What are the neuroglia of the CNS?
- Ependymal cells
- Astrocytes
- Oligodendrocytes
- Microglia
What are the neuroglia of the PNS?
Schwann cells
Where are ependymal cells located?
Line central canal and ventricles
What % of nervous tissue do neuroglia make up?
> 90%
What is the basic structure of neuroglia?
Small cells with little cytoplasm; only its nucleus can be seen with routine stains.
What is the division rate of neuroglia?
Continue to divide throughout life.
Ependymal cells and astrocytes provide optimal _____ environment for neurons.
extracellular
What is on the apical surface of ependymal cells?
Cilia
What is the role of ependymal cells?
Assist with CSF circulation
What do ependymal cells form?
choroid plexus
What is the choroid plexus made up of and what does it do?
choroid epithelium; produces CSF
What cells make up the choroid epithelium?
modified ependymal cells lined with microvilli
Why do the modified ependymal cells of the choroid epithelium have microvilli and not cilia?
To increase SA due to production of CSF
What are the cell types/shapes of ependymal cells?
Cuboidal to columnar
What does the choroid epithelium serve as a barrier for?
Blood-CSF barrier
What type of junctions are present in the choroid epithelium and why?
tight junctions so that nothing can travel between cells
What is special about the c.t. of the choroid plexus?
Has fenestrated capillaries that cause it to be “leaky” so that Na+ can leave endothelial cells
What is CSF?
Filtrates of the blood that pass through capillary endothelium and choroid epithelium of the choroid plexus.
Where does CSF circulate?
Ventricles and subarachnoid space
How does CSF get from the ventricles to the subarachnoid space?
Through a channel
What are the 3 functions of the CSF?
- Physical support of the CNS
- Maintains chemical environment of the CNS
- Regulates intracranial pressure
What does CSF remove from the CNS?
metabolites
How is the ICP maintained within normal limits?
CSF volume and blood volume vary inversely
What occurs with CSF absorption/production in regulation of ICP?
Absorption increases, production decreases
What are astrocytes?
Most abundant neuroglia of the CNS (~50%)
What 3 things do astrocytes do?
- Respond to injury
- Proliferate to form scar tissue
- Maintain optimal CSF environment
What are the 5 ways in which astrocytes maintain optimal CNS environment?
- Induct and maintain capillary endothelium as the BBB
- Help transport glucose to neurons
- Store glycogen - energy reserves
- Promote neuronal survival
- Prevent glutamate toxicity
What is the morphology of astrocytes?
Neuroglia with numerous cell processes
What does the capillary endothelium/BBB do?
Regulates exchange of solutes between blood and CNS tissue
What do astrocytes release?
Glial cell line-derived neurotrophic factor (GDNF)
Why do astrocytes release GDNF?
To promote formation and maintenance of capillary tight junctions
What is the structure of the capillary endothelium?
Perivascular endfeet of astrocytes contact the basement membrane, which contacts the endothelium
What are 3 ways in which things get across the BBB?
- Diffusion
- Transporter
- Carrier-mediated transport
What 3 things can get thru the BBB by diffusion?
- Water
- Gases
- Lipophilic substances (alcohol, heroin, nicotine, cyanide)
What can get thru the BBB by transporter?
Glucose
What is the transporter for glucose that gets it across the BBB?
GLUT 1
What 2 things can get thru the BBB by carrier-mediated transport?
- Amino acids
2. Vitamins
What AAs are transported vs. which ones aren’t?
Transported if not synthesized in brain (large neutral)
Not transported if synthesized in the brain
What 4 AAs are large and neutral and not synthesized in the brain?
- Leucine
- Tyrosine (NTM = catecholamine)
- Valine
- Tryptophan (NTM = serotonin)
What AAs are small and neutral and synthesized in the brain?
- Glycine
2. GABA