SPC Ramuel
for Biology E-100
for Biology E-100
Raagas Making Sense
James S. Lee: Teaching Fellow
Karel Liem, Ph.D. : Instructor
Harvard Extension School
January 2004
    article outline
  1. receptors
      senses per se
    1. smell
    2. equilibrium
    3. sight
    4. lateral line
  2. cranial nerves
  3. bibliography


From whence do we sense? Receptors, receptors, that's the thing. According to Hickman, Roberts & Larson (Integrated Principles of Zoology, 11th ed, page 736), "Sense organs are specialized receptors designed for detecting environmental status and change."

Status, for example, may be the issue for a terrestrial animal on its feet keeping conscious of its balance in relation to the center of the earth. i.e., a skateboarder, will know if he is some quite obtuse angle from a vertical normal to the surface on which he rolls.

Even when a fish does not touch the bottom of the sea or ocean (or dwell on the bottom as is the habit of selachians such as manta rays), the fish has to know if its ventral surface indeed faces the center of the earth, and consequently have its dorsal surface face the sunlight (though it be many dozens of meters distant from both) by means of its membranous labyrinth in its innner ear, so that it can make most of its counter-shading so as not to be visually conspicuous to either predators or prospective prey.

Proprioceptors, Cutaneous Receptors, and Chemoreceptors (such as the terminal nerve, and the chemical receptors part of the vomeronasal organ and the olfactory system) among other receptors are involved in receiving sensory stimuli.

Receptors are cells which became more complex, active and advanced in development compared to other cells.

They act as transducers. Receptor cells convert energy from one form to another. According to Bemis, Walker etc., receptors are quite sensitive to VERY SLIGHT changes in energy ensuing from specific environmental signals, such as smell, taste, sound, pressure or light, but I say that though some signals indeed be energy-tweak based, other signals have got to do more to particulate presence of MATTER, (such as taste and smell) rather than energy going around per se (of course, aromatic particles, going about do disperse due to their KINETIC energy). The physical aspect indicating the stimulatory character of odor particles is more their concentration rather than their energy of movement, or velocity therefrom.

Furthermore, minute-ness need not be an aspect of what would be sensorily received. Sure enough, man has devised floods of stimuli which now and then are not exactly what even are own animal bodies are meant to handle. Communists in India and other countries from decades back have suffered blinding interrogations whereby their eyes just couldn't take extreme wattages of bulbs flooded into their brave eyes. But in the normal world, outside man's perversion, not even thunder or volcano explosions deafen animals. Only man was stubborn in enough to expressly institude habitats volcanoside (as had been the case in Mount Thera). Of course, man drags innocent vertebrates into whatever reckless addresses he may choose.

The sense of smell is the most minutae-sensitive of all senses. Even we people can detect vapours of synthetic cleaning compounds present in very low pressures (like even less than micro-atmospheres). Sharks can pick up an odor a kilometer away (and then act accordingly). People only conquer such distance within a moment's space in communicating by means of the tools we've technologically devised, as the well as the logos of our information-posting. Felis like man unequipped (i.e., a leftist or oppositionist thrown into solitary confinement) and unlike shark is more bound to detect stimuli bodily if stimuli are within the periphery of about the size of a room.

According to Wilson-Pauwels (page 16), the olfactory epithelium, tracts, bulbs and pertinent brain areas comprise the olfactory system.

In squalus, in heptanchus maculatus and vertebrates in general, olfactory sensations are carried caudad by the olfactory peduncles/tracts to the forebrain's olfactory lobes (J. Frank Daniel).


The sense of sight is the sense which most handles organism-sized sources of stimuli (i.e., bodies of mass, even other organisms, which reflect light).

Detection and perception of organism-sized stimuli facilitates the capture of prey, or even mere vegetative feeding.

For the sense of vision, animals have photoreceptor cells, which according to Roger M. LeBlanc (cf. Vision in Fishes: Ali, general editor) use the energy of quanta of light as transducers, converting such into neural signals.

Vertebrates have rods and cones, but not every single vertebrate has got cones to receive the stimuli from light rays. Rods work great in dim lighting. Cones are more known for picking up color.

Here I have marked on the sheep brain its optic chiasma, as well as cranial nerve II (the optic nerve).

The way vision is processed UNTIL it gets on its way out of eyeball is quite an electrical activity. The receptor, the horizontal cell and the bipolar cell are the neurouns that form the receptive field (RF) in the ganglion cell (Tsuneo Tomita, "Microelectrode study of the physiology of neurons in the fish retina" from Ali, Vision of Fishes).

Eyes are composite bodies of mass normally exposed to a medium which is a fluid mixture (such as common air or sea water). Different parts the eye has, but those different parts are different too from the surrounding medium, and thus the cornea and lens are in a position to refract the light waves which they receive from the medium. The eyes is a very moist organ, however, so the cornea doesn't really bend light with an index of refraction so different from water's own value of 1.33.

According to Munz, "The lens is usually spherical and protrudes through the pupil." Munz contrasts the way that elasmobranchs (such as Squalus) have a protractor muscle to pull forward the eye lens very slightly so as to accomodate vision whereas bony fish have retractor muscles tug the opposite way (Fish Physiology page 3)

For us humans, the visual pathway (Cranial Nerves: Wilson-Pauwels, Akesson, Stewart, Spacey) goes from the optic canal to the optic nerve, then optic chiasma to suprachiasmatic nucleus of the hypothalamus, then to the optic tract, cerebral peduncle, lateral geniculate body, pretectal area, rimary visaual cortex right calarine fissure, cut left cortex, and so on.

What are the primary sources of incoming stimuli?

Electromagnetic and electrical stimuli are not one and the same thing.

In fact electrical stimuli are more akin to mechanical stimuli than to electromagnetic stimuli.


For the sense of equilibrium , the inner ear, especially the otoliths within it, play the key role; the same otoliths are also needed for perceiving sound (cf. J. Tomas, J. Geffen, p. 1384, Journal of Fish biology). Calcium carbonate (same stuff which makes which makes grand limestone formations) normally comprise otoliths. CaCO3 forms into network solid clusters of aragonite mineral. When some other mineral is formed from precipitating calcium carbonate, the fish becomes abnormal in development.


What kind of receptors do animals have? Animals have chemical receptors such as olfactory cells for smell and taste buds for taste.

Animals also have electrical, temperature-sensitive and mechanical receptors.

Tonic receptors are receptors which are always active.

The felis has sinus hairs in the form of whiskers , such are sensitive to touch and presssure, Merkel's disks, Meissner's corpuscles, Pacinian corpuscles and Eimer's organs as well as Ruffini endings also all are sensitive to touch and pressure, and are found in many animals, especially terrestrial vertebrates.

But since whiskers are an advanced forms of sense organ, they are not really needed for the survival of the cat in the house or on the streets. Or am I mistaken, and do whiskers pick up a gush of wind so as to notify a cat if a motor vehicle is charging towards it?

The optic and olfactory nerves have got special sensory (special afferent) aspects to them. The optic and olfactory nerves are not quite like the other ten cranial nerves in that they are both rather more of extension of the brain. Some scholars thus see the structure of the retina as a model for the structure of the brain itself.

Neither cat nor shark nor any monkey has got the extent of sense of touch that man does. Still, the cat has a much more tactile sense than sharks, reptiles or most animals. Domesticated Dogs and cats have highly advanced tactile sense: say, when compared to reptiles.

Felis has the most advanced tactile sense of animals which aren't people.

Nonethless, so clear it is that such advanced tactile sense has the end only of the domestic cat being an extensively touched animal rather than an extensively touch-performing animal. Moreover, when a cat touches something, it more of pushes it, rather than to touch the thing per se so as to examine texture. Non-human mammals tend to have paws and hooves (ungulates constituting the latter case) rather than our palms, which are so advanced, we may even use them to relieve stress ensuing from too much word-processing by squeezing on a yuppie rubber stress ball.

People are the animals best equipped in using touch cognitively (even blind people). Although the tactile sense is a general sensory modality cutaneously distributed up and down the mammalian body, we people have noted via homunculus schematics that our face, feet-soles and hands are all the more sensitive to being touched than our, say, the pot belly, or a couple of inches up and away from the smalls of our backs.

The reason why face and extremities are so sensitive to touch is due to innervation. The face has, of course, the facial nerve, and even the trigeminal nerve.

No animal touches the way that man does; monkeys arent' to be compeared to people when it comes to touching. I guess that we people have the hand of God, being made in His image.

The non-human tactile sense is, like the human tactile sense, a general sensory rather a special sensory one.

A domesticated cat can roll a ball of yarn (they've been doing that for at least the latter part of the previous century. But cats have only been able to do that thanks to people . Cats may "touch" food, their containers and garbage forms, but such objects for cats to touch and avail of were constructs of man.

To be cat means not be just an animal, but to be by default associated with the habitats of people. Even a cat on the streets has its existence confined wthin the streets OF PEOPLE. Felis humani. Felis homini.

Middle-class man and cat both act with tact. Proletarian man and dog both act with resolve and brazen efficiency, at best. It is more with the "What up, dog?" kind of man that I identify with.

Tactile sense is a physiological matter. The sense of tact is a disposition of behavior summed up as "Why do?" or "Why bother go there?" A qui vadis? rather than a quo vadis? mentality (the latter being the dog's, or that of the unwrinkled achiever).

hence, later down the previous century, middle-class people hanging out in socializing bars proudly y-cleped the males among them as "cats."

The shark however is not so welcome in the human home in alive form in the way that cat is. A shark TOUCHES nothing. in that it doesn't really make a habit of touching anything for the sake of touching. The shark doesn't go "Ooh! I want to touch this!" I even doubt if the shark will keep its rostrum in gentle contact with, say some panel of a sunken ship---- for like a third of a minute or some other ponderous amount of time.

It is terrestrial vertebrates such as koalas, kitties and monkeys which are more bound to fiddle with objects: in sum, bipeds or at least quadruped vertebrates given enough to an upright position.

Man is the man animals that loves to touch., No animal touches the way man does. Man's hands are not just sensorially enhanced. Well man's hands are so sensorially enhanced that touch thereabouts

Arabs and Greeks from centuries ago have studied the sense organs. There was Khazali. Khazali did lavish diagrams and treatises on the eye, although due to religio-legal constraints, he and other Arabs did not have much of a hand in dissecting organs themselves, but Khazali, Avicenna any numerous other Arabs zealously translated and studies Greek science and philosophical texts, to an extent unbecoming of Extension School students, moreso the vocational flock of the Health Careers Program.

Lateral Line

According to Olav Sand, lateral line organs are epidermal sense organs. According to Homeberger and Walker, the lateral line and electroreceptive organs of sharks, besides numerous aquatic amniotes and larval amphibians are innervated by SPECIAL somatic sensory nerves. The lateral line organs are no longer construed as being innervated by nerves component to the standard among dozen vagus, glossopharynegeal and facial nerves, but are rather appreciated as being innervated by six lateral line nerves, which are in their own right recognized as separate and distinct cranial nerves. After all, they come from not the exact same neurogenic placodes, and they end up not in the brain nuclei becoming of any of the dozen pan-vertebral cranial nerves.

The six lateral line nerves no longer seen as mere derivative of the pan-vertebral cranial dozen may be dichotomized into preotic and postotic groups.

The cochlea is efferently innervated (H. Spoendlin).

cranial nerves

How are the senses related to the cranial nerves?

The senses have got to do with the cranial nerves, but not all cranial nerves are involved with the senses. Shakrs perhaps typically have ten pairs of cranial nerves, if we go by Kavita juneja's nerve count for the other shark known as Scoliodon (Recent Trends in chordates, volume 2, new delhi) CN 0-II have sensory functional components. The trochlear nerve and the oculomotor nerve both control the eye, and so have a somatic motor functional component, although the oculomotor has got more control of the eyeball's movement than does the trochlear nerve. The trigeminal nerve has at least three branches (opthalmic , maxillary and mandibular) and these all have general cutaneous sensory componenets.

Special somatic sensory fibers do comprise the statoacoustic nerve (XIII), which has part of it come from the ampullae of the anterior vertical and lateral semicrcular ducts of the inner ear.

The glossopharyngeal nerve, identified with the third visceral arch and the first of five definitive gill pouches, is a dorsal root nerve. We see it crossing the floor of the otic capsule posterior to the inner ear's sacculus. When doing dissections, we must take care not to confuse the glossopharyngeal nerve with the statoacoustic nerve, the caudal branch of which is ventrally passed through by CN IX.

The vagus nerve (X) is a dorsal root nerve, and is associated with the posteriormost gill arches. Reference:
Homeberger, Walker

superficial origins

The superficial orgin of many a cranila nerce is the lateral wall of the myelenbcephalon (which is the part of the rhombencephalon or hindbrain even more posteripor than the metenchephaol)


The cranial nerves pass through holes in the neurochranium of the chondrocchandrium of the dogfish. The holes are called foramina.

According to Lazier, the terminal and olfactory nerves both pass through the olfactory foramen. The optic, oculomototr, trochlear, abducens, auditory/acoustic and glossopharyngeal nerves pass through pretty muych eponymous foramen. The facial nerve (VII) passes through the orbital fissure.

According to Lazier, "the [dogfish] organs of special sense consist of olfactory organs, the eyes and the acousticolateral system." What comes to mind Today we will discuss a few aspects of vertebrate sensory systems.

We will focus on cat and shark.

Just about the squalus

The squalus is the spiny dogfish because it has spines on its dorsal fins, as opposed to the mustelus or smooth dogfish. The squalus acanthias, according to R. Mcneill Alexander, does not lay its eggs, but keeps embryos in its uterus for almost two years until such offspring may go about the water themselves. (p. 120, The Chordates).

In page 122 of R. Mcneill Alexander's The Chordates (Cambridge University press) we see the same diagram as we do see in our Bemis, Liem textbook, that is the dogfish (Sclyliorhinus, rather than our own squalus per se) was experimented with, as to its electroception.

Dogs have been known (before the days of constant feeding of for dogs onluy processed dog food) to be able to bury their bones in the backyard under rthe dirt. Well, the dogfish Scyliorhinus has been known to dig up for food under the sand at the bottom of a body water. Aquatic animals produce action potentials; potentials are potential differences where there is a shift in energy per unit charge going from one place to another.

Cat and shark are animals famous for their sensory systems. But The cat (Felis) has indeed a more advanced sensory system. The cat is more cognitive than the shark. So advanced is the cat's sensory system to that of the First we study the olfactory. There's the olfactory bulb up front. Then we follow caudad the olfactory tract. then we study optic.

The MORE ADVANCED A SENSORY SYSTEM IS, the more suppressible are the involved organism's impulses to responsive action. Sense eventually becomes a thing in itself. As our Liem-Bemis-Walker-Grande text shows, the sharks electroception can get so crude, that it can be fooled to attack an electrode instead of morsels of food. The domestic cat felis on the other hand has so advanced a sensory system (even in relation to its jungle counterparts) Thus the immune system is quite complementary to the sensory system. The immune system responds (especially in the case of us people) often without conspicuous announcements in store for the sensory system. What's the use of sensing without responding?

The more developed an animal's sensory system is, the LESS USEFUL need be it, for it itself fulfills the gratification of cognition. To sense something, and not be moved by it, represents an advancement in development.

Biological advancement SHOVES ASIDE the compulsion of expression--- whether it be regards to sense-response or gene presence.

Why viruses continue to hit this late stage of Earthly life is an inevitable manifestation of the protracted insurgence of the abiotic against people and their cows---- expression is in the manifesto of viruses, and we people in our late mode of civilization have lunged into a chronic disposition of non-expression.

The more useful some sensory phenomenon is, the more we may suspect it be crude or primitive.

The human sensory system

The more advanced a property is, the more SEVERED it may be made from its original conception. Thus an advanced form of Coca-Cola need only have Coke at its banner name, need neither caffeine, nor sugars infused into it, AND NEED NOT EVEN KEEP A SEMBLANCE of the original taste, once Lysol-ic lemon goes into the new product.

We will start with the shark (squalus acanthias, which we have right here in our SC 4th floor labs). Squali may also be procured from Nebraska Scientific. The squalus acanthias is an elasmobranch, a selachian. It is a shark not given into growing so much as three feet long.

What do we mean by sensory? Sensory system allows for reception of stimuli. There's reception of stimuli from the external environment: exteroception. There's consciousness of internal conditions: interoception

One form of exteroception is hearing. To hear the animal has got to have ears. Hearing is different for felis and homo than it is for squalus and other chondrichthyans besides teleosts. Sound is sound, which is a longitudinal propagated wave, causing alternating compressions and rarefactions of matter as medium. But felis and squalus receive sound by different media (we people have got radio). Sound is louder and water, although air allows for more enriching subtle variations in sound modulation, which make the cat's meow so adorable. Air is the medium best suited for the propagation of animal voice. Sure dolphins can make sounds, and other aquatic vertebrates such as whales can use echolocation, but the contours of sound have enhanced possibilities of quality in the fluid medium for sound that is air.

Hearing for felis and homo (quote Bemis Walker p. 415, 2001) is the detection of airborne pressure waves.

Electroreception is more becoming of aquatic rather than terrestrial vertebrates. Aquatic vertebrates may both detect and GENERATE electric fields. On land, it is man that is the vertebrate that generates electric fields, but not with his body alone, but with his implements and technology. For some small glee, people may rub their combs vigorously and see how the static charge they produce causes hair to rise from its natural draping placement will rise due to an F = qE greater than the F = mg due to hair's inertia and gravity's force per unit mass on the surface of our Earth.

Let's talk about photoreception. Metazoans need to detect CHANGES in light. Animals receiving light have cells geared for photorecpetion. Sharks, unlike cats or people, never developed tear glands, since the eyes of the shark qare not bound to dry up. The squalus has only got immovable upper and lower eyelids, although some sharks do have a nictitating membrane. May we compare the ears of our cat specimens with the lateral lines of our sharks? The sensory system deals with both the external environment a Sensory Squalus

Let's check out the ampullae of Lorenzini, the openings of which are pores on the snout through which jellylike material may be squeezed right out of. The ampullary organ has a receptor opening. The organ is an invagination beneath the skin surface at the end of which are found receptor cells. Past the bottom of receptor cells, a lateralis nerve wires up.

The Squalus, like fishes and larval amphibians, has a lateral line system. The cat does not. The motor and sensory fibers REMAIN separate in Squali & other elassmobanchs (Smeets 1983 page 23) Liem The forebrain is the prosencephalon, which branches into the telencephalon and the diencephalon. The Olfactory and optic senses are both prosencephalic, but the olfactory is telencephalic whereas the optic is diencephalic. To study the sensory system of All animals have sensory systems, but what advances do vertebrate All organisms respond to the environment, sensing is a level advanced above mere response. To sense means to detect We've got the olfactory sac, then the olfactory bulb. What olfactory things are we looking for?
According to Biemis etc. we people cannot sense SMALL changes in electric fileds in the way that aquatic vertebrates sych as Squalus can. Of corse, humans are the only animals to subject each other to GREAT currents of electricity, or om a more productive tone, grand mangnitudes of Voltage (i.e. Tesla

Does a shark even care what it's food tastes like? Should it bite into something its tongue may find odd, would it spit out the food? Is the cat conspicuously taste-selective?.... considering that cats rummage through garbage anyways. We know pigs eat anything, even filth. But what about dogs? We know cows go crazy when people incompetently feed them feeds which are derivative from cow flesh itself, but that goes to show that the cow cannot discrimnate taste enough so as top prevent itself from swallowing stuff that might turn it into a mad cow. It's people, even prepubescents not yet sexually mature, who can get so picky with taste so as to reject whole classes of food. What is the purpose of the sense of taste, then, for non-humans?

The sense of taste must be then quite an advanced thing, especially if it entails tasting not just AGAINST poisons or toxins, The sense of taste of humans is so advanced that the anti-toxin taste buds at the base of our tongue have been relegated so posteriorly, whereas the anterior two thirds innervated by one of the cranial nerves is all for the pleasure of taste. Pleasure is an advanced sensation, multi-faceted, which humans and domesticated cats may indulge in.

Before cutting the shark, what do we see?

The nose of the shark has got two nares. Each one has got two sub-

According to R. Mcneill Alexander, dogfish, like other sharks, have heterocercal tails: "The posterior end of the vertebral column turns upwards and extends into the dorsal lobe of the fin (pp. 100-1, Chordates, 1975)."

Shark eyelids don't move (and hence are like the residents of hell from Jean Paul Sartre's drama Huis clos). Well, real people, even dead ones do get to close their eyelids, although it's still true that "L'enfer, c'est les autres [hommes]!"

One of the first things we may examine is squalus is its upper and lower eyelids. Notice how simple and few are the elements (not even four things are out there when we view what's there laterally. It's not as complicated as in a terrestrial vertebrate such as a rabbit or a cat, where there would be tear glands or Harderian glands. Actually, many sharks do have nictitatng membranes (Fish Physiology, Hoar, volume 5) Sharks can also move their eyeballs, as six innervated muscles fo support our squalus eyeball. although the squalus might not remarkable y exhibit retinomotor skills. We don;'t do any vivisection for Bio E100, but others who have done so have noted that they could shut off the dogfish's electric sense by the cutting the cranial nerves innervating the ampullae of Lorenzini. The ampullae of Lorenzine is one of the first thigbs we see on the surface of our shark.

Lab mission

The mission of this lab project is to rehash familiar resources on shark anatomy study into a format which takes advantage of current digital camera photography.


General Sensory modality is spread all over the organism, such as touch FELT upon the mammalian integument.
But don't the special sensory modalities (especially for exteroception) reside mainly in the head?
General Sensory modality is spread all over the organism, such as touch FELT upon the mammalian integument,

more sense out there

So many sensory mechanisms vertebrates and other chordates and have that we won't get to see a lot of them today in our lab.

Squalus has lateral line and neuromasts associated with it, as do lampreys, hagfish, selachians and teleosts (although lampreys and hagfishes have their lateral line neuromasts stick out from their integument, wheras selcahinas and teleosts have neuromasts both on their integumentary surface and inside sunken canals) (Alexander, 1975, page 121).

We've got sensory features, even entire sensory organs not present in cat or shark

Snakes, for example, limbless tetrapods they are, have pit organ cells which detect EM radiation of longer wavelength than the red we people see.

What kinds of eneteroception need we note of? Accoridng to Bemis, internal chemoreceptors continuous;ly monitor some facets of what goes beneath the integument of the vertebrate organism itself.