...taste, being the lowest or least intellectual of our five senses,
is incapable of registering impressions on the mind;consequently, we cannot
recall or recover vanished flavours as we can recover, and mentally see
and hear, long-past sights and sounds. Smells, too, when we cease smelling,
vanish and return not...
W. H. Hudson, Far Away and Long Ago, 1918
Many years ago, I enjoyed reading a book, The magic of the senses, V. B.
Droscher, E. P. Dutton & Co., Inc. New York, 1969 (and that is how I
like to think of this material)
Campbell first half of Chap. 49
In the framework of Stimulus - NS - Response, we covered NS=nervous system,
now how stimuli are perceived by senses, after that, how muscles generate
Transduction is the way an energy gets turned into a nerve cell potential
Modalities refer to the different senses like seeing vs. hearing
There are Receptors (cells) for various Stimulus energies
5 (special) senses Taste, smell, touch, hearing & seeing (the order
in which I will cover this material)
Taste [for human, on tongue mostly] - Gustation - chemicals - water -salt,
sour, bitter, sweet
Several types of papilla including the circumvallate papillae on the back
of the tongue, shown in this picture
from our histology course
Within each papilla are numerous clusters of cells called taste
buds shown in this histology picture.
How does chemoreception work?
TRANSPARENCY (Fig. 49.2) cells are excited by receptor proteins and increase
There are (1) ion channels and (2) molecules like rhodopsin (and neurotransmitter
Our notion that taste is richer than that is because smell mediates much
of what we call taste.
Taste is mediated in the fly by "hairs" (setae) on body and labellum
Fig. 49.23 TRANSPARENCY
There are cells which respond preferentially to attractants like sugar and
repellants like salt
VGDethier, To know a fly, San Francisco, Holden-Day, 1962
Smell- Olfaction chemicals (air) - Complex (unusual primaries like aromatic
and putrid, many primaries, receptors difficult to reach, brain projection
complicated), related to motivational affect, especially in other animals
(consider how male dogs mark their "territories" with urinary
pheromones and check for other dog smells)
Olfaction in humans TRANSPARENCY Fig. 49.24 Olfactory epithelium with receptors
having cilia projecting to olfactory bulb in brain
Pheromones in moths, females release sex attractants, mate at night, male
finds female from miles away using large feathery antennae loded with recptors,
Salmon fingerlings get olfactory imprinting (memory) of the stream in which
they spawned; then after 5 years of foraging at sea, they go up their home
streams to mate, sometimes overcoming hurdles
It's funny how odors bring back memories.
Touch (somesthesis) TRANSPARENCY Fig. 49.3
Receptors - There are different specialized receptor types in the epidermis
To some extent, different receptor cell types, with their specialized encapsulations
mediate sensation of heat, cold, light touch, touch, and strong pressure,
and these are very different sub-modalities within athe modality of somesthesis.
The text's coverage o this is oversimplified.
here is a Pacinian
corpuscle from our histology course
For instance, specific spinal tracts are important for touch vs. pain
Look back to previous chapter TRANSPARENCY Fig. 48.25 for description of
where in the somatosensory cortex different parts of the body project. Note
that these areas are adjacent to the corresponding areas in the motor cortex
where voluntary muscle movements are initiated. There is a relative "magnification"
for areas with high touch sensitivity, hands, lips, tongue, genitals.
Before I cover Sight (Vision) and Hearing (Audition), let me say that the
"5" (special) senses are just the tip of the iceberg
Examples of other human senses:
(1) Stretch receptors in muscle [used in knee jerk reflex] (Fig. 48.3) contribute
to the sense of Kinesthesia - knowing where your body is in space.
(2) There is the sense of balance, mediated by the vestibular apparatus
associated with inner ear TRANSPARENCY Fig. 49.19
(3) There are many senses which mediate physiology like CO2 for respiration,
Examples of amazing animal senses:
Magnetism involved in migration in birds (covered later under the topic
of animal behavior) and Baluga whales (Fig. 49.5 b)
Electric sense in fish
Infrared (heat) snakes (Fig. 49.5 a)
Hearing EAR TRANSPARENCY Fig. 49.17
bones: hammer (malleus), anvil (incus), stirrup (stapes)
Eustachian tube to equaliz pressures to middle ear
The cochlea is where auditory receptor cells (hair cells) reside.
Hair cells are stimulated as the basilar membrane moves relative to the
tectorial membrane creating
pressure in hair cells.
Audibility is measured in the sound pressure (relative to a standard) needed
to hear, measured in dB (deciBels), and the sense of hearing is very sensitive.
Frequency discrimination - how different tones are perceived.
Frequency is measured in Hz (cycles per sec) of vibration for frequencies
from 20 to20,000 Hz
Ultrasound is above 20,000 Hz
Cochlea - basilar membrane - high vs low Pitch - freq
TRANSPARENCY Fig. 49.18
very good frequency discrimination ability
Another amazing animal sense:
Bats (p. 1057 Figure) are nocturnal predators finnding insect prey by echolocation
(sonar) using ultrasound.
Moths avoid bats
EYE - TRANSPARENCY Fig. 49.9
iris, lens, aqueous, vitreous, retina, fovea, optic nerve
Accomodation TRANSPARENCY Fig. 49.10 - Presbyopia (inability to accomodate
with age, need re3ading glasses or bifocals)
Myopia (near-sightedness), Hyperopia (far-sightedness),
Glaucoma - high eye pressure kills optic nerve
Cataract - lens loses its transparency
Diabetic retinopathy - new fragile blood vessels bleed into vitreous
TRANSPARENCY Fig. 49.11 a
Rod (sensitive black and white vision) and cones (color vision, acuity)
Outer segment- organelle
Inner segment the whole rest of the cell
Rods are very sensitive - can see 1 photon (quantum) of light
visual pigment - TRANSPARENCY Fig. 49.11 b
Rhodopsin - vitamin A & protein
TRANSPARENCY Fig. 49.12 - vitamin A is pigment which goes from cis to trans
because of light.
TRANSPARENCY Fig. 49.14 - transduction mechanism is that light closes a
sodium channel, stops release of exciatory neurotransmitter glutamate
TRANSPARENCY FIG. 49.13 active opsin -> transducin (a G protein)->PDE
breaks down cGMP (ligand for channel)
Retina wiring TRANSPARENCY Fig. 49.15
Cones (for yellow, green and blue light) are at the fovea (point of fixation),
and mediate color vision at high acuity.
Evolutionarily related, red and yellow are on X chromosome in humans and
old world monkeys.
Bottleneck hypothesis - lower vertebrates have color vision, lost in early
mammalian evolution with nocturnal life - had to re-evolve.
Color blindness in people - on X chromosome and hence most noted in males
400-700 nm, UV bees, IR snakes
Visual connections through optic chiasm, to lateral geniculate nucleus (part
of the thalamus) to the visual cortex - TRANSPARENCY Fig. 49.16 - development
(exposure to form vision) is very important
Insect ommatidia of compound eyes TRANSPARENCY Fig. 49.8b
Sensory processing, lateral inhibition, Feature detection like for color,
contour and contrast, and movement
postcentral gyrus - map on postcentral gyrus of brain (see Fig. 48.19) of
sense of touch
hair cells (SEM)
bat catching moth in stroboscopic illumination
UV sensitivity in insects Flower
another example, Zygadenus
nuttalii, my work with
olfaction - male moth
olfaction - male salmon
vision - eye dissection
frog catching fly is an example of feature detection
three cone types
There is a course in Biomedical Engineering (BMEP-415-01) "Sensory
systems (Dr. Thomas). My interests center around vision, so a visit to the
research interests of my home page will offer various topics about vitamin
A, ultraviolet light, and Drosophila mutants. Dr.
Fliesler in SLU's Ophthalmology Department and Dr.
Ariel in SLU's Anatomy and Neurobiology Department are some of my fellow
wizards in visual science. I corresponded with Dr.
Lindemann who has an interesting site about taste.
return to Stark home page
this page was last updated 3/27/03