The Human Balance System

Discussion in 'The Universe' started by wallflower, Jun 11, 2013.

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    Here is a diagram of the ear.

    From left to right: the ear canal, tympanic membrane (the eardrum), the ossicles (smallest bones in the body - malleus, incus and stapes - otherwise known as hammer, anvil and stirrup), semicircular canals and the cochlea.

    Located between the semicircular canals and the cochlea are the utricle and saccule (they are not shown in this diagram.) The semicircular canals, the utricle and the sacccule make up the vestibular system which enables us to keep our balance.

    http://brandyoumedialab.net/identify-symptoms-of-ear-infection-in-children/

    (The words in the diagram are in small print that might be hard on the eyes. The semicircular canals are in light blue and the cochlea looks like a brown snail.)

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    http://en.wikipedia.org/wiki/Semicircular_canals

    There are 3 semicircular canals inside each ear.

    Horizontal canal
    Superior (or anterior) canal
    Posterior canal

    The horizontal canal detects head movements made in the horizontal direction. For example, when we spin around or look behind us.

    The superior and posterior canals detects head movements made in the vertical direction. For example, when we bend forward or nod our head.

    Each canal contains a fluid called endolymph. The base of each canal opens into the utricle and contains an enlarged sac called an ampulla.

    The ampulla contains hair cells. The hair cells are made of cilia (very tiny hairs or lashes.) The hair cells are attached to the cupula. (The cupula is a structure inside the ampulla.)

    When the head makes a movement, this moves the semicircular canal. But the endolymph (fluid inside the canal) doesn't keep pace with the movement and is slightly behind.

    This bends the cupula (that holds the cilia - very tiny hairs or lashes) and makes the cilia bend as well. The bending of the cilia sends a signal to the brain and tells the brain that the head and the body are moving.

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    The utricle and the saccule are located below the semicircular canals. They are called “otolith organs.â€￾ These organs use otoliths (small crystals of calcium carbonate) and a viscous (sticky, consistency between solid and liquid) fluid to make the hair cells detect movement, gravity, balance and orientation.

    The utricle contains a small area (2 by 3mm) of hair cells which are positioned horizontally on the base or “floorâ€￾ of the organ. Tiny hairs called steriocilia, are attached to the otolithic membrane (this membrane contains the otoliths – the crystals of calcium carbonate and the sticky fluid.) The hair cells can feel the weight of the calcium carbonate crystals (otoliths) and can feel if the crystals move. The hair cells can feel if the tiny hairs (steriocilia) bend from the weight of the crystals. This causes the hair cell to send a signal to the brain that tells the brain that the head is moving in a horizontal direction, the speed at which the body is moving and the position of the head.

    The utricle can detect if the head tilts, horizontal movements and the speed at which the body is moving.

    The saccule is located below the utricle. The saccule also contains hair cells, tiny hairs (steriocilia), the otolithic membrane (crystals of calcium carbonate and the sticky fluid) and detects movement in the same way as the utricle does. It detects vertical movements (such as travelling in an elevator.)

    http://en.wikipedia.org/wiki/Utricle_(ear)

    http://en.wikipedia.org/wiki/Saccule

    http://en.wikipedia.org/wiki/Otolith

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    The cochlea is shaped like a snail. Its base is near the middle ear and the oval window. The top or centre of the spiral is the apex.

    It contains 3 chambers:

    The scala media (or the cochlear duct) runs along the length of the cochlear and lies between 2 other chambers.

    The scala vestibuli is located on one side of the cochlear duct. The oval window opens into this chamber.

    The scala tympani is located on the other side of the cochlear duct. This round window is the exit for this chamber.



    The basilar membrane is a structure that supports the cochlear duct and separates it from the scala tympani (which exits through the round window.)

    Each of the chambers are filled with fluid. The scala vestibuli (entrance is the oval window) and the scala tympani (exits through the round window) contain a fluid called perilymph. Perilymph has a high concentration of sodium ions.

    The scala media (cochlear duct) is filled with a fluid called endolymph. Endolymph has a high concentration of potassium ions.

    The helicotrema is the point where the scala vestibuli (enters through the oval window) and the scala tympani (exits through the round window) meet at the top (or apex) of the cochlea.

    http://en.wikipedia.org/wiki/Cochlea
    (The 3rd picture shows a diagram of the inner chambers of the cochlea. Its the picture that refers to the oval and round windows.)

    Will add to this as I go.

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    (Ok....I've finished posting notes for the Annual General Meeting and the District Convention, so picking up where I left off.)


    The organ of Corti is like a "microphone" for the body - it is able to determine the pitch and volume of sound. It can do this by sensing the pressure changes in the fluid contained within the tympanic (round window) and vestibular (oval window) canals.

    The organ of Corti contains 4 rows of hair cells which are able to detect movement.

    http://en.wikipedia.org/wiki/Cochlea

    (The 3rd picture shows a diagram of the inner chambers of the cochlea. Its the picture that refers to the oval and round windows.)

    http://hyperphysics.phy-astr.gsu.edu/hbase/sound/corti.html


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    The three bones in the ear are called the malleus, incus and stapes (also known as the hammer, anvil and stirrup.) They transmit the vibration of the eardrum through to the oval window of the vestibular canal of the cochlea.

    The bones move in the same manner as a compound lever - they have some flexibility. The "lever" action may help amplify or magnify a soft-sounding signal. It can also allow a measure of "protection" (but not totally) from louder sounds.

    http://hyperphysics.phy-astr.gsu.edu/hbase/sound/oss.html#c2
    (Scroll down to see the diagram about sound vibration.)

    (Some time ago I remember that JIG posted something about how young children can hear frequencies that adults cannot. I wondered what was the cause of that. Gonna read a little about that.

    Tossing around in my head what the next topic should be for the next thread - heart, kidneys or the skin? The skin is considered to be an organ in itself.)

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    http://scienceblogs.com/startswithabang/2010/05/10/dont-you-hear-that/

    The cochlea is lined with cilia (tiny hairs) that measure sound waves as they are transmitted from the 3 small bones of the ear.

    Children are able to hear sound levels up to 20 000 Hz. As people grow older, the cilia become brittle and are easily damaged. This means that the sound waves have to travel further along the length of the cochlea, to reach cilia that can still register the sound waves and then pass this messge to the brain.

    There are other causes of hearing loss and these are mentioned in the link (e.g loud music.)

    There are some sound files also included in the link but I'm not sure how well they work. I could hear 12 000 Hz clearly. At 14 000 Hz, I could hear the tone but not the sound (if you know what I mean.)

    My cat could hear the 17 000 Hz - Puss gave me "the look" and went off and slept in another room. ("Can't you see I'm trying to get some sleep here?" :mad:)

    Scroll down the page to see the diagram of the cochlea (looks like a snail) and the sound files are listed after the cochlea diagram.

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