The Senses
The Olfactory and
Optical/Visual Senses
(Smell and Sight)
General Senses:
• Temperature
• Pain
• Touch
• Pressure
• Vibration
• Proprioception (body position)
– The receptors for these senses are distributed
throughout the body
Special Senses
• Olfaction
• Gustation (taste)
• Vision
• Equilibrium (balance)
• Hearing
– These receptors are located within specific
structures
Sensory Receptors
• Specialized cells that, when stimulated, sends a
sensation to the CNS
– Simple receptors are free nerve endings
– Complex receptors are specialized to respond to
only specific stimuli
Sensory Information
• Relayed by action potentials traveling through
sensory fibers (collection of axons)
• Increase stimulus = Increase frequency of
action potentials
– Interpreted by the CNS depending on the area of
the brain that is stimulated
Adaptation
• A reduction in sensitivity in the presence of a
constant stimulus
– Due to changes in receptor sensitivity or inhibition
along the sensory pathway
Olfaction
• Location:
– Nasal cavity on either side of the nasal septum
– Inferior to the cribiform plate of the ethoid bone
• Structure:
– Olfactory epithelium
•Olfactory receptors (neurons sensitive to chemicals)
•Supporting cells
•Basal stem cells
Olfactory Glands
• Secrete mucus to prevent a build-up of
dangerous or overpowering stimuli
• Also keeps the area moist and free of debris
Receptors
• Highly modified neurons with elongated cilia
(between 10-20 million receptors in an area 5
sq. cm)
• Canines have 72 times greater surface area than
humans in their olfactory organs = better
smellers
Olfactory Pathway
• Axons penetrate the cribiform plate
• Trigger the olfactory bulbs
• Travel along the olfactory tract
• Reach the olfactory cortex of the cerebrum
• Also affect the hypothalamus and parts of the
limbic system
How “smell” works
Fun Fact
• Olfactory stimuli is the only sensory
information to reach the cerebral cortex without
first synapsing in the thalamus. The
connections to the limbic system and the
hypothalamus help explain the emotional and
behavioral responses triggered by smells.
Visual (the eye)
The Retina
• The neural tunic: contains several layers of cells,
the outermost layer contains the photoreceptors
– Photoreceptors: detect photons of light…humans
only sensitive to the spectrum of visible light
Rods
• Do not discriminate color…only provide the
CNS with info about the presence or absence of
photons
• Very light sensitive and enable us to see in dim
light (enhanced in most animals)
• Located around the sides of the retina (approx.
12 million)
Cones
• Color vision- provides info about the wavelength of
photons
• Three types: red, blue, green- in different
combinations provide the perception of different
colors
– Color blindness= one ore more classes of cones are absent
or not functioning
• Located in the macula lutea with the highest
concentration in fovea – when you look directly at an
object this is where the image falls on the retina
Bipolar Cells
• Cells that synapse with the rods and cones
(roughly 6 million)
Ganglion Cells
•Synapse with the bipolar cells and relay
information to the brain
Horizontal and Amacrine Cells
• Regulate communication between
photoreceptors and ganglion cells, adjust
sensitivity of the retina by sending inhibitory or
excitatory signals
Optic Disc
• The origin of the optic
nerve, next to the fovea,
also has blood vessels
and lacks
photoreceptors
– The blind spot
Lens and Visual Accommodation
• Accommodation- focusing the image on the
retina by changing the shape of the lens
– Rounder = focuses the image of a nearby object
– Flatter = focuses a distant object
Accommodation Problems
• Astigmatism:
– irregularities in the shape of the lens or cornea
• Myopia:
– “near-sightedness”; the eye is too deep so images
focus in front of the retina
•Corrected by a diverging lens
• Hyperopia:
– “Farsightedness”; The eye is too shallow so images
focus past the retina
•Corrected with a converging lens
Masters of Illusion
Focus on the dot and move your head
side to side or forward to back…
How many legs does the elephant have?
Stare at the black dot and watch the haze disappear…
Shapes that don’t exist
The Kaniza Effect
What do you see?
The Impossible Trident
Straight or Crooked?
Count the Black Dots
Circles or Spirals?
Crooked or Straight?
Optical Illusions in Shapes
Floating Sphere?
Make ‘em stop spinning!!
Image Credits
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http://waynesword.palomar.edu/images/blckdots.jpg
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http://www.is.svitonline.com/malinman/optic/spirkrug.gif
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http://www.sapdesignguild.org/resources/optical_illusions/images/couple.gif
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http://waynesword.palomar.edu/images/lines.jpg
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http://www.eyesearch.com/optical.vase.gif
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http://www.sackville.ednet.ns.ca/art/gallery/exhibit/draw/Escher,M.C.-Relativity-1953.jpg
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http://www.math.technion.ac.il/~rl/M.C.Escher/2/escher-hands.gif
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http://www.cbu.edu/~jvarrian/252/eye.gif
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http://www.city.ac.uk/colourgroup/spectrum.gif
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http://medweb2.bham.ac.uk/image_database/bain/images/229339c.jpg
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http://www.eyesearch.com/astigmatism.jpg
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http://www.whiteeye.net/images/myopia.jpg
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http://www.colorado.edu/epob/epob1220lynch/image/figure6n.jpg
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http://www.rktekt.com/ck/im/FineArt/eye.jpg
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http://mathworld.wolfram.com/gifs/ouchi.gif
http://www.aetheronline.com/mario/images/Favourite%20Images/Optical%20Illusions/14_jpg.jpg
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http://www.mercola.com/2003/sep/27/illusion4.gif
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http://members.cox.net/mystic-warrior/mag2.jpg