2. Physiology of the brain

Question 1

What are the 3 main types of glia?

Answer 1

Astrocytes
oligodendrocytes
microglia

Question 2

What are the functions of astrocytes?

Answer 2

structural support
nutritional support for neurones (glucose to lactate)
reuptake of neurotransmitters
maintain ion concentrations in extracellular fluid (particularly potassium esp when brain highly active)
contribute to blood brain barrier (induce expression of tight junctions)
form scar tissue and repair damage
forms a synctium which calcium waves can propagate through for cognitive function
synaptic function
role in stroke and tumours

Question 3

What are the functions of oligodendrocytes?

Answer 3

myelinate CNS axons (one oligodendrocyte myelinates multiple axons

Question 4

in what disease are oligodendrocytes damaged?

Answer 4

multiple sclerosis

Question 5

what are the functions of microglia?

Answer 5

act like macrophages and remove debris and help clean up sites of damage
can cause collateral damage by injuring cells

Question 6

what happens to the morphology when microglia cells are activated?

Answer 6

inactivated - branched morphology so can scan the intracellular space for antigens
activated - morphology of a macrophage

Question 7

what disease is caused by interruption to the blood brain barrier?

Answer 7

seizures caused by electrolyte imbalances

Question 8

what is the purpose of the blood brain barrier?

Answer 8

limits diffusion of substances from brain capillaries to brain parenchyma by acting like a selective barrier - eg: oxygen, glucose and ions and some fat soluble molecules can cross

Question 9

why is tight regulation of the immune system so important?

Answer 9

if a strong inflammatory response in the brain would cause swelling and lead to an increase in intracranial pressure

Question 10

what makes up a neurone?

Answer 10

axon terminal - axon - cell body - dendrites - synapse

Question 11

how are neurotransmitters released?

Answer 11

1. action potential arrives
2. this causes opening of voltage gated calcium channels
3. the entry of calcium into the cell causes vesicles to fuse with the presynaptic membrane and release transmitter
4. the transmitter diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane and causes a response

Question 12

what types of neurotransmitter are excitary and which are inhibitory?

Answer 12

excitatory - glutamate, ACh

inhibitory - GABA

Question 13

what are the types of receptor the neurotransmitter will bind to ?

Answer 13

ion channel - NMDAR for glutamate

GPCR - mACHr for ACh

Question 14

what is a type of amino acid neurotransmitter and what are some of its properties?

Answer 14

• GABA
  diffuse quickly and involved in direct signalling
  many present in the cerebral cortex and basal ganglia
• glutamate
  found all over CNS
  can bind to AMPA (Na and K), Kainate (Na and K), NMDA (Na, K and Ca) and various mGluRs (Q in QISS QIQ)
• glycine
  released in spinal cord during REM sleep to inhibit lower motor neurones = paralysis

Question 15

how does gaba cause a response?

Answer 15

opening of GABAA leads to opening of the chloride channels so there is a Cl influx which hyperpolarises the cell causing an inhibitory postsynaptic potential

Question 16

how is gaba’s activity increased and what are the risks associated?

Answer 16

barbitrates, benzodiazepines and alcohol

but risk of overdose and addiction

Question 17

what is a type of biogenic amines neurotransmitter and what are some of its properties?

Answer 17

Ach
found within PNS at neuromuscular junction, autonomic ganglia, postganglionic parasympathetic, sympathetic cholinergic fibres
also found within CNS acting at nicotinic and muscarinic receptors found at presynaptic terminals which act to enhance release of other molecules, eg: dopamine
NA
acts at GPCRs
dopamine

Question 18

what are the main pathways ACh is involved in?

Answer 18

arousal
learning and memory
motor control

Question 19

what are the main pathways NA is involved in?

Answer 19

behaviour arousal 
mental state (low levels - depression)

Question 20

what are the main pathways dopamine is involved in?

Answer 20

motor control (through nigrostriatal pathway, ie: from substantia nigra to striatum)
mood, arousal and reward (neocortical, ie: from midbrain to cortex
mood, arousal and reward (mesolimbic, ie: from midbrain to limbic system, eg: hippocampus)

Question 21

what is a type of dopamine therapy?

Answer 21

L-DOPA crosses the BBB via the LNAA which is converted to dopamine in the brain by AADC. but it can also be converted to dopamine in the periphery by AADC, and so there will be high levels of dopamine in periphery causing side effects affecting heart, GI tract and urinary. this can be inhibited by the coadministration of carbidopa which is a peripheral AADC inhibitor

Question 22

what pathways are serotonin involved in?

Answer 22

sleep and wakefulness and regulation of mood

low levels = depression, so Selective serotonin uptake inhibitors increase level of serotonin in brain and can help

Question 23

what pathways are histamine involved in?

Answer 23

sleep and wakefulness by stimulating cortex

Question 24

what is a type of peptide neurotransmitter and what are some of its properties?

Answer 24

diffuse slowly and sometimes widespread

dynorphin, encephalin, orexin - pain transmission

Question 25

how are excitatory post synaptic potentials induced?

Answer 25

binding of a ligand to an ionotropic receptor causes influx of cations causes depolarisation in post synaptic terminal = ESPS. if this exceeds the threshold, action potentials will be triggered. large amounts of trnasmitter = increased magnitude of ESPS = increased frequency of action potentials

Question 26

how do glutamatergic synapses work?

Answer 26

1. release of glutamate activates AMPA receptors that cause depolarisation
2. depolarisation leads to the removal of a Mg ion in the pore of the NMDA receptor
3. this allows entry of calcium through NMDA receptors
   if lots of AMPA = sympase will transmit more readily = long term potentiation = learning and memory