Cells in the CNS

Question 1

What are the types of neurones found in the CNS

Answer 1

Sensory pseudo-unipolar - one axon with the cell body being found in a ganglion

Bipolar - cell body is the middle of the axons

Multipolar - has many dendrites so can form multiple synapses with other neurones

Question 2

Name the glial cells found in the CNS

Answer 2

Astrocytes

Oligodendrocytes

Microglia

Question 3

What are astrocytes and what are their functions

Answer 3

Astrocytes are supporting cells of the CNS and are the most abundant glial cell

Functions:

• Help provide nutrition for neurones via the glucose-lactate shuttle
• Help remove neurotransmitters by re-uptake mechanisms to control concentration of neurotransmitter in the synaptic cleft
• Maintains ionic environment of the brain ECF by buffering K
• Help form the blood brain barrier

Question 4

Describe the glucose-lactate shuttle

Answer 4

Neurones do not store or produce glycogen so get their nutrients directly from the blood or from astrocytes via the glucose-lactate shuttle

Astrocytes take up glucose and convert it to glycogen and then convert it back to glucose when required, then convert it into lactate which is then transported into the neurone

Question 5

How do glial cells help maintain the ionic environment of the brain ECF

Answer 5

Astrocytes help prevent the K level becoming high as after high levels of neuronal activity, the K level can rise in the ECF causing neurones to depolarise which has harmful effects on the brain

Astrocytes take up K to prevent a high K in the ECF

Astrocytes have a very -ve membrane potential which helps in K re-uptake

Question 6

What are oligodendrocytes

Answer 6

Oligodendrocytes are cells responsible for myelinating axons of neurones in the CNS

They myelinate multiple axons at once

Question 7

Describe microglia

Answer 7

Microglia are immune cells found within the CNS that if activated become macrophages

They are immunocompetent cells that recognise foregin material and become activated

Once activated, the microglia processes become wider, allowing them to phagocytose material and remove it

Question 8

Describe the immune system of the CNS

Answer 8

The CNS is immune privileged/specialised as inflammatory responses cannot occur within the CNS because the rigid skull does not allow for volume expansion

Inflammatory responses would result in increased pressure and damage to the brain so cannot occur

Microglia act as APC while T-Cells can enter to help with immune responses, though CNS inhibits initiation of pro-inflammatory T-Cells repsonse

Question 9

What forms the blood brain barrier

Answer 9

Tight junctions between endothelial cell to prevent movement of charged molecules

Basemement membrane surrounds the capillary

End feet of astrocytes processes help form the barreir and send signals to help endothelial cell form the barrier

Question 10

Why is there a need for a blood brain barrier, give some examples why

Answer 10

BBB is required to separate the brain ECF from blood becuase blood is not a suitable environment for neurones

E.g. blood K increases during exercise and amino acids can act as neurotransmitters in the CNS