Utricle - U --> the shape of the U with hair cells pointing up Saccule - S -> shape of S with haircells pointing out Then envision the direction of movement that would cause the prongs of the letter to sway. i.e. left to right or horizontal for U and up and down or vertcal for S
hello zach, i think i owe you and your team a big big thankyou as a person from a middle class family living in a place with high inflation rates someone who cant afford tuitions your channel and lectures mean alot to me, i rely on this channel for anatomy physio and sometimes biochem as well, ninja nerds was a huge part of my first year mbbs and i ended up getting distinction in each subject i dont understand local tutors at all but you're here saving my day, thank you so much
You are truly a blessing to all of us, medical students. I wish if i could dedicate my tuition to you and if I wasn’t a poor medical student, I would have definitely donated!! Thank you so much for your enthusiasm, i was never more excited to learn about the vestibule but your excitement is contagious
As an old pilot, skier, motorcyclist I've been telling anyone that would listen, it's all about your scan, what you're focusing on and how you hold your head. Now I can see why. Thanks for sharing
Dude I just have to tell you how much I appreciate you making these videos. I'm halfway through my second year of Audiology school and your vids have been a lifesaver all along! I've watched all the ear related ones and now that I'm starting to study the vestibular system I REALLY need help. Keep it up! Much love!
literally thank you i was rewatching the same parts of one lecture for two hours and i didn't even pause once throughout this video to clarify what you said because you explained everything so well
I know you read the grateful comments for your job and maybe sometimes you just...but I also feel I have to thank you. I do it under this lecture because yesterday was my last exam (physiology) and my main theme to write was for the vestibular alongside semicircular canals. Also I had exchange of CO2 and pancreatic juice. The examiners were impressed how well I understod the material and I passed it with A. This whole 2nd year I was studying alone using your videos and other ones and they helped me a lot (mostly you did help me) and so again I wanna thank you your passion and great way for teaching many people like us,medics,or just curious one. Keep going with the same spirit! P.S. I know maybe I'll be annoying but I see many people have problem with Physics. I think you should make such content,with your way of explanation all will understand the laws from the 1st time :)
Hey there, I am a novice with no background of science and anatomy but I am able to understand the way you explain. Making the concepts real through drawings and life examples, is especially helping me. thank you.
Im watching all of these vids on 1.5-2x speed so that i can cram as many as i can xD i love that he actually speaks clearly enough that you can understand him even twice as fast
im a first year medical audiology student.....and im really satisfied with the way u teach....its very easy for me to understand it...thank you bro....u are better than my lecturers.
You are seriously saving me. My teacher barely explains these topics and just expects us to understand it. I can now say I understand and can participate in class. You explain things so well and the drawings make such a difference. Not to mention you make some seriously funny commentary. Thank you so much for doing what you do it truly makes a difference.
a good way to remember the direction of the hair cells of the utricle and the saccule is to remember that hair cells of the U-tricle are pointing U-pwards, while those of the S-accule are pointed S-idewards. :)
A sincere appreciation comment from me and probably many other students - this has been the most helpful, precise and detailed explanation available to me, after hours of effort put into understanding. Thank you so much for this video!!
Agreed! Your videos are my first step in introducing myself to the material and then I check out the professors notes and it makes so much sense! Thank you so much for what you are doing!
I'm getting my Doctorate in Audiology and all of your cochlea videos and ME stuff got me through A&P!! Now i'm in Vestibular class and I recommend your videos to all of my classmates!! I'm very visual so your videos are amazing!!!
I loved this video, ive been doing an entire semester of physiology and only this video has managed to actually break it down from the beginning and explain each section and what it does and what its called. you dont assume knowledge. thank you.
Awesome video! Thanks for the recap, helped a lot! One tiny thing though, when you break or slow down in your car, the otolithic membrane doesn't move forward because it ''makes you tilt your head down'' but because of inertia. Your cranium stops moving but the otoconias don't, which is why they move forward (toward kinocilium) and depolarize the hairy cells. Good luck with your exams!
See this is what tripped me up. His physics was weird here. Do you think you could clarify things further? Imagine you have otoconias in the utricle. As you accelerate in the car, the cranium moves forward and the otoconias are dragging behind, stimulating hair cells. When you stop, suddenly the otoconia slide forward, stimulating the hair cells. Are those two subsets of the hair cells distinct? Is that how the brain decodes the direction of linear acceleration? Is the orientation of the stereocilia really the key here? Hence the utricle is only sensitive to acceleration in a 2D plane (forward back, left right), and the saccuule to a different 2D plane (up down, left right).
I don't know. I feel like if you slammed the breaks, and your head shot forward, the otoliths would move backward. Then when your cranium stopped, they would catch up and move forward.
@@jacobpickett5085 How I got it: Head = solid mass, endolymph = viscuous. When you suddenly move forward, your head manages going anterior but the pudding (endolymph) in your head doesn't yet, so it remains posterior. Since endolymph kind of sticks to otoliths, remaining posterior means otoliths remain posterior; otoliths are attached to the otolithic membrane, so they drag the otolithic membrane also posterior; otolithic membrane remaining posterior equals hair cells bending posterior. When slamming the break it's just reverse. Essentially, head moves faster posterior than otolithic membrane, so hair cells are bending anterior. Please correct me if I am wrong though. EDIT: You can skip the part with the endolymph, I just checked the Boron and it seems like it's not even involved in the otolithic organs. It's purely the otoliths' inertia that matters. Endolymph movement is only important for the semicircular canals where it leads to bowing of the cupula. EDIT2: Ok, I think I got know why it was confusing at first. The whole thing with the inertia does only apply to acceleration. If you tilt the head the otoliths will trigger ipsilateral AP firing while contralateral no AP are fired. EDIT3: "If you tilt the head the otoliths will trigger ipsilateral AP firing while contralateral no AP are fired." this is not entirely correct. Actually, e.g., even though you tilt the head to the right, even some fibers from the left side will fire. Boron has a nice pic.
I have holiday right now , but I'm still watching you . you're really helped and I really thank you ninja nerd you made my study easier and more fun thank you so much
Thank you SO much! You break things down really well, & help turn "general ideas" into "well-understood concepts", & do an amazingjob of incorporating ALL important info. I need to know for exams. I'm 100% sure that watching your vids have raised my grade by "at least" 1 whole grade:) TY! I'm a Nuclear Medicine student, & "NinjaNerds" vids, are Req. for my A&P courses. My peers love you & my professor does, too:)
@chris actually we some Indian's love to speak in English to maintain status 😂. literally those status maintained people haven't idea about spelling and also grammar hahaha. By this attitude some Indian's wanna divided us via lower class 😂... by so-called speak in english .... beleave me or not literally that's going on here... Some people who only knows only 2 slangs f***!!! And shit!!! 😂 Out of this they have no knowledge...and they simultaneously use that!!! It doesn't matter if it's a good place or a bad place but they have to use ..lol
You're awesome. I'm searching for tons of video and till I find you everything seem bright and clear totally. I really appreciate what you've done and do you know that this help me alot. Thank you bro
Dear Zach, you are truly the best teacher I have ever listen. I am ENT and I am from Serbia. It was always and still is very difficult to understand vestibular system and examination. So, I would like to ask you to make a video for clinicians about HINTS testing, central and periferial vertigo dif.dg.. Also nystagmus examination and dif. dg. How to approach to a patient with vertigo- chronic and acute? Also it would be nice to make some more videos about tinnitus. This is a huge and very difficult area in medicine and you will help to many clinicians. Thank you
Thanks for this, very helpful! Minor correction, mainly from a physics point of view. When you're driving along and you slam the brakes, your head doesn't accelerate forwards. It appears to move forwards in the car, but in reality your head is accelerating backwards (i.e. slowing down). This is important because it means that the otoliths in the utricle will move forwards in your head (similar to how your head moves forwards in the car) because they are actually trying to keep moving forwards at the same speed (they have inertia), but the utricle is slowing down.
Reading 4 pages about the same thing and not understanding and learning made me depressed, but after watching videos in this channel taught me whole thing i dint learn by reading😅 Thanks for beautiful lectures☺
i observed this.....his material is as good as dr. najeeb lectures .......but one advantage is he is way faster and to the point without missing out the concepts....
I LOVE your endless enthusiasm for whatever the subject you're teaching, it makes learning so much fun!! 😊 Can't THANK YOU enough❤💕❤💕❣ What a weird & beautiful & awesome & complicated system we all have within our bodies... There will always be questions that remain unanswered. Take care, best wishes from Finland 🇫🇮💕❣
I feel like crying, you've made such a difficult topic a piece of cake 😃 I was going through my teacher lecture's note & couldn't get it. After that I give it a read in guyton but that was of no use. Then I came here & boom 🤗🤗🤗 thanks you so muchh...
This is really excellent. Thank you for making it. Just one point of clarification- if your head is tilting forward or backwards, you are actually stimulating the anterior SCC. The utricle senses horizontal linear acceleration/deceleration when the head is stationary.
This is the first video I have watched of yours and it was incredibly helpful !! I was so confused by the action potentials and the macula and you totally cleared it up for me !! Super grateful for your time and energy! You are very good at explaining the concept and I love the drawings, labeling and different colors, that is exactly how I write how my notes. Thank you !!!
I have complete absence of signals to the brain from one saccule and suspect that I have some utricle issues too given that the car example is exactly the thing that makes me one of the most dizzy. Elevators that aren't smooth-gliding cause me major issues too when they bounce when landing on the floor. My brain also fails to compensate for my saccule's inability to send signals to my brain. This is so helpful to me in understanding my medical issue. Thank you!
Utricle - U --> the shape of the U with hair cells pointing up
Saccule - S -> shape of S with haircells pointing out
Then envision the direction of movement that would cause the prongs of the letter to sway. i.e. left to right or horizontal for U and up and down or vertcal for S
amazing! thankyou for this tip
wonderful! And I myself do a little bit modification: U -> Up, and S -> Sideways
@@janusbanana2017 same here ;)
thanks😊
👌
This guy's the one saving my med studies now. Love from india♥️ Great job
i wont be able to my my exams without him lol
"It's so cool .I promise " this line was so motivating 👍👍👍
hello zach, i think i owe you and your team a big big thankyou as a person from a middle class family living in a place with high inflation rates someone who cant afford tuitions your channel and lectures mean alot to me, i rely on this channel for anatomy physio and sometimes biochem as well, ninja nerds was a huge part of my first year mbbs and i ended up getting distinction in each subject i dont understand local tutors at all but you're here saving my day, thank you so much
You are truly a blessing to all of us, medical students. I wish if i could dedicate my tuition to you and if I wasn’t a poor medical student, I would have definitely donated!! Thank you so much for your enthusiasm, i was never more excited to learn about the vestibule but your excitement is contagious
16:15 "GOING DOWN !!!! GOING DOWN !!!!" love him so much!!! :))))
As an old pilot, skier, motorcyclist I've been telling anyone that would listen, it's all about your scan, what you're focusing on and how you hold your head. Now I can see why. Thanks for sharing
Dude I just have to tell you how much I appreciate you making these videos. I'm halfway through my second year of Audiology school and your vids have been a lifesaver all along! I've watched all the ear related ones and now that I'm starting to study the vestibular system I REALLY need help. Keep it up! Much love!
literally thank you i was rewatching the same parts of one lecture for two hours and i didn't even pause once throughout this video to clarify what you said because you explained everything so well
This video deserves WAY more views! Thanks for sharing!
I agree. Already shared it on fb and twitter
How on earth does he understand everything and is capable to explain it in such an easy way 😂?
Isn't he .. ✨
he is the messiah.
@@samo2616no one is laughing bro
Hard work, Research and study plus a good team .
I don't think I'll ever be able to express how much this channel is saving me during my didactic year of PA school
I know you read the grateful comments for your job and maybe sometimes you just...but I also feel I have to thank you. I do it under this lecture because yesterday was my last exam (physiology) and my main theme to write was for the vestibular alongside semicircular canals. Also I had exchange of CO2 and pancreatic juice. The examiners were impressed how well I understod the material and I passed it with A. This whole 2nd year I was studying alone using your videos and other ones and they helped me a lot (mostly you did help me) and so again I wanna thank you your passion and great way for teaching many people like us,medics,or just curious one. Keep going with the same spirit!
P.S. I know maybe I'll be annoying but I see many people have problem with Physics. I think you should make such content,with your way of explanation all will understand the laws from the 1st time :)
Hey there, I am a novice with no background of science and anatomy but I am able to understand the way you explain. Making the concepts real through drawings and life examples, is especially helping me. thank you.
Watching this in 1.5x and it feels like you're on speed, loving it
Im watching all of these vids on 1.5-2x speed so that i can cram as many as i can xD i love that he actually speaks clearly enough that you can understand him even twice as fast
im a first year medical audiology student.....and im really satisfied with the way u teach....its very easy for me to understand it...thank you bro....u are better than my lecturers.
I always watch your videos as part of my study schedule and it freshens things up and helps me a lot ! Best of luck to you good sir :D.
You’re awesome bro, made me understand the toughest topic in easy way
You are seriously saving me. My teacher barely explains these topics and just expects us to understand it. I can now say I understand and can participate in class. You explain things so well and the drawings make such a difference. Not to mention you make some seriously funny commentary. Thank you so much for doing what you do it truly makes a difference.
Teşekkürler.
Thank you so much for helping us in our exams
a good way to remember the direction of the hair cells of the utricle and the saccule is to remember that hair cells of the U-tricle are pointing U-pwards, while those of the S-accule are pointed S-idewards. :)
A sincere appreciation comment from me and probably many other students - this has been the most helpful, precise and detailed explanation available to me, after hours of effort put into understanding. Thank you so much for this video!!
Jazakallah
May Allah reward you with better!
Alhamdulillah sensory physio just finished!
Agreed! Your videos are my first step in introducing myself to the material and then I check out the professors notes and it makes so much sense! Thank you so much for what you are doing!
I'm getting my Doctorate in Audiology and all of your cochlea videos and ME stuff got me through A&P!! Now i'm in Vestibular class and I recommend your videos to all of my classmates!! I'm very visual so your videos are amazing!!!
Very amazing and understandable videos, much love from Uganda
I'm 34 and thinking about getting into hearing care and these videos are so interesting. Thanks for your time.
I loved this video, ive been doing an entire semester of physiology and only this video has managed to actually break it down from the beginning and explain each section and what it does and what its called. you dont assume knowledge. thank you.
saying thanks isnt enough anymore
a million of thanks
Awesome video! Thanks for the recap, helped a lot!
One tiny thing though, when you break or slow down in your car, the otolithic membrane doesn't move forward because it ''makes you tilt your head down'' but because of inertia. Your cranium stops moving but the otoconias don't, which is why they move forward (toward kinocilium) and depolarize the hairy cells.
Good luck with your exams!
See this is what tripped me up. His physics was weird here.
Do you think you could clarify things further?
Imagine you have otoconias in the utricle. As you accelerate in the car, the cranium moves forward and the otoconias are dragging behind, stimulating hair cells.
When you stop, suddenly the otoconia slide forward, stimulating the hair cells.
Are those two subsets of the hair cells distinct? Is that how the brain decodes the direction of linear acceleration?
Is the orientation of the stereocilia really the key here? Hence the utricle is only sensitive to acceleration in a 2D plane (forward back, left right), and the saccuule to a different 2D plane (up down, left right).
I don't know. I feel like if you slammed the breaks, and your head shot forward, the otoliths would move backward. Then when your cranium stopped, they would catch up and move forward.
@@jacobpickett5085 How I got it: Head = solid mass, endolymph = viscuous.
When you suddenly move forward, your head manages going anterior but the pudding (endolymph) in your head doesn't yet, so it remains posterior. Since endolymph kind of sticks to otoliths, remaining posterior means otoliths remain posterior; otoliths are attached to the otolithic membrane, so they drag the otolithic membrane also posterior; otolithic membrane remaining posterior equals hair cells bending posterior.
When slamming the break it's just reverse. Essentially, head moves faster posterior than otolithic membrane, so hair cells are bending anterior.
Please correct me if I am wrong though.
EDIT: You can skip the part with the endolymph, I just checked the Boron and it seems like it's not even involved in the otolithic organs. It's purely the otoliths' inertia that matters. Endolymph movement is only important for the semicircular canals where it leads to bowing of the cupula.
EDIT2: Ok, I think I got know why it was confusing at first. The whole thing with the inertia does only apply to acceleration. If you tilt the head the otoliths will trigger ipsilateral AP firing while contralateral no AP are fired.
EDIT3: "If you tilt the head the otoliths will trigger ipsilateral AP firing while contralateral no AP are fired." this is not entirely correct. Actually, e.g., even though you tilt the head to the right, even some fibers from the left side will fire. Boron has a nice pic.
@@xDomglmao seems right!
You rock! Thank you for making neuroscience enjoyable and more interesting
After 5 years of medicine this is still the coolest thing in the human body to me
Watching ninjanerd videos makes me fly over my textbook is seconds!
You're just a blessing to medical students Prof 💖💖
I have holiday right now , but I'm still watching you . you're really helped and I really thank you ninja nerd
you made my study easier and more fun
thank you so much
Sir ur the only one whom I understand your lecture I was watching so many videos but didn't understand sir love you from Kashmir
Thank you SO much! You break things down really well, & help turn "general ideas" into "well-understood concepts", & do an amazingjob of incorporating ALL important info. I need to know for exams. I'm 100% sure that watching your vids have raised my grade by "at least" 1 whole grade:) TY!
I'm a Nuclear Medicine student, & "NinjaNerds" vids, are Req. for my A&P courses. My peers love you & my professor does, too:)
OH MY GOD, I LOVE YOU SO MUCH SIR FOR DOING THIS FOR US, YOURE DOING MORE THAN AN AMAIZNG JOB HERE!!!!
Studying for boards and you made it easier for me to understand things I barely remember. Thank you so muuuch!
the most underrated channel ever... you deserve all the credit
I watch this for one of my class and it was the clearest explanation i’ve had in a long time! Thank you !
Awseome, u ar the best teacher that i had during these years in my medical carier
Vestibule-
Outer bony labyrinth
Perilymph.
Saccule utricle
Inner membranous labyrinth
Endolymph
Special detector
Sensory epithelium
Macula
Hair cell on saccule facing outside on wall.
Hair cell utricle on floor facing upward...
Supporting cell
Vestibular dark cell
Hair cells1 n2.
Otolithic membrane
Otoconia......
Utricle linear acceleration and head tilting.
Saccule vertical acceleration....
Thank you sir
Awesome and understandable lecture. Love from india 🇮🇳❤️
This guy is so f**king underrated...!!!The only Profesor I respect...🤪
Yeah, well it's professor. You should of threw some respect at your middle school English teacher.
@chris actually we some Indian's love to speak in English to maintain status 😂. literally those status maintained people haven't idea about spelling and also grammar hahaha. By this attitude some Indian's wanna divided us via lower class 😂... by so-called speak in english .... beleave me or not literally that's going on here... Some people who only knows only 2 slangs f***!!! And shit!!! 😂 Out of this they have no knowledge...and they simultaneously use that!!! It doesn't matter if it's a good place or a bad place but they have to use ..lol
Doctor!!!!! I don't know what i would've became without ur help! thanks a lot
You're awesome. I'm searching for tons of video and till I find you everything seem bright and clear totally. I really appreciate what you've done and do you know that this help me alot. Thank you bro
Dear Zach, you are truly the best teacher I have ever listen. I am ENT
and I am from Serbia. It was always and still is very difficult to understand vestibular system and examination. So, I would like to ask you to make a video for clinicians about HINTS testing, central and periferial vertigo dif.dg.. Also nystagmus examination and dif. dg.
How to approach to a patient with vertigo- chronic and acute?
Also it would be nice to make some more videos about tinnitus.
This is a huge and very difficult area in medicine and you will help to many clinicians.
Thank you
You’re a great teacher. You make this stuff so interesting and fun to learn.
Thanks for this, very helpful!
Minor correction, mainly from a physics point of view. When you're driving along and you slam the brakes, your head doesn't accelerate forwards. It appears to move forwards in the car, but in reality your head is accelerating backwards (i.e. slowing down). This is important because it means that the otoliths in the utricle will move forwards in your head (similar to how your head moves forwards in the car) because they are actually trying to keep moving forwards at the same speed (they have inertia), but the utricle is slowing down.
SIr you are awesome .. don't have words enough to thank u,you make medical lectures so fun and easy. Lots and lots of love to you from India.
All med student on earth or I would say 97% of med students watched your videos
And your like the godfather of doctors around the world.
Thank you Ninja nerd because of you I passed my 2 ND year exam
You’re actually making me become a biology lover, I can leasing to you the whole day
You’re born to teach man. Ur message r so clear n easy to understand!!
You are the boss of physiology concepts
I just love how you always save me before exams, i used to hate this topic but i very much enjoyed watching this ❤️❤️😭😭
My only regret is not finding you earlier. God bless you man.
So informative. This is what I’m looking for. Highly commendable
This very visual teaching style is just what I needed ! Thank you !
You've helped me so much with my studies and you explain everything so clearly. Please continue making these video's! :D
Reading 4 pages about the same thing and not understanding and learning made me depressed, but after watching videos in this channel taught me whole thing i dint learn by reading😅
Thanks for beautiful lectures☺
May god bless your heart and your life, you’re such a hero!
It makes so much fun learning with you!!!
Thank you so much!!! You are literally making everything fun and easy. Love from Turkey!🇹🇷❤️
you are AWESOME. You saved my life several times till now. I hope you always stay this excited with your job, keep up the good work!! love from Greece
i observed this.....his material is as good as dr. najeeb lectures .......but one advantage is he is way faster and to the point without missing out the concepts....
I really hope that u would add a smell and taste lecture under special senses. Thanks btw Zach :)
I LOVE your endless enthusiasm for whatever the subject you're teaching, it makes learning so much fun!! 😊 Can't THANK YOU enough❤💕❤💕❣ What a weird & beautiful & awesome & complicated system we all have within our bodies... There will always be questions that remain unanswered. Take care, best wishes from Finland 🇫🇮💕❣
I loved your video. It made my concept clear. Thanks for making it so easy for us. Love from Pakistan.
Wonderful explanation.. Keep it up. Love from India ❤️
A huge thank you Prof. Murphy🎉🎉🎉🎉
you are awesome .you saved my life many times
Thank you so much man, extremely helpful. You’re a great teacher. -Veterinary Student
You are saving my degree. Thank you
This is just so amazing he teaches with such passion thank you soo much for this ❤
I understand. Your lectures are just brilliant!
BRUH U ARE A NINJA NERD NOT US
BIG UP AND THANK YOU SO MUCH
I feel like crying, you've made such a difficult topic a piece of cake 😃 I was going through my teacher lecture's note & couldn't get it. After that I give it a read in guyton but that was of no use. Then I came here & boom 🤗🤗🤗 thanks you so muchh...
I really appreciate your videos!! I honestly wished more people supported your channel!!!
am in love with this perfection
Clear, concise, with great analogy. Can't thank you enough.
This is really excellent. Thank you for making it. Just one point of clarification- if your head is tilting forward or backwards, you are actually stimulating the anterior SCC. The utricle senses horizontal linear acceleration/deceleration when the head is stationary.
This is the first video I have watched of yours and it was incredibly helpful !! I was so confused by the action potentials and the macula and you totally cleared it up for me !! Super grateful for your time and energy! You are very good at explaining the concept and I love the drawings, labeling and different colors, that is exactly how I write how my notes. Thank you !!!
Thankyou for being a saviour 💜
MAAAAANNNNNNNNN I'm enjoying this science because of uuuuu🙏🏻🙏🏻🙏🏻🙏🏻🙏🏻🙏🏻💗💗💗💗💗💗 god bless u and all the team 🌹🌹💙
Please make a video on postural reflexes as well.. would be very grateful
I have complete absence of signals to the brain from one saccule and suspect that I have some utricle issues too given that the car example is exactly the thing that makes me one of the most dizzy. Elevators that aren't smooth-gliding cause me major issues too when they bounce when landing on the floor. My brain also fails to compensate for my saccule's inability to send signals to my brain. This is so helpful to me in understanding my medical issue. Thank you!
I have Ménière's disease and PBBB and this really helped yo explain it!
I love ur tips and tricks for remembering hard words, like utricle :))
Thanks Zack! You’re the best everrrr!!!
You are amazing at what you do. Really appreciate your teaching skills
what an excellent demonstration, stay blessed
You explaination and information has really helped me
Perfect as always, thank you Zach the Goat
Class will always be a class ❤
Bruh I learn more from you than from med school. Thanks man!
It's an awesome work you have done ❤️❤️love from India
MESSI of inner ear lecture.......just awesome
BEGGING US TO SUBSRIBE!? Man, you don't have to, please! You're literally really really amazing! Thank you for all your hard work and efforts!
Watching this for a second time just for emphasis. Thank you
You put a lot of effort in your vedios and they're great. Thank you so much , I deeply appreciate it
Thanks for making this topic clear