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The ependyma: a protective barrier between brain and cerebrospinal fluid
https://pubmed.ncbi.nlm.nih.gov/7615341/
Some cells lining the neural tube are committed at an early stage to becoming ependymal cells. They serve a secretory function and perhaps act as a cellular/axonal guidance system, particularly during fetal development. In the mature mammalian brain ependymal cells possess the structural and enzymatic characteristics necessary for scavenging and detoxifying a wide variety of substances in the CSF, thus forming a metabolic barrier at the brain-CSF interface.
Coronavirus tests: Swabs don't damage the brain
https://www.bbc.com/news/53443429
A swab stick inserted into the nose would need to break through multiple layers of tissue and drill through a bone and into the blood vessels to reach the blood-brain barrier.
"The swab cannot reach the blood brain barrier without significant force that breaks several layers of tissue and bone. We have not seen any complications from Covid swabs in our neurology practice", says Dr Liz Coulthard, a committee member of the British Neuroscience Association (BNA).
The nasopharyngeal swab checks for coronavirus in the back of the nasal passage and is one of a range of swabbing techniques.
If you only breathe on a slim swab head, you might not catch the viral particles or the cells that carry the virus. However, if you insert the swab in the nose and throat and rotate it at the site of infection, you are more likely to get infectious material that will yield a result.
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Read the BBC 'fact-check' and note the concessions made and then note the misrepresentations of the concern that is presented so as to be 'checked'.
Compromising the membrane is the key, not poking through it on a single twist of the 'clue-tip'. Repeated PCR sample-taking leads to letting down one's guard both as the individual being subjected to the sample-taking and as the technician taking yet another of thousands of samples. ERRORS are to be expected. WEARING DOWN resistance is to be expected.
This is why they are now starting to refer to it as a 'routine nose swab'. It is invasive. It is supposedly a light cost to the individual, like mask-wearing, that is a small thing to ask in the great effort to PROTECT OTHERS from your spreading disease.
Yeh. Ok.