Sensory Receptor Organs Detect Energy or Substances
• Sensory receptor organs are organs specialized to detect a
certain stimulus.
• Receptor cells within the organ convert the stimulus into an
electrical signal a “transduction” process.
• Receptor organs are very diverse because they specialize in
detecting different types of stimuli in the environment.
• An adequate stimulus is the type of stimulus to which a
sensory organ is particularly adapted.
• photic (light) energy for the eye
• mechanical energy for touch
The Variety of Eyes
Classification based on type of information detected by specialized
sensory receptors each of which has an adequate stimulus type.
Do You Hear What I Hear?
Evolutionary influence on auditory perception.
What do bees see?
Regular photograph
Photograph with Ultraviolet filter
to simulate bee vision
Different types of sensory information comes in on different pathways
the so called “Labeled Lines” concept.
Receptors in Skin are Transducers
They can change mechanical energy into action potentinals.
The Structure and Function of the Pacinian Corpuscle as an example of
transduction of mechanical to action potentials
Intensity Coding correlated to amount “intensity” of stimulus detected by
the receptors measured by frequency of action potentials.
Sensory Adaptation occurs even with constant stimulation so frequency of action
potentials decreases after an initial high frequency at the onset of the stimulus.
Sensory information is processed through several levels of Sensory Circuits
Somatosensory Receptive Field is the area on the skin with receptors that send
touch information to particular neurons in the somatosensory cortex.
Representation of the Body Surface in Somatosensory Cortex
The Chemical Senses: Taste and Smell
• The Human Tongue Discriminates at least
Five Basic Tastes
• salty, sour, sweet, bitter, umami and maybe
• Taste receptor cells are located within taste
buds on papillae on the tongue.
• Taste cells extend cilia into the taste pore
to contact tastants.
• Chemicals in the Air Elicit Odor Sensations
• Flavor is the perception of taste and smell
together.
Figure 9.22 A Taste Bud and Taste Receptor Cells
Figure 9.21 A Cross Section of the Tongue
Salty and Sour Transduction
Maybe TRPV1
May require PKD2L1
ion channel
Sweet and Bitter Transduction
T1R2 + T1R3
T2R
30 different types
It’s All a Matter of Taste Buds
Number of taste buds and type of T2R receptors determine sensitivity to bitter taste.
Is Oleogustus the sixth taste ?
• Criteria for “primary tastes,” including that the sensation:
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1) has ecological consequence
2) is elicited by a distinctive class of chemicals
3) stems from activation of specialized receptors
4) is detected through gustatory nerves and is processed in taste centers
5) has a quality nonoverlapping with other primary qualities
6) evokes a behavioral and/or physiological response
• Oleogustus “fat taste” is triggered by nonesterified fatty acids (NEFA)
• medium and long-chain NEFA
• oleic acid, linoleic acid or 9-decenoic acid
• have a taste sensation that is distinct from other basic tastes
Oleogustus: The Unique Taste of Fat. Cordelia A. Running, Bruce A. Craig, and
Richard D. Mattes. Chemical Senses, 2015, 1–10.
Anatomy and Main Pathways of the Human Gustatory System
Chemicals in the Air Elicit Odor Sensations
The sense of smell starts with receptor neurons in the nose-within the
olfactory epithelium.
Three types of cells in the epithelium:
– Receptor neurons
– supporting cells
– basal cells
From the receptor cell an apical dendrite extends to the mucosal
surface.
Cilia emerge from the dendritic knob.
An axon extends from the other end of the receptor cell to the
olfactory bulb.
Anatomy and Main Pathways of the Human Olfactory System
Steps in Olfactory Sensory Transduction
Different Kinds of Olfactory Receptor Molecules on the Olfactory Epithelium
~ 1000 different receptor proteins which can be divided into four different
subfamilies of about 250 receptors each
Each subfamily of receptors is synthesized in a separate band of the epithelium.
Organization of Odor Projections in the Brain