Lecture 20 Flashcards
Describe the vestibular sense
- Not major component of consciousness
- Only aware in case of malfunctions or overstimulation
What are symptoms of a malfunctioning or overstimulated vestibular sense?
- Vertigo
- Nausea
- Dizziness
How many Peripheral Apparati are there in the vestibular system?
2
- One per ear
What can happen when you lose the vestibular peripheral apparatus on one ear?
- You will adapt to using the other
Why do we have a vestibular apparatus in each ear?
- Gives better resolution of the code
What is required to use the vestibular input to make inferences about body position in space?
Information from
- Skin
- Vision
- Proprioception
What are the different directions of movement in the vestibular system?
- Pitch (y-axis): anterior/posterior (front/back)
- Roll (x-axis): coronal
- Yaw (z-axis): Rotational
Where does the Vestibular System Reside?
Inner Ear
- Very close to the cochlea
- Next to very dense bone
What is the vestibular system innervated by?
- Cranial Nerve VIII: Vestibulocochlear Nerve
- Afferent axons go to receptors in vestibular system and auditory system
What is the bony labyrinth
- Bunch of tunnels and holes carved out of the petrous temporal bone
Where is the Bony Labyrinth Located?
- Petrous Temporal Bone
Where is the Bony Labyrinth Located?
- Petrous Temporal Bone
What is be between the membranous and bony labyrinth?
Fluid
- Perilymph
What is the membrane within the tunnels of the bony labyrinth called?
- Membranous labyrinth
What is the Membranous Labyrinth filled with?
- Endolymph
Where does the membranous labyrinth sit?
- Floats inside the bone
- thin layer of fluid separating it from bone
What are the 3 semicircular canals?
- Anterior
- Posterior
- Horizontal
What happens to the anterior and posterior canals?
- Join together
- Merge within the vestibule
What goes through the 3 semicircular canals?
- membranous semicircular ducts
What is the Ampulla?
- slight swelling in the tubes of the vestibular system
- contain hair receptors for semicircular ducts
What connects up with the cochlea?
- Continuous fluid-filled tubing
What are the two otolith organs?
- Saccule
- Utricle
Where are the otolith organs located?
- vestibule
What does the vestibule contain?
- Otolith Organs
- Hair Receptors
- Membranous sac that are specialized
What are the ducts and vestibule embedded in?
- Solid, dense petrous temporal bone
Why are the ducts and vestibule embedded in solid, dense petrous temporal bone?
- So acceleration is transferred directly into the vestibular system
How is the vestibular on one-side compared to the other?
- They are perfectly mirrored
What does each side of the vestibular system contain?
- 3 semicircular canals
- 3 semicircular ducts
- swellings that contain otolith organs
How are the semicircular ducts orientated?
Orthogonal on Each Other
- at right angles
What does the orientation of the semicircular ducts do?
- allows them to work in pairs
What plane is the horizontal duct in?
- Slightly off horizontal
How can you line up the horizontal ducts in the horizontal plane?
- tilt head down
How are the anterior ducts orientated with one another?
- 90 degrees orthogonal to each other
How would you line up the anterior ducts with the other anterior ducts?
turn head 45 degrees to one side
How are the posterior and anterior ducts orientated?
- 90 degrees from anterior canal on one side is aligned with the posterior duct
What does the orientation of the semicircular ducts make?
- a perfect 3D plot
What are Hair Cells in the Vestibular and auditory systems?
- Receptors
What sticks out of the top of every Hair Cell?
- Cilia
What are the 2 types of Hair Cells?
- Kinocilium
- Stereocilia
Describe Kinocilium
Celia
- Tall
- thick
- Rigid Cilia
- 1 per cell
Describe Stereocilia
Cilia of Hair Cells
- 40-70 per cell
- increase in length from one end of cell towards kinocilium
- Shortest are further from kinocilium
Are the Hair Cells polarized? Why?
Yes
- morphological axis of polarity
Why
- Something about the way the hairs move that is critical
What is the Hair Cell Connected to?
- Afferent Neurons
- Sits on top of afferent sensory axon
What happens when you bend the stereocilia toward the kinocilium?
- depolarize, would drop more Neurotransmitters out of it
What happens when you push the stereocilia away from the kinocilium?
- Hyperpolarize
How does the hair cell depolarize?
- Stereocilia bends towards the kinocilium
How does the hair cell hyperpolarize?
- Stereocilia bends away from kinocilium
What kind of receptor are hair cells?
- mechanoreceptors
What causes the change in the membrane potential of the hair cells?
- a movement of the hairs
What does the movement of the stereocilia relative to the kinocilium determine?
- The leakiness of the membrane
What kind of background discharge does the 8th afferent nerve have?
- High
- NT dropping out of the hair cells constantly
- spontaneous firing at 100Hz
How does the magnitude of the bending of the stereocilia determine the leakiness of the membrane?
- the more it bends the more it changes it
- higher bend towards kinocilium = higher leakiness
- higher bend away from kinocilium = less leakiness
What does the leakiness of the hair cell mean?
- How much NT is being released
What happens to the firing rate of the hair cells when there is nothing pushing against the kinocilium?
- Normal firing rate
Where do the hair cells congregate?
Ducts
- Ampullae (swelling)
Otolith Organs
- Macula
What is the crista ampullaris of the ampullae?
- All hair cells are orientated in the same direction
- Kinocilium on one side with stereocilia staircase down
What is the Macula?
- Sensory Region of the Otolith Receptors
How are the hair cells orientated in the macula? Why?
very specific pattern
- so hair cells will deform in different proportions
What is the specific pattern of the macula hair cells?
- lined up with axis of morphology in many directions
- line in the middle of the macula called the striola
What is the line in the middle of the macula called?
- Striola
How does the macula work?
- depolarized/hyperpolarized during movement
- the specific hair cells that are changed tells the direction distortion
- Can sheer in any direction
- deals in planes
- mirrored on other side
What planes of movement do the hair cells in the utricle work in?
- Lateral motion
- forward/backward (redundant plane)
Where is the kinocilium located in the utricle?
- closest to the striola
Where are the cilia located in the Utricle?
- sticking straight up from floor
- Vertical and oriented in horizontal plane
- Kinocilium close to striola
What does the movement of hair cells mean in the Utricle?
- Towards the striola = depolarization
How are the hair cells orientated in the Saccule?
- On the walls
- Hairs stick out horizontally
- Kinocilium furthest from striola
What causes depolarization in the Saccule?
- Movement of hairs away from striola
What are some key structural features of the Otoliths?
- Hair Cells: project up into the overlying membrane
- Otolithic Membrane: overlying membrane
- Otoconia: small crystals, imbedded in membrane
What are Otoliths sensitive to?
- Linear Acceleration
What are Otoconia? What do they do?
Otoconia
- Small Crystals imbedded in Otolithic Membrane
Do
- Give mass to otolithic membrane
How does the otolithic membrane cause bending?
- Otoconia give mass
- Gravity pulls membrane down
What does the shifting of the otolithic membrane do?
- causes cilia to move
- Pulls stereocilia towards or away from kinocilium depending on the orientation
What happens if acceleration is constant?
- the shearing stops
How does polarization work in the Utricle?
- sheering in the horizontal plane will cause hyperpolarization or depolarization
- Picks up linear acceleration in the horizontal plane
How does polarization in the Saccule work?
- Movement in forward/backward and up/down will cause hyperpolarization or depolarization (same time)
How is 3D linear acceleration covered by the Otoliths?
- Utricle and Saccule are mirrored on each side
What is different about hair cells in the Ampullae compared to the Macula?
Ampullae
- all orientated in same way
- Either hyperpolarize or depolarize
Macula
- Oriented in different ways
- Hyperpolarized and Depolarized at same time
What is the Cupula?
- Gelatinous material that welds across the duct
- Membrane that divides the ducts in two
Where do the hair cells of the ampullae project?
- The Cupula
What causes the bending of the cilia in the ampullae? how?
What
- Movement of the fluid (endolymph)
How
- Endolymph has natural inertia
- Rotation cause fluid to lag behind
- Fluid pushes against cupula
- Cilia bends
What happens when you spin your head to one side?
Moves right away
- membranous duct
- cupula
- hair cells
Does not move right away
- endolymph
What does the movement of endolymph measure?
- angular acceleration in any direction in 3D
What happens when you spin at constant velocity?
- Fluid stops bending the cupula, and hair cells go back to normal
- afferent goes back to normal firing rate
How do the Hair Cells in the vestibular system work in pairs?
- Morphological axis of polarity
- when one side depolarizes, the other hyperpolarizes
Why does the fluid lag behind the rest of the vestibular structure?
- The structure is attached to bony system, fluid is not attached
