Lecture 6 : Glia - Form and Function Flashcards
What is glia?
Glia (or glial cells) are non-neuronal cells in the nervous system that support and protect neurons. There are several types of glia:
Astrocytes: Support neurons, maintain the blood-brain barrier, and regulate blood flow.
Oligodendrocytes (in the CNS) / Schwann cells (in the PNS): Form myelin sheaths, speeding up signal transmission.
Microglia: Act as the brain’s immune cells, clearing debris and responding to injury.
Ependymal cells: Line the ventricles and produce cerebrospinal fluid (CSF).
Glia play crucial roles in maintaining brain homeostasis, supporting neuron function, and aiding in repair.
It is not seen by electrophysiological techniques, more seen by immunohistochemical identification
Find out what all of those look like
What is the astrocytic syncytium
The astrocytic syncytium refers to the interconnected network of astrocytes, which are a type of glial cell in the brain. These cells are linked by gap junctions, allowing them to function as a unified system. This network enables astrocytes to:
Coordinate signaling: Astrocytes can communicate and respond to signals as a group rather than individually.
Regulate extracellular space: They help maintain ion balance, remove neurotransmitters, and control blood flow.
Support neuronal function: Astrocytes regulate synaptic activity, support the blood-brain barrier, and contribute to metabolic support for neurons.
Astrocytes in homeostasis (mechanisms)
- Maintaining balance of K+ and Na+ in extracellular space during neuronal activity
- Expresses transporters to take up these ions
- Prevents accumulation of K+
Astrocytes in controlling the synapse (mechanisms)
- Express neurotransmitter transporters
- Prevent diffusion of neurotransmitters outside of the synapse
Astrocytes in protecting the synapse (mechanisms)
- Express various transporters
- Prevent entry from outside the synapse
- Cover synapse from extracellular fluid
Astrocytes in neurovascular coupling
When astrocytes regulate blood flow in response to neuronal activity
- Release neurotransmitters
- Provide energy to neurone
- Their ‘feet’ envelops capillaries and neurones, causing vasodilation which increases blood flow to these regions
- Neurons release glutamate which bind to receptors on astrocytes and intracellular Ca2+ levels are increased
Astrocytes in responding to insult
- Damaged cells release ATP and glutamate
- Astrocytes proliferate and form glial scars around CNS injury
- Produce inhibitory molecules which inhibit growth of damaged or severed axons
What is microglia
- Smallest glial cell
- 10% of total glial cells
- Come from bone marrow monocytes
- Migrate to nervous system during development
- Act as the brain’s immune cells, clearing debris and responding to injury
How does microglia get activated?
- They have receptors for neurotransmitters and are activated upon binding
- Stimuli could be tissue injury (ATP is the stimuli)
- Pathogen derived triggers
- Neuronal signalling (ATP also stimuli)
How do microglia respond to activation?
- Proliferate
- Release pro-inflammatory signalling substances such as cytokines
- However activated microglia can be neurotoxic, and long lasting effects can be linked to pathological processes, eg. Alzheimers, parkinsons)
- Activation of microglia -> astrocyte activation
- Disruption of homeostatic mechanism
How are myelinating cells different in PNS and CNS
PNS (Schwann Cells):
- Each Schwann cell myelinates one axon.
- They can also aid in nerve regeneration after injury by forming regenerative tubes.
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CNS (Oligodendrocytes): - Each oligodendrocyte myelinates multiple axons (up to 50).
- They do not promote regeneration after injury in the CNS, and damage to oligodendrocytes leads to scarring.
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In summary, Schwann cells in the PNS myelinate one axon and aid regeneration, while oligodendrocytes in the CNS myelinate many axons but do not support regeneration.
