Term
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Definition
| Conscious and unconscious sense of posture and balance by monitoring head movements |
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Term
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Definition
| Adjustment of muscular contraction to maintain posture and balance |
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Term
| Define vestibuloocular reflex |
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Definition
Adjusting eye movements so that visual target remains on retina in
response to head movements |
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Term
| What is the basic physiological mechanism for balance? |
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Definition
| For the otolith organs and the semicircular canals, movement of the cilia ultimately changes the action potential firing frequency in vestibular neurons by a mechanism similar to that in the cochlea. |
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Term
| What are the otolith organs? What are otoliths? |
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Definition
| The organs are the utricle and saccule, which contain otoliths (crystals of calcium carbonate in gel) that move against cilia. |
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Term
| What do the otolith organs detect? |
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Definition
| Linear acceleration and displacement of the head (e.g., tilting) |
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Term
| Describe cilia depolarization in the otolith organs |
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Definition
When the head changes its angle, the change in gravity cause otoliths (and the gel surrounding them) to move. This causes cilia movement, which depolarize similarly to in the auditory system
(towards kinocilium= depolarization, away kinocilium=hyperpolarization) |
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Term
| How do just two otolith organs (utricle and saccule) detect any angle tilted by the head? |
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Definition
| The macula in the utricle is arranged in the horizontal axis, and the macula in the saccule is arranged in the vertical axis. |
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Term
Describe the structure of the semicircular canals.
What is the ampulla, crista, and cupola? |
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Definition
| -Oriented 90 degrees of each other
-Filled with endolymph
-Has a bulge called the ampulla with a sheet of cells (the crista) that contains cilia
-The cilia project into gelatinous mass called the cupola |
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Term
| What do the semicircular canals detect? How? |
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Definition
Angular acceleration of the head (i.e., sudden turning movements).
The endolymph in the canals exert a force opposite to the rotation due to inertia |
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Term
| If the head rotated to the left, what would happen to the semicircular canal sterocilia? |
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Definition
In the left horizontal canal, the endolymph would bend cilia towards the kinocilium
In the right horizontal canal, the opposite would occur
(Note: there is always some afferent discharge, even at rest or inhibition) |
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Term
| Why are the horizontal semicircular canals not exactly parallel to the ground? |
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Definition
| Because most of the time when we walk we are looking at the ground, so a 30 degree angle would make more sense |
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Term
| Where are the cell bodies of vestibular bipolar cells? |
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Definition
| In the vestibular (aka Scarpa’s) ganglion, located in the internal auditory meatus |
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Term
| Describe the neural pathway of the vestibular system |
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Definition
1. Vestibular ganglion
2. Vestibulocochlear nerve (CN VIII)
3. Termination in vestibular nuclei in brainstem
4. Connection with cranial nerve eye muscle nuclei (III, IV, VI)
5. Some ascend to ventral posterial thalamic nucleus
6. Parietal (sensory) and frontal (motor) cortex |
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Term
| How does the lateral rectus (CN VI) move the eye? |
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Definition
| Laterally, toward the ear (abduction) |
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Term
| How does the medial rectus (CN III) move the eye? |
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Definition
| Medially, towards the nose (adduction) |
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Term
| How does the superior rectus (CN III) move the eye? |
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Definition
| It elevates the eye if eye is lateral, it rotates the eye inward if eye is medial |
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Term
| How does the inferior rectus (CN III) move the eye? |
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Definition
| It depresses the eye if eye is later, it rotates the eye outward if eye is medial |
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Term
| How does the superior oblique (CN IV) move the eye? |
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Definition
| It rotates the eye inward (intorsion) if eye is lateral, it depresses the eye if eye is medial |
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Term
| How does the inferior oblique (CN IV) move the eye? |
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Definition
| It rotates the eye outward (extorsion) if eye is lateral, it raises the eye if eye is medial |
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Term
| Define conjugate eye movements |
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Definition
| Eyes move in the same direction. |
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Term
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Definition
Fast movement of the eye from one fixation point to another.
If no saccades, the eye is "staring" and images will disappear because the eye is too used to it |
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Term
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Definition
| Slow movements that track a target across the visual field. |
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Term
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Definition
This combination of smooth pursuit movement and saccadic movement. The direction is defined by the rapid movement.
Ordinary, but very common in drunkenness |
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Term
| Define the vestibuloccular reflex |
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Definition
The reflex that maintains a visual image on the retina during head turning.
It does this by automatically adjusting eye position for the movement of the head.
Thus, if the head turns toward the left, the eyes will move toward the right, due to contralateral excitation/inhibition of eye muscles |
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Term
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Definition
| Illusion of movement, typically spinning |
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Term
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Definition
| Excess endolymph produces excessive force on the hair cells. Result can be deafness, tinnitus, and vertigo. |
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Term
| What often causes motion sickness? |
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Definition
| A mismatch between vestibular signals (eye thinks we're not moving, but vestibular canals say we are) |
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