...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 responses

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 transmitter release.
There are (1) ion channels and (2) molecules like rhodopsin (and neurotransmitter receptors)
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, Fig. 49.5
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 and dermis.
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, blood pressure.

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
pinna, eardrum,
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
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

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
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 -
Spectrum -
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 Peter Bernhardt
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.

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this page was last updated 3/27/03