W11 Hearing and Equilibrium 1 Flashcards
(27 cards)
What type of receptor cell is used in both the auditory and vestibular systems?
Hair cells
What are 3 modalities detected by the vestibular system?
- Sense of position of head (sensing gravity)
- Linear acceleration of the head
- Rotation of the head
What modality is detected by the auditory system?
Rapid vibration of the air surrounding the ear (sound) in the 20 to 20,000 Hz range
What type of reflexes involve the vestibular system?
Vestibulo-spinal reflexes and vestibulo-ocular reflexes
Generates skeletal muscle contraction to maintain balance and orientation
Dyfunction of the vestibular system leads to what condition?
Vertigo
Hair cells are a modified form of what type of cell?
Epithelial cells
What neurotransmitter(s) are secreted by hair cells when they are stimulated?
Glutamate primarily, but also Aspartate
These NT’s go to the innervating neurons and stimulate action potentials
What two lymphatic compartments are separated by the epithelial cell layers (some of which are hair cells) ?
Endolymph and Perilymph
What are the potassium and sodium concentrations of Perilymph? What bodily fluid compartment is this composition similar to?
[K+] ~ 2mM
[Na+] ~ 140 mM
Similar to CSF
What are the potassium and sodium concentrations of Endolymph? What bodily fluid compartment is this composition similar to?
[K+] ~ 150mM
[Na+] ~ 1 mM
Similar to Cytosol
What is the potential (voltage) of endolymph in the cochlea?
And the vestibular system?
Cochlea endolymph = +80mV
Vestibular endolymph = 0 mV
Hair cells have 1 long mobile cilium, what is its name?
What are the many shorter cilia called? What connects them?
1 long mobile cilium = Kinocilium
other cilia = Stereocilia. There are 50-150 of them
Connected by Tip Links
What are the 4 types of hair cells?
2 Vestibular hair cells: Type I and II (the difference is not hugely important in this class, slight difference in the placement of efferent axon)
2 Cochlear hair cells: Inner and Outer (difference is more important, but so far the difference hasn’t been explained. outer hair cells have stronger connections to efferent nerves that allow for fine tuning)
Where is endolymph produced in the cochlea? How does it work?
(see lecture slide/drawing)
Produced in the Stria Vascularis
Layer of epithelial cells separates perilymph from endolymph. On the first layer of the perilymph side, the Na+,K+,2 Cl- Transporter brings those 3 in, Na+ and Cl- are brought back to perilymph, whereas K+ ions are transported towards endolymph over several epithelial layers
What type of mechanosensitive ion channel at the top of the stereocilium is responsible for hair cell depolarization?
TRPA1 (transient receptor potential A1), a non-selective cation channel. Allows K+, Na+ and Ca2+ influx from the endolymph side, but mostly K+ is important because endolymph is full of potassium
What is positive mechanical deformation of hair cells?
Mechanical stimulation occurs on the side of the stereocilia, pushing them towards the kinocilium. This causes the TRPA1 channels to open, potassium enters the hair cell, the cell depolarizes, NT’s are released, and increased frequency of action potentials results.
What is negative mechanical deformation of hair cells?
Mechanical stimulation pushes the kinociulm over the stereocilium, causing their TRPA1 channels to close. This causes hyperpolarization, less NT’s are released, and so action potential frequency is lower
What is the electrochemical gradient of potassium in the vestibular hair cells versus the endolymph space?
And in the cochlear hair cells?
Vestibular hair cells is only +40mV (because endolymph has 0 potential, hair cell has -40mV)
Cochlear hair cell is +120mV (80mV endolymph + 40mV of hair cell)
There is no chemical gradient because the concentration of K+ is ~ the same in hair cell cytoplasm and endolymph. Only an electrical gradient.
What are the two “otolith organs?”
The Saccule and Utricle
(two of the three vestibular locations for hair cells)
These are sensitive to linear acceleration
What is the otolithic membrane?
Membrane on top of the macula (where saccule and utricle hair cells are located)
Otolithic membrane is a gel composed of mucopolysaccharides and otoliths (small CaCO3 stones) that give the membrane a high density which can be affected by inertia/gravity
Movement of the membrane moves the stereocilia, influencing AP frequency
When in anatomical position, what is the direction of the stereocilia in the utricle?
And in the saccule?
Utricle stereocilia = vertical orientation
Saccule = horizontal
What is the function of the striola in the otolithic organs?
The striola is a line through the middle of the otolithic organs. In the saccule, all hair cells point away from the striola (opposite directions on either side of the line). In the utricle, all hair cells face towards the striola.
In any position, hair cells on one side of the striola will be depolarized, and on the other side will be hyperpolarized.
How are semicircular canals different than the otolithic organs? (both are in the vestibular system)
Semicircular canals have no otolithic membrane and cannot detect linear acceleration. Instead they have a cupula gel with no otoliths. With this gel and the orientation of the semicircular canals, they can detect rotation of the head which causes the gel to flow and stimulate hair cells.
What is the name of the region where hair cells are located in the semicircular canals?
Crista Ampullaris
again, to differentiate, the saccule and utricle have hair cells in the macula
