full transcript

From the Ted Talk by Eleanor Nelsen: Why do your knuckles pop?

Unscramble the Blue Letters

What's that sound? Depending on whom you ask, the crackle of popping joints is either the sound of sweet reelif or the nuooixs tones of a stomach-turning hiabt. Really, though. What's that snuod? I mean, why does bending your joints in a certain way make them pop like that? Scientists have oereffd several epnaloaxnits, including rapidly stretching lanetmigs, and in severe cases, autacl bones grinding against each other. But the most common explanation for why your stretched-out joints sound like bubbles popping is that, well, there are bubbles in there. The joints in your fingers are the easiest ones to crack, but many ppoele also crack the jitnos between vertebrae in their neck and back, and even their hips, wsrtis, shoulders and so on. All these joints are synovial joints, and they're the most flexible ones in your body. The space between the two bones is filled with a viscous liquid, synovial fluid, which contains long, lubricating molecules, like hyaluronic acid and liriubcn. Synovial fliud is more or less the tuxetre of egg yolk and its primary purpose is to cushion the bones and help them glide past each other. It also contains phagocytic clles that help clean up any bone or cartilage debris that ends up in the joint. But the reason it's important for knuckle ckncairg is that, like other flduis in your body, it contains lots of dissolved gas molecules. Knuckle-crackers know that to get that syifntisag pop, you stretch the joint farther than it normally goes by beinndg your fingers backwards, for example. When you do that, the bones move away from each other. The scpae between bones gets bigger, but the amount of synovial fluid stays constant. That creates a low-pressure zone that pulls dissolved gases out of the synovial fluid, just like the carbon dioxide that fizzes out of soda when you twist open the cap. Inside the joint, the escaping gases form a bubble with a pop. But the bubble doesn't last long. The surrounding fluid presses on it until it finally collapses. The bubble's gsaes steactr throughout the synovial cavity and slowly dissolve back into the fluid over the course of about twenty minutes, which is why it can take a while before you can pop the same joint again. Some scientists think there may actually be two pops. One when the bubble forms, and another when it btsrus. Popping a joint temporarily erngleas it, which may be why dedicated knuckle-, neck- and back-crackers say the habit makes their joints feel looser and more flbielxe. But you may have heard from a concerned relative or annoyed offcietame that cracking your joints will give you arthritis. A doctor named Donald Unger hread this, too. So, determined to disprove his mother's warnings, he cracked the knuckles of his left hand repeatedly for 50 years, while the right-hand kucenkls went unpopped. 36,500 cracks later, both hands were arthritis-free. For this selfless act of devotion to science, Dr. Unger received an Ig neobl pzire, a parody of the Nobel Prize that recognizes wacky, but weirdly faaicintsng, scientific accomplishments. Unger wrote that his results should prompt investigation into other parental beliefs, like the importance of eating spinach. The jury's still out on that one. As for knuckle-cracking, one study suggests that all that joint stretching and bubble bursting can cause your hands to swell and weaken your grip. But the biggest proven danger seems to be aynnonig those around you.

Open Cloze

What's that sound? Depending on whom you ask, the crackle of popping joints is either the sound of sweet ______ or the _______ tones of a stomach-turning _____. Really, though. What's that _____? I mean, why does bending your joints in a certain way make them pop like that? Scientists have _______ several ____________, including rapidly stretching _________, and in severe cases, ______ bones grinding against each other. But the most common explanation for why your stretched-out joints sound like bubbles popping is that, well, there are bubbles in there. The joints in your fingers are the easiest ones to crack, but many ______ also crack the ______ between vertebrae in their neck and back, and even their hips, ______, shoulders and so on. All these joints are synovial joints, and they're the most flexible ones in your body. The space between the two bones is filled with a viscous liquid, synovial fluid, which contains long, lubricating molecules, like hyaluronic acid and ________. Synovial _____ is more or less the _______ of egg yolk and its primary purpose is to cushion the bones and help them glide past each other. It also contains phagocytic _____ that help clean up any bone or cartilage debris that ends up in the joint. But the reason it's important for knuckle ________ is that, like other ______ in your body, it contains lots of dissolved gas molecules. Knuckle-crackers know that to get that __________ pop, you stretch the joint farther than it normally goes by _______ your fingers backwards, for example. When you do that, the bones move away from each other. The _____ between bones gets bigger, but the amount of synovial fluid stays constant. That creates a low-pressure zone that pulls dissolved gases out of the synovial fluid, just like the carbon dioxide that fizzes out of soda when you twist open the cap. Inside the joint, the escaping gases form a bubble with a pop. But the bubble doesn't last long. The surrounding fluid presses on it until it finally collapses. The bubble's _____ _______ throughout the synovial cavity and slowly dissolve back into the fluid over the course of about twenty minutes, which is why it can take a while before you can pop the same joint again. Some scientists think there may actually be two pops. One when the bubble forms, and another when it ______. Popping a joint temporarily ________ it, which may be why dedicated knuckle-, neck- and back-crackers say the habit makes their joints feel looser and more ________. But you may have heard from a concerned relative or annoyed __________ that cracking your joints will give you arthritis. A doctor named Donald Unger _____ this, too. So, determined to disprove his mother's warnings, he cracked the knuckles of his left hand repeatedly for 50 years, while the right-hand ________ went unpopped. 36,500 cracks later, both hands were arthritis-free. For this selfless act of devotion to science, Dr. Unger received an Ig _____ _____, a parody of the Nobel Prize that recognizes wacky, but weirdly ___________, scientific accomplishments. Unger wrote that his results should prompt investigation into other parental beliefs, like the importance of eating spinach. The jury's still out on that one. As for knuckle-cracking, one study suggests that all that joint stretching and bubble bursting can cause your hands to swell and weaken your grip. But the biggest proven danger seems to be ________ those around you.

Solution

  1. joints
  2. nobel
  3. offered
  4. enlarges
  5. prize
  6. flexible
  7. cracking
  8. fluids
  9. wrists
  10. satisfying
  11. relief
  12. scatter
  13. explanations
  14. space
  15. knuckles
  16. actual
  17. bursts
  18. lubricin
  19. texture
  20. habit
  21. annoying
  22. sound
  23. noxious
  24. heard
  25. people
  26. fluid
  27. bending
  28. officemate
  29. fascinating
  30. gases
  31. ligaments
  32. cells

Original Text

What's that sound? Depending on whom you ask, the crackle of popping joints is either the sound of sweet relief or the noxious tones of a stomach-turning habit. Really, though. What's that sound? I mean, why does bending your joints in a certain way make them pop like that? Scientists have offered several explanations, including rapidly stretching ligaments, and in severe cases, actual bones grinding against each other. But the most common explanation for why your stretched-out joints sound like bubbles popping is that, well, there are bubbles in there. The joints in your fingers are the easiest ones to crack, but many people also crack the joints between vertebrae in their neck and back, and even their hips, wrists, shoulders and so on. All these joints are synovial joints, and they're the most flexible ones in your body. The space between the two bones is filled with a viscous liquid, synovial fluid, which contains long, lubricating molecules, like hyaluronic acid and lubricin. Synovial fluid is more or less the texture of egg yolk and its primary purpose is to cushion the bones and help them glide past each other. It also contains phagocytic cells that help clean up any bone or cartilage debris that ends up in the joint. But the reason it's important for knuckle cracking is that, like other fluids in your body, it contains lots of dissolved gas molecules. Knuckle-crackers know that to get that satisfying pop, you stretch the joint farther than it normally goes by bending your fingers backwards, for example. When you do that, the bones move away from each other. The space between bones gets bigger, but the amount of synovial fluid stays constant. That creates a low-pressure zone that pulls dissolved gases out of the synovial fluid, just like the carbon dioxide that fizzes out of soda when you twist open the cap. Inside the joint, the escaping gases form a bubble with a pop. But the bubble doesn't last long. The surrounding fluid presses on it until it finally collapses. The bubble's gases scatter throughout the synovial cavity and slowly dissolve back into the fluid over the course of about twenty minutes, which is why it can take a while before you can pop the same joint again. Some scientists think there may actually be two pops. One when the bubble forms, and another when it bursts. Popping a joint temporarily enlarges it, which may be why dedicated knuckle-, neck- and back-crackers say the habit makes their joints feel looser and more flexible. But you may have heard from a concerned relative or annoyed officemate that cracking your joints will give you arthritis. A doctor named Donald Unger heard this, too. So, determined to disprove his mother's warnings, he cracked the knuckles of his left hand repeatedly for 50 years, while the right-hand knuckles went unpopped. 36,500 cracks later, both hands were arthritis-free. For this selfless act of devotion to science, Dr. Unger received an Ig Nobel Prize, a parody of the Nobel Prize that recognizes wacky, but weirdly fascinating, scientific accomplishments. Unger wrote that his results should prompt investigation into other parental beliefs, like the importance of eating spinach. The jury's still out on that one. As for knuckle-cracking, one study suggests that all that joint stretching and bubble bursting can cause your hands to swell and weaken your grip. But the biggest proven danger seems to be annoying those around you.

Frequently Occurring Word Combinations

ngrams of length 2

collocation frequency
synovial fluid 2

Important Words

  1. accomplishments
  2. acid
  3. act
  4. actual
  5. amount
  6. annoyed
  7. annoying
  8. arthritis
  9. beliefs
  10. bending
  11. bigger
  12. biggest
  13. body
  14. bone
  15. bones
  16. bubble
  17. bubbles
  18. bursting
  19. bursts
  20. cap
  21. carbon
  22. cartilage
  23. cases
  24. cavity
  25. cells
  26. clean
  27. collapses
  28. common
  29. concerned
  30. constant
  31. crack
  32. cracked
  33. cracking
  34. crackle
  35. cracks
  36. creates
  37. cushion
  38. danger
  39. debris
  40. dedicated
  41. depending
  42. determined
  43. devotion
  44. dioxide
  45. disprove
  46. dissolve
  47. dissolved
  48. doctor
  49. donald
  50. dr
  51. easiest
  52. eating
  53. egg
  54. ends
  55. enlarges
  56. escaping
  57. explanation
  58. explanations
  59. fascinating
  60. feel
  61. filled
  62. finally
  63. fingers
  64. fizzes
  65. flexible
  66. fluid
  67. fluids
  68. form
  69. forms
  70. gas
  71. gases
  72. give
  73. glide
  74. grinding
  75. grip
  76. habit
  77. hand
  78. hands
  79. heard
  80. hips
  81. hyaluronic
  82. ig
  83. importance
  84. important
  85. including
  86. investigation
  87. joint
  88. joints
  89. knuckle
  90. knuckles
  91. left
  92. ligaments
  93. liquid
  94. long
  95. looser
  96. lots
  97. lubricating
  98. lubricin
  99. minutes
  100. molecules
  101. move
  102. named
  103. neck
  104. nobel
  105. noxious
  106. offered
  107. officemate
  108. open
  109. parental
  110. parody
  111. people
  112. phagocytic
  113. pop
  114. popping
  115. pops
  116. presses
  117. primary
  118. prize
  119. prompt
  120. proven
  121. pulls
  122. purpose
  123. rapidly
  124. reason
  125. received
  126. recognizes
  127. relative
  128. relief
  129. repeatedly
  130. results
  131. satisfying
  132. scatter
  133. science
  134. scientific
  135. scientists
  136. selfless
  137. severe
  138. shoulders
  139. slowly
  140. soda
  141. sound
  142. space
  143. spinach
  144. stays
  145. stretch
  146. stretching
  147. study
  148. suggests
  149. surrounding
  150. sweet
  151. swell
  152. synovial
  153. temporarily
  154. texture
  155. tones
  156. twenty
  157. twist
  158. unger
  159. unpopped
  160. vertebrae
  161. viscous
  162. wacky
  163. warnings
  164. weaken
  165. weirdly
  166. wrists
  167. wrote
  168. years
  169. yolk
  170. zone