Exam 3 Flashcards
(49 cards)
Parts of the vestibular system (5 sense organs in the inner ear)
3 Semicircular canals
-Anterior, Posterior, Horizontal
2 Otolith organs
-Saccule, Utricle
What is the movement and the semicircular canals responsible for Pitch
=nodding your head “yes”
-Anterior and Posterior canal
What is the movement and the semicircular canals responsible for Yaw
=shaking your head “no”
-Horizontal canal
What is the movement and the semicircular canals responsible for Roll
=touching your ear to your shoulders
-Anterior and Posterior canal
How do semicircular canals transduce head movement into a neural signal?
Firing rates increase or decrease depending on the AMPLITUDE of the rotation and the DIRECTION
-Amplitude coding
-Direction Coding
Amplitude Coding
(Semicircular canals)
= each pair of semicircular canals works in a push-pull arrangement
□ Movement in one direction increase the rate of firing on one side by hyperpolarizes the other
Direction Coding
(Semicircular canals)
= each semicircular canal transduces the component of head acceleration perpendicular to its plane
-the brain combines these signals to sense direction
Amplitude Coding
(Otolith organs)
= when larger accelerations move the otoconia more, leading to greater deflection of the hair cells and larger neural signals
-Size of accelerations = size of neural signals
□ Populations of hair cells on each macula have their stereocilia organized in different directions
□ This causes hair cells in one region of the utricle macula to be sensitive to forward/ backward acceleration and hair cells in another region to be sensitive to side-to-side acceleration (same is true for saccule and vertical acceleration)
Direction Coding
(Otolith organs)
= occurs from the orientation of the otoliths
-Saccule
-Utricle
□ Populations of hair cells on each macula have their stereocilia organized in different directions
□ This causes hair cells in one region of the utricle macula to be sensitive to forward/ backward acceleration and hair cells in another region to be sensitive to side-to-side acceleration (same is true for saccule and vertical acceleration)
What is the function of the Saccule?
= vertical
ex: riding in an elevator, jumping up and down in a potato sac race
What is the function of the Utricle?
= horizontal
ex: accelerating in a car
Bar stool illusion
- When rotating at a constant velocity there is little or no hair cell movement, because endolymph and cupula are moving together
- When you stop the cupula stops moving quickly but the endolymph has a momentum- deflecting the hair cells in the opposite direction
Visual-Vestibular Integration
= self-motion perception requires a combination of visual and vestibular signals (and maybe somatosensory and proprioceptive cues)
□ Vestibular system can put the brakes on visually induced vection (perception of self-movement)
□ The Vestibular system can also trick the visual system with deadly consequences- somatogravic illusion
Somatogravic illusion
= rapid forward acceleration makes you feel like you-re pitching up, compelling you to lower the aircraft’s nose
What is the Vestibulo-ocular reflex?
=allows eye rotations that help compensate for angular rotations of the head
-Eyes counter rotate in response to head motion sensed by vestibular system
-ex: ability to read a road sign while driving
What brain regions are involved in the Vestibulo-ocular reflex?
Pons (Afferent neurons carry information to the abducens nucleus
-> Vestibular nuclei
-> Midbrain (oculomotor nuclei)
Vestibulo-spinal response
= a family of reflexes that adjust for correct body posture when the ground shifts
□ Vestibular system synapses on vestibular nuclei, where the primary afferent neurons synapse on descending interneurons that carry information through the lateral and medial vestibulo-spinal tracts
□ Interneurons which synapse on motor efferent neurons
□ Motor efferent neurons activate muscles that control balance
□ How far these neurons carry information down the spinal
What brain regions are involved in the Vestibulo-spinal reflex?
Vestibular afferent neurons
-> one of the vestibular nuclei (some project to the cerebellum)
-> carry information via vestibulo-spinal tracts downward through the brainstem and spinal cord
-> until synapse on efferent neurons that activate the muscles that control balance
Why isn’t their a vestibular cortex?
Hypothesis/theory that the information is not useful in other things and gets integrated with other things rather than being useful enough to be on its own
What are the 5 Vestibular problems mentioned in class?
-BPPV (Benign Paraoxysmal Positional Vertigo)
-Acoustic Neuroma
-Meniere’s Syndrome
-Motion Sickness
-Mal de Debarquement Syndrome
What is the cause of BPPV (Benign Paraoxysmal Positional Vertigo)?
□ Caused when otoconia become dislodged from the utricle and migrate to the semicircular canals
-These otoconia interfere with normal fluid motion and send false signals to the brain
□ Most common cause of vertigo (false sense of spinning)
What is the cause of Acoustic Neuroma?
□ Nonmalignant tumor that develops on the vestibulo-cochlear nerve
□ When a tumor develops on the vestibular cochlear nerve
□ As it grows it compresses / damages the nerve causing hearing loss, tinnituss, dizziness or loss of balance
What is the cause of Meniere’s Syndrome?
= people who have dizziness so severe that they have to sit down
□ Afflicts 1/500 people and occurs in mid-adulthood
□ Exact cause is unknown. But may be due to an abnormally large amount of endolymph in the inner ear
What is the cause of Motion Sickness?
□ Usually caused by a disagreement between the motion and orientation signals provided by the semicircular canals and vision (argument between the systems)
□ ex: being below on a ship, the rocking stimulates the semicircular canals but there is no change in the relative motion (since you and the boat are both moving)
