023 + 024 Glia Flashcards
what type of cell make up the majority of the brain?
glial cells
what is the difference between neurons and glial cells?
- neurons can conduct action potentials
- glial cells cannot conduct action potentials
what are the names of main types glial cells in the CNS(5)?
- astrocytes
- oligodendrocytes
- microglia
- ependymal cells
- NG2 cells
what are the names of main glial cells in the PNS(4)?
- myelinating Schwann cells
- non-myelinating Schwann cells
- satellite cells
- enteric glia
what were glial cells described as when they were first discovered?
’ glue ‘ of the CNS
what is the most common glial cells in the brain?
astrocytes
what is the function of astrocytes (5)?
- developmental role in migration of neurons and axon guidance
- homeostasis of neuronal microenvironment: ionic, metabolic, neurotransmitter uptake
- Blood-brain barrier induction and maintenance
- nutrition of growth factors
- synaptogenesis and synapse remodeling
describe the structure of astrocytes
= star shaped highlt ramified glial cells
- attach to neuron body and axon and connect to ependymal cells to link to vasculature
- interact with synpases, nodes of Ranvier, blood vessels…
give some examples of astrocyte subtypes
- protoplasmic astrocytes
- fibrous astrocytes
- radial glial cells
- Bergmann glia
- Muller glia
what is the structure and function of protoplasmic astrocytes?
- biggest astrocyte population in grey matter
-mainly found in hippocampus and cerebral cortex - very highly ramified (can touch multiple synapses in 1 area)
- involved in neuromodulatory role
what is the structure and function of fibrous astrocytes?
- organized along white matter tracts
- less ramified and smaller
- can contact nodes of Ranvier
- maintain homeostasis in their region
what is the structure and function of radial glia cells?
- long thin cells stretching from apical to basal
- used in neuronal migration during cerebral cortex development
- known as the main neuronal/glial progenitor present during brain development
what is the structure and function of Bergmann glia?
- specific astrocytes for cerebellum
- ensheaths and controls cerebellar synapses
- also involved in granular cell migration
what is the structure and function of Muller glia?
- astrocyte type specific for retina
- involved in cell migration, neuronal generation and control of synapses of the retina
describe the function of astrocytes and the neurovascular unit
- astrocytes have connections called ‘end feet’ which signal to blood vessels to expand or narrow the blood vessels to control flow of oxygen and nutrients
- astrocytes can release gliotransmitters (like glutamate) to send signals to neighboring neurons
- so this allows a sense of synaptic activity to control delivery of oxygen and nutrients
what are pericytes?
- multifunctional cells embedded in the walls of capillaries in the CNS that connect to astrocytes
- important for blood vessel formation, maintenance of the blood-brain barrier, regulation of immune cell entry to the central nervous system (CNS) and control of brain blood flow
what is the tripartite synapse?
- 3 part synapse
- pre-synaptic synapse
- postsynaptic synapse
- enwrapped by the astrocytic process
- allows astrocytes to modulate synaptic transmission by increasing or decreasing the amounts of ions or taking up/releasing more or less neurotransmitter like glutamate
what are oligodendrocytes?
- type of glial cell
- myelinates neurons in the CNS = white matter
describe the structure and function of myelination from oligodendrocytes
- myelin deposition is an active process
- oligodendrocytes wrap around axon in multiple layers
- different lengths and thickness of myelin on axon determines its function and speed of transmission
- it organizes the neuronal network and the types of information transfer
- allows for local communication between neurons and immune cells
what is active myelination of the CNS?
- increasing the myelination/white matter of the brain
- increased when learning motor skills
- e.g. study showed increased white matter in forebrain after learning piano
what cells myelinate the CNS?
oligodendrocytes
what cells myelinate the PNS?
schwann cells
what is a Remark bundle?
- Schwann cells bundle unmyelinated C-fibres together to form Remark bundles
- they provide protection and trophic support to unmyelinated axons
- upon injury, Schwann cells recruit macrophages to clear away damaged debris and then actively promote and support axonal regeneration through the synthesis and secretion of growth factors, extracellular matrix molecules and cell adhesion molecules
what are NG2 cells?
- also called oligodendrocyte precursor cells (OPCs) or polydendrocytes
- exist throughout grey and white matter of the developing and mature CNS
- they transform into different kinds of glia such as oligodendrocytes and astrocytes, but also into neurons (replace injured cells)
- important in MS
what are ependymal cells?
- create CSF and line ventricles of the brain and central canal of the spinal cord
- the cells are cuboidal/columnar and have cilia/microvilli to circulate and absorb CSF
- regulate osmotic pressure and ion homeostasis
what are the functions of microglia (4)?
- immune cells of CNS = surveillance of the surrounding tissue for infection, if detect then can become phagocytic to remove
- important for brain development and homeostasis
as they prune synapses (remove excess connections in fetus during development) via complement cascade - involved in neurodegenerative disorders and pain, can cause programmed cell death of neurons
- involved in neuroplasticity (ability in nervous system to change in response to damage)
what is microglia’s immune function?
- surveillance of surrounding tissue in CNS for infection and injury
- if detect, move towards damage and become phagocytic to remove
what is microglia’s function in development?
- synapse pruning
- remove excess synapses and connections and strengthen important ones via complement cascade
- in fetal and adult development
what is a possible theory of microglia’s role in autism spectrum disorder?
- problem in microglial complement cascade in pruning synapses
- less synaptic pruning in early life (through C3?)
- more abnormal connections/synapses left
what is a possible theory of microglia’s role in schizophrenia?
- mutation in MHC –> higher expression of C4a in complement
- causes increased synaptic pruning
- loss of grey matter and reduced synaptic density
what is a possible theory of microglia’s role in Alzheimer’s disease?
- mutation in microglial genes
- microglia usually attract to and clear away amyloid plaques and debris, but cannot with this mutation = distressed = release cytokines
- this causes inflammation = synaptic loss and then cognitive decline in the CNS linked with Alzhiemer’s disease
what is microglia’s role in neuropathic pain?
- peripheral nerve injury –> damaged primary afferent fibres express and release CSF1 in dorsal horn
- spinal microglia excessing the CSF1R and adopt a reactive phenotype characterised by the upregulation of P2X4Rs
- activation of these receptors stimulate BDNF which in the intercellular signalling molecule
- BDNF activates neuronal TrkB, downregulating KCC2 resulting in neuronal disinhibition –> pain neurones hyper excitable
