 |
| Unit 10: Demos |
|
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) |
Hair Cells HAIR CELLS OF THE INNER EAR ARE IMPORTANT IN ESTABLISHING EQUILIBRIUM Being human, we naturally think of the ear as the organ of hearing, but in our vertebrate ancestors its primary function was equilibrium, and the inner ear remains an organ of equilibrium in all vertebrates from fish to humans. However, many fishes are able to hear; in such fishes the bones of the skull conduct sound vibrations to the inner ear for sound reception. But it is in the amphibians that the inner ear took on the function of sound reception in addition to equilibrium. One of the gill slits found in the ancestral amphibians was modified to form a middle ear and a covering formed over it that could be used to pick up sound vibrations from the air. Tiny bones conducted sound vibrations to the inner ear. Most terrestrial vertebrates have an ear that functions for both sound reception and equilibrium. Moreover, the sensory receptors for both hearing and equilibrium have remained the same: the all-purpose hair cells. The human inner ear is a complicated labyrinth of interconnected fluid-filled chambers and canals. The two chambers of the vestibule contain beds of hair cells, upon which rests a gelatinous membrane containing embedded crystals of calcium carbonate, called otoliths. Because gravity pulls objects downward, any change in the position of the head or change in speed of motion (i.e., linear acceleration) of the head causes the membrane and its otoliths to move and exert more pressure on some hairs than on others. Similar sensory devices are found in invertebrates. For example, crayfish and lobsters have organs of equilibrium called statoliths, which consist of sand grains resting on beds of sensory hair cells (see Figure ). When the animal molts it loses the lining of the statolith and with it the sand grains, but the animal normally shovels in new sand grains when it has finished molting. If a crayfish is kept in a tank containing iron filings instead of sand, it will replace the sand with filings after molting. If we then hold a strong magnet near the crayfish, its iron otoliths will be pulled toward the magnet near the crayfish and the animal will orient itself as if the magnet were the pull of gravity. When the magnet positioned above them, such disoriented crayfish swim upside down!
|
|
|