Final answer:
The thick gelatinous cap in the crista ampullaris is known as the cupula, which assists in detecting head movements and rotational acceleration.
Step-by-step explanation:
The thick gelatinous cap in the crista ampullaris is known as the cupula. This structure is not directly mentioned in the provided information but it is a well-known feature of the crista ampullaris, which is part of the inner ear's vestibular system.
The cupula sits atop the crista ampullaris, which is a sensory organ that detects head movements and rotational acceleration. It functions similarly to the otolithic membrane in the utricle and saccule, which is composed of hair cells surrounded by support cells and contains a layer of calcium carbonate crystals called otoliths.
The cupula is involved in the detection of dynamic equilibrium or rotational acceleration, not static equilibrium which is the role of the otolithic membrane. The bending of stereocilia embedded in the cupula or otolithic membrane during movement is what helps the brain interpret the body's position and maintain balance.