Eyes and Ears Flashcards
Lens and Layers
• Lens and its layers– responsible for focusing the light that enters through the pupil onto the retina; transparent proteins fill the center
o Capsule – secreted by subcapsular epithelium; ALIVE
o Subcapsular epithelium
o Lens fibers
Sclera and Vitreous Humor
- Sclera – tough outer white part of the eye
* Vitreous humor – jelly-like substance that makes up majority of the eye
Retina Structure
– back of the eye; interprets the different light that passes through the cornea, pupil, and lens
o Nerve fibers from retina converge at the optic disk to form the optic nerve
o Interconnecting neurons – sense hyperpolarization of rods and cones and communicate the information to the ganglion neurons
Send signal to primary visual cortex of the brain in the occipital lobe
o Macula – middle of retina and contains the fovea
o Fovea – indentation as a result of lack of ganglion cell axons in the area; where light from lens is primarily focused
Where majority of rods and cones are localized
Rods and Cones General Mechanism
o Rods and cones are situated behind the optic nerve, ganglion, and interconnecting neurons
o Rod cells – interpret light and dark; black/white
Light – Na+/Ca+ ion channels are closed hyperpolarizes the cells (-75mV)
• Na+/K+ pump continues to work
NO light – Na+/Ca+ ion channels open depolarizes the cells (-45mV)
NO action potentials
o Cone cells – 3 diff. populations (red, green, blue) – each interpret different wavelength of light
Red gene is on X chromosome so guys more likely to be red color blind
Retina Mechanism in Response to Light
o Light hits rods converts 11-cis-retinal to trans-retinal activates rhodopsin
o Rhodopsin is connected to intracellular G protein replaces GDP with GTP T-alpha-GTP complex activates phosphodiesterase (PDE) which breaks down cGMP decrease in cGMP closes the Na+/Ca+ channel hyperpolarization
o Guanylyl cyclase raises intracellular cGMP concentration reopen the Na+/Ca+ channels depolarizing the cell trans-retinal is converted back to 11-cis retinal
o EXTREME LIGHT: all the cells hyperpolarize and need to undergo recover/adaptation which takes a few seconds (reason why we still see light even after we look away from the sun)
After Rods and Cones
o Send signals to horizontal cell s and then bipolar cells
o Bipolar cells transfer information to ganglion cells
o Ganglion cells generate action potentials along axons to the optic nerve
Pigmented Epithelium
– found inferior to the rod and cone cells
o Important for there to be a black background in order to stimulate a specific rod/cone
o Pigment produces melanin which causes the retina to be black and absorb light
o If epithelium wasn’t pigmented the light would be reflected back after it hit and vision would not be as accurate because more cells would be excited
Occulocutaneous albinos
– suffers from unpigmented retinal epithelium
o Vision has a lot of glare due to over activation of rod and cone cells
o Eyes are pink because light bounces off the red capillaries in the retina instead of being absorbed by the black retina
Peripheral Movement
– brain uses peripheral light receptors to notice movement; we turn our eyes to the sight of the movement to focus the image on our fovea to see it better
Hemidecasation and Visual Pathway
o Optic nerve optic chiasm lateral geniculate body of thalamus optic radiations visual cortex of the occipital lobe
o Medial portion of retina crosses over to opposite side of brain at optic chiasm
o Allows nerves from right and left field of vision to merge together allowing the brain to process the information together
o Right visual field hits medial right eye and lateral left eye and is processed on left side of brain
o Left visual field hits medial left eye and lateral right eye and is processed on right side of brain
o As you focus on something, the medial and lateral portions get more out of sync
Bitemporal hemianopia
– typically caused by pituitary tumor; damage the optic chiasm
Muscles of the Eye
– controlled by cranial nerves 3,4,6
o Medial rectus – inserts medially – CN 3
o Superior rectus – inserts superior – CN 3
o Inferior rectus – inserts inferiorly – CN 3
o Lateral rectus – inserts laterally – CN 6
o Superior oblique – pulls eye down and rotates
Runs through the trochlea (hinge/pivot)
Cranial nerve 4
o Inferior oblique – pulls eye up and rotates – CN 3
Strabismus, Diplopia, Amblyopia, Nystagmus
• Strabismus – failure to converge; can cause diplopia
• Diplopia – cross-eyed, double vision
• Amblyopia – lazy eye
• Nystagmus – alternating smooth and jerky eye movements; can be normal or pathological
o Pathological – caused by problem with vestibular system; eye will drift away and snap back
Myopia and Hyeropia
• Myopia – near sighted (cant see far); parallel rays of light are brought to a focus in front of retina
o Child may develop if they regularly read or watch TV up close
• Hyperopia – far sighted (cant see near); parallel rays of light come to a focus behind the retina in the unaccomodative eye
Simple Myopia Astigmatism, Presbyopia
• Simple myopia astigmatism - lens is not symmetrically shaped, making it difficult for light to be focused
o Vertical bundle of rays is focused on the retina; horizontal rays are focused in front of retina
• Presbyopia – involves loss of near vision due to loss of accommodation; eyes “stuck” in distance vision
o Lens doesn’t bend as well; natural position of lens is to see distance and bends in order to focus on near vision
o Occurs in older people
Leading Causes of Blindness (River blindness, cataracts, glaucoma, macula degeneration, diabetic retinopathy)
o River blindness – parasitic worms destroy retina; NOT seen in US; leading cause worldwide
o Cataracts – clouding of the lens prevents light from penetrating through; pupil is enlarged
Diabetics – this occurs more rapid
o Glaucoma – increased pressure in the anterior chamber; pushes back on lens and causes damage to optic nerve
Diagnose via pressure test
o Macula degeneration – degeneration of the macula; causes central (high acuity) blindness
o Diabetic retinopathy – increased vascular permeability and angiogenesis destroys retina
Ear Systems
o Auditory System – external, middle, & inner ear for hearing
o Vesibular system – relays information regarding balance and rotational acceleration
External Ear
o Auricle – allows sound waves to bounce off appropriately and enter the ear canal
o External auditory meatus (ear canal)
Middle Ear
o Tympanic Membrane (eardrum) – translates sound waves into mechanical forces onto the auditory ossicles – malleus (hammer), incus (anvil), & stapes (stirrup)
o Stapes – transfers vibrations onto the oval window; moves back and forth as result of interactions with other auditory ossicles and creates changes in pressure in the cochlea
Inner Ear
o Oval window creates pressure changes inside the cochlea – tube curled on itself and filled with a fluid known as perilymph; curls 2.5x and then curls back 2.5x
o One end of tube is connected to oval window and other is connected to the round window
o Fluid inside the tube cannot compress and the volume cannot change, therefore the round window vibrates along with the oval window
Hearing Mechanism
o Oval window creates standing waves throughout the cochlea
o Each wave/harmonic has a certain frequency that equates to a certain distance within the tube
o Cochlea is lined with hair cells (specialized nerve cells) that sense where the nodes of the harmonics exist (“frequency deposition” of the sound)
o Hair cells depolarize and send their signals to the temporal lobe via vestibulocochlear nerve
o Hearing can be characterized by frequency and loudness (detected through hair cells in cochlea)
Frequency – measured in Hz
Intensity (loudness) – measured on exponential scale in decibels (db)
Vestibular System
o 3 semicirucular canals filled with fluid (endolymph) each responsible for one dimension
o Saccule and Utricle – relay information regarding linear acceleration
3 Semicircular Canals and Mechanism
- filled with fluid (endolymph) each responsible for one dimension
Fluid moves in the tubes and denotes 3 dimensional orientation (pitch, roll, and yaw) and rotational acceleration
Ampulla of Semicircular ducts – at end of each tube; collection of hair cells that have stereocilia imbedded in gelatinous substance known as cupula
• Stereocilia bend due to motion
Saccule and Utricle Mechanism
– relay information regarding linear acceleration
2 otoliths – heavy and want to stay in place
During acceleration, otoliths create a backwards pull on gelatinous layer and cause stereocilia of hair cells to bend and sensory signal being sent to brain ; each curved so they each cover 1.5 dimension
Hair cells line each structure and interact with a gelatinous layer
• bent forward signal inhibition/hyperpolarization
Hair Cells and Mechanism
– specialized nerve cells
o Interpret the bending of their stereociliary as either stimulatory or inhibitory signal
More stereocilia bent = greater change in the firing rate
o Resting state – stereocilia are NOT bent; sends signals to brain at a constant rate saying they are undisturbed
o Active state – stereocilia bent towards kinocilia (largest stereocilia at the apex of the cell) results in the cell being stimulated and depolarize at a faster rate
o Active state – stereocilia bent away from kinocilia results in cell being inhibited and hyperpolarize; cells fire at slower rate
Vertigo
o Peripheral – problem with vestibular system – saccule, utricle, or semicircular canals
o Central – problem with the brain’s “balance” centers
o Eyes are able to fix any slight issues it detects with the vestibular system
o Closing their eyes leads to loss of balance, head spinning, and other symptoms of vertigo
o Symptoms: dizzy; motion sickness; balance loss; vision problems (trouble focusing, nystagmus)
o Incidence: ~5% of people report a year; 7% lifetime incidence; women 3x more likely
Audiogram
– used to test frequency and loudness
o Can hear from 20Hz – 40,000Hz
Hearing Loss
o Conductive hearing loss – problem with conduction of sound
o Sensoneural hearing loss – problem with detection of sound or brain
o Severity: 20-40db = mild; >90 db = profound
o Causes – exposure to loud noises, diseases (esp. ear infections), drugs/chemicals, genetics
o Incidence: 1 per 1000 are deaf before 18; 4 per 1000 deaf in lifetime; >10% lifetime incidence of “hard of hearing” mostly >65 yo
Prebyacusis
– sloping high-frequency hearing loss; synonymous with aging process; can hear low frequency find but can’t hear high frequency sound
Examples of Hearing Loss
o < 1000Hz = low frequency loss
o 1000-2000 Hz = mid frequency loss
o >2000 Hz = high frequency loss most common with older people
o Most speech is 300-3000Hz
Hearing Aid Syles
o Larger hearing aids are required for greater gain in order to prevent feedback
o Basically a microphone at one end and speaker at the other end
Small hearing loss can have entirely IN canal hearing aid
Large hearing loss microphone is external and speaker is deep inside ear (FARTHER apart)
