Anatomy and Physiology of the Eye and Ear Chapter 16: 11/18 and 11/28

1. Anatomy and Physiology of the Eye and Ear Chapter 16: 11/18 and 11/28 Much of this material is also found in this weeks Eye and Ear Lab manual and will be on the lab exam so examine it closely. This lecture material will be included on the final exam, not on lecture exam #3 (Mon 21 of Thanksgiving)

2. Lab Exam #3 and AP211 • Blue Card Registration Trouble  If you took AP 211 this Fall and received a “C” or better you WILL get in next Spring, no problems. Just see us in January and we will write up a blue card for you. • Lab Exam#4: Wed 11/30 and 12/1 • Signup sheets go up Monday 11/21 • Eye and Ear Lab • Brain and Nervous System Lab

3. How does the eye detect light and how does the brain interpret what you see? • Part I: How does image get to retina? • 1) Light Quality: intensity and wavelength • 2) Lens and light refraction/ focusing: • 3) Light refraction in aqueous/vitreous humor: • 4) Inverted light (photons) reach the retina after passing through different cell structures! • 5) Light reaches rod and cone cells at back • 6) Pigmented epithelium of choriod absorbs extra light to prevent reflection back int orods/cones and blurring.

4. How does the eye detect light and how does the brain interpret what you see? • Part II: How does the brain detect image/APs? • 1) Light hits one of two pigments: rhodopsin on rods OR iodopsin on cones. • 2) Light changes molecular shape and enzyme function. • 3) Modified function modifies Action Potential output! • 4) Action potentials sent from ganglion cells to optic nerves to brain via optic nerve! • 5) Primary visual center in occipital lobe receives modified train of action potentials • 6) Association areas interpret action potentials.

5. Blood vessels and nerves run across the surface, with the photodetector cells (rods and cones) at the back of the retina! Photons of light pass through several structures before reaching the photodetectors. Light modifies the way detector cells send APs to the brain via the optic nerve.

8. Our eye has to regulate the amount of light reaching the retina for protection. Our eye also has to modify the lens shape to focus the image. Both of these activities are involuntary! Ciliary muscles and suspensory ligaments: modify lens shape and help to focus the inverted image on the retina. VS. Pupillary muscles and iris: modifies pupil diameter and light access to retina to protect in strong light and help in dim light. Color vision vs. Night vision High acuity vs High Sensitivity Fovea centralis vs. Peripheral vision Lots of cones vs. Lots of rods • Optic Disc is your blind spot: location of optic nerve exit!

9. We need a flat lens to bring an inverted image of a distant object into focus on the retina. Lens accomodation allows us to look at objects that are close. The suspensory ligament and ciliary muscles have a natural tension that pulls them tight towards the margin of the retina. Constriction of the ciliary muscles draws these structures away from the edge of the retina, relaxing the suspensory ligaments which lets the elastic lens become round for near vision.

10. Visual projection can be easily understood by looking at the effects of lesions on images from lateral and nasal fields. Consider cutting the tracts at the above “letter” locations! What would you see? “DARK” means loss of image

11. DARK: cGMP opens Na+ channels and DEpolarizes rod/cone membrane and inhibitory glutamate is released to bipolar cell. DARK: Bipolar cell is hyperpolarized by glutamate (turned off) LIGHT: trans-retinol is created and leads to cGMP destruction. Na+ entry stopsHYPERpolarization LIGHT: Bipolar cell not inhibited, so it sends EPSPs to ganglion cell LIGHT: Ganglion cell sends APs into optic nerve. Trans-retinol is formed is formed in the light and leads to the breakdown of cyclic GMP.

12. Light causes the ganglion cells to send APs to the brain. Why may “seeing a blue-green haze” be a Viagra side effect?

13. Why do rods give better sensitivity? Why do cones give better acuity?Consider the number of rods/cones per ganglion cell (AP output to brain) Why do cones let you see the best fine detail (fovea centralis) and why do rods let you see faint stars in the night with peripheral vision?

14. Six extrinsic muscles determine where you look.What are the muscles and how are they controlled? Voluntary Ability to track objects with the eye: Lateral Rectus: Abduction- Abducens Nerve VI Medial Rectus: Adduction- Occulomotor Nerve III Superior Rectus: Elevation- Occulomotor Nerve III Inferior Rectus: Depression- Occulomotor Nerve III Superior Oblique: Depression/Rotation-Trochlear Nerve IV Note unique pulley system of trochelear trochlea Inferior Oblique: Elevation/Rotation- Occulomotor Nerve III Remember to contrast these activities with the involuntary activity of Ciliary and Pupillary muscles!

15. What are some common diseases of the eye? Myopia (nearsightedness)-image IN FRONT OF retina Hyperopia (farsightedness)-image BEHIND retina Astigmatism (non-uniform lens shape)-non uniform image Effect of stroke- effect in tracts and areas Glaucoma-elevated occular pressure and reduced blood supply to retina Cataracts- precipitate occurs inside lens that causes cloudiness: UV light, smoking, and/or diabetes Detached Retina- most retinal blood supply from choroid, detachment causes ischemia/infarct Macular Degeneration- oxidative or UV injury to the macula densa (fovea centralis)

16. How do eye glasses move the focal point of an image?

17. Our sense of hearing and equilibrium is dependent on displacements of a fluid called endolymph and hair cells to detect the movement. Hearing Basics: • Sounds is directed to the tympanic membrane and converted to displacements of perilymph (in Scala Vest. and Scala Tympani) and then endolymph (in Cochlear Duct) by the Stapes • Endolymph displacements occur at a frequency specific locations in the cochlea • Localized displacements create site specific action potentials in hair cells of Organ of Corti that travel to CNS in vestibulocochlear nerve • APs delivered to thalamus and primary auditory cortex Equilibrium (Balance) Basics: • Endolymph movement in semicircular canals agitates hair cells in ampulla • Otolith crystals shift position in saccule/utricle and agitate hair cells. • APs sent to CNS in new fashion based on new position of haircells/otoliths

18. Supported by elastic hyalin cartilage! Poor blood flow if cold! Function is to focus and magnify sound into the external auditory meatus and ear drum (tympanic membrane) Turn the pinnae at a slightly skewed angle to help improve your ability to localize the source of sounds. (Curious Dog Effect) The outer ears (auricles or pinnae)!

19. Tympanum covers an air cavity behind it is the middle ear! Muscles: Stapedius/TensorTympani Muscles help sensitive ear! Obstruction of Eustacian Tube: Ear infection=Pressure Changes Oval Window vs Round Window O.W. of cochlea is where sound is converted to perilymphatic and endolymphatic vibrations! What is pushed in at OW, must have a place to be pushed out at the Round Window. The middle ear is an air filled cavity that functions to convert sound into motions in the Malleus>Incus>Stepes and finally into vibrations of the oval window of the cochlea.

20. The stapes compresses the fluids of the cochlea. It is within the cochlea that mechanosensitive hair cells can be found. The cochlea is wound up into a snail-like structure so it can fit in the skull! Action potentials exit cochlea via the vestibulocochlear (auditory) nerve.

21. Stapes creates compressions of the scala vestibula that are transmitted down the length of the cochlea, with low frequency sounds passing the longest distance. Compressions resonate at specific cochlear locations on organ of corti/tectorial membrane. These motions agitate site-specific hair cells that change the way they send action potentials to indicate that motion is occurring (hearing).

22. How does the shearing motion of the tectorial membrane across hair cells on the organ of corti change their membrane potentials? Remember endolymph has tons of extracellular potassium (K+)!↑Number of Hair cells agitated  ↑Sound Amplitude

24. How do we measure sound qualities? • Loudness: Amplitude in units called Decibeles 0 dB-threshold of sound Each 10 dB step is X10 greater loudness You feel pain at 120 dB You can damage the ear at 90 dB • Pitch is a term for sound frequency that is measured in units called Hertz (Hz) • Infrasonic: low frequency=vibrations in the body • Ultrasonic: high frequency heard by a dog • Repetitive sound exposure and tone deafness is a huge problem in the work place and the legal system!

25. Our sense of balance comes from the inner ear’s vestibular apparatus and changes in the motion of fluids and or otoliths. What are the primary structures for our sense of motion, balance and equilibrium? 1)Semicircular canals/ampulla, 2)Utricle and 3)Saccule

26. What is dynamic motion? What is static condition? Crista ampularis and cupula 1) Endolymph and bone of skull move at different rates, resulting in de/acceleration and currents in canals. 2) Currents bend hair cell streocilia! 3) Membrane permeability changes! 4) Action potentials are sent to vestibulocochlear nerve! APs stop when accel/decel of fluid/body stops! There are 3 semicircular canals that detect dynamic motion (acceleration and deceleration) across three different planes of the body!

27. Inertia created during acceleration/decceleration causes the fluid to move in/through the semicircular canals along the angles of motion that are experienced. Dynamic Motion

28. Detection of Static changes in body orientation! Utricle sits on top! And the Saccule on bottom! Macula (U or S) is sensitive site where hair cells are located! The Trick: Contains crystals of otolith Gravity pulls them down Otolith touches hair cells Tickle changes AP output Why are long-time bed ridden people often unable to walk at first when they leave the bed? The utricle and saccule detect whether changes in position are maintained in a stationary manner (no inertia) for longer periods of time. Static Equilibrium

29. The confusing nature of the fluids of the ear! • Perilymph: nonsensory Fills spaces between semicircular canals/bone Fills scala vestibuli and tympani • Endolymph: in contact with sensory cells Fills cochlear duct Fills semicircular canals Fills utricle and saccule • A loss of fluid in these cavities causes a loss in hearing and/or balance! • Why do we become delirious and stumble when dying of dehydration in the desert?