2. Cellular Physiology Of The Brain

Question 1

What are the general functions of the glial cells?

Answer 1

Support, nourish and insulate neurones and remove ‘waste’

Question 2

What are the 3 main types of glial cells?

Answer 2

Astrocytes
Oligodendrocytes
Microglia

Question 3

What is the role of astrocytes?

Answer 3

Structural support
(Most abundant type of glial cell)
Remove neurotransmitters
Help to provide nutrition for neurones - glucose-lactate shuttle
Maintain ionic environment - K+ buffering
Help to form blood brain barrier

Question 4

What is the general role of oligodendrocytes?

Answer 4

Responsible for myelinating axons in CNS

Question 5

What is the general role of microglia?

Answer 5

Immune response

• recognise foreign material and become activated
• phagocytosis to remove debris and foreign material

Question 6

How can astrocytes provide energy to neurones when glucose levels are low?

Answer 6

Astrocytes store glycogen which can be converted to lactate
This is then shuttled across to neurones via MCT1 and MCT2
Lactate is then converted to pyruvate, which is used to release ATP

Question 7

How can K+ move into astrocytes?

Answer 7

K+ channels
Na+/K+ ATPase transporter
Na+/K+/2Cl- transporter

Question 8

What is the purpose of the blood brain barrier?

Answer 8

Limits diffusion of substances from the blood to the brain extracellular fluid
Maintains correct environment for neurones

Question 9

What are the features of brain capillaries that form the blood brain barrier?

Answer 9

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

Question 10

Which substances are transported across the BBB?

Answer 10

Glucose
Amino acids
Potassium
O2, CO2 and water can freely move across

Question 11

Why is the brain immune privileged?

Answer 11

Rigid skull will not tolerate volume expansion

Too much inflammatory response would be harmful

Question 12

What makes the brain immune privileged?

Answer 12

Microglia can act as antigen presenting cells
T cells can enter the CNS
CNS inhibits initiation of pro-inflammatory T cell response

Question 13

Describe the process of neurotransmitter release at the synapse

Answer 13

Depolarisation in terminal opens voltage-gated Ca2+ channels, Ca2+ ions enter the terminal
Vesicles fuse with pre-synaptic membrane and release neurotransmitter
Neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic membrane

Question 14

What does the postsynaptic response depend on?

Answer 14

Nature of transmitter

Nature of receptor - ligand-gated ion channels, G-protein-coupled receptors

Question 15

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

Answer 15

Amino acids - glycine, GABA, glutamate
Biogenic amines - ACh, NA, dopamine, histamine
Peptides - cholecystokinin, somatostatin, dynorphin, enkephalins

Question 16

Name an excitatory amino acid neurotransmitter

Answer 16

Glutamate

Question 17

Name 2 inhibitory amino acid neurotransmitters

Answer 17

GABA - brain

Glycine - brainstem and spinal cord

Question 18

What are the 2 groups of glutamate receptors?

Answer 18

Ionotropic - contain integral ion channel

Metabotropic - contain G protein-coupled receptor

Question 19

What happens during fast excitatory responses?

Answer 19

Excitatory neurotransmitters caused polarisation of the postsynaptic cell by acting on ligand-gated ion channels
Depolarisation causes more action potentials

Question 20

Which receptors do glutamatergic synapses have?

Answer 20

AMPA - mediate initial fast response

NMDA - permeable to Ca2+

Question 21

What do glutamate receptors have an important role in?

Answer 21

Learning and memory

Question 22

How do glutamate receptors have a role in learning and memory?

Answer 22

Activation of NMDA receptors can up-regulate AMPA receptors
Strong, high frequency stimulation causes long term potentiation (LTP)
Ca2+ entry through NMDA receptors important for induction of LTP

Question 23

How do GABA and glycine receptors cause inhibitory effects?

Answer 23

Have integral Cl- channels
Opening the Cl- channel causes hyperpolarisation
Inhibitory postsynaptic potential
Decreased section potential firing

Question 24

Which drugs bind to GABAa receptors?

Answer 24

Barbiturates - sometimes anti-epileptic drugs
Benzodiazepines - anxiety, insomnia, epilepsy
Both enhance the response to GABA

Question 25

What are the roles of cholinergic pathways in CNS?

Answer 25

Arousal, learning and memory, motor control

Question 26

What happens to cholinergic neurones in Alzheimer’s disease?

Answer 26

Degeneration of cholinergic neurones in nucleus basalis

Question 27

What are dopaminergic pathways in the CNS involved in?

Answer 27

Mood, arousal, reward, motor control

Question 28

Name 2 conditions associated with dopamine dysfunction

Answer 28

Parkinson’s disease

Schizophrenia

Question 29

Where does most NA in brain come from?

Answer 29

Group of neurones in locus coeruleus

Question 30

What are the functions of serotonergic pathways in CNS?

Answer 30

Sleep/wakefulness

Mood

Question 31

What are SSRIs?

Answer 31

Serotonin selective reuptake inhibitors
Used in treatment of depression and anxiety disorders
Increases amount of serotonin around