Module 8 Flashcards
light pathway
• First refracted by lens and cornea
• Focused onto the retina
• Once light has been converted to an electrical impulse by retina neurons, the signal exits the eye via the OPTIC NERVE
o No photoreceptors=BLIND SPOT
Accommodation
• Lens contributes to the ability to focus on both near and distant objects
o Distant objects: LENS IS FLAT
o Near objects: CILIARY MUSCLES BEND AND ROUND OUT THE LENS
emmetropia
- Light focuses directly on retina
* 20/20 vision
myopia
- light is focused just short of the retina bc of mis-shaped lens or eyeball
- near sighted
- Cornea: imperfect curvature
- Eyeball is too long
- Need bi-concave lens
hyperopia
- far sighted
- light is focused just behind the retina
- lens accommodation is too thin
- cornea: imperfect curvature
- eyeball is too short
- need bi-convex lens
retina
• neural portion of the eye
two types of photoreceptors
- rods and cones
* sensitive to light
rods
o activated when light levels are low
o if one loses rod function=night blindness
cones
o activated when light levels are high
o contribute to color vision
o loss of cone function: legally blind
o 3 different types which respond to different colors (red, blue, green); lacking=colorblindness
astigmatism test
- All lines equally dark=no astigmatism
* Opposite=astigmatism
color blindness test
- Ishihara plates
- Each plate consists of colored spots and concealed number or shape
- Say what each plate has
- Depending on the amount of correct=determines colorblindness
auditory system
converts pressure waves (sound) into a neural signal
Pathway of auditory system
• Sound first reaches the external ear and enters the external auditory canal
• Vibrations then travel to the tympanic membrane which vibrates
o Attached are three auditory ossicles
• Malleus
• Incus
• Stapes
• These three exert a force onto the oval window
• Oval window transmits the sound to the inner ear
cochlea
inner ear
o Most critical structure for hearing
o Movement of oval window causes movement for cochlea fluid (action potentials are generated
if a person has hearing loss
one can determine if the cause is related to bony transmission or neural deficits by applying a vibrating tuning fork to the skull
conduction deafness
o If a patient can hear the tuning fork, the neural structures are intact
nerve deafness
o If individual cannot hear anything when the tuning forks are against the sku
Weber test
- Strike a tuning fork against the heel of a hand
- Place stem of fork in the middle of subject’s forehead
- If sound is more loudly heard in one ear, conduction deafness or nerve deafness is present in one of the subject’s ears
rinne Test
- Determines if deafness is nerve or conduction related
- Plug one ear with an ear plug
- Place fork directly on mastoid process (bump of bone behind ear) until sound is no longer heard
- Then place tuning fork just outside the ear
- If sound cant be heard, patient may have conduction deafness
olfaction
o Begins in the epithelial tissue
o Olfactory receptor neurons convert the chemical signals into neural impulses
• When an odorant molecule binds to a specific olfactory receptor, it activates that receptor and results in an action potential
Each receptor is specific to a type of odorant
olfactory fatigue
olfactory receptors adapt quickly to odo
