Cells of the CNS Flashcards
How is the CNS organised?
Into functional regions/nuclei
List the types of glial cells
- Astrocytes
- Microglia
- Oligodendrocytes
- Ependymal cells
How many neurons and glia are there in the brain?
In adult brain ~ 1 x 1011 neurons; ~ 5-fold more glia
Describe the cell composition of the brain
Typically: neurons 10-20%
astrocytes ~ 50%
microglia ≤ 20%
Is the cell composition dependent on brain region?
Yes
Give examples of cell compositions in different regions of the brain
- astrocytes out number neurons in cortex
- neurons out number astrocytes in cerebellum
Describe the steps of brain formation
Neurogenesis (Neural stem cells make neurons) —> Gliogenesis (then they make glia), synaptogenesis —> Synaptic pruning (particular networks undergo planned death)
What does the post-mitotic nature of neurons mean for cell number?
Their number declines with age
What does post-mitotic mean?
No longer dividing
Which regions of the brain exhibit adult neurogenesis?
olfactory bulb, hippocampus and striatum
Which cells of the brain divide by mitosis throughout life?
Astrocytes, oligodendroctyes, ependymal cells
Where do microglia come from?
– derived from bone marrow stem cells
(same as macrophages, leukocytes):
precursor cells cross in to brain early in development before blood brain barrier forms
What is the cell body also known as?
Soma
What is the part of the neuron that initiates the action potential called?
Axon hillock
What is another name for nerve terminals?
Synaptic boutons
What does neuronal morphology depend on?
Function and neuron type
What does the number of dendritic branches correlate to, give examples?
The number of synaptic contacts
motor neurons ~ 9000; Pukinje cells ~ 1 x 10^6
What are interneurons?
Neurons completely within CNS
Describe interneurons
axons tens-hundreds mm
- small cell body (5 mm)
What are efferent neurons?
neurons directly controlling glands/muscles e.g. motor neurons
Describe efferent neurons
- axon length can be ˃ 1 m
- cell body > 100 mM
Which are the most common glial cells in the CNS?
Astrocytes
What do astrocytes do?
1.Modulate brain oxygen levels by regulating blood flow via end feet at BBB
2.Regulate glucose and other metabolites to neurons
3.Remove excessive neurotransmitters at synapses allowing precise signalling
4.Take up K+ at synapses – essential for neuronal signalling
5.Release factors that control synapse formation
e.g. brain derived neurotrophic factor (BDNF)
6.Cause physical barriers between different neuronal circuits
7.Part of the neuroinflammation response – become mobile
Describe astrocyte morphology
astrocyte leaflet lies close to dendrites, synapses and axons of neurons; sparse around soma
What are microglia like under resting conditions?
stationary but continually sending out and retracting projections
What happens to the morphology go microglia upon activation?
have amoeboid shape, become mobile
What do microglia interact with?
neurons (synapses and dendrites), astrocytes, blood vessels
Describe the functions of microglia
phagocytose dying neurons / bacteria, present antigens to immune cells
implicated in synaptic formation, maintenance and pruning
Where are oligodendrocytes found?
white matter
What do oligodendrocytes do?
They form the myelin sheath around axons
How do oligodendrocytes get into the brain (development)?
Oligodendrocyte precursor cells migrate to destination
Proliferation controlled by neurons and astrocytes
Describe oligodendrocyte morphology
Mature oligodendrocytes envelop up to 50 axonal segments.
Each segment termed an internode and are several hundred mm long.
Internodes separated by nodes of Ranvier
Where are ependymal cells found?
In the choroid plexus
Describe ependymal cell morphology
Columnar epithelial-like cells containing cilia and microvilli
What do ependymal cells do?
They are involved in producing CSF
Give examples of diseases and the spcific neuronal population deaths which they are associated with
- Amyotrophic lateral sclerosis: upper and lower motor neurons
- Huntington’s disease: neurons of the basal ganglia
- Parkinson’s disease: dopaminergic neurons of substantia nigra
What diseases are associated with Activation of microglia and astrocytes?
Parkinson’s disease, Alzheimer’s disease, neuronopathic Gaucher disease
