- I'm Dr. Natalie Cheng, neurologist
and assistant professor of clinical neurology.
I'm here today to answer your questions from the internet.
This is Nerve Support.
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@emylieflower asks, "If your brain doesn't have
"any sensory nerves,
"that's why you can be awake during a brain surgery,
"then what the heck are headaches?"
It's true that the brain does not have any sensory nerves.
It has no pain receptors.
Many other structures in the head and neck do.
So the meninges, which is the covering of the brain,
as well as the blood vessels in the head
and the muscles in the head and neck all have pain fibers.
These can all be affected when you have a headache.
@KellieShakur asks, "Why do they call it a funny bone?
"Ain't nothing funny about hitting that."
The funny bone sensation
is when you actually hit the ulnar nerve,
which is pretty superficial right here
as it comes around the medial epicondyle
of your upper arm bone.
Most people think that it's called the funny bone
because it feels funny when you hit it,
but it's actually a really bad dad joke
from the 19th century.
This bone is called the humerus,
and some people thought back then
that instead of calling it the humerus
they would call it the funny bone.
@COCANOIR asks, "Why do our limbs fall asleep?"
The sensation of our limbs falling asleep
is called paresthesias.
It's that pins and needle sensation
when we've compressed a peripheral nerve for too long.
And what happens isn't really that the blood flow
has stopped to that limb.
It's more that that nerve can't send
those electrical signals back to the brain
to tell them that there's feeling in that limb.
When you stop that compression of that nerve,
like when you wake up and you feel that pins and needles,
it's really the electrical signals kind of going crazy
'cause they're like, "Oh, finally,
"we're no longer being compressed."
@ErlynHenriquez asks, "So how does general anesthesia work?"
General anesthesia's actually one
of the great modern marvels of medicine
and really laid the foundation
for surgery as we know it today.
Before general anesthesia, if you had to have, let's say,
a limb amputated, you were awake, you could see everything,
and there was really not much pain control.
Now you would undergo general anesthesia,
which is made up of several components.
So number one is being unconscious.
Number two is not remembering anything.
Three is pain control.
Four is maintaining your body's functions while you're out.
And then lastly, we wanna make sure
that you have muscle relaxation and paralysis.
You can imagine all these things are important
because if a surgeon is operating on you,
you don't want a moving patient.
You also don't want a muscle to be really rigid,
and you really don't wanna smell your burning flesh.
@kellyhogaboom asks, "Is the sympathetic
"versus parasympathetic nerve system concept real?
"And also, if so, what is the difference?
"In terms I can understand.
"For reference, I am like a wily but well-meaning caveman."
Well, well-meaning caveman, imagine a saber-toothed tiger
is running after you and you need to respond.
The sympathetic nervous system
is part of the autonomic nervous system
and it helps mediate your automatic functions
like breathing, heart rate, sweating, and digestion.
If the saber-toothed tiger's chasing you,
you want your heart rate to go up
so that blood can get to all the organs in your body.
You want the arteries that supply your muscles to dilate
so that you can run away from the saber-toothed tiger.
And you really don't wanna send blood
to your gastrointestinal system
'cause now is not the time to digest that food
that you just ate.
In contrast, the parasympathetic nervous system
is more our rest and digest, or feed and breed functioning,
and this is where digestion becomes a priority
as well as reproduction.
@duncle_uglas asks, "Is the nervous system
"what causes anxiety?
"'Cause my system is freaking nervous."
Technically, yes, the nervous system does promote
the actual feeling of anxiety.
So a fast heart rate, trouble breathing,
kind of queasiness in our gastrointestinal system,
this is a fight-or-flight response being activated.
Now when people have anxiety,
this response is on all the time,
which can be pretty taxing for our minds, our bodies,
as well as our emotions.
@MOHOSAOfficial asks, "About how fast
"do nerve impulses travel?"
Action potentials can travel as quickly
as 100 meters per second, which is about 224 miles per hour
for us non-metric system users.
They can travel more quickly
if the nerve is covered in myelin.
Myelin acts like insulation, just like on an electrical wire
that helps the impulse travel more quickly.
Instead of having the electrical signal
travel continuously down,
it can jump in between these fatty segments.
@filmcarstairs ask, "I wanna know how I can move my body.
"Like, how can my brain send signals to my toes
"and tell them to move?
"I don't get it."
The way your body moves
is through a system called the corticospinal tract,
and this is a big part of your motor system.
Let's say you want to move your toes.
Our brain actually has a map of the body in the motor cortex
and there is a toe center actually here in the middle
that will then send a signal to the spinal cord.
It sends fibers to your spinal cord
on the opposite side of the body.
It crosses in the medulla,
which is at the base of your brainstem.
@saphrodyte asks, "The nervous system is so weird.
"Like, what is itching?"
Well, itching is pretty annoying,
but it's a pretty smart defensive mechanism.
So let's say you have a mosquito who's crawling on your arm.
You definitely wanna know about that
so that you can hopefully flick it away
and it doesn't bite you.
This is sort of like a pain response,
but it kind of tickles.
But that's what itching's purpose is.
@_jennatee asks, "Why can we be tickled?
"Like, what response is that?"
Tickling is a type of itch almost,
and we found that when people have done
functional neuroimaging studies of the brain
while being tickled that two areas light up.
So the somatosensory cortex lights up
when you're being tickled,
so that's our touch processing center,
but also the anterior cingulate cortex, which is right here,
and this is our emotional center.
So there definitely is a touch,
but also emotional component to being tickled.
In terms of why we laugh when we're tickled,
some think it's a form of social bonding
like between a baby and its parent.
Others think it's more of a sign of submission
to your tickler that you're done being tickled
and they've won.
@Melody_B123 asks,
"The difference between central nervous system
"and peripheral nervous system is confusing me
"and I think it's meant to be straightforward."
The central nervous system includes your brain
and spinal cord.
The peripheral nervous system is basically
anything that is outside of the skull
or outside of the spinal column.
So in this diagram,
the peripheral nervous system starts basically
where these branches come off the spinal cord,
and you can see more peripheral nerves
in the limbs here and here.
@kagan_ellen asks, "Does acupuncture work for chronic pain?"
Yes.
About 39 clinical trials found that doing acupuncture
significantly improved the control of chronic pain.
@jessdozaa asks, "Why does pain have to be
"so painful, you know?"
So pain is a really smart defense mechanism by our bodies
to avoid things that might potentially injure
the body permanently.
Like if you step on a nail, you don't wanna keep walking
on that foot because every time you step down
you're injuring your foot further.
It's a signal to you to fix whatever is hurting you
so that you prevent further damage.
@ProfCooler asks, "How do nerves regenerate?"
Nerves in the peripheral nervous system can regenerate,
and what happens is, let's say there's some injury
to a nerve, the immune system is activated
and it's kind of like New Year's Day in Times Square.
The cleaning crew comes up
and just gets rid of all that debris.
Until that debris is cleaned up,
the cell body in the main part of the neuron
can't really give out directions
to produce new axon endings.
@thighmaster asks, "During a physical,
"why does the doctor tap your knee with a hammer?"
When we're testing your reflexes in the exam room,
we're checking to see if your motor
and sensory neuron reflex is intact.
When we tap your, let's say your patellar tendon
that causes a stretch in a muscle spindle,
this sends a signal back to the sensory neuron,
which activates a motor neuron in the spinal cord
to cause your knee to kick up.
If this reflex is absent, it could indicate
that you have a lower motor neuron problem.
If it's overactive, meaning it's too jumpy,
it can signal a problem with an upper motor neuron,
something in the spinal cord above the level
of the knee jerk reflex, which is L3, L4,
or something in the brain.
@Emartin_11 asks,
"Why do people have such different pain tolerances?"
Pain is actually both a physical
and an emotional phenomenon.
It's been studied that various factors
like a history of prior trauma, lack of sleep, female sex,
can give folks lower pain tolerances.
Higher pain tolerance is associated with older age,
exercise activity, as well as more social support.
@Eater asks, "Seriously, what is carpal tunnel?
"What are you guys doing with your wrists?
"I have never suffered this issue, but I'm intrigued."
So carpal tunnel's when there's compression
of the median nerve here in your wrist,
which is where the carpal tunnel is.
It's a pretty small tunnel where the tendons
of a lot of the forearm muscles run through as well.
If you get any type of repetitive stress injury,
like the common one is typing,
other people notice it with cooking
or other types of frequent manual labor,
they can cause compression of this nerve.
@amnon96 asks, "How does local anesthesia work?"
Medications like lidocaine or Xylocaine,
which you typically get at the dentist
or for some minor procedures, basically block the opening
of voltage-gated sodium ions,
which means that you can't really have
those action potentials spread.
So it really stops electrical impulses.
@AnastasiaBeav asks, "Would you fill me in
"on what brain zaps are?
"That sounds terrifying."
So brain zaps are actually something
that's more recently described in the early 2000s
where people would notice
that they would feel these electrical shocks in their head
or it feels like buzzing.
We found that they're associated
with stopping antidepressant medication.
It's also been described after people use ecstasy
or stop taking other medications like benzodiazepines.
It might be some change to neurotransmitter levels
as you've stopped taking these medications,
but we're still trying to figure out why they happen.
@ragdeibuyan31 asks, "Why do nerves in the teeth
"have to exist?
"Freaking toothaches, man."
Your teeth are kind of precious in terms of, you know,
once you have your permanent teeth you don't get new ones.
If you think about it, it's also in the mouth,
which is where we put a lot of things
that could harm us, right?
You could eat bad food.
You could eat something sharp
that could cause a perforation of your stomach.
So if there's a problem with your teeth,
you wanna know quickly rather than letting it slowly decay
and potentially cause an infection.
Those are all the questions.
Hopefully you learned something today.
See you next time.
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