You and Your Hormones

Volcanoes: Volcanoes!

10 Signs You Might Have a Brain Tumor
After all, gut bacteria have been quietly producing neurotransmitters ever since humans walk the face of this planet until scientists discovered it one day. If ETI is detected through electromagnetic emissions over interstellar distances that are not intended to communicate with emerging civilizations such as earth's, then humanity will have to introduce itself. Chimps are more closely related to humans than to gorillas. This page is a fold-out page and is a graph of our Five Senses Taste Test. Over the coming months, I will detail some of the lessons that go with these walls. Do space and time have absolute existence independent of their contents?

ADDITIONAL MEDIA

Short Term Memory Test

Over the past six months, several environmental health officers have contacted the HPA about the dangers of fish pedicures, leading to the present investigation, which hopes to discover whether fish spa pedicures spread infections. If commercial fish pedicures are banned, the UK would be following the lead of 14 U. Customer Max Langton, from North London, said: I was put off when a man sitting opposite me said he had something wrong with his foot and hoped the fish were enjoying it.

I wanna go there, too! Ahh… leave it to the government to aggressively and expensively solve a problem that does not actually exist. The KOH preparation has an excellent positive predictive value, but occasionally false negative results may be obtained, especially if treatment with an antifungal medication has already begun. The spa owners have said repeatedly that the water is changed in the tank after each use and no group of fish is used in the same day.

They rotate the fish. Add that to the fact that no one has produced evidence of this spread of disease. I think this is a great idea. Besides any pedicure can be dangerous. A friend of my aunt had to have an amputation after a regular pedicure. She was a diabetic and got an infection after a pedi. The sanitation depends on the diligence of the spa.

Come to southern Mexico. I had a rash on my foot and the fish helped it. By Patrick Morgan February 28, That person has one ugly foot. Discover's Newsletter Sign up to get the latest science news delivered weekly right to your inbox! The differences arise, at least in part, from the accessory mechanisms that aid in the utilization of sound energy.

In most fishes, especially in many marine forms, the auditory mechanism is relatively simple, consisting of macular endings that evidently have been diverted from their primitive functions as detectors of gravity and motion.

The important change is not in the structure of the end organ but in its innervation—the nerve supply has connections that transmit auditory information. It is thought that in most teleosts the change to an auditory function has occurred in the saccular macula, and probably the lagenar macula as well, and that the utricular macula continues as a receptor for gravity and motion. The simple macular ending of the teleost ear is stimulated by sound through the operation of an inertia principle.

Sound waves pass readily through the water and into the body of the fish, causing most of the tissues to vibrate in a uniform manner. The macular otolith, however, represents a discontinuity; because its density is greater than that of the other tissues, it exhibits an inertia effect resistance to movement. Its motions not only lag behind those of the surrounding tissues but are probably of lesser amplitude as well. Accordingly, a sound creates a relative motion between the otoliths and the other tissues.

More specifically, there is relative motion between the bodies of the hair cells, which rest on a tissue base, and the cilia of these cells, the tips of which are in contact with the otolith. This method of stimulating the auditory hair cells is inefficient, however, because of the relatively small difference in density between the body tissues and the otoliths.

In certain groups of teleosts the efficiency of hair-cell stimulation has been increased by a discontinuity that is nearly 1, times greater than the one between tissue and otolith ; this is the discontinuity between the otolith and a gas bubble. Although there are varying anatomical methods of achieving it, the simplest arrangement, which is found in clupeids, mormyrids, labyrinthine fishes, and a few others, consists of a gas-filled sac that lies against one wall of the labyrinth.

In the mormyrids , which include the elephant-nosed fish , a similar condition exists in early life; during adult development, however, the connections with the swim bladder disappear, leaving the air sacs connected with the saccular and lagenar endings. The gas content of these sacs is then maintained by special glands that extract gas from the blood. Air sacs arise in various other ways. One large group of fishes, referred to as the Ostariophysi e. A chain of three or four small bones, known as the Weberian ossicles , extends from the anterior wall of a part of the swim bladder to a fluid-filled chamber called the atrium, which in turn connects by fluid passages with the two labyrinths in the region of the saccule-lagena complex.

In this arrangement the discontinuity is between the air of the swim bladder and the chain of ossicles in contact with it; the relative motion arising from sound stimulation is communicated through the ossicular bony chain and the fluid channels to the macular endings.

Regardless of the mechanism employed, however, the ear of all teleost fishes is basically a macular organ. Because it is stimulated by sound that is transmitted to tissues adjacent to the sensory cells and that acts differentially on these cells, this ear is of the velocity type. Although only limited experimental data are available, it appears certain that, in general, fishes with the accessory mechanisms described above have greater sensitivity and a higher frequency range than do those lacking such mechanisms; while upper frequency limits are about 1, hertz for many fishes, they are about 3, hertz for the Ostariophysi and other specialized types.

Many experiments have dealt with the problem of auditory sensitivity in fishes, but the species most extensively tested has been the goldfish , a variety of carp belonging to the Ostariophysi. In one well-controlled investigation, the sound intensities required to inhibit respiratory movements, after conditioning with electric shock , were studied. The greatest sensitivity was found to be around hertz; above 1, hertz sensitivity declined rapidly.

In view of the simple anatomical character of the ear, the question of whether fishes can distinguish between tones of different frequencies is of special interest. Two studies dealing with this problem have shown that the frequency change just detectable is about four cycles for a tone of 50 hertz and increases regularly, slowly at first, then more rapidly as the frequency is raised.

There are three orders of living amphibians: Although members of all three orders have ears, the structures vary greatly in the different groups, and little is known about them except in such advanced types as frogs.

Although the frog has no external ear structures on the outside that direct sound vibrations inward , the middle-ear mechanism is well developed. On each side of the head, flush with the surface, a disk of cartilage covered with skin serves as an eardrum. From the inner surface of this disk, a rod of cartilage and bone, called the columella, extends through an air-filled cavity to the inner ear.

The columella ends in an expansion, the stapes, which makes contact with the fluids of the inner-ear otic capsule through an opening, the oval window. A second opening in the otic capsule, the round window, is covered by a thin, flexible membrane; it is bounded externally by a fluid-filled space that can expand into the air-filled cavity of the middle ear. When the alternating pressures of sound waves cause the eardrum to vibrate, the vibrations are transmitted along the columella and through the oval window to the inner ear, where they are relayed to the round window in a path across the otic capsule by movements of the inner-ear fluids.

Along this path are two auditory endings, the amphibian and basilar papillae, the sensory hair cells of which are stimulated by the fluid movements. These movements are transmitted to the ciliary tufts of the sensory cells by a tectorial membrane, which is suspended from the hair cells in such a way that it can be moved by the oscillations of the inner-ear fluids.

As sense organs for hearing, the papillae, which appear for the first time in amphibians, have cells like those in lower vertebrates that serve the same purpose. There are two types of papillae: Because they are located in different places in the inner ear, the papillae probably represent two distinct evolutionary developments.

Moreover, they operate on a mechanical principle found in no other animal group: In all higher types of ears, on the other hand, the sensory cells themselves are set in motion by the sound vibrations, while the tips of the ciliary tufts are restrained in one of several ways. Although it is presumed that all amphibians possess hearing of some kind, the evidence is sparse; only salamanders other than anurans have been studied experimentally. Salamanders trained to come for food at the sound of a tone responded only at low frequencies, up to hertz in one specimen and to hertz in three others.

Frogs, which are of special interest because they first live in the water as tadpoles and then undergo a metamorphosis that equips them for life on land, have been studied more extensively. Considerable modifications of the middle-ear mechanism occur during metamorphosis. Presumably, the tadpole larva has an aquatic ear that is later transformed into an aerial type. Interest in the hearing of adult frogs has been stimulated by their active and often loud croaking during the breeding season.

Evidently, their vocalizations assist in the location and selection of mates. The first experimental study of auditory sensitivity in frogs, carried out in , showed that leg movements in response to strong tactual stimuli may be enhanced or even inhibited by sounds. Somewhat later, following some unsuccessful attempts to train frogs to make behavioral responses to acoustic stimuli, two other methods were employed to determine the sensitivity and range of their hearing.

One of these was the recording of changes in the electrical potentials of the inner ear and auditory nerve; the other was the observation of changes in the potentials of the skin electrodermal responses to acoustic stimuli. As a result of these investigations, inner-ear potentials and electrodermal responses in the bullfrog have been recorded over a range from to 3, hertz.

In the treefrog , these same responses have been found in a range that extended from 50 to 3, hertz, with the greatest sensitivity from to hertz, and again at 2, hertz. The recording of impulses from single fibres in the auditory nerve of bullfrogs and the green frog indicates that two types of auditory nerve fibres are present. This has led to the suggestion that they represent the different characteristics of the amphibian and basilar papillae.

It is believed that the amphibian papilla is more sensitive to low tones and that the basilar papilla is more sensitive to high tones. The living reptiles belong to four orders: The reptile ear has many different forms, especially within the suborder Sauria lizards , and variations occur in all elements of its structure—the external ear is often absent or may consist of an auditory meatus passage of varying length; the middle ear shows several forms in the different groups; and the inner ear varies in the degree of development of the auditory papilla and also in the ways by which the sensory cells are stimulated by sound.

There are about 20 families of lizards, ranging from the chameleon , a divergent type, to the gecko , certain species of which have the most highly developed ears found in the group.

The chameleons, of those species studied thus far, have only a few sensory hair cells 40 to 50 in the auditory papilla. The geckos, on the other hand, have several hundred hair cells, and the Gekko gecko has about 1,, the largest known number of hair cells in any saurian.

Other lizard species fall between these two extremes in inner-ear development, with the iguanids , the most common lizards in the Western Hemisphere , having from 60 to hair cells, according to the species.

What may be regarded as the standard type of middle-ear structure in the lizards consists of a tympanic membrane and a two-element ossicular chain that extends from the inner surface of this membrane to the oval window of the otic capsule.

The ossicular chain is made up of two parts: Geckos have a single middle-ear muscle attached to the lateral part of the extracolumella; evidently, contractions of this muscle stiffen the extracolumella, thereby dampening the ossicular motions and protecting the ear against excessively intense sounds.

The auditory part cochlea of the inner ear consists of a basilar membrane lying in an opening in the limbus, which is a plate of connective tissue.

The form of the basilar membrane, which is unlike the structure of the same name in amphibians and is clearly of different origin, varies from a simple oval in iguanids to a long, tapered ribbon in gekkonids.

In many species the middle portion of the basilar membrane is greatly thickened, especially in some regions of the cochlea. Over this thickening, which is called the fundus, lies the auditory papilla proper—i. The hair cells usually occur in regular transverse rows, with the number of cells in a row varying along the cochlea.

They have a tuft of cilia, the so-called sensory hairs, of graduated lengths, the longest of which are usually attached either directly or indirectly to a tectorial membrane. This membrane arises from a region of the limbus that is usually elevated, often strikingly so, and runs as a thin web or sheet to the region of the hair cells.

Only rarely does the free edge of the tectorial membrane connect directly with the cilia of the hair cells; usually there are intermediate connecting structures that take a variety of forms, from simple fibres to relatively massive plates. The function of the tectorial membrane and its connections to the ciliary tuft of a hair cell is to immobilize the tuft when the body of the hair cell moves in unison with the basilar membrane on which it rests.

This produces a relative motion between the ciliary tuft and the body of the cell and stimulates the cell. All auditory stimulation depends ultimately upon this relative motion, and the means just described for achieving it can be regarded as the most fundamental process by which sounds are perceived. Although it is employed in the great majority of ears, it is not the only mode of stimulation.

Another mode is that in the ears of fishes, in which an otolith lies upon the ciliary tufts and, by its inertia, reduces and alters the motion of the tuft relative to the cell body.

Still another method is the one in the frog papilla, in which the tectorial membrane is moved by the cochlear fluids while the body of the sensory cell remains at rest. In some lizards the inertia principle has a form different from that found in fishes. In the former, a body called a sallet lies upon the ciliary tufts of a group of hair cells and, by its inertia or by an equivalent means , restrains the movement of the cilia when the cell body is made to move. The result is a relative motion and a stimulation of the hair cells, like the more common restraint by a tectorial membrane.

The ears of two lizard families show only the inertial restraint method of stimulation; in several other families this method functions in some regions of the cochlea for certain hair cells.

Hair-cell stimulation by two or more different arrangements within the same cochlea, however, is the rule rather than the exception because of its many advantages. Although the tectorial-restraint method provides great sensitivity for individual cells, the sallet system also attains good sensitivity, but in another way: The sallet system has the advantage of being more resistant to damage by overstimulation from intense sounds.

In such lizards as the geckos, for example, in which the hair cells are divided nearly equally between tectorial and sallet systems, an exposure to excessive sound has been observed to break all the tectorial connections to the hair cells while leaving the sallet connections intact. But even though the most sensitive hair cells are inoperative, the animal can respond to sounds, although with lesser acuity. The lizards are the lowest vertebrates to have a well-developed spatial differentiation of the cochlea in which different regions respond to different frequencies of tone.

The problem of tonal discrimination has been somewhat solved in frogs, in which the differential responses to tones by the two papillae may provide some information concerning the pitch of sounds. The mechanism in frogs, however, is a poor one, as it can give only crude and uncertain cues at best.

In some lizards, such as iguanids and agamids, a minimum of structural variation occurs along the cochlea. Most geckos are nocturnal in habit and use vocalizations to maintain individual territories and probably to find mates.

Although it has been possible to train two species of lizards Lacerta agilis and Lacerta vivipara to make feeding movements in response to a variety of sounds, including tones between 69 and 8, hertz, most attempts to train lizards to respond reliably to tonal stimuli have failed. The one useful method thus far developed to study the sensitivity of these animals to sounds involves recording electrical responses in the ear and in the auditory nervous system.

Although such observations have provided information about peripheral response to sounds, they do not reveal anything about other processes in the nervous and behavioral systems. Electrical responses in the cochlea of many lizard ears show considerable variations: It has been concluded that most lizards have good auditory sensitivity over a range from to 4, hertz and relatively poor hearing for lower and higher tones. This auditory range is not very different from that of humans, although somewhat more restricted than that of most mammals.

Without much doubt, snakes developed from some types of early lizards but lost their legs when they adopted habits of burrowing in the ground. Although some snakes burrow, others have taken up different habits: All, however, show drastic ear modifications that reflect their early history as burrowers; for example, there is no external ear—i.

This fact, together with a seeming indifference to airborne sounds, has led to the supposition that snakes are deaf or that they can perceive only such vibrations as reach them through the ground on which they crawl. This supposition is incorrect; snakes are sensitive to some airborne sound waves and are able to receive them through a mechanism that serves as a substitute for the tympanic membrane.

This mechanism consists of a thin plate of bone the quadrate bone that was once a part of the skull but that has become largely detached and is held loosely in place by ligaments.

It lies beneath the surface of the face, covered by skin and muscle, and acts as a receiving surface for sound pressures. The columella, attached to the inner surface of the quadrate bone, conducts the received vibrations to its expanded inner end, which lies in the oval window of the cochlea. If the columella is severed, the sensitivity of the ear is significantly reduced. Although the sensitivity of the snake ear varies with the species, it is appreciably sensitive only to tones in the low-frequency range, usually those in the region of to hertz.

For this low range the large mass of the conducting mechanism and the presence of tissues lying over the quadrate bone are not of any great consequence. Moreover, while the sensitivity of most snakes to the middle of the low-tone range is below that of most other types of ears, it is not seriously so.

In a few snakes, however, the sensitivity is about as keen as in the majority of lizards with conventional types of ear openings and middle-ear mechanisms. That the ears of the snake receive some aerial sound waves instead of depending exclusively on vibrations transferred from the ground has been proved by recording the potentials in the cochlea of one ear while rotating the animal in front of a sound-wave source so that the ear being studied was sometimes facing the source and sometimes directed away from it.

The recorded potentials were significantly greater when the ear was facing the source. There would have been no difference in the responses if the sound first set up vibrations in the ground and these were then transmitted to the body. This observation also shows that the ears of the snake can determine the direction of a sound in terms of its relative intensity in the two ears.

Although snakes can perceive vibrations from the ground that are present at a sufficient intensity, this ability is not peculiar to them; all ears respond to vibrations transmitted to the head.

Click on a Topic: