Vestibular Anatomy
Where is the vestibular system located?
Labyrinth
What are the three angular movements of the head that the semicircular canals can detect?
Yaw - left/right
Pitch - nose up/down
Roll - ears up/down
What is myopia, what is it caused by, and how can it be fixed?
Near-sighted - inability to see things far away
Caused when eyeball is too long or normal aging of lens
Fixed with concave lens
What is the thick, outer white layer of the eye called and what does it do?
Sclera
Protects eye and attaches to eye muscles that move eyeball
What is the visual system?
Part of nervous system that detects photons of light (sense of sight)
Where do hair cells release ____________ to when they depolarize?
Glutamate
Vesibulocochlear nerve (C.N. VIII)
What is angular acceleration and when does it occur?
Force is applied to an object that moves about an axis
Occurs when whole body turns or head moves around neck
What is Night Blindness and what is it caused by?
Inability to see well in low-light conditions
Caused by Vitamin A deficiency (Vitamin A is an important component of rhodopsin)
What is the thin, clear layer at the front of the eye and what does it do?
Cornea
Bends 2/3 of light entering eye
What is the difference between on-center and off-center bipolar and ganglion cells when light directly hits their center photoreceptor cell?
On-center - both turns on (depolarized)
Off-center - both turned off (hyperpolarized)
What is the sensory apparatus in the ampulla of each of the semicircular canals called?
Crista Ampullaris
What do otolith organs detect?
Force of Linear Acceleration - when objects move in a line
Gravity - position of head with respect to ground
What is positional vertigo and how is it treated?
Small piece of otolithic membrane breaks off and presses against cupula
Treated with repositioning exercises so it eventually breaks down
What is the convergence ratio in the different regions of the retina? Which is better for visual acuity?
Fovea - 1:1 (better)
Peripheral retina - 1000:1
What does the dorsal stream process vs the ventral stream?
Dorsal Stream - spatial features of moving objects in visual field ("Where" pathway)
Ventral Stream - shape, color, and form of objects for recognition ("What" pathway)
What are the sterocilia embedded in?
gel called Cupula
What brain regions do the vestibular nuclei receive input from?
Cerebellum
Visual System
Muscle Spindles
CN VIII
What is Scotoma, what is it caused by, and how can location damage be predicted?
Blind spot in normal visual field
Caused by damage to optic nerve, optic chiasm, or optic tracts
Specific visual deficits can be used to predict where damage is located
What is the receptive field?
Part of body or environment where stimulus is applied that changed the activity of a neuron (excite or inhibit)
What are complex cortical cells and how is their receptive field created?
75% of cells in V1
Complex receptive field that responds to moving bars of light
Created by multiple simple cortical receptive fields overlapping
What brain regions do the vestibular nuclei project to?
Cerebellum
Cranial nerve nuclei for nerves III, IV, and VI in brainstem
Vital Centers of Medulla
Ventroposterior (VP) Thalamus
What are all the functions of the vestibular system?
Detects head position and movement
Relays signals to motor neurons to control posture and maintain balance
Relay signals to motor neurons that control eyes to aid in visual fixation during head movement
Produces sense of up vs down and where our bodies are in space
Changes respiration and circulation based on body position
What happens when excessive alcohol is consumed?
Enters cupula of crista ampullaris
Makes it denser than surrounding endolymph instead of same density
Turns crista ampullaris into otolith organ, giving spinning sensation and overcompensation of movements
What are the three cell layers of the eye and what do they do?
Photoreceptor Cells - rods and cones respond to light
Bipolar Cells - middle connecting cells
Ganglion cells - fire action potentials in response to signals from bipolar/photoreceptor cells (send electrical signals to brain)
What are the two photopigments, where are they found, what do they respond to, and what type of vision are they responsible for?
Rhodopsin - rods; all wavelengths of light; black/white (night) vision
Photopsins - three photopigments found in cones; one responds to red, one blue, and green; color (day) vision