MadSci Network: Neuroscience |
Hi there! Vertigo is a sense of dizziness and disorientation, and it often arises due to problems with the vestibular system. Your vestibular organs are contained in two structures called the labyrinths, which are often referred to as the "inner ear." There is one labyrinth on each side of your head, located near your cochlea (the primary sensory organ for hearing). The labyrinth is composed of two principal organs: the semicircular canals, and the otoliths. Each semicircular canal consists of three "loops" organized at right angles to each other. If you imagine an X-Y-Z set of axes, one loop lies in the XY plane, one in the XZ plane, and one in the YZ plane. The canals are, indeed, filled with fluid. A specialized expansion at the base of each canal contains neurons with little hairs (or cilia) sticking into a membrane. When the head moves in an appropriate fashion, the fluid in the canals move accordingly. This fluid movement causes the membrane to bulge in the direction of head turning, which bends the cilia of the hair cells. When the cilia bend, ion channels in the neurons open or close, which sends an electrical signal to other neurons. So, the semicircular canals manage to translate head movement into fluid movement into electrical (ion) movement. The semicircular canals are most sensitive to head rotations, like looking to your side. The other labyrinth organ is called the otoliths, and their structure is slightly different. The otolithic organs are located in the same part of the body, and also contain hair cells with their cilia embedded in a membrane. Instead of containing fluid, though, the otoliths contain a rocky sheet of calcium carbonate crystals (that's where the otolith gets its name: oto + lith = ear rock!). When the head tilts or is subject to acceleration/ deceleration (like in a car or an airplane), the rock moves, and the hair cell cilia are bent. Again, this sends an electrical signal to other neurons. By letting your brain know how your head is moving, the labyrinths help you maintain a sense of orientation. They also keep your gaze fixed as your head moves, so that your eyes can maintain a continuous picture of the world around you. So, when they're not working properly, patients experience disorientation, and may also have inappropriate eye movements. Vertigo is thought to be caused by a disruption of the various components that make up the vestibular system. It is known that certain antibiotics can disrupt hair cell cilia, causing vertigo and hearing problems (because hair cells in your cochlea are similar to hair cells in your labyrinth). Alterations in the fluid composition or pressure could produce vertigo, as well. Another idea is that particles of the otolith could become mislocalized, resulting in inappropriate stimulation of hair cells. Hope this helps, Amanda amandak@phy.ucsf.edu Most good neuroscience textbooks have information about the vestibular organs -- try looking for Kandel's _Principles of Neuroscience_ or Purves' _Neuroscience_. A picture of the labyrinths, as well as information/support options/ treatment plans can be found at the following site: http://www.teleport.com/~veda/ Additional information about various types of vertigo and dizziness can be found at a clinic's website: http:// www.earaces.com
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