EXCLUSIVE

Nichelle Nichols -- best known for playing Lieutenant Uhura in "Star Trek" -- is suffering from severe short-term memory loss and needs protection from being taken advantage of ... according to her son.

Nichols' son, Kyle Johnson, filed legal docs Friday nominating 4 fiduciaries to become his 85-year-old mom's conservators -- which would give them control of her finances and decisions related to her health.

According to Johnson, this is necessary because her dementia is "impacting her executive functioning" and makes her "susceptible to undue influence."

He adds ... "Certain individuals have unduly exerted themselves into Ms. Nichols' life to her detriment."

Aside from her classic "Star Trek" role, Nichelle's been very active in Hollywood -- she even has 3 projects coming out this year.