sensory systems: touch, temperature, taste, smell
Post on 18-Jan-2018
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Sensory Systems:
• Touch, temperature, taste, smell
There
are
a variety
of touch receptors
• Touch receptors send signals to the somatosensory cortex via long axons in the spinal cord
• Signals are sent to the opposite (contralateral) side of the brain
• Wilder Penfield - Montreal Neurological Institue - 1940’s
• Found somatotopic map by stimulating brain during surgery
The
Homunculus
• Two-point discrimination threshold- How far apart do the points have to be to be perceived as two points?
Touch
Discri
mination
To Brain
Skin
Receptors
• Two-point discrimination threshold varies dramatically across the skin surface
• Where is it smallest? Where is it largest?
Touch
Discri
mination
• Two-point discrimination threshold varies dramatically across the skin surface• Where is it smallest? Where is it largest? • Best (smallest) threshold is on finger tips, tounge, and face• Worst (largest) threshold is on legs and back
Touch
Discri
mination
• Cortical representation correlates with two-point discrimination threshold
Touch
Discri
mination
• Two classes of thermoreceptors: warm and cold
Thermoception
Taste (Gustation)
Taste buds contain
chemical receptors
Taste
What are the various “tastes”?
• Multi-dimensional scaling reveals several “varieties” of tastes:
– sweet
– salt
– bitter
– sour
– umami (MSG) - protein receptor?
– fat receptor?
Taste
• What you “taste” depends critically on what you’ve recently been tasting– taste receptors adapt and reduce firing over time– for example: eating something salty reduces the perceived saltiness of subsequent foods
Taste is
Relative
• Olfactory bulb receives input from olfactory receptors which contact mucus in nasal cavity
Smell
• There are thousands of different receptors for different kinds of molecules
Smell
• Olfactory receptors use a “lock-and-key ” mechanism - only specif ic molecules will bind with a given receptor
Smell
Receptor
Odor Molecules
• Odor recognition is excellent in humans
• but odor identification (naming) is very poor
• Women tend to be (slightly) better than men at naming smells
Smell
• Smell is strongly influenced by “top-down” processes such as what you are expecting to smell
Smell
• Pheromones are not smells
• Pheromones are chemical signals sent from one animal to another
Pheromones
• Pheromones either induce a behavior in another animal or cause some physiological change
• Very common in insects...not so common in mammals...unclear role in humans
Pheromones
• For example: Alpha Androstenol, found in male pig saliva, causes a female pig to allow the male to mate with her
Fun
Facts
about
Pheremones
• Alpha androstenol is also found in the sweat of human males!
• Does alpha androstenol (or pheromones in general) affect humans?
• Design an (ethical) experiment…
Fun
Facts
about
Pheremones
• Kirk-Smith & Booth (1980) sprayed some of the seats in a dentist’s waiting room with alpha androstenol• Compared to a control condition, more women used the alpha androstenol seat
Fun
Facts
about
Pheremones
• Fewer men used the alpha androstenol seat !
Fun
Facts
about
Pheremones
• Other possible ways in which pheromones influence humans:
– synchronization of menstrual cycles
– mate selection - attraction to opposite major histocompatibility complex
Pheromones
• Pheromones do not control behavior!
• Human behavior is largely under top-down influences, but may be affected subtly by pheromones
Pheromones
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