Touch, Smell and Taste
Cutaneous Senses
 The skin has mechanoreceptors which respond to
different stimuli:
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Pressure
Vibration
Heating
Cooling
Pain
 Three main layers
 Epidermis
 Dermis
 Subcutaneous tissue
Mechanoreceptors of the Skin
 The ion channels in the mechanoreceptors
open when the cells are stretched
 Hairy skin
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Ruffini corpuscles
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Pacinian corpuscles
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Indentation (pressure) and stretch
Rapid vibrations (texture)
Free nerve endings
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temperature changes, pain
hair movement
 Glabrous skin
 All of the above AND
 Meissner’s corpuscles
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Low freq. vibrations and taps
Merkel’s disks
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indentation
Touch
 Touch is perceived through a combination of:
 Pressure (hardness)
 Vibration (roughness)
 Kinesthetic sensation (how your muscles move as you interact
with the object)
 Sensitivity
 The mechanoreceptors in glabrous skin are much more
numerous and sensitive than the ones in hairy skin

Lab: 2 pt discrimination test
Temperature
 The skin is covered with receptors. Within 1mm of
receptors, skin responds to temp; between those
areas, skin doesn’t respond.
 We have at least 6 receptors responding to
temperature
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Each receptor responds to a specific range of temperature
between 10C and 52C
Warmth increases the sensitivity of cold receptors and
decreases the sensitivity of warm receptors and visa versa
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Lab: adaptation to different temperatures
One of the “cool” receptors also responds to menthol, which is
why “mint” flavored things give you the feeling of coolness
Pain
 Feeling pain is necessary for life
 Pain is perceived through the action of nociceptors.
 They respond to:
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Extreme temperature
Mechanical injury
Capsasin (spicy food)
Acids
 The sensation of pain is hugely influenced by other
neurological processes
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Attention
Expectation
Sense of control
Pathways to the Brain
 Sensory information from the skin travels to:
 The thalamus hypothalamus - for temperature regulation
 Somatosensory cortex
Olfaction
 Most chemicals that we respond to
have a molecular weight of 15 to 300
(will be volatile) and are fat-soluble
and organic.
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Lab: organic vs. inorganic chemicals
 The sense of smell is affected by:
 Colds
 Car accidents
 Alcoholism
 Depression
 Schizophrenia
 Our olfactory organ is located in the
upper nasal cavity where an
estimated 10 million receptors lie.
Smelling
 In the olfactory epithelium,
receptor cells have cilia
which protrude into mucus
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Support cells make mucus
Stuffy nose blocks smelling
Receptor cells are regenerated
every few months (one of only
cases in nervous system)
Smelling
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There are approximately 10,000
receptor types (each responding to a
particular chemical)
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The receptors synapse with olfactory
neurons at the glomeruli.
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The binding of the chemical causes
an action potential
Each glomerulus only receives input
from one type of receptor cell
Information is passed to the
olfactory bulb and then olfactory
cortex

Perception of unique smells is
probably due to chemicals bonding
to multiple receptors in specific
patterns
Gustation
 The sensation of taste probably developed to help us
determine which foods are safe to eat
 Taste buds can detect 5 flavors:
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Sweet (sugars) – ripe fruits
Salty (NaCl) – necessary for cellular functions
Bitter (bases) – poisons
Sour (acids) – unripe fruit
Umami (MSG) – protein/meat
 Tongue also has:
 pain receptors
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Respond to capsacin
Ability to detect fat
Taste buds
 Your tongue is covered with approx. 10,000 taste
buds.
 Inside the taste buds are up to 50 receptor cells
which have cilia projecting into a saliva-filled cavity
 When the chemical is
picked up by the cilia, the
message is passed to the
medulla, to the thalamus
and ends up in the
cerebral cortex.
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Diff tastes activate diff.
regions
Some info goes to area
governed by smell
Lab: Tasting candies
Synesthesia
 You tube video