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Aquatic Team

A question to consider as you read . . .

Considering how the sensory structure in humans works, why does dizziness not immediately go away when the stimulus goes away.

Vocabulary that will help you understand this section

vestibular

Most living creatures have a sensory structure for detecting gravity. These structures, referred to as vestibular functions, give cues for self orientation and balance. In vertebrates with jaws, this sensory system is called the labyrinth, and it has the same basic structure in creatures from fish to humans. The interior of the labyrinth is lined with tiny hair cells which are connected to nerves, and when triggered, send signals to the brain. The "trigger" is a tiny stonelike structure in snails and fish and is fluid in humans. Depending on the angle or tilt of the head, the trigger will, in the presence of gravity, weigh down upon different groups of hair cells that send orientation signals to the brain. The Aquatic Team, consisting of two independent investigators using aquatic animals, is studying the development and functioning of the vestibular system in the absence of gravity.

photo of snails in a fish tank

Dr. Wiederhold's Study

Dr. Wiederhold is focused on the development of the vestibular system in fresh-water snails (Biompharlaria glabrata) and in the swordtail fish (Xiphophorus helleri). The purpose of the study is to determine the effects of microgravity on the formation of the stonelike structure that triggers the hair cells to send the signals. In snails, this structure is called a statocyst; in fish it is called an otolith. In theory, the size of the otolith is determined by its weight; thus in microgravity, otoliths should develop to a larger size than they do in the presence of gravity on Earth. While experiments flown on a previous mission give evidence to support this theory, more study is needed. Therefore, embryonic snails and swordtail fish will be flown on the Colombia during their developmental stages, and their otoliths will be compared to a normal, or control, group of snails and fish that have matured on Earth in the presence of gravity.

The functioning of the vestibular system in microgravity will be monitored in two ways.

First, the crawling behavior of the snails in microgravity will be videotaped for observation and comparison to the crawling behavior of the control snails on Earth. Past studies have shown that, in the presence of gravity, both newly hatched and adult snails crawl preferentially in a downward direction. Whether this behavior is constant in the absence of gravity remains to be determined.

photo of toadfish

Second the functioning of the vestibular system in microgravity will be monitored by Dr. Highstein in his study involving toadfish (Opsanus tau). As mentioned previously, the fish vestibular system compares favorably with that of mammals. Dr. Highstein's project focuses on the self-orientation signals that are sent from the labyrinth to the brain and, in turn, generate physical movement by toadfish. Continuous monitoring of these signals before, during and after the flight will provide data representative of the same vestibular signals occurring in the astronauts.

Data from this and Dr. Weiderhold's experiment are expected not only to yield a better understanding of why astronauts experience motion sickness in space but also to provide additional insight into common motion sickness experienced by many here on Earth.