glial cells

Question 1

what does the glia do?

Answer 1

the glia (neuroglia) support cells and different types of glia are specialised to ensure the normal functioning of neurones

Question 2

what are the 4 types of glia in the CNS?

Answer 2

-astrocytes:has multiple neuron supporting functions
-oligodendrocytes:form the myelin and cause a loss in demyelination
-microglia: phagocytotic, immune cells
-ependyma

Question 3

what are the 3 types of glia in the PNS?

Answer 3

-schwann cells:there is myelinating and non myelinating SC
-satellite cells:astrocyte like functions in the PNS ganglia
-enteric glia:astrocyte like functions in the GI tract

Question 4

what is the blood brain barrier (BBB)?

Answer 4

a permeability barrier that protects the brain from harmful substances in the blood
-also pre-empt immune checks from crossing the body’s circulation into the brains bloodstream

Question 5

contrast the PNS blood vessels to the CNS bloods vessels

Answer 5

PNS=leaky blood vessels
CNS=tight blood vessels

Question 6

what are endothelial cells connected by?

Answer 6

tight junctions and are surrounded by astrocyte processes

Question 7

what is the brains/CNS immune system called?

Answer 7

the microglia,they have highly active cells that continuously sample the environment, detect damage and respond rapidly

Question 8

when is the microglia activated?

Answer 8

-it is activated following injury, inflammation and immune insults and then increases macrophage and immune functions and becomes phagocytic

Question 9

what are macrophages?

Answer 9

-white blood cells that enter the CNS before birth and before the BBB forms and they surround and kill microorganisms

Question 10

what is the myelin?

Answer 10

-multiple layers of cell membrane (phospholipid bilayers) and insulates axons and greatly increases the speed of nerve conduction
-along the Xon consecutive myelin sheaths are separated by the nodes of ranvier
-action potentials jump from node to node (saltatory conduction)

Question 11

why is the myelin essential for nervous system functioning?

Answer 11

myelination has allowed the development of massive computing power of the vertebrate brain, it does this by increasing the nerve conduction velocity which also leads to a decrease in the size of the nerves
-without myelination each optic nerve would have a diameter of 0.75m

Question 12

what does the Schwann cell myelinate in the PNS?

Answer 12

In the PNS,each Schwann cell myelinated a single axon with a 1: 1 ratio

Question 13

what does the ogliodendrocytes myelinate in the CNS?

Answer 13

In the CNS,for the ogliodendrocytes each cell myelinated 20-30 axons with a 1:30 ratio

Question 14

what is white matter?

Answer 14

-WM is bundles of myelinated axons interconnecting brain regions
-it is a prominent feature of the human cortex and underlines the massive computing power of the human brain
-it enables rapid integrated communication

Question 15

what can a loss of myelin and white matter in other neuropathologies lead to?

Answer 15

Alzheimer’s disease,neuropsychiatric disorders, injury and stroke

Question 16

what can a loss of myelin lead to in general?

Answer 16

-axonal conduction block and degeneration

Question 17

what are demyelinating diseases of the CNS and PNS?

Answer 17

-demylenating diseases of the CNS and PNS are diseases of ogliodendrocytes and schwann cells
for the CNS it results in multiple sclerosis
-for the PNS it results in Charcot-Marie-tooth disease and Guillain Barre syndrome

Question 18

what are astrocytes?

Answer 18

astrocytes=star cells and they have multiple neurone supporting functions?

Question 19

what do astrocytes do?

Answer 19

-give the brain its structure
-critical for brain development
-they help form the BBB
-they are involved in injury
-they signal neurons to help coordinate synaptic transmission through neuroglia signalling
-they are important for metabolism
-they help with potassium regulation
-they help with neurotransmitter uptake

Question 20

why are astrocytes critical for brain development?

Answer 20

-they regulate neurogenesis and gliogenesis (generation of neurons) and neuronal pathfinding, synaptogenesis(formation of synapses

Question 21

why are astrocytes important for metabolism?

Answer 21

-astrocytes provide metabolic support for neurons
-neurons account for about 90% of the brain’s energy consumption but glucose is accumulated to equal levels by neurons and astrocytes use it as an additional energy source for neurons through the process of the astrocyte-neuron lactate shuttle:

Question 22

what is the process of the astrocyte-neutron lactate shuffle?

Answer 22

-Astrocytes store glucose as glycogen
-They convert it to lactate -when neurons need energy
They release lactate for neurons

Question 23

how do astrocytes help with potassium regulation?

Answer 23

everytime there is an action potential,potassium is released from neurons and astrocytes take up this potassium and recycle it and stop it building up,if this didn’t happen there would be unregulated neuronal activity

Question 24

what is the clinical connection between epilepsy and astrocytes?

Answer 24

epilepsy is caused by changes in astrocytes which means they are unable to take up potassium and so the high potassium ;eats to uncontrolled neuronal activity which is a feature of epilepsy

Question 25

how do astrocytes help with neurotransmitter uptake?

Answer 25

-they are responsible for taking up glutamate ay synapses and glutamate is the main excitatory neurotransmitter in the brain
-it also helps with the conversions in the glutamate-glutamine shuffle which helps stop glutamate building up to toxic levels

Question 26

describe the glutamate-glutamine shuffle..

Answer 26

astrocytes convert glutamate into gluttamine and the glutamine is given back to the presynaptic neuron and the neurones turns it back to glutamate-recycling happens and the activity of the glutamate is terminated at the synapse

Question 27

what happens if the astrocytes stop taking up the glutamate?

Answer 27

the glutamate gets too high in the extracellular space, this makes it too toxic for the neurones destructing them, this is known as excitotoxicity

Question 28

what is the clinical connection between astrocytes and ischemia?

Answer 28

-the most common cause for astrocytes not being able to take up glutamate is ischemia during stroke,a a lack of oxygen causes glutamate transporters to fail and the glutamate then accumulates

Question 29

why are the functions that the astrocytes help with essential?

Answer 29

it is essential for a healthy brain and neuronal function and without astrocytes these processes would not be able to happen and the BBB would not be able to form and the brain would not be able to protect itself

Question 30

why are astrocytes able to perform their multiple functions?

Answer 30

-because they have specialised morphological and physiological features

Question 31

why does neuronal injury succeed in the PNS but fails in the adult CNS?

Answer 31

-nerves can regenerate in the PNS but not the CNS
-in the CNS,regeneration is inhibited by astrocytes which form a glial scar( a cut in scar tissue)

Question 32

what happens when we injure the PNS?

Answer 32

-if we injure the PNS,the PNS regeneration is supported by schwann cells and they form a regeneration tube that guides and stimulates regrowth of the axon

Question 33

what is the clinical connection between spinal injury and the CNS?

Answer 33

-in the CNS if there was a spinal injury there would be no regeneration and there would be paralysis below the injury site