Audition I
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- What fluid bathes the apical surface of hair cells in the cochlea? What special properties does this fluid have?
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*endolymph
*unique in that it has a very high [K+] as well as some [Ca++] - What fluid bathes the basolateral surface of hair cells in the cochlea?
- Perilymph
- Name three things that can cause destruction of hair cells and thus hearing loss.
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1.Noise
2.Presbyacusis (i.e. age)
3.Ototoxic drugs
4.Infections
5.Genetic syndromes - What is the structure of the kinocilium? How does this differ from the structure of stereocilia?
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*kinocilium has a typical microtubule structure
*stereocilia are not true cilia at all and in fact more closely resemble microvilli; they have an actin core - How are adjacent stereocilia connected to each other?
- The smaller of the two has a tip link fiber that is attached to an insertional plaque on the taller one.
- What happens when a hair bundle is moved in the direction of the tallest stereocilia?
- The tip links pull open mechanically gated channels which allows a depolarizing influx of K+. More neurotransmitter is released from the basolateral surface and an AP is generated in the afferent nerve fiber.
- What happens when a hair bundle is moved in the direction of the shorter stereocilia?
- Mechanically-gated channels are pulled shut, resulting in the hyperpolarization of the cell. Less neurotransmitter is released from the basolateral surface and no AP is generated in the afferent nerve.
- What happens when a hair bundle is moved in a lateral direction?
- This type of movement has no effect on the polarization of the cell. However there is still a baseline tonic release of neurotransmitter from the basolateral surface.
- How are hair cells able to adapt in situations of prolonged noise?
- The myosin arm that connects the channel gate to the actin core of the stereocilia moves up or down the actin core to restore tension to the gate. This movement is initiated by Ca++.
- What are three signs of Meniere's syndrome?
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1.Progressive hearing loss
2.Attacks of vertigo
3.Tinnitus
4.A sense of fullness in the ear - What is the pathology associated with Meniere's syndrome?
- A dilation of the membraneous labyrinth with occasional rupture which leads to mixing of endolymph and perilymph. This alters the conductile properties of the hair cells.
- What is the difference between conductive and sensorineural hearing loss?
- Conductive deafness is due to a defect in the conduction of sound to normally functioning hair cells. Sensorineural deafness is due to a loss of functional hair cells or auditory neurons; also it typically involves defects in the vestibular system as well.
- What are two categories of hereditary deafness?
- Syndromic (i.e. part of a constellation of symptoms) or non-syndromic (i.e. a singular deficit).
- What class of antibiotics are sometimes ototoxic? How do these drugs damage hearing ability?
- Aminoglycosides may block mechanically gated channels on the stereocilia, thus interfering with transduction.
- How can acute acoustic trauma cause hearing loss?
- Excessive movement of the stereocilia can cause them to be sheared off.
- What is a temporary threshold shift? What is the pathogenesis involved? How is it remedied?
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*a temporary decrease is hearing ability due to prolonged exposure to loud noise
*believed to be associated with shearing of tip links
*regeneration of tip links, which occurs in hours - What is presbyacusis?
- Hearing loss due to old age.
- What two aspects of position are sensed by the otolith organs? Name the two otolith organs.
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*linear acceleration and static head position
*utricle and saccule - Describe the attachments of the hair cells found in the otolith organs.
- They are attached to maculae and their tips are embedded in a gelatinous mass that is weighed down with otoliths (calcium carbonate crystals).
- What type of head movement is sensed by hair cells in the utricle? By those in the saccule?
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*utricle: side to side movement
*saccule: up and down movement - Describe the attachments of the hair cells found in the semicircular canals.
- They are attached to the ampullary crests of the canals and their tips are embedded in the cupula.
- What is the primary symptom of damage to the vestibular system? Specifically, what symptoms are seen with damage to the semicircular canals? To the otolith organs?
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*vertigo - a sensation of spinning
*canals - a sensation of horizontal rotation
*otoliths - a sensation of being pushed down - Why might the vestibular systems of avalanche victims be of little help in helping them determine their position in snow?
- Because the vestibular system is more sensitive to changes in position rather than absolute position.
- What is sensed by hair cells in the semicircular canals?
- Dynamic head movement - i.e. angular acceleration.