3. Neurones And Glia

Question 1

Give 4 roles of astrocytes

Answer 1

Structural support.
Help provide nutrition for neurones.
Remove neurotransmitters.
Maintain ionic environment.
Help to form the blood brain barrier.

Question 2

How do astrocytes provide energy for neurones?

Answer 2

Astrocytes produce lactate which can be transferred to neurones - glucose lactate shuttle.

Question 3

How do astrocytes help remove neurotransmitters?

Answer 3

Astrocytes have transporters for transmitters eg glutamate. Glutamate is broken down to glutamine in the astrocytes and transported back to the presynaptic terminal.

Question 4

Why do astrocytes need to help provide energy for neurones?

Answer 4

Neurones do not store glycogen so the lactate supplements their supply of glucose.

Question 5

Why do astrocytes need to help remove neurotransmitters?

Answer 5

To help keep the extracellular concentration of neurotransmitters low as they can be toxic at high concentrations eg glutamate.

Question 6

Why are astrocytes needed to help buffer K+ in the brain?

Answer 6

High levels of neuronal activity can lead to a rise in [K+] in the brain ECF. Increased [K+] causes depolarisation of neurones. Inappropriate firing of neurones can lead to epilepsy.

Question 7

What are oligodendrocytes?

Answer 7

Cells responsible for myelinating axons in the CNS. Myelinate many neurones at once

Question 8

What are microglia? What do they do?

Answer 8

Immunocompetent cells which recognise foreign material, become activated and phagocytose to remove debris and foreign material.

Question 9

What 3 cels/structures form the blood brain barrier?

Answer 9

Tight junctions between epithelial cells.
Basement membrane surrounding capillary.
End feet of astrocytes processes.

Question 10

Describe neurotransmitter release at axon synapses.

Answer 10

Depolarisation in the terminal opens voltage-gated Ca2+ channels. Ca2+ ions enter the terminal. The increased [Ca2+] causes the vesicles to fuse with the membrane at the presynaptic terminal and release the transmitter.

Question 11

What does the postsynpatic response at a synapse depend on?

Answer 11

The nature of the transmitter.

Nature of the receptor eg ligand-gated ion channels or GCPR.

Question 12

What are the 3 chemical classes of neurotransmitters in the CNS?

Answer 12

Amino acids.
Biogenic amines.
Peptides.

Question 13

Glutamate is the main excitatory amino acid neurotransmitter in the CNS. What are the two types of receptors?

Answer 13

Ionotropic - is ligand gated.

Metabotropic - is a GCPR.

Question 14

What are the 3 types of ionotropic glutamate receptors and what ions are each permeable to?

Answer 14

AMPA - Na/K+.
Kainate - Na+/K+.
NMDA - Na+/K+ and Ca2+.

Question 15

What is the one type of metabotropic glutamate receptors and how do they work?

Answer 15

mGluR1-7 - linked to either changes in IP3 and Ca2+ mobilisation of inhibition of adenylate cyclase and decreased cAMP.

Question 16

How do excitatory transmitters such as glutamate cause fast excitatory responses?

Answer 16

Excitatory neurotransmitters cause depolarisation of the postsynaptic cell by acting on ligand-gated ion channels. This causes an excitatory postsynaptic potential and depolarisation causes more action potentials.

Question 17

How do glutamate receptors have an important role in learning and memory?

Answer 17

Activation of NMDA receptors can up-regulate AMPA receptors. Strong, high frequency stimulation causes long term potentiation. Ca2+ entry through NMDA receptors is important for induction of the long term action potential.

Question 18

What does too much Ca2+ entry through the NMDA receptors cause? Give an example of when this can occur.

Answer 18

Excitotoxicity, as causes the release of too much glutamate. Eg stroke.

Question 19

Give 2 examples of inhibitory amino acid neurotransmitters - one in the brain and one in the brainstem and spinal cord.

Answer 19

Brain - GABA.

Brainstem and spinal cord - glycine.

Question 20

Describe the action of GABA and glycine (inhibitory amino acid neurotransmitter) receptors

Answer 20

Have integral Cl- channels. Opening of Cl- channel causes hyperpolarisation, this is an inhibitory post-synaptic potential, which results in decreased action potential firing.

Question 21

What are benzodiazepines, which bind to GABA receptors, used to treat?

Answer 21

Have sedative and anxiolytic effects so are used to treat anxiety, insomnia and epilepsy.

Question 22

Degeneration of cholinergic neurones in the nucleus basalis is associated with what disease? And so what can be used to alleviate the symptoms?

Answer 22

Alzheimer’s disease.

Cholinesterase inhibitors.

Question 23

What 3 functions of the brain are cholinergic pathways involved in?

Answer 23

Arousal.
Learning and memory.
Motor control.

Question 24

Where do neurones in the cholinergic pathways of the CNS originate and project to?

Answer 24

Originate in the basal forebrain and the brainstem.

Give diffuse projections to parts of the cortex and hippocampus.

Question 25

Similar to the cholinergic pathways in the CNS, there are also dopaminergic pathways. What are the 3 pathways and what functions are each associated with?

Answer 25

Nigrostriatal pathway - motor control.

Mesocortical pathway and mesolimbic pathway - mood, arousal and reward.

Question 26

What changes in the CNS is Parkinson’s disease associated with and so what can be used to treat it?

Answer 26

Associated with loss of dopaminergic neurones, and substantia nigra input to the corpus striatum.
Can be treated with levodopa.

Question 27

What changes in the CNS may cause schizophrenia and so what class of drugs are antipsychotics?

Answer 27

Increased amphetamine in the brain leading to increased dopamine and noradrenaline release in the dopaminergic and noradrenergic pathways of the CNS.
Antipsychotic drugs are antagonists at dopamine D2 receptors.

Question 28

Through what receptors does noradrenaline operate?

Answer 28

Alpha and beta GCPRs in both the ANS and CNS.

Question 29

Where do noradrenergic pathways in the CNS originate from?

Answer 29

Cell bodies of noradrenaline containing neurones are located in the brainstem, in the locus ceruleus.

Question 30

What happens to noradrenaline release in the CNS when asleep and during behavioural arousal?

Answer 30

Sleep - locus ceruleus neurones are inactive.
Arousal - locus ceruleus neurones activity increases. Amphetamines increase release of noradrenaline and dopamine and increase wakefulness.

Question 31

What condition may be associated with a deficiency of noradrenaline?

Answer 31

Depression

Question 32

What are the functions of serotonergic pathways in the CNS and so what class of drugs can be used in treatment of depression and anxiety disorders?

Answer 32

Sleep/wakefulness and mood.

SSRIs (serotonin selective reuptake inhibitors).