• Helps to form BBB

Question 5

How do astrocytes help to provide energy for neurones?

Answer 5

Neurones do not store or produce glycogen as they lack the enzymes needed to use glycogen

Astrocytes do store glycogen, they produce lactate which can be transfered to neurones
-Supplements their supply of glucose, can support neurones for a short peirod of time

Question 6

Describe the glucose lactate shuttle

Answer 6

Glucose enters astrocytes via GLUT1

Glucose then converted into pyruvate, then into lactate

Lactate leaves through MCT1and enters neurone via MCT2, lactate then is converted back to pyruvate generating ATP for the neurone

Question 7

How do astrocytes remove neurotransmitters?

Answer 7

Astrocytes have transporters for transmitters such as glutamate

Helps to keep the extracellular concentration low, acts to stop depolarisation lasting for long periods of time

Glutamate can be toxic if too high

Question 8

Why do astrocytes buffer K+ in the brain?

Answer 8

Increased K+ depolaries neurones and can potentially lead to unwanted APs

Astrocytes have a very negatively charged iternal environment therefore K+ ions can move in easily

Question 9

How do astrocytes buffer potassium ions?

Answer 9

Very negative RMP

K+ enters via NaKATPase, NaK2Cl transports and K+ channels

Lowers the ECF concentration, astrocytes are coupled, K+ can travel between them, concentration does not rise highly in 1 cell

Question 10

What do oligodendrocytes do?

Answer 10

Myelinate multiple axons in the CNS

Question 11

What happens in multiple sclerosis?

Answer 11

Autoimmune degeneration of myelin around axons

Oligodendrocytes are also damaged

Less myelination of neurones which slows down the speed of action potential conduction

Can affect any white matter pathway

Question 12

What do microglia do?

Answer 12

• Immunocompetent cells
• Mesodermal origin
• Recognise foreign material
• Phagocytosis and can act as APCs
• Brains main defence system

Question 13

How do microglia phagocytose foreign material?

Answer 13

Dendrities swell up until they become phagocytic

Question 14

Why is the CNS immune priveliged?

Answer 14

If an allograft (cells from someone else) added to brain into does not undergo rapid enjection

Cannot tolerate volume expansion, would compress tissues

Question 15

What does the blood brain barrier do?

Answer 15

• Limits diffusion of substances form the blood to the brain ECF
• Maintains environment for neurones

Question 16

How does the blood brain barrier form?

Answer 16

Tight junctions between endothelial cells
Basement membrane surrounding capillary
End feet of astrocyte processes

Question 17

What substances can freely pass across the BBB?

Answer 17

Lipophilic gases e.g.
-CO2
- O2
- H2O

Question 18

What substances have to be transported across the BBB?

Answer 18

Glucose
Amino acids
K+

Question 19

What happens to K+ concentration after intense exercise?

Answer 19

Intense exercise causes K+ concentration to rise

If this got to the brain there would be unwated responses, hence the BBB prevents free movement of K+

Question 20

Why are amino acids transported across the BBB?

Answer 20

Amino acids can act as neurotransmitters, so if they could pass freely would cause unwated actions of the brain

Question 21

Why does the brain not have a profound immune response?

Answer 21

Rigid skull
Too much inflammation would be harmful as would compress brain contents

T-cells can enter the CNS but monocytes cannot
CNS inhibits initaiton of pro-inflammatory T-cell response

Question 22

How does depolarisation occur?

Answer 22

Stimulis received at soma, threshold is reached causing AP to spread down axon

Voltage-gated Na+ channels open and sodium ions enter and depolarise the cell

AP closes Na+ channels, previous parts of the axon are now in the refraction period while RMP is reached

Repolarisation occurs with the opening of K+ channels, K+ leaves the cell

Hyperpolarisation now occurs as K+ channels open, they then close and return to RMP.

Question 23

What are the 4 sections of a neurone?

Answer 23

Soma (cell body)
Dendrites
Axon
Terminals

Question 24

What happens at the synapse when depolarisation occurs?

Answer 24

AP travels down axon, depolarisation in the terminal opens voltage-gated Ca2+ ions

Vesicles fuse and release transmitter

Neurotransmitter diffuses across the synpatic cleft and binds to receptors on the postsynaptic membrane

Question 25

What does postsynaptic response depend on?

Answer 25

Nature of transmitter
Nature of receptor e.g.
- Ligand-gated ion channels
- GPCR