Anatomy and Physiology of the Eye and Ear Chapter 16: 1120 and 1130 - PowerPoint PPT Presentation

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Anatomy and Physiology of the Eye and Ear Chapter 16: 1120 and 1130

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Color vision vs. Night vision. High acuity vs High Sensitivity. Fovea centralis vs. Peripheral vision. Lots of cones vs. Lots of rods ... – PowerPoint PPT presentation

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Title: Anatomy and Physiology of the Eye and Ear Chapter 16: 1120 and 1130


1
Anatomy and Physiology of the Eye and Ear
Chapter 16 11/20 and 11/30
  • Much of this material will also be fair game on
    the lab exam so examine it closely.
  • This material will be included on the final exam,
    not on lecture exam 3 (Mon 23 of Thanksgiving)

2
Lab Exam 3
  • Muscle Physiology Computer Program and a bit of
    Muscle Histology
  • Brain/Spinal Cord
  • Eye/Ear
  • 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.

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.
6
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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
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.

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 endolymph 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 and
    utricle and agitate hair cells.
  • APs sent to CNS in new fashion based on new
    position of haircells/otoliths

18
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)

19
The middle ear is an air filled cavity that
functions to convert sound into motions in the
MalleusgtIncusgtStepes 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
    infectionPressure 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.

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
23
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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 frequencyvibrations 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 ears
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
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!

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
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?

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?
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