00:00 I'm Dr. Natalie Chang, neurologist and assistant professor of clinical neurology.
00:04 I'm here today to answer your questions from the internet.
00:06 This is Nerve Support.
00:12 @emilyflower asks, "If your brain doesn't have any sensory nerves, that's why you can
00:16 be awake during a brain surgery, then what the heck are headaches?"
00:20 It's true that the brain does not have any sensory nerves.
00:22 It has no pain receptors.
00:24 Many other structures in the head and neck do.
00:26 So the meninges, which is the covering of the brain, as well as the blood vessels in
00:31 the head and the muscles in the head and neck all have pain fibers.
00:35 These can all be affected when you have a headache.
00:38 @kellychakour asks, "Why do they call it a funny bone?
00:41 Ain't nothing funny about hitting that."
00:43 The funny bone sensation is when you actually hit the ulnar nerve, which is pretty superficial
00:49 right here as it comes around the medial epicondyle of your upper arm bone.
00:54 Most people think that it's called the funny bone because it feels funny when you hit it,
00:57 but it's actually a really bad dad joke from the 19th century.
01:01 This bone is called the humerus, and some people thought back then that instead of calling
01:06 it the humerus, they would call it the funny bone.
01:08 @coconoir asks, "Why do our limbs fall asleep?"
01:11 The sensation of our limbs falling asleep is called paresthesias, that pins and needles
01:16 sensation when we've compressed a peripheral nerve for too long.
01:20 And what happens isn't really that the blood flow has stopped to that limb.
01:23 It's more that that nerve can't send those electrical signals back to the brain to tell
01:28 them that there's feeling in that limb.
01:31 When you stop that compression of that nerve, like when you wake up and you feel that pins
01:35 and needles, it's really the electrical signals kind of going crazy because they're like,
01:40 "Oh, finally, we're no longer being compressed."
01:42 @erlinhenriquez asks, "So how does general anesthesia work?"
01:47 General anesthesia is actually one of the great modern marvels of medicine and really
01:51 laid the foundation for surgery as we know it today.
01:54 Before general anesthesia, if you had to have, let's say, a limb amputated, you were awake,
01:59 you could see everything, and there was really not much pain control.
02:03 Now you would undergo general anesthesia, which is made up of several components.
02:07 So number one is being unconscious.
02:10 Number two is not remembering anything.
02:12 Three is pain control.
02:14 Four is maintaining your body's functions while you're out.
02:17 And then lastly, we want to make sure that you have muscle relaxation and paralysis.
02:22 You can imagine all these things are important because if a surgeon is operating on you,
02:27 you don't want a moving patient.
02:29 You also don't want a muscle to be really rigid, and you really don't want to smell
02:33 your burning flesh.
02:34 @kellyhogaboom asks, "Is the sympathetic versus parasympathetic nerve system concept real?
02:40 And also, if so, what is the difference?
02:42 In terms I can understand.
02:43 For reference, I am like a wily but well-meaning caveman."
02:46 Well, well-meaning caveman.
02:48 Imagine a saber-toothed tiger is running after you, and you need to respond.
02:52 The sympathetic nervous system is part of the autonomic nervous system, and it helps
02:58 mediate your automatic functions like breathing, heart rate, sweating, and digestion.
03:03 If the saber-toothed tiger is chasing you, you want your heart rate to go up so that
03:07 blood can get to all the organs in your body.
03:09 You want the arteries that supply your muscles to dilate so that you can run away from the
03:14 saber-toothed tiger.
03:16 And you really don't want to send blood to your gastrointestinal system because now is
03:19 not the time to digest that food that you just ate.
03:22 In contrast, the parasympathetic nervous system is more our rest and digest or feed and breed
03:27 functioning.
03:28 And this is where digestion becomes a priority as well as reproduction.
03:33 @dunkelugless asks, "Is the nervous system what causes anxiety?
03:37 Because my system is freaking nervous."
03:40 Technically, yes.
03:41 The nervous system does promote the actual feeling of anxiety.
03:45 So fast heart rate, trouble breathing, kind of queasiness in our gastrointestinal system.
03:50 This is the fight or flight response being activated.
03:53 Now when people have anxiety, this response is on all the time, which can be pretty taxing
03:58 for our minds, our bodies, as well as our emotions.
04:02 @mohosaofficial asks, "About how fast do nerve impulses travel?
04:07 Impulsive potentials can travel as quickly as 100 meters per second, which is about 224
04:12 miles per hour for us non-metric system users.
04:15 They can travel more quickly if the nerve is covered in myelin.
04:18 Myelin acts like insulation, just like on an electrical wire that helps the impulse
04:23 travel more quickly.
04:24 Instead of having the electrical signal travel continuously down, it can jump in between
04:29 these fatty segments."
04:30 @filmcarstairs asks, "I want to know how I can move my body.
04:34 Like how can my brain send signals to my toes and tell them to move?
04:38 I don't get it."
04:39 The way your body moves is through a system called the corticospinal tract, and this is
04:44 a big part of your motor systems.
04:46 Let's say you want to move your toes.
04:48 Our brain actually has a map of the body in the motor cortex, and there is a toe center
04:54 actually here in the middle that will then send a signal to the spinal cord.
05:00 It sends fibers to your spinal cord on the opposite side of the body.
05:04 It crosses in the medulla, which is at the base of your brain stem.
05:08 @saphrodite asks, "The nervous system is so weird.
05:11 Like what is itching?"
05:13 Itching is pretty annoying, but it's a pretty smart defensive mechanism.
05:17 So let's say you have a mosquito who's crawling on your arm.
05:20 You definitely want to know about that so that you can hopefully flick it away and it
05:24 doesn't bite you.
05:25 This is sort of like a pain response, but it kind of tickles, but that's what itching's
05:31 purpose is.
05:32 @jenna_t asks, "Why can we be tickled?
05:35 Like what response is that?"
05:37 Tickling is a type of itch almost, and we found that when people have done functional
05:42 neuroimaging studies of the brain while being tickled, that two areas light up.
05:47 So the somatosensory cortex lights up when you're being tickled, so that's our touch
05:51 processing center, but also the anterior cingulate cortex, which is right here, and this is our
05:58 emotional center.
05:59 So there definitely is a touch, but also emotional component to being tickled.
06:05 In terms of why we laugh when we're tickled, some think it's a form of social bonding,
06:10 like between a baby and its parent.
06:12 Others think it's more of a sign of submission to your tickler that you're done being tickled
06:17 and they've won.
06:19 @melodyb123 asks, "The difference between central nervous system and peripheral nervous
06:24 system is confusing me, and I think it's meant to be straightforward.
06:28 The central nervous system includes your brain and spinal cord.
06:31 The peripheral nervous system is basically anything that is outside of the skull or outside
06:36 of the spinal column."
06:38 So in this diagram, the peripheral nervous system starts basically where these branches
06:44 come off the spinal cord, and you can see more peripheral nerves in the limbs here and
06:50 here.
06:51 @kaganellen asks, "Does acupuncture work for chronic pain?"
06:55 Yes.
06:56 So far, 39 clinical trials found that doing acupuncture significantly improved the control
07:02 of chronic pain.
07:03 @jessdoza asks, "Why does pain have to be so painful, you know?"
07:08 So pain is a really smart defense mechanism by our bodies to avoid things that might potentially
07:13 injure the body permanently.
07:14 Like if you step on a nail, you don't want to keep walking on that foot because every
07:18 time you step down, you're injuring your foot further.
07:20 It's a signal to you to fix whatever is hurting you so that you prevent further damage.
07:26 @profcooler asks, "How do nerves regenerate?"
07:30 Nerves in the peripheral nervous system can regenerate, and what happens is, let's say
07:35 there's some injury to a nerve, the immune system is activated, and it's kind of like
07:39 New Year's Day in Times Square.
07:41 The cleaning crew comes up and just gets rid of all that debris.
07:44 Until that debris is cleaned up, the cell body in the main part of the neuron can't
07:49 really give out directions to produce new axon endings.
07:54 @thymaster asks, "During a physical, why does the doctor tap your knee with a hammer?"
07:59 When we're testing your reflexes in the exam room, we're checking to see if your motor
08:04 and sensory neuron reflex is intact.
08:07 When we tap your, let's say your patellar tendon, that causes a stretch in a muscle
08:13 spindle.
08:14 This sends a signal back to the sensory neuron, which activates a motor neuron in the spinal
08:20 cord to cause your knee to kick up.
08:23 If this reflex is absent, it could indicate that you have a lower motor neuron problem.
08:28 If it's overactive, meaning it's too jumpy, it can signal a problem with an upper motor
08:32 neuron, something in the spinal cord above the level of the knee jerk reflex, which is
08:37 L3, L4, or something in the brain.
08:40 @emartin11 asks, "Why do people have such different pain tolerances?"
08:45 Pain is actually both a physical and an emotional phenomenon.
08:48 It's been studied that various factors like history of prior trauma, lack of sleep, female
08:54 sex can give folks lower pain tolerances.
08:57 Higher pain tolerance is associated with older age, exercise activity, as well as more social
09:02 support.
09:03 @eater asks, "Seriously, what is carpal tunnel?
09:06 What are you guys doing with your wrists?
09:08 I have never suffered this issue, but I'm intrigued."
09:11 So, carpal tunnel is when there's compression of the median nerve here in your wrist, which
09:17 is where the carpal tunnel is.
09:18 It's a pretty small tunnel where the tendons of a lot of the forearm muscles run through
09:22 as well.
09:23 If you get any type of repetitive stress injury, like the common one is typing, other people
09:29 notice it with cooking or other types of frequent manual labor, they can cause compression of
09:35 this nerve.
09:36 @amnon96 asks, "How does local anesthesia work?"
09:40 Medications like lidocaine or xylocaine, which you typically get at the dentist or for some
09:44 minor procedures, basically block the opening of voltage-gated sodium ions, which means
09:51 that you can't really have those action potentials spread.
09:54 So it really stops electrical impulses.
09:56 @anastasiabeave asks, "Would you fill me in on what brain zaps are?
10:01 That sounds terrifying."
10:02 So brain zaps are actually something that's more recently described in the early 2000s,
10:06 where people would notice that they would feel these electrical shocks in their head
10:10 or it feels like buzzing.
10:12 We found that they're associated with stopping antidepressant medications.
10:16 It's also been described after people use ecstasy or stop taking other medications like
10:21 benzodiazepines.
10:22 It might be some change to neurotransmitter levels as you've stopped taking these medications,
10:27 but we're still trying to figure out why they happen.
10:30 @ragdaybooyon31 asks, "Why do nerves in the teeth have to exist?
10:34 Freaking toothaches, man."
10:35 Your teeth are kind of precious in terms of, you know, once you have your permanent teeth,
10:40 you don't get new ones.
10:41 If you think about it, it's also in the mouth, which is where we put a lot of things that
10:44 could harm us, right?
10:45 You could eat bad food, you could eat something sharp that could cause a perforation of your
10:50 stomach.
10:51 So if there's a problem with your teeth, you want to know quickly rather than letting it
10:54 slowly decay and potentially cause an infection.
10:57 Those are all the questions.
10:58 Hopefully you learned something today.
11:00 See you next time.
11:01 (upbeat music)
11:03 (bells chiming)
