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| Unit 10: Demos |
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All sensory receptors are transducers Role of otoliths (6a) Eye
diagrams Rods versus cones (8a) Muscle
Contraction video tutorial (From Campbell website) Fatigue (optional) Bone structure (optional) Muscle Slides How Vision Works The Nocturnal Eye The Eye and Retina Major bones of the vertebrate(from the University of the Western Cape, South Africa - Internet Bio-Ed Project) |
Hearing Examine the SEMs to see what happens to the hair cells of the organ of Corti after exposure to intense sound. Intense sound includes traffic sounds if your car windows are open, airport runway noise, and loud music, particularly with head phones. Notice the rows of hairs at the top and bottom of the picture below. These hairs are suspended in a liquid matrix called perilymph, in the organ of Corti in the inner ear. As the eardrum moves, these hair cells move back and forth in the perilymph. The ear performs two vital functions: it detects the rapid fluctuations in air pressure that we recognize as sound, and it senses motion and direction so that the brain can maintain bodily equilibrium. To perform these functions, it contains two exquisitely designed sets of sensors.
The fan-like clusters at the top of the Figure are made up of inner hair cells; the Vs at the bottom are outer hair cells. They rest on a complicated structure called the organ of Corti deep within the inner ear. The organ of Corti, in turn, is located on the basilar membrane, which runs through the spiral-shaped cochlea. When a sound-pressure wave strikes the eardrum, the motion it causes is transmitted through a network of small bones to a fluid, the perilymph, the pressure wave deforms the basilar membrane surrounding the cochlear duct. As the membrane moves, the inner and outer hair cells wave back and forth, suspended in the endolymph that fills the cochlear duct. Research suggests that the endolymph fluid tends to remain stationary.
As each hair cell moves, it generates small electrical signals that are transmitted to the brain and there interpreted as sound. The large cylinder disappearing at the top of the picture is an outer hair cell. The several flattened structures attached to the base of the hair cell in the center of the photo are nerve endings that sense the changing electrical potential in the sensor cell.
A guinea pig was exposed to high-intensity sound; this is the result. The first row of outer hair cells is severely damaged, the center row somewhat less so. The ear serves not only for hearing, but also for balance. To perform this function, it contains sensors that detect changes from a resting to moving state or changes in the rate of speed (acceleration). In principle, these detectors are not unlike the accelerometers that perform the same function in airplanes and space vehicles. But in construction and operation, they are totally different. A spaceship’s motion sensor is a gyroscope whose spinning rotor remains pointed in the same direction no matter how the vehicle around it moves. The ear achieves the same end with these minute bundles of hairlike cilia.
The structures in the Figure above are motion sensors from a region of the ear of a bullfrog (Rana catesbeiana) known as the sacculus. Near the top of each clump of cilia can be seen a small bulbous object. This structure connects the cilium directly beneath it—called the kinocillium—to the many similar but distinct stereocilia that make up the remainder of the cluster. Except for the bulb at the end, the kinocilium looks precisely like all of the other cilia. But it differs in several important ways, and is the key element in the animal’s motion-detection system. |
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