Transcript Senses

The Retina
• Retina is a delicate tissue
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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
Photoreceptors
Cones
• Low sensitivity (bright light is needed for stimulation) dim light does not excite cones (you can’t 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
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
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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
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
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Taste bud
Smell (Olfaction)
• We have about 12 million olfactory receptor
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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