Vestibular System - Henkel - Exam 1

Question 1

•What is the vestibular sense?

–Sense of movement, tilt, or rotation

•What are the vestibular stimuli?

–___ rotation (head turning)

–____ acceleration (head tilt with respect to gravity)

•How does vestibular sense affect ‘behavior’?

–Reflexes that maintain balance and posture, visual fixation, orientation in space

Answer 1

•What is the vestibular sense?

–Sense of movement, tilt, or rotation

•What are the vestibular stimuli?

–Angular rotation (head turning)

–Linear acceleration (head tilt with respect to gravity)

•How does vestibular sense affect ‘behavior’?

–Reflexes that maintain balance and posture, visual fixation, orientation in space

Question 2

1. The vestibular apparatus is located in the dense petrous bone posterior to the cochlea and is comprised of five sensory structures: three ___ _____ (lateral or horizontal, superior or anterior, and posterior) and two __ organs (___ and ___). As in the cochlea, the vestibular labyrinth has a bony part that is filled with ____ (high sodium ion concentration) and a membranous part that is filled with ___ (high potassium ion concentration).
2. A small endolymphatic duct extends into the cranium where fluid may diffuse through dura into CSF; a perilymphatic canal is continuous with the subarachnoid space.
3. The vestibular end organs are innervated by __ and ___ branches of the vestibular nerve.
4. Stimulation of the vestibular apparatus excites the primary ___ fibers of sensory neurons in the vestibular (___’s) ganglion.

Answer 2

1. The vestibular apparatus is located in the dense petrous bone posterior to the cochlea and is comprised of five sensory structures: three semicircular canals (lateral or horizontal, superior or anterior, and posterior) and two otolith organs (saccule and utricle). As in the cochlea, the vestibular labyrinth has a bony part that is filled with perilymph (high sodium ion concentration) and a membranous part that is filled with endolymph (high potassium ion concentration).
2. A small endolymphatic duct extends into the cranium where fluid may diffuse through dura into CSF; a perilymphatic canal is continuous with the subarachnoid space.
3. The vestibular end organs are innervated by superior and inferior branches of the vestibular nerve.
4. Stimulation of the vestibular apparatus excites the primary afferent fibers of sensory neurons in the vestibular (Scarpa’s) ganglion.

Question 3

When you move in an angular rotation, you will activate the transducers in the semi-circular canals. The semi-circular canals transduce ___ acceleration on the vestibular part of CN VIII, and the hair cells in the utricle and saccule will tranduce ___ acceleration.

There will then be primary nerve endings that will conduct the impulse back to the brain stem (____’s ganglion).

Answer 3

When you move in an angular rotation, you will activate the transducers in the semi-circular canals. The semi-circular canals transduce angular acceleration on the vestibular part of CN VIII, and the hair cells in the utricle and saccule will tranduce linear acceleration.

There will then be primary nerve endings that will conduct the impulse back to the brain stem (scarpa’s ganglion).

Question 4

1. Each semicircular canal has a swelling at the end called the ___.
2. The sensory epithelia at the base of this swelling form the __ ___
3. The ___ is a curtain-like gelatinous partition across the ampulla.
4. The hair bundle of the vestibular hair cells of the crista are embedded in the ____.
5. When the head accelerates in the plane of a canal, inertia causes the ___ in the canal to lag behind the motion of the canal.
6. Endolymph effectively moves in the opposite/same direction as the head.
7. Pressure exerted by endolymph during ___ acceleration deflects the ____ causing shearing of the__ __ of the epithelia.

Answer 4

1. Each semicircular canal has a swelling at the end called the ampulla.
2. The sensory epithelia at the base of this swelling form the crista ampullaris.
3. The cupula is a curtain-like gelatinous partition across the ampulla.
4. The hair bundle of the vestibular hair cells of the crista are embedded in the cupula.
5. When the head accelerates in the plane of a canal, inertia causes the endolymph in the canal to lag behind the motion of the canal.
6. Endolymph effectively moves in the opposite direction as the head.
7. Pressure exerted by endolymph during angular acceleration deflects the cupula causing shearing of the hair bundles of the epithelia.

Question 5

1. The hair bundle of vestibular cells is polarized There are rows of ____ of increasing height as in the cochlea.
2. Transduction of angular acceleration by the hair cells will either depolarize or hyperpolarize them depending on their orientation with respect to the direction of movement.
3. Primary afferent fibers of cells in the vestibular (____’s) ganglion up-regulate their firing rate with movement in the direction that depolarizes the hair cells and down-regulate their firing rate with movement in the direction that hyperpolarizes the hair cells.

Answer 5

1. The hair bundle of vestibular cells is polarized There are rows of stereocilia of increasing height as in the cochlea.
2. Transduction of angular acceleration by the hair cells will either depolarize or hyperpolarize them depending on their orientation with respect to the direction of movement.
3. Primary afferent fibers of cells in the vestibular (Scarpa’s) ganglion up-regulate their firing rate with movement in the direction that depolarizes the hair cells and down-regulate their firing rate with movement in the direction that hyperpolarizes the hair cells.

Question 6

1. There are 3 semicircular canals oriented in orthogonal planes: lateral (horizontal), anterior, and posterior.
2. Opposite canals on each side lie in the same plane. Each canal pair is sensitive to angular acceleration in a different direction (just like the extraocular muscles.
3. The ____ canals are activated by turning the head back and forth to say ‘no’ whereas the ___ and ___ canals are activated by movement in the vertical plane such as nodding the head up and down to say ‘yes’.

Answer 6

1. There are 3 semicircular canals oriented in orthogonal planes: lateral (horizontal), anterior, and posterior.
2. Opposite canals on each side lie in the same plane. Each canal pair is sensitive to angular acceleration in a different direction (just like the extraocular muscles.
3. The horizontal canals are activated by turning the head back and forth to say ‘no’ whereas the anterior and posterior canals are activated by movement in the vertical plane such as nodding the head up and down to say ‘yes’.

Question 7

1. The saccule and utricle are sensitive to head tilt (with respect to gravity) and linear acceleration of the head fore to aft or side to side or up-down.
2. The ___ is a region of specialized sensory epithelia within both the saccule and the utricle (which are ___ organs).
3. Vestibular hair cells within the macula have a polarized hair bundle of stereocilia (and a single kinocilium) that extends into the otolith membrane.
4. The otolith membrane is comprised of a gelatinous drape floating above the hair cells and sprinkled with otoconia (otoliths) – calcified crystals sprinkled on the gelatinous layer.
5. These otoconia provide mass that tends to remain stationary when the head moves thereby causing shearing of the hair bundles.

Answer 7

1. The saccule and utricle are sensitive to head tilt (with respect to gravity) and linear acceleration of the head fore to aft or side to side or up-down.
2. The macula is a region of specialized sensory epithelia within both the saccule and the utricle (which are otolithic organs)
3. Vestibular hair cells within the macula have a polarized hair bundle of stereocilia (and a single kinocilium) that extends into the otolith membrane.
4. The otolith membrane is comprised of a gelatinous drape floating above the hair cells and sprinkled with otoconia (otoliths) – calcified crystals sprinkled on the gelatinous layer.
5. These otoconia provide mass that tends to remain stationary when the head moves thereby causing shearing of the hair bundles.

Question 8

1. The polarized hair cells are organized systematically on the macula with respect to the macular plate so that sensitivity to all angles or positions of head tilt and linear acceleration are accounted for.
2. Movement of the otoliths or otoconia relative to the fluid in the utricle and saccule deflects the hair bundle and depolarizes or hyperpolarizes the cells.
3. The macula is oriented horizontally in the wall of the utricle and vertically in the wall of the saccule.

Answer 8

1. The polarized hair cells are organized systematically on the macula with respect to the macular plate so that sensitivity to all angles or positions of head tilt and linear acceleration are accounted for.
2. Movement of the otoliths or otoconia relative to the fluid in the utricle and saccule deflects the hair bundle and depolarizes or hyperpolarizes the cells.
3. The macula is oriented horizontally in the wall of the utricle and vertically in the wall of the saccule.

Question 9

_____ : small crystals of calcium carbonate in the saccule and utricle of the ear that under the influence of acceleration in a straight line cause stimulation of the hair cells by their movement relative to the gelatinous supporting substrate containing the embedded cilia of the hair cells—called also statoconia

Answer 9

Otoconia: small crystals of calcium carbonate in the saccule and utricle of the ear that under the influence of acceleration in a straight line cause stimulation of the hair cells by their movement relative to the gelatinous supporting substrate containing the embedded cilia of the hair cells—called also statoconia

Question 10

1. Vestibular nerve fibers from cells in ____’s ganglion project to ipsilateral vestibular nuclei. The vestibular nuclei is a complex of nuclei. After synapsing, one part goes to the cerebellum (vestibulocerebellum)…it gets a direct input from the 8th nerve.
2. Another fiber goes to synapse on the vestibular nucleus. From there, there is a commissural relay from the vestibular nuclei on one side to vestibular nuclei to the other side. These are inhibitory and can turn off the other side.
3. Given the input to vestibular nuclei on both sides the neurons of the vestibular nuclei may respond to either activation or deactivation of co-planar canals.

Answer 10

1. Vestibular nerve fibers from cells in Scarpa’s ganglion project to ipsilateral vestibular nuclei
2. Commissural relay from the vestibular nuclei on one side to vestibular nuclei on the other side are inhibitory.
3. Given the input to vestibular nuclei on both sides the neurons of the vestibular nuclei may respond to either activation or deactivation of co-planar canals.

Question 11

With an AICA and PICA stroke, you can get ___ problems because the vestibular nuclei exist in both

Answer 11

balance

Question 12

Central Vesticular Connections:

• Vestibular (Scarpa’s) ganglion gives rise to the vestibular part of CN VIII.
• All primary vestibular afferent axons in the vestibular nuclei are on the same side
• Other vestibular nerve fibers end in the ___ (flocculus and nodulus).
• Important __ input from contralateral ___ nuclei serves subtracts movement in the coplanar canal.

Outputs from vestibular nuclei

–Vestibulo-ocular reflex circuits through MLF medial longitudinal fascicle) to extraocular nuclei and gaze centers

–Vestibulospinal tracts

–Ascending vestibulo- thalamo-cortical pathway

-Many other systems (somatosensory, visual, etc.)

Answer 12

• Vestibular (Scarpa’s) ganglion gives rise to the vestibular part of CN VIII.
• All primary vestibular afferent axons in the vestibular nuclei are on the same side
• Other vestibular nerve fibers end in the vestibulocerebellum (flocculus and nodulus).
• Important inhibitory input from contralateral vestibular nuclei serves subtracts movement in the coplanar canal.

Outputs from vestibular nuclei

–Vestibulo-ocular reflex circuits through MLF to extraocular nuclei and gaze centers

–Vestibulospinal tracts

–Ascending vestibulo- thalamo-cortical pathway

-Many other systems (somatosensory, visual, etc.)

Question 13

1. Dizziness is a general symptom for which there are many causes. A true sensation of movement is better defined as vertigo.
2. Benign paroxysmal positional vertigo (Jason Day) - a sensation of head movement caused when otoconia (crystals) have dislodged from the macula and floated against the cupula of a semicircular canal.
3. ___ (halmonee) is inflammation of the membranous labyrinth in response to viral or bacterial infection. Nystagmus, tinnitus, and hearing loss may result.
4. Meniere’s and other similar vestibular disorders (hydrops) are related to excess endolymph.
5. ___ - a beating movement of the eyes and is described in the next slide.

Answer 13

1. Dizziness is a general symptom for which there are many causes. A true sensation of movement is better defined as vertigo.
2. Benign paroxysmal positional vertigo- a sensation of head movement caused when otoconia have dislodged from the macula and floated against the cupula of a semicircular canal.
3. Labyrinthitis is inflammation of the membranous labyrinth in response to viral or bacterial infection. Nystagmus, tinnitus, and hearing loss may result.
4. Meniere’s and other similar vestibular disorders (hydrops) are related to excess endolymph.
5. Nystagmus is a beating movement of the eyes and is described in the next slide.

Question 14

1. _____ test : the head is turned to one side and then the patient is laid back quickly on the exam table. This activates the posterior or lateral canal. It tests whether their damage is peripheral or central.
2. With peripheral injury, horizontal nystagmus beating to the same side (or rotary around the axis of the pupil-hard to observe I would think) is elicited with some delay. Patient may feel a sense of vertigo. Adapts in about a minute.
3. With central damage, nystagmus may be immediate, horizontal or vertical in direction, and may even change directions. See Table 12.7 in Blumenfeld text (page 493).

Answer 14

1. The Dix-Hallpike positional test (also called Bárány test – why didn’t they let those guys duke it out and come out with a winner in the contest to name the darn test). The head is turned to one side and then the patient is laid back quickly on the exam table. This activates the posterior or lateral canal.
2. With peripheral injury, horizontal nystagmus beating to the same side (or rotary around the axis of the pupil-hard to observe I would think) is elicited with some delay. Patient may feel a sense of vertigo. Adapts in about a minute.
3. With central damage, nystagmus may be immediate, horizontal or vertical in direction, and may even change directions. See Table 12.7 in Blumenfeld text (page 493).

Question 15

Explain the COWS test.

Answer 15

1.The caloric vestibular test uses warm or cool water to stimulate the canals.

COWS - cold - eyes move to opposite side of where you added water, warm - same

2. With the patient in the supine position and head slightly elevated on the exam table, warm or cool water in the ear canal causes thermal changes and movement in the endolymph toward (warm water) or away from (cool water) the ampulla of the lateral (horizontal) canal.
3. Activation of the primary afferents to the vestibular nuclei elicits the vestibulo-ocular reflex and a nystagmus generator in the reticular formation resets the eye position rapidly.
4. To remember the direction of the normal caloric test results:

• ‘warm up’ – nystagmus with slow phase toward opposite side and beating toward same side
• ‘cool down’ – nystagmus with slow phase toward same side and beating toward opposite side

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Question 16

Explain the doll’s head reflex

What does a negative doll’s head reflex indicate?

Answer 16

A negative doll’s head reflex indicates brainstem damage. It is also called: oculocephalic reflex.

a test for central nervous system brainstem damage in a comatose patient. The head is quickly rotated from side to side. Normally the eyes deviate to the opposite direction. Failure of the eyes to make the movement is an indication of severe brainstem damage..

1. In a conscious patient who has been asked to maintain visual fixation on a target, the doll’s head maneuver elicits compensatory eye movements that are driven by both the vestibular system and visual-motor tracking systems
2. In an unconscious patient the doll’s head maneuver will elicit compensatory eye movements if the canals, nerve, vestibular nuclei, and their vestibulo-ocular connections are intact (positive Doll’s head reflex).
3. However, if the brainstem is damaged in the unconscious patient the eyes will remain fixed in the head (negative Doll’s head reflex).