“The Big Bang Theory” (TBBT) cast, which includes Mayim Bialik (Dr Amy Farrah Fowler), Jim Parsons (Dr Sheldon Cooper), Simon Helberg (Howard Wolowitz), Kunal Nayyar (Dr Rajesh "Raj" Koothrappali), Kaley Cuoco (Penny), Melissa Rauch (Bernadette Rostenkowski-Wolowitz) and Johnny Galecki (Dr Leonard Hofstadter), will have an upcoming episode titled "The Celebration Reverberation," which will air in the US on Thursday. It will show Sheldon and Howard planning birthday celebrations for Amy and Halley (voiced by Pamela Adlon).

Spoiler alert: This update has 'The Big Bang Theory' spoilers 2017. Read on if you want to know more about 'The Celebration Reverberation.'

"The Big Bang Theory" season 11, episode 11 will feature Sheldon planning Amy's birthday party with an authentic "Little House on the Prairie" theme. Meanwhile, Howard will also plan a party for her daughter Halley. As for Leonard, he'll receive a Christmas letter from his brother. However, it will make him compare his accomplishments with his sibling's achievements. Mark Cendrowski directed this episode, which was written by Steve Holland, Eric Kaplan and Alex Ayers (story). The teleplay was written by Dave Goetsch, Maria Ferrari and Jeremy Howe.

'TBBT' episodes: 'The Confidence Erosion'

The TBBT episode prior to "The Celebration Reverberation" was "The Confidence Erosion," which aired in the US on Dec. 7. Mark Cendrowski directed the episode. The story was written by Bill Prady, Maria Ferrari and Adam Faberman. Its teleplay was written by Tara Hernandez, Steve Holland and Eric Kaplan.

Amy and Sheldon almost got married at City Hall

"The Confidence Erosion" showed Amy and Sheldon developing a unique system for their wedding planning that involves the use of math. They randomly divided up wedding tasks. However, they kept arguing about it. Finally, they agreed to just get married at City Hall. Sheldon eventually changed his mind and decided that he wanted the first dance with Amy so they went home to plan their wedding again.

As for Raj, he lost a job interview at a planetarium. His dad told him that he doesn't have any confidence because Howard always mocks him. When Raj tried to stay away from Howard, he was able to get the job. Howard tried to make amends with Raj but backed off when he saw his friend getting a date.

Watch "The Big Bang Theory" episodes on CBS in the US every Thursday from 8-8:30 pm ET/PT. Stay tuned for more updates about Sheldon and the gang.