Now after the pain comes numbness and weakness it’s those nerves again (entry level neurophysiology and a bit of muscle physiology coming up) Let me explain: a thread... https://twitter.com/tjqpni/status/1343969647402622976

#Nerves are a part of your body which exist to pass information. They bring info to the brain, and spinal cord, (afferent) and information from the brain and spinal cord (which are also nerve cells but with different set up and packaging).

Nerves pass information by electricity and this ‘electrical jolt’ is called an “action potential”. Imagine back when we could a line of party goers standing side by side all with party poppers firing them only when the one next to them goes off..

This creates a ‘Mexican wave’ or “propagates” the signal along the whole length of the nerve. In nerves it’s not party poppers though, it’s “ion channels” [which are teeny tiny gates to let charged metal ions flood in and out] but same same really!

The speed that this Mexican wave can move at is slowed down by the cold. Imagine all the line of people are chilly and have to get their hands out of their pockets when they hear their neighbour pulling their popper before getting ready to pull theirs it slows things down.

The actual reason is the cold affects a nerve in so many ways- the actual ‘skin’ of the nerve the “cell membrane” is made of fat [a clever lipid bilayer] is changed by the cold - like butter it gets harder when cold and works less well.

Some nerves wear sporty clothing too (a “myelin” sheath) to help them function better and faster. This layer is also changed by cold meaning the loud fast nerves can be more effected than the smaller slower nerves.

So this reduction in function of nerves in the cold means they start to work less well. As #nerves tell you about how things feel (sensation) body position (“proprioception”) & tell your muscles how and when to move your limbs. All these functions slow down and become less good.

You loose feeling in your fingers and toes (as the peripheries are further away from the warm core body, have no big muscles to warm them and also have a high surface area to volume ratio- the nerves in them cool quickest)

This is called a conduction block - the nerve stops passing or conducting messages. It’s similar to what happens when you have local anaesthetic (the numbing injections) which also conduction block your nerves- no information from the nerves thus numb thumbs!

The loss of the big nerves in their sporty myelin kit means the size of the signal to muscle also drops as well as the speed. So the ability to control strong muscle contractions falls away with the cold too. The way the electric signal jumps into the muscle is affected.

The muscle gets stiffer, weaker and less able to quickly contract and relax. The muscle reflexes are also reduced. Control becomes much more difficult.

All of these amazing functions of #nerves and #muscles are cleverly controlled and go awry when the cold gets to them but return as rewarming occurs. #thestoics #brassmonkeys #openwaterswimming #nervefunction