Vestibular System

Question 1

ReviewWhy is visual acuity greater at the fovea?

Answer 1

The fovea is the focal point where the lens focuses the images. Visual acuity is greater here because there are higher amounts of cones, a 1:1 ratio (each photorecetor is associated with a single bipolar cell), and light does not have to pass through the layers of cells before reaching the photoreceptors within the fovea.

Question 2

Less diffraction of light equals…?

Answer 2

Greater visual acuity

Question 3

How does each eye contribute to depth perception and “making the picture whole”?

Answer 3

Eyes have two inputs, which cross and create depth perception. Each eye contributes a different part of the visual field.

Question 4

Where is the first level of visual processing in the brain and influences how we feel?

Answer 4

The LGN (thalamus)

Question 5

What is cortical blindness?

Answer 5

Lesions to the primary visual cortex

Question 6

What is visual agnosia?

Answer 6

Damage to more anterior cortex such as the posterior occipital and/or temporal lobes

Question 7

What are cortical receptive fields?

Answer 7

Receptive fields that respond best when the stimulus is of a certain shape with a given orientation and/or moved in a given direction.

Question 8

What is orientation selectivity?

Answer 8

This is expressed by cells within the visual cortex, when such cells increase impulse or signal activity for specific oriented degree of shape-presented within the visual field.

Question 9

What is direction selectivity?

Answer 9

When a neuron fires action potentials in response to moving bar of light

Question 10

What is parallel processing?

Answer 10

Perception combines individual identified properties of visual objects, achieved by simultaneous, parallel processing of several visual pathways.

Question 11

What is a good example of parallel processing?

Answer 11

The sound produced by an orchestra of visual areas rather than the end product of an assembly line

Question 12

What is an afterimage?

Answer 12

An afterimage is a type of optical illusion in which an image continues to appear briefly even after exposure to the actual image has ended

Question 13

What are positive afterimages?

Answer 13

Images that retain the colors of the original stimulus

Question 14

What are negative afterimages?

Answer 14

Images that have their colors in reverse

Question 15

What are conditions that favor the production of afterimages?

Answer 15

Brief exposures to intense or very bright stimuli in dark conditions, prolonged exposures to colored stimuli in well-lighted conditions

Question 16

What does the vestibular system control?

Answer 16

Balance, equilibrium, posture, head, body, eye movement

Question 17

What do the semicircular canals control?

Answer 17

Head rotation by the use of hair cells, like auditory system, to detect changes

Question 18

What is going on within the semicircular canals as the head rotates?

Answer 18

There is a push-pull activation as the fluid within the canals moves around.

Question 19

Why does disorientation happen in the clouds?

Answer 19

Vestibular and visual systems disagree.

Question 20

What do the otolith organs do?

Answer 20

Detect changes in head angle and linear acceleration (and gravity)

Question 21

If otoliths are displaced, what might happen?

Answer 21

They activate hair cells within the semicircular canals and can make it to where the patient feels extreme vertigo and their quality of life significantly decreases.

Question 22

Where are utricles placed? Where are saccules placed?

Answer 22

They are linear to measure acceleration in the horizontal plane.

On the vertical plane

Question 23

What does the vestibulo-ocular reflex do?

Answer 23

Senses rotations of head, commands compensatory movement of eyes in opposite direction and stabilizes image on retina during head movement

Question 24

What is Meniere’s Disease?

Answer 24

There is a lot of swelling in the inner ear which causes episodes of vertigo, ringing in the ears (tinnitus), feeling of fullness or pressure, fluctuating hearing loss

Question 25

There are three types of vestibular illusions. What are they?

Answer 25

The leans, inversion illusion and coriolis illusion

Question 26

What happens during “the leans”?

Answer 26

You feel as though you’re upright but you’re actually turning

Question 27

What happens during an inversion illusion?

Answer 27

Pitching down too quickly which can make you feel like you’re tumbling backwards.

Think of plane spinning in circles as it plummets towards the ground

Question 28

What happens during the coriolis illusion (most common)?

Answer 28

During prolonged turns, fluid in the semicircular canals as equalized, and there is no sense of movement. The pilot experiences an overwhelming head-over-heels tumbling sensation

Question 29

What is motion sickness?

Answer 29

A sensory conflict - a disagreement between the vestibular and visual systems

Question 30

What is intra-vestibular conflict?

Answer 30

Otolithic sensors suggest that the head is turning at a different rate than the canals

Question 31

What is the Epley maneuver?

Answer 31

Treatment of benign paroxysmal positional vertigo (BPPV) and uses gravity to relocate free floating particles from affected semicircular canal back into the utricle

relieving the patient of vertigo