(CNN) It started with one woman. Then it became dozens.

By the time Larry Nassar was sentenced on Wednesday for criminal sexual conduct, 156 people had appeared in a Michigan courtroom to share stories of sexual assault at the disgraced doctor's hands.

The former USA Gymnastics and Michigan State University doctor received a prison term of up to 175 years. But Olympic champion Aly Raisman said she doesn't think justice has been served.

"It's not something where you just instantly feel better," Raisman told NBC's "Today" show Thursday.

"We need to hold these organizations accountable -- USA Gymnastics, United States Olympic Committee, MSU. They need an independent investigation. This is bigger than Larry Nassar."

JUST WATCHED Watch Aly Raisman confront Nassar in court Replay More Videos ... MUST WATCH Watch Aly Raisman confront Nassar in court 01:35

And many said the problem extends beyond the sports world.

"Larry is sentenced, but there's still so much more work to to do," survivor Lindsey Lemke said. "We're not going to heal all the way until we know exactly who knew what, when, and how they're going to fix it."

Celebration, then silence

After she won gold medals in the last two Olympics, Raisman said USAG and USOC were quick to celebrate and capitalize on her success

But since she testified about Nassar's abuse, Raisman said, she's heard nothing from those two organizations.

"I have not been contacted by anyone," she told "Today" on Thursday.

Raisman said she believes the culture of such organizations contributes to their silence.

"For so long, they put medals, reputation and money over the safety of athletes," she said.

But survivors of Nassar's abuse are speaking up louder than ever.

Strength in numbers

When she testified on day one, Kyle Stephens said a mood of fear and apprehension was palpable in the courtroom. As more people stepped up to the podium to read victim impact statements, she said the tone shifted.

"You could really feel the momentum in the courtroom begin to pick up," she said.

Stephens linked what the women did to broader efforts to stem sexual violence as part of the #MeToo movement.

"I'm really proud that we were able to start something that I think has snowballed and grown outside the courtroom," said Stephens, the first woman to testify in Nassar's sentencing. "But the army is not limited to Larry Nassar's victims."

Tarana Burke, the woman credited with launching the "Me Too" movement a decade ago , praised the courage and camaraderie of Nassar's survivors, saying they embodied the movement's power.

"It's about survivors drawing strength from other survivors," Burke tweeted Thursday.

Woke up with the brave Olympic gymnast and all the girls who testified against LN on my heart. They are the embodiment of the #metoo MOVEMENT. It's about survivors drawing strength from other survivors. @Aly_Raisman is a hero and so are all of the others. 💕 — Tarana (@TaranaBurke) January 25, 2018

Survivors find their voices

Initially, 88 survivors wanted to speak at Nassar's sentencing hearing, and most of them did not want to be publicly identified, prosecutor Angela Povilaitis said. Each day, the number of people willing to step up and be identified grew, she said.

"I absolutely believe they took that shame and they put it on him. And they no longer had to carry that around, because they did nothing wrong."

It was a cumulative effect, said Larissa Boyce. At first, most people wanted to remain anonymous. Then, with each person's statement, they saw a chance to reclaim what Nassar had stolen from them.

"In that courtroom, seeing women start to take back their power, there was really a sense of a shift ... of women saying, 'wait a minute, I'm not a number. I am a name. I am a real person,'" Boyce said.

As a teen gymnast, Boyce said she told an MSU coach that she was uncomfortable with the intravaginal treatments Nassar performed on her for an injury. She said her concerns were not only ignored, but she was made to think that she had maligned a respected doctor.

In the courtroom, everything changed, she said.

"Because we were backed by such a wonderful army who we knew experienced the same things, we just started gaining confidence."

Actress Akemi Look, a former member of USAG's rhythmic national team, submitted a written statement to the judge. Prosecutors read it aloud in court on day two of sentencing. Then, Look said the bravery of the other women inspired her to take a last-minute flight to Michigan to stand with them. Because her statement was already shared she could not speak in court. Instead, she spoke at the post-sentencing news conference.

She commended Judge Rosemarie Aquilina for putting the women's stories at the center of Nassar's sentencing. Throughout the hearing, Aquilina consoled the women and offered words of support.

"We are so grateful for how she has handled so delicately our souls and our lives," Look said. "We need change. This needs to end here."

Sterling Riethman said she and others had received messages of gratitude from people around the world "who have not had the voice to come forward." The messages served as reminders that they're not alone, and that a cultural shift is underway, she said.

"We are just a small part of this movement happening," she said. "There is no doubt there is a movement."

'The why and the how has yet to be uncovered'

Rachael Denhollander , the first woman to publicly accuse Nassar of sexual abuse, called the sentence a victory. But she demanded further investigation of what she called the worst sexual assault scandal in history, starting with institutions connected to him.

She identified four by name: Michigan State University and USA Gymnastics, both of whom employed Nassar during his decades of abuse, as well as the United States Olympic Committee and Twistars Gymnastics Club in Michigan, where Nassar admitted to sexually abusing athletes.

After the sentencing, MSU, USAG and USOC released statements condemning Nassar's actions and pledging internal investigations. But Denhollander said those statements were too little, too late, and didn't go far enough.

"We survivors have taken our stand. We have demonstrated the desperate need for change at MSU, USAG and organizations like Twistars. But in order to make that change, we must identify each and every breakdown that occurred which allowed Larry to prey on women and children for so long," Denhollander said.

She called on the media to stay with the story to identify those breakdowns.

"The who, the what, the when and the where was answered this week, as my survivor sisters and I took the stand," she said. "But the why and the how has yet to be uncovered."

On Wednesday evening, Michigan State University Lou Anna Simon announced her resignation . But many questions remain unanswered.

"Why could Nassar get away with sexually abusing little girls for so very long? How could two major institutions surrounding him so abhorrently fail at protecting the children and women under their care?" Denhollander said.

"It's the biggest sexual assault scandal in history, and we should want to know why it happened. And if we don't, it's not going to get better."