eSagan 🇮🇳 @crackurbones@qoto.org
Joined Nov 2019
🔴 SPINAL CORD INJURY
🔸 While the sympathetic nervous system is entirely contained within the thoracic cord (all the preganglionic neurons are in the thoracic cord), the parasympathetic preganglionics are split between the brain stem and the sacral cord.
🔸 And this has one very important consequence — for virtually any spinal cord injury, it doesn't matter where, any lesion that is anywhere near complete is going to isolate the sacral cord.
🔸 Now, the sacral cord does not make decisions. The spinal cord does not make decisions. It depends on input from the brain.
🔸 So, for example when an individual wants to wants to void urine, there is a whole part of front, pre-frontal cortex which decides micturation to occur.
🔸 The sacral cord is responsible for executing micturation, but it's not responsible for making the decision.
🔸 So, if we have a lesion somewhere in the chord that's rostral (towards the brain) from sacral cord, the sacral cord no longer has instructions from the brain.
🔸 Under normal circumstances micturition depends on two things:
1️⃣ The bladder, which is a smooth muscle, is contracted And it's contracted by neurons in the sacral cord, which is a parasympathetic effect. Parasympathetic neuron contacts a ganglionic neuron in the wall of the bladder, and that ends up contracting the the bladder wall.
2️⃣ In addition there's an external urethral sphincter that has to relax in order to let the urine out. And that is a voluntary muscle that your brain controls.
🔸 Now, in the case of a spinal cord injury, the sacral cord is on its own. So, as the bladder fills up, it starts to contract. It will contract. But this will never relax.
🔸 And so, what you have is the bladder contracting against a fixed, tight, closed sphincter. This is called "bladder dyssynergia". And it is a huge problem in spinal cord injury.
🔸 If somebody suffers from a spinal cord injury, a physician is going to make sure, is going to test, whether, the person is able to void urine or not. And if they're not, they're going to need medical intervention immediately.
👁️ Up in the most rostral part of the thoracic column that provides pregangloinics to the sympathetics, our preganglionics go to the eye. They go to the pupil they go to a few other places, but they also go to this eyelid.
👁️ The eyelid has two different muscles in it.
It has a muscle which is called "levator palpebrae", which is innervated, is a skeletal muscle and is voluntarily controlled; so, it has a voluntary muscle.
And it has a muscle in the back which is called the "superior tarsus", and the superior tarsus is a smooth muscle.
👁️ So, the superior tarsus is innervated by the sympathetics. And so, when you're asleep, having very low sympathetic tone — your eye closes.
👁️ When you wake up, sympathetic tone automatically comes up to some minimum, including a contraction of the superior tarsus, and up comes your eyelid.
🖼️ Image source: screen-grab from https://www.coursera.org/learn/neurobiology/lecture/UCGLm/spinal-cord-injury
#Coursera for Campus will be available globally at no cost to any university impacted by #COVID19
https://www.coursera.org/coronavirus?utm_campaign=website&utm_content=c4cv-top-banner-dotorg&utm_medium=coursera&utm_source=home-page
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https://twitter.com/MiShee54/status/1239960873982144512?s=09
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🐤 https://twitter.com/guardianscience/status/1239841417389723648
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🐤 https://twitter.com/DiscoverMag/status/1239854066190159872
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http://on.forbes.com/60161sngg
🐤 https://twitter.com/ForbesScience/status/1239782266022363138
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🐤 https://twitter.com/PopSci/status/1239816362530426883?s=20
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🐤 https://twitter.com/Rainmaker1973/status/1239816818421891073?s=20
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https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3551767
🐤 https://twitter.com/DKThomp/status/1239622203278340096?s=20
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Joined Nov 2019
