2. Physiology of the brain Flashcards
What are the 3 main types of glia?
Astrocytes
oligodendrocytes
microglia
What are the functions of astrocytes?
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
What are the functions of oligodendrocytes?
myelinate CNS axons (one oligodendrocyte myelinates multiple axons
in what disease are oligodendrocytes damaged?
multiple sclerosis
what are the functions of microglia?
act like macrophages and remove debris and help clean up sites of damage
can cause collateral damage by injuring cells
what happens to the morphology when microglia cells are activated?
inactivated - branched morphology so can scan the intracellular space for antigens
activated - morphology of a macrophage
what disease is caused by interruption to the blood brain barrier?
seizures caused by electrolyte imbalances
what is the purpose of the blood brain barrier?
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
why is tight regulation of the immune system so important?
if a strong inflammatory response in the brain would cause swelling and lead to an increase in intracranial pressure
what makes up a neurone?
axon terminal - axon - cell body - dendrites - synapse
how are neurotransmitters released?
- action potential arrives
- this causes opening of voltage gated calcium channels
- the entry of calcium into the cell causes vesicles to fuse with the presynaptic membrane and release transmitter
- the transmitter diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane and causes a response
what types of neurotransmitter are excitary and which are inhibitory?
excitatory - glutamate, ACh
inhibitory - GABA
what are the types of receptor the neurotransmitter will bind to ?
ion channel - NMDAR for glutamate
GPCR - mACHr for ACh
what is a type of amino acid neurotransmitter and what are some of its properties?
- 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
how does gaba cause a response?
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
how is gaba’s activity increased and what are the risks associated?
barbitrates, benzodiazepines and alcohol
but risk of overdose and addiction
what is a type of biogenic amines neurotransmitter and what are some of its properties?
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
what are the main pathways ACh is involved in?
arousal
learning and memory
motor control
what are the main pathways NA is involved in?
behaviour arousal mental state (low levels - depression)
what are the main pathways dopamine is involved in?
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)
what is a type of dopamine therapy?
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
what pathways are serotonin involved in?
sleep and wakefulness and regulation of mood
low levels = depression, so Selective serotonin uptake inhibitors increase level of serotonin in brain and can help
what pathways are histamine involved in?
sleep and wakefulness by stimulating cortex
what is a type of peptide neurotransmitter and what are some of its properties?
diffuse slowly and sometimes widespread
dynorphin, encephalin, orexin - pain transmission
how are excitatory post synaptic potentials induced?
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
how do glutamatergic synapses work?
- release of glutamate activates AMPA receptors that cause depolarisation
- depolarisation leads to the removal of a Mg ion in the pore of the NMDA receptor
- this allows entry of calcium through NMDA receptors
if lots of AMPA = sympase will transmit more readily = long term potentiation = learning and memory
