cellular diversity Flashcards
what are main types of cells in nervous system, what is a key difference between them
neurones and glial cells
neurones are electrically excitable, glia are not
how does number of neurones relate to glia, how does this relate to system function
several times more glia than neurones, however they have equal in terms of weight and volume in CNS, in PNS relative number of glia is greater, they are intermixed throughout CNS and PNS,
other animals have less glia than neurones; more intellegent systems have more glia as well as more complex glia
what are different types of glia
in CNS: oligodendrocytes, astrocytes, microglia
in PNS: myelinating schwann cells, non myelinating schwann cells, satellite cells, enteric glia
what are functions of glia
homeostasis of extracellular space; ion concentrations/ neurotransmitters
aid in the metabolic needs of neurones; control neuronal survival and brain blow flow
myelination of axons
formation of synapses, elimination of innapropriate synapses, maintenance of synapses as well as control of synaptic function
they are also multipotent progenitors; in development they give rise to neurones, fibroblasts and mature glia, in adult systems glia generate neurones
regulate repair after injury
describe the physiology and function of astrocytes
they are highly branched cells, with cell body in the centre
they modulate synaptic function, blood supply to brain
many synapses in brain are enveloped by astrocyte processes
astrocytes have neurotransmitter receptors which respond to synaptic signals, activation of these receptors elevates astrocytes calcium which causes release of gliotransmitters which act on pre or post synpatic elements to modulate synaptic transmission
gliotransmitters include glutamate, ATP, d-serine and BDNF
also considered signalling cells
how is the astrocyte interaction with synapse described
described as a tri-partite synapse as opposed to classical bi-partite synapse
give an example of receptors found in glial cells, what effects does this have
cannabinoid type 1 receptor:
CB1R, is one of the most abundant G protein coupled receptors, found on glial cells as well as neurones;
major effect of cannabis is impairment of memory; astrocytes with CB1Rs are found at CA3-CA1 synapses in hippocampus which have major involvement in memory
activation of cannabinoids on these receptors cause release of glutamate from astrocyte which act on AMPA receptors, which inhibit normal depolarisation from glutamate from neurones mediated by NMDA receptors
how do astrocytes communicate with eachother
via gap junctions, gliotransmitters and calcium waves
how do astrocytes compare in humans and mice
humans have more astrocytes per neurones, they also have more complex/branced astrocytes
astrocytes from human embryos that are transplanted into neonatal mice produce mice which perform better in memory tests
tests used were auditory fear conditioning, contextual fear conditioning and a barnes maze test, transplanted mice consistantly performed better in all tasks and showed much greater long term potentiation
how do astrocytes aid in homeostasis of synapses
they contain potassium channels and neurotransmitter transporters allowing the clearance of the extracellular space
what affect do astrocytes have on blood flow
astrocytes shift blood flow to active areas, allowing for more oxygen and glucose for more metabolically active areas, astrocytes recognise more active neurones via neurotransmitter receptors detecting activation of synapses
activation of neurotransmitter receptors on glia cause increase in intracellular calcium which then release signalling molecules which act on blood vessles leading to vasodilation of vessels near active neurones
what are microglia
they are immune cells of CNS (are the macrophages of the CNS)
they migrate to CNS during development where they stay
cell bodies are stationary but they have processes which are constantly moving, which monitor brain tissue
what are different states of microglia
they have a surveillance/resting state, they are activated by disturbances of brain homeostasis
once activated to may turn into a phagocytic state
what is a model for chronic pain
placement of a ligature around peripheral sensory nerves is a model of chronic neuropathic pain
the ligature mimics sensory neurone distress,a few days after ligature placement light touch of limb activates nocicpetive neurones
what is mechanism of glia in pain
damaged axons release neuregulin
neuregulin turns resting microglia into active state, these then release BDNF which makes pain neurones hyper excitable
BDNF release by microglia is stimulated by ATP acting on P2X receptors on microglia, ATP is released by astrocytes
P2X adenosine receptor antagonists have analgesic effects
