Download Rods vs Cones

3/10/2014
Example 1: Light Sensitive Visual
Receptors
• The “typical” neuron is designed to receive
neurotransmitter messages from other
neurons.
• Sensory receptors, on the other hand, are
specialized to receive sensory input from the
outside world.
• Specialized to response to light waves, a form
of electromagnetic energy
Book Fig. 6.5 & 6.8
(Book Fig. 6.7)
(Billionths of a meter)
Light waves are a small range of wavelengths
(~350-750 nanometers) of electromagnetic energy.
Turning Light Waves Into Electrical
Messages (Transduction)
Rods & cones have molecules of light sensitive
photopigments (11-cis-retinal+an opsin) embedded in
cell membrane.
Rods – rhodopsin
Cones – 1 of 3 iodopsins
Like the G-proteins of some
neurotransmitter receptors, except they receive light!
Absorption of light triggers change in protein releasing
second messenger inside the cell.
Rods
• ~120 million/eye
• more in periphery
• very sensitive (low
threshold)
• ~100 rods share same
optic nerve fiber to
brain
• night vision (scotopic
vision)
vs Cones
• ~6 million/eye
• most in center,
especially in the fovea
• Need bright light to
reach threshold
(photopic vision)
• have 1-to-1 lines to
brain- good for detail
vision or “acuity”
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Example 2
• Olfactory receptors are metabotropic
receptors activated by molecules of odorants.
Olfactory Nerves
Book Fig. 7-21
Book Fig. 7-19
Olfactory Receptors
G-protein type
receptors on cilia.
100’s of different
types of olfactory
receptors. In the rat
1% of its genome is
devoted to making
these receptors. In
humans at least
350-400 such
genes.
Examples 3 and 4
• Hair cells in the auditory and vestibular
systems open ion channels
Cilia are dendrites
dangling down from
your nasal membranes
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Book Fig. 7.2
Cross section of Cochlea
Organ of Corti
Book Fig. 7.2
http://www.youtube.com/watch?v=8wgfowbbTz0
Tectorial Membrane
Auditory Nerve fibers
Basilar Membrane
Basilar Membrane
http://www.youtube.com/watch?v=8wgfowbbTz0
Friction on tips of hair cells opens
mechanically-gated K+ ion channels
K+ enters hair cells causing depolarization & transmitter release!
(fluid in cochlea has a different ion balance – disruption of that
balance can lead to hearing abnormal sounds (tinnitus))
Fluid Waves Traveling Thru Cochlea Cause
Basilar Membrane Movement
Georg von Bekesy – 1961 Nobel Prize for his research on the traveling
waves in the cochlea. Where the wave peaks varies with pitch.
http://www.youtube.com/watch?v=dyenMluFaUw&feature=related
http://www.youtube.com/watch?v=WO84KJyH5k8&feature=related
Book Fig. 7.10
Book Fig. 7.2
The Outer, Middle & Inner Ear
Semicircular Canals
Sense rotation
(forward/back)
Sense linear movement
(up& down)
http://www.youtube.com/watch?v=BbKU0AbbARg
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Vestibular System
• Senses movement/position
of head (and body)
• Uses that input to :
– Connect to cerebellum - help
maintain balance
– Control eye movements
when head moves
http://www.youtube.com/watch?v=
BbKU0AbbARg&feature=related
Rocks in Your Head
(in your otolith organs)
Saccule
Fluid imbalances in
vestibular system can
cause Meniere’s
Disease- extreme
dizziness, nausea,
dysequilibrium,
difficulty moving and
impaired hearing.
Utricle
Example 5
Taste
• Our taste system has both ionotropic and
metabotropic receptors.
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Book Fig. 7.18
Fungiform Papillae
on the front of tongue)
these don’t have taste buds so
center of your tongue can’t taste
Book Fig. 7.18
Tste Buds Along Sides of Papilla
Book Fig. 7.18
Tastes Buds on Sides of Papillae
(Other papillae may have a taste bud on the top)
Taste Bud
Taste Bud
With cilia
• Many receptors in a bud
• Specialized skin cells replaced every
10-14 days
• But have excitable membranes and
release transmitter like neurons
• Receptors sensitive to salty, sour,
sweet, bitter & “umami”
• Salty opens Na+ channels,
• The hydrogen in acid (sour) closes
normally open K+ channels &
opens Na+ channels in sour
receptors.
• The others activate G proteins (like
metabotropic receptors)
• Certain chemicals can alter one
type of receptor changing your
experience of that taste
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