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
