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Lecture 20

PNB 2264 Lecture Notes - Lecture 20: Inner Ear, Eustachian Tube, Far-Sightedness

Physiology and Neurobiology
Course Code
PNB 2264

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Notes Day 20
Special Senses Part 2
- Size and thickness of postage stamp
- Light β†’ electrical info
- Bipolar cell, rhodopsin (pigment and protein) – retinal A
- 700 doubled membrane disks
- 500 nm is maximal absorption
Dark: light cycle
- dark β†’ 11-cis-retinal + opsin
- light β†’ 11-cis-retinal β†’ all-trans-retinal β†’ opsin changes
- activation of G protein (tansducin) β†’ close Na+ channels β†’ hyperpolarize β†’ stop
inhibitory transmitter release
- dark current
o rods/cones
Bipolar cell
- when a cone become hyperpolarized the bipolar cell has a graded potential which is
enough of a signal to activate the ganglionic cells which communicate with the brain to
say there is an image of light falling on the retina
- up or down rhodopsin in response to light
- cell to cell connections
- pupil reflex
- rate at which rhodopsin is recycled in the absence of light in order of the process t
- pupil closes to limit light hitting retina
- color vision
- greater acuity, fewer
- iodeosin pigment
o red – 560-565 nm
o green – 535-540 nm
o blue – 430-440 nm
- brightest – 555 nm (yellow green)
- millions of colors, only 3 pigments
- orange – 99% red, 42% green and 0% blue
- fovea – 35,000 cones no rods
- 120 million over rest and 6-7 million cones
Information to CNS
- rod or cone β†’ bipolar (convergence for rods) β†’ ganglion cells β†’ exit as optic nerve
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- horizontal β†’ rods and cones and bipolar cells
- amacrine β†’ bipolar and ganglion cells
Ganglionic cells
- visual processing occurs at the ganglionic cells
- on-center and off-center cells
Light β†’ rods and cones β†’ bipolar cells β†’ ganglionic cells β†’ M cells and P cells β†’ lateral
geniculate nucleus → M pathway: movement, P blob: color, P interblob: form and depth→
Primary Visual Cortex or Association areas
- rods – B/W stimulus, high sensitivity and low acuity
- Cones – color, low sensitivity, high activity
- Bipolar – visual processing begins
- Ganglion cell – optic nerve, visual processing
Depth perception
- Image to both eyes is not the same
- Difference is used to construct distance form eyes
Common problems
- Tunnel vision
o Tumor pressing an optic nerve
- Myopia and hyperopia
o Image focused in front of or behind the retina
- Presbyopia
o Loss of accommodation with age
- Astigmatism
o Malformed cornea, blurred circle
- Color blindness
o Lack of pigment
- Visual system very complex
o Light detecting cells, retina, two eyes
o Processing of information occurs in many portions of the brain
o Allows of amazing vision of rapidly moving objects, depth perception
Auditory System
- Hearing and balance
o Mechanoreceptors
- Outer, middle and inner ear
- External ear – auricle, external auditory meatus
o Sound collection
o Avascular
o Focusses sound onto a tube which focuses sound onto tympanic membrane
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