Transcript Practice Quiz for 12/3 Notes:

Anatomy and Physiology of the
Eye and Ear
Chapter 16: Nov 18 and Nov 28
Much of this material is also found in this weeks
Eye and Ear Lab manual and will be on the lab
exam #4 so examine it closely.
This lecture material will be included on the final
exam, but not on Monday Nov 21 unit test.
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.
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.
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.
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
High acuity
Fovea centralis
Lots of cones
vs.
vs
vs.
Night vision
High Sensitivity
Peripheral vision
vs.
Lots of rods
• Optic Disc is your blind spot: location of optic nerve exit!
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.
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
Trans-retinol is formed is formed in the light and leads to the
breakdown of cyclic GMP.
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.
Light causes the ganglion cells to send APs to the brain. Why
may “seeing a blue-green haze” be a Viagra side effect?
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?
Six extrinsic muscles determine where you look.
What are the muscles and how are they controlled?
Occular Muscle Innervation: LR6+SO4= three
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!
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)
How do eye glasses move the focal point of an image?
Nearsightedness (myopia): close objects seen clearly, objects farther appear blurred
Farsightedness (hyperopia): distant objects seen clearly, close ones do not focus.
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
The outer ears (auricles or pinnae)!
• 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 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.
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 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.
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).
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
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!
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
There are 3 semicircular canals that detect dynamic
motion (acceleration and deceleration) across three
different planes of the body!
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!
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
The utricle and saccule detect whether changes in
position are maintained in a stationary manner (no
inertia) for longer periods of time. Static Equilibrium
• 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 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?
10 point Review Assignment Final Exam Summary
Due in class Wednesday Nov 30th
• The comprehensive final is based on the materials in the three
prior lecture units.
• Lab materials will not be on the lecture final unless the
information was also presented in lecture.
• Review your notes to prepare for the final exam, the
comprehensive exam is based on what is in the notes, not the
practice exam.
• For each unit (see syllabus) provide a sheet of paper (sheets)
with 50 specific things (#1-#50 X 3 = 150 items) that you
learned in Anatomy and Physiology 211 (handwritten). Be
sure each item consists of a sentence with at least 10 words.
Photocopy this review before handing it in if you want to use it
as a review study guide.
• STAPLE the sheets together when you hand it in (no
paperclips, dog-ears, bubble gum).