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[37] All vital activities of living beings are controlled by their nervous systems. These communications networks, much like those of a large telephone system, carry information that is derived either from the five specialized senses or internally produced stimuli to the brain. The brain and spinal cord make up the central nervous system and, with the peripheral nerves, control voluntary activities such as reaching and walking. The autonomic nerve system, with the endocrine system, controls most of the involuntary activities such as breathing.
The spinal cord contains the nerves controlling reflex actions. From these reflex centers, motor nerves lead to all of the muscles in the arms and legs and most of the trunk. The spinal cord also carries the sensory nerve signals between the brain and parts of the body below the neck.
The largest part of the brain, the cerebrum, contains sensory, motor, and association regions. The sensory portion is made up of centers which are responsible for such functions as seeing, hearing, smelling, tasting, and touching. The motor region controls all voluntary movements of the body. The least well-known area of the brain is the association region. It is apparently responsible for an individual's awareness of the meaning of things. It allows him to relate sensory perceptions to motor actions. These three parts of the brain are interconnected so that signals can be carried from centers in one area to those in others.
Two of the student experiments involved investigations of the nervous system. One was directly concerned with the effects of prolonged weightlessness on man's motor-sensory performance. The other studied the web-spinning characteristics of spiders.
Motor-Sensory Performance
The Mercury, Gemini, and Apollo programs proved that man could function in a capable manner in space. However, in each of these programs there was some evidence of physiological damage, loss of bone calcium and general muscle tone being the most often mentioned. None of the missions included tasks that produced a quantitative measure of the physiological effect, if any, on man's capability to perform delicate tasks with his hands. Since the early beginning of man's exploration of space, there have been questions concerning his ability to perform such movements. The establishment of large space stations and interplanetary travel involve extended tours of duty in an alien environment. The possible establishment of space manufacturing facilities, and certainly the need to make repairs, require that the crew perform a variety of tasks with hands and fingers. Without knowing whether or not man can retain a high level of competency in the performance of such tasks after long exposure to weightlessness, this capability could not be fully known. Skylab, with its long-duration missions, provided an ideal testing situation.
Kathy Jackson of Clear Creek High School,
....Houston, Tex., proposed a very simple but effective test to measure the potential degradation of man's motor-sensory skills while weightless. It is generally accepted that fatigue can affect both the sensory and motor centers of the brain. The....
![Docking one spacecraft with another requires one of the greatest tests of the motor-sensory capabilities of man. [link to a greater picture.]](p38bs.jpg)
[39] .....sensory receptors must recognize the requirement for action. The association center of the brain then calculates the proper action necessary to respond to the sensory center's signal, and the motor center issues the necessary commands for the muscles to react appropriately. The experiment Kathy Jackson proposed is similar in application to the tasks involved in docking one spacecraft to another using manual control. It is a familiar manual tracking task.
She suggested use of a standard eye-hand coordination test developed by the industrial engineering department of the University of Michigan. It was designed to measure an individual's capacity to direct hand movements with the aid of visual monitoring. The test consisted of a visual maze and aiming pattern with 119 holes connected by straight lines. The astronauts inserted a probe in each hole in sequence, following the maze pattern. Thus, the visual perception and motor response was measured quantitatively by recording both the total time required to traverse the entire maze and the time required to move the probe from hole to hole.
The test was performed by each member of the third Skylab crew. They worked through the maze early in the mission, again approximately at mid-mission, and then late in the mission. The crew reported that they enjoyed this test and regretted that there was not time to work with the maze more often.
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Analysis of preflight, inflight, and postflight data indicated that there was no significant change in the eye-hand coordination of the crew. This fact was further evidenced by the outstanding performance records of all three Skylab crews. The installation of the Sun-shield parasol by the first crew, the twin-pole Sun shield by the second crew, and the repair of the coolant system by the third crew are but a few examples of the normal motor-sensory capabilities of the Skylab astronauts. Further, none of the crews reported any noticeable deterioration throughout the missions in performing tasks that required them to handle experiments and controls.
Web Formation
Motor response is an indication of the functioning of the central nervous system. Drugs such as stimulants and sedatives affect the nervous system by causing degradation of certain motor responses. In an effort to study the effects of drugs, researchers have often utilized spiders as test subjects. The geometrical structure of the web of an orb-weaving spider provides a good measure of the condition of its central nervous system.
After reading an article in the National Geographic magazine describing the behavior of the spider, Judith Miles of Lexington High School, Lexington, Mass., suggested a study of the spider's behavior while weightless. Since the spider senses its own weight to determine the required thickness of web material and uses both the wind and gravity to initiate construction of its web, the lack of gravitational force in Skylab would provide a new and different stimulus to the spider's behavioral response.
The common Cross spider (Araneus diadematus), an orb-weaving spider that produces a web of nearly concentric circles, was selected for the experiment. The Cross spider can live approximately 3 weeks without food if an adequate water supply is available. The female spider will build a web each day at approximately the same time, in the pre-dawn hours. The web is constructed in a very orderly fashion, starting with a bridge and frame. Using this rudimentary structure, the spider adds radial threads. A temporary spiral emanating from the hub is constructed next. It serves to give the spider a measure of the distance around the hub or central region of the web. Thus, the spider is able to judge the amount of silk required for the....
![Orb-weaving spiders spin webs familiar to everyone; however, their construction technique is a complicated one.[link to a greater picture]](p43s.jpg)
....web, and it establishes the mesh size. The next step is the construction of the sticky, or catching, portion of the web. A free section of the web provides an area for spinning a signal thread from the spider's retreat to the limb of the web. This thread alerts the spider to the presence of prey in the catching spiral. The normal adult spider will utilize 66 to 98 feet of silk thread in constructing her web and will usually eat the sticky portion of the web daily. The web will generally consist of 30 to 40 radials and 25 to 35 spiral turns.
A specially constructed cage, provided with attachments for two portable utility lights, a camera-mounting bracket, and an ultrasonic actuator for a movie camera, was launched aboard Skylab. Two spiders, named Arabella and Anita, were each fed a housefly, installed in a small vial provided with a water-saturated sponge and an additional housefly, and launched in the Apollo spacecraft with the second Skylab crew.
On August 5, 1973, Scientist Pilot Garriott placed Arabella's vial in position on the cage and....
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.... fully expected her to move out into the cage from the cramped quarters. However, she refused to do so. After several hours Garriott forcibly shook her from the vial into the cage. Arabella bounced back and forth, moving erratically in a swimming motion before she affixed herself to the screen covering on the cage surface. The crew reported the next day that Arabella had constructed a [46] rudimentary web in the corners of the cage. Her first complete web was observed after 2 days in the cage.
At this point, Garriott expressed interest in carrying this experiment beyond the planned protocol of terminating the experiment after allowing one spider to build three webs. As a result of this request, a new protocol was approved which involved feeding the spiders rare filet mignon, providing an additional water supply, deploying Anita at mid-mission, and returning both spiders together with samples of the webs.
Both spiders were subsequently fed, and on August 13, Garriott removed half of Arabella's existing web. She promptly ingested the remaining half and refused to rebuild. Garriott then provided Arabella with water, whereupon she proceeded to build a new web. On August 21, Arabella's web....
....was completely removed, and the web found in her cage the following day was observed to be her best to date.
On August 26, Arabella was returned to her launch vial, and Anita was placed in the cage. A videotape recording and 16-mm movies were made of Anita's first reactions to weightlessness. She, too, had to be forcibly ejected from her vial and, in fact, had to be picked off Garriott's arm before she could be induced to "swim" into place on the side of her cage. Anita performed in a manner similar to Arabella until September 16, when the astronaut found her dead in the cage. The dead spider was transferred to her launch vial for return to Earth.
Back on Earth, Arabella was found to have died also. Both spiders showed signs of dehydration, the only visible evidence of the cause of their death. Examination of the returned web materials indicated that the thread spun in flight was signifi-....
....-cantly finer than that spun preflight, giving positive evidence that the spider utilized a weight-sensing organism to size her thread.
It appeared that Arabella adapted quite well to the weightless environment. Control tests on Earth indicated that confinement in the launch vial did not affect the spider's ability to construct a quality web. Similar confinement, accompanied with vibration at the levels encountered during launch and followed by a "rest" period corresponding to the flight delay in deployment, resulted in an adaptation period of 2 to 3 days before the control spiders built webs comparable to their pretest quality. While Arabella performed her space task, the extended "rest" period experienced by Anita in her launch vial allowed her to build at least one [49] quality web almost immediately when she entered the cage.
Had the original planning included keeping the spiders in the cage for the full mission rather than 3 to 5 days, a method could have been developed for feeding them and providing them with water in a more reliable fashion than was done.
Judy Miles' experiment received a great deal of attention both within NASA and in the world press and indicated that there was keen interest in space experiments involving living organisms. It also established that biological experiments involving simple life forms are compatible with manned spaceflight.
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