Chapter 12 Study Questions
Vestibular Contributions to Equilibrium
1. What are the vestibular organs?
Answer: They are the set of five sense organs—three semicircular canals and two otolith organs—located in each inner ear that sense head motion and head orientation with respect to gravity.
2. What is our sense of equilibrium composed of?
Answer: It is composed of spatial orientation perception—encompassing our perception of linear motion, angular motion, and tilt—combined with reflexive vestibular responses like posture, vestibulo-autonomic reflexes, and vestibulo-ocular reflexes.
Modalities and Qualities of Spatial Orientation
3. What are the otolith organs?
Answer: They are the mechanical structures in the vestibular system that sense both linear acceleration and gravity. Each otolith organ contains an utricle, a saccule, and maculae.
4. What are the semicircular canals?
Answer: They are the three toroidal tubes in the vestibular system that sense angular motion.
5. What are the three axes of movement coded by the vestibular system?
Answer: Relative to an observer facing forward, the axes are:
x-axis: The axis of motion forward and backward
y-axis: The axis of motion leftward and rightward
z-axis: The axis of motion upward and downward
6. What are the three directions of rotation coded by the vestibular system?
Answer: Roll: rotation around the x-axis
Pitch: rotation around the y-axis
Yaw: rotation around the z-axis
The Mammalian Vestibular System
7. What do hair cells do in the vestibular system?
Answer: Hair cells support the stereocilia that transduce mechanical movement in the vestibular labyrinth into neural activity sent to the brain stem.
8. What are mechanoreceptors?
Answer: Mechanoreceptors are sensory receptors responsive to mechanical stimulation such as pressure, vibration, or movement.
9. What is a receptor potential?
Answer: It is a change in voltage of sensory receptor cells—hair cells for the vestibular system—in response to stimulation.
10. What are cristae?
Answer: Cristae are the specialized detectors of angular motion located in each semicircular canal in a swelling called the ampulla.
11. What is an utricle?
Answer: An utricle is one of the two otolith organs, and is a saclike structure that contains the utricular macula. Also called utriculus.
12. What is a saccule?
Answer: A saccule is one of the two otolith organs, and is a saclike structure that contains the saccular macula. Also called sacculus.
13. What are maculae?
Answer: Maculae are specialized detectors of linear acceleration and gravity found in each otolith organ.
14. What are otoconia?
Answer: Otoconia are tiny calcium carbonate stones in the ear that provide inertial mass for the otolith organs, enabling them to sense gravity and linear acceleration.
Spatial Orientation Perception
15. What do subjects report sensing when they are rotated in the dark (or with their eyes closed) for an extended period of time?
Answer: Subjects first feel a sense of motion consistent with their actual motion, but report feeling less and less motion over time until finally reporting no sensation of motion at all.
16. How well do subjects do at reproducing passive translations of the body experienced in the dark?
Answer: Subjects do quite well at this task. When reproducing the translations with a joystick, subjects also reproduce the velocity of the passive-motion trajectory, indicating that the brain remembers and replicates the velocity trajectory.
Sensory Integration
17. What is vection?
Answer: Vection is an illusory sense of self motion produced when one is not, in fact, moving.
18. What happens when a subject looks at a rotating display for an extended period of time?
Answer: They report an illusory sensation of tilt in the direction opposite to the rotation of the stimulus.
Reflexive Vestibular Responses
19. What is the vestibular-ocular reflex?
Answer: It is a compensatory eye movement that adjusts for changes in head position in order to keep the eye fixated on a target.
20. What is the autonomic nervous system?
Answer: It is the part of the nervous system innervating glands, heart, digestive system, etc., and is responsible for regulation of many involuntary actions.
21. What is a situation in which the autonomic nervous system interacts with the vestibular system?
Answer: A good example is motion sickness, which results from a discrepancy between visual and vestibular motion signals and results in the autonomic response of dizziness, nausea, and sometimes vomiting.
Spatial Orientation Cortex
22. What area of the cortex is exclusively devoted to processing vestibular information?
Answer: There isn’t one. There are areas of the cortex that respond to vestibular input, but they also tend to respond to visual input.
23. What area of the brain is involved in spatial orientation perception?
Answer: The multisensory temporo-parieto-insular cortex. It receives input from both the semicircular canals and the otolith organs and if it is damaged by a stroke, patients report illusory tilts and/or illusory translation.
When the Vestibular System Goes Bad
24. What is mal de debarquement syndrome?
Answer: After spending time on a boat or in the ocean, it is normal for people to feel a rocking sensation for a few hours. However, if the illusory sense of spatial disorientation, imbalance, and rocking lasts for a month or more, the person might be suffering from “disembarking sickness” or mal de debarquement syndrome.
25. Describe Ménière’s syndrome.
Answer: Patients suffering from this syndrome experience the sudden onset of dizziness, imbalance, and orientation as well as tinnitus, an illusory ringing sound. This combination of symptoms can cause patients to lose their balance or vomit, and unfortunately the symptoms can strike at any time.