The Retina

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The Retina

• Retina is a delicate tissue composed of two
  layers
• Sensory layer contains photoreceptors (rods and
  cones) that sense light
• Sensory layer consists of photoreceptors (rods
  and cones), bipolar cells, and ganglion cells
• Continuous with the optic nerve at the back of
  the eye

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Photoreceptors

• Rods
• Highly sensitive (stimulated by dim light) - good
  for night vision
• Are scattered throughout the retina, most on the
  peripheral parts of the retina (few near center
  of retina)
• Produce fuzzy images
• Light absorbing pigment is rhodopsin (made from
  vitamin A) - long term vitamin A deficiency can
  impair night vision

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Photoreceptors

• Cones
• Low sensitivity (bright light is needed for
  stimulation) - dim light does not excite cones
  (you cant see color or detail in the dark)
• Are clustered at the center of the retina (fovea
  and surrounding macula)
• Allow us to see with high visual acuity (detail)
• Three types of cones - red, green, blue
• Colorblindness results from lack of one or more
  types of cones

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Regions of the ear

• Outer ear (pinna, lobule, helix and external
  auditory canal)
• Middle ear Tympanic membrane (eardrum),
  ossicles (Malleus, Incus, Stapes), oval and round
  windows, auditory tube
• Inner ear cochlea, semicircular canals,
  vestibule

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How does hearing occur?

• Sound waves enter the external ear and vibrate
  the eardrum
• Vibrations of the tympanic membrane are
  transmitted by the ossicles to the oval window to
  the cochlea
• Fluid in the cochlea is set in motion which is
  detected by tiny hair cells on the basilar
  membrane of the cochlea which become depolarized
  and send impulses along the auditory nerve to the
  brain to be interpreted
• animation

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Hair cells damaged by loud noise
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Balance and equilibrium

• Monitored by the vestibular system (semi-circular
  canals and maculae)
• Maculae sense linear forces (nodding of the
  head)
• Semi-circular canals sense rotational forces of
  the head (spinning)
• Vestibular system sends signals to brain stem and
  cerebellum to help maintain posture and affect
  eye movements

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Smell and Taste

• Olfactory
• Olfactory neurons are depolarized by chemicals
  from the air
• We have about 12 million olfactory cells and can
  recognize about 10,000 smells

• Gustatory
• Gustatory neurons are depolarized by chemicals
  dissolved in saliva
• We have about 10,000 taste buds

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Taste (Gustation)

• We have about 10,000 taste buds on tongue,
  palate, cheek, pharynx (back of throat)
• Each taste bud has 50-100 taste cells that have
  tiny hairs projecting through the taste pore of
  the taste bud
• The hairs bind chemicals dissolved in saliva and
  impulses are sent along nerves traveling to the
  gustatory cortex (in parietal lobe)

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Papillae with taste buds
Taste bud
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Smell (Olfaction)

• We have about 12 million olfactory receptor cells
  which can recognize about 10,000 smells
• Hair-like cilia from the cells project into the
  nasal passageways, binding chemicals that are
  inhaled and dissolve in mucous surrounding the
  cilia
• Impulses are then sent along olfactory nerves
  traveling to the olfactory cortex (in temporal
  lobe) and to lower brain areas