LN13 - LECTURE 13 Balance and Hearing(Note Professor Gregg...

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2010 NPB 12, Note 13, Page: 1 LECTURE 13: Balance and Hearing (Note: Professor Gregg Recanzone will give the lecture) VOR (Vestibulo-Ocular Response) A different kind of eye movement is involuntary, or at least in the sense that you don't have to think about it, and that relates to keeping the visual world stationary in spite of the fact that you are continuously moving your head. If you take a video recorder and record what you are looking at while you walk, when you watch the tape you will see that the images are very jumpy and bouncy. Yet, when you walk you do not perceive the visual world as jumping around, it is very stationary. This is due to a reflex of the brainstem: the vestibulo-ocular response (VOR). A classic demonstration of the VOR is to look at your finger, and then move your head back and forth while still looking at your finger. As you move your head, your eyes move in an equal and opposite direction, keeping your eyes still in the world although your head is moving. This keeps the image of your finger stationary on your retina. In order to do this, you could use your knowledge that you are moving your head, and use the motor commands that move your head to drive the eye movements in the opposite direction. However, you are still able to keep your eyes fixed on one object even though you move passively, like in a car. As a passenger, you have no control of how your head is going to move in space, yet keeping your eyes fixed on something outside the car, like a road sign, is very simple. That is because you have another sense, the vestibular sense or sense of balance, that provides the information your brain needs to know how the head is moving. The vestibular apparatus, as it is called, is located in the temporal bone in a complex that also houses the sensory endings for hearing. It is believed that the receptors for balance and hearing are exactly the same, so I'll describe how balance works, and we will assume that it is essentially the same thing for hearing. The balance/hearing apparatus is contained within the temporal bone, right opposite the ear. It is composed of the cochlea (hearing) the semi-circular canals, the saccule and the utricle. In each of these structures there are a series of receptor cells called hair cells. They are called hair cells because they have small processes out of the top that look like hairs. They all have a longest one, called the kinocilium, and many shorter ones, called stereocilia. In all the hair cells, there is a membrane separating the cilia from the rest of the neuron, called the reticular lamina. This effectively makes a barrier dividing the outside of the neuron into two different compartments. The outside of the cell next to the hairs is called endolymph. This has actually a very high concentration of potassium (K+), much higher even than the inside of the cell. The other compartment has the same old ionic concentration that we have seen before. What is important is
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This note was uploaded on 11/18/2010 for the course NPB 72121 taught by Professor Hwai-jongcheng during the Spring '10 term at UC Davis.

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LN13 - LECTURE 13 Balance and Hearing(Note Professor Gregg...

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