The utricle, along with the saccule, is one of the two otolith organs located in the vertebrate inner ear. The utricle and the saccule are parts of the balancing apparatus located within the vestibule of the bony labyrinth; these use a viscous fluid to stimulate hair cells to detect motion and orientation. The utricle detects linear head-tilts in the horizontal plane; the word utricle comes from Latin uter, meaning'leather bag'. The utricle is larger than the saccule and is of an oblong form, compressed transversely, occupies the upper and back part of the vestibule, lying in contact with the recessus ellipticus and the part below it; the macula of utricle is a thickening in the wall of the utricle where the epithelium contains vestibular hair cells that allows a person to perceive changes in longitudinal acceleration as well as effects of gravity. The gelatinous layer and the statoconia together are referred to as the otolithic membrane, where the tips of the stereocilia and kinocilium are embedded.
When the head is tilted such that gravity pulls on the statoconia the gelatinous layer is pulled in the same direction causing the sensory hairs to bend. Within the utricle is a small 2 by 3 mm patch of hair cells called the macula of utricle; the macula of utricle, which lies horizontally on the floor of the utricle, contains the hair cells. These hair cells are mechanoreceptors which consist of 40 to 70 stereocilia and only one true cilium called a kinocilium; the kinocilium is the only sensory aspect of the hair cell and is what causes hair cell polarization. The tips of these stereocilia and kinocilium are embedded in a gelatinous otolithic membrane; this membrane is weighted with calcium carbonate-protein granules called otoliths. The otolithic membrane increases their inertia; the addition in weight and inertia is vital to the utricle's ability to detect linear acceleration, as described below, to determine the orientation of the head. The macula consists of three layers; the bottom layer is made of sensory hair cells which are embedded in the bottom of a gelatinous layer.
Each hair cells consists of 40 to 70 stereocilia and a kinocilium, which lies in the middle of the stereocilia and is the most important receptor. On top of this layer lie calcium carbonate crystals called otoconia; the otoliths are heavy, providing weight to the membrane as well as inertia. This allows for a greater sense of motion. Labyrinthine activity responsible for the nystagmus induced by off-vertical axis rotation arises in the otolith organs and couples to the oculomotor system through the velocity storage mechanism; that portion, lodged in the recess forms a pouch or cul-de-sac, the floor and anterior wall of which are thickened and form the macula acustica utriculi, which receives the utricular filaments of the acoustic nerve. The cavity of the utricle communicates behind with the semicircular ducts by five orifices; the ductus utriculosaccularis comes off of the anterior wall of the utricle and opens into the ductus endolymphaticus. The utricle contains mechanoreceptors called hair cells that distinguish between degrees of tilting of the head, thanks to their apical stereocilia set-up.
These are covered by otoliths which, due to gravity, tilt them. Depending on whether the tilt is in the direction of the kinocilium or not, the resulting hair cell polarisation is excitatory or inhibitory, respectively. Any orientation of the head causes a combination of stimulation to the utricles and saccules of the two ears; the brain interprets head orientation by comparing these inputs to each other and to other input from the eyes and stretch receptors in the neck, thereby detecting whether only the head is tilted or the entire body is tipping. The inertia of the otolithic membranes is important in detecting linear acceleration. Suppose you are sitting in a car at a stoplight and begin to move; the otolithic membrane of the macula utriculi lags behind the rest of the tissues, bends the stereocilia backward, stimulates the cells. When you stop at the next light, the macula stops but the otolithic membrane keeps going for a moment, bending the stereocilia forward; the hair cells convert this pattern of stimulation to nerve signals, the brain is thus advised of changes in your linear velocity.
This signal to the vestibular nerve does not adapt with time. The effect of this is that, for example, an individual lying down to sleep will continue to detect that they are lying down hours when they awaken; this article incorporates text in the public domain from page 1051 of the 20th edition of Gray's Anatomy Diagram at ipfw.edu
In physics, sound is a vibration that propagates as an audible wave of pressure, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Humans can only hear sound waves as distinct pitches when the frequency lies between about 20 Hz and 20 kHz. Sound waves above 20 kHz is not perceptible by humans. Sound waves below 20 Hz are known as infrasound. Different animal species have varying hearing ranges. Acoustics is the interdisciplinary science that deals with the study of mechanical waves in gases and solids including vibration, sound and infrasound. A scientist who works in the field of acoustics is an acoustician, while someone working in the field of acoustical engineering may be called an acoustical engineer. An audio engineer, on the other hand, is concerned with the recording, manipulation and reproduction of sound. Applications of acoustics are found in all aspects of modern society, subdisciplines include aeroacoustics, audio signal processing, architectural acoustics, electro-acoustics, environmental noise, musical acoustics, noise control, speech, underwater acoustics, vibration.
Sound is defined as " Oscillation in pressure, particle displacement, particle velocity, etc. propagated in a medium with internal forces, or the superposition of such propagated oscillation. Auditory sensation evoked by the oscillation described in." Sound can be viewed as a wave motion in air or other elastic media. In this case, sound is a stimulus. Sound can be viewed as an excitation of the hearing mechanism that results in the perception of sound. In this case, sound is a sensation. Sound can propagate through a medium such as air and solids as longitudinal waves and as a transverse wave in solids; the sound waves are generated by a sound source, such as the vibrating diaphragm of a stereo speaker. The sound source creates vibrations in the surrounding medium; as the source continues to vibrate the medium, the vibrations propagate away from the source at the speed of sound, thus forming the sound wave. At a fixed distance from the source, the pressure and displacement of the medium vary in time.
At an instant in time, the pressure and displacement vary in space. Note that the particles of the medium do not travel with the sound wave; this is intuitively obvious for a solid, the same is true for liquids and gases. During propagation, waves can be refracted, or attenuated by the medium; the behavior of sound propagation is affected by three things: A complex relationship between the density and pressure of the medium. This relationship, affected by temperature, determines the speed of sound within the medium. Motion of the medium itself. If the medium is moving, this movement may increase or decrease the absolute speed of the sound wave depending on the direction of the movement. For example, sound moving through wind will have its speed of propagation increased by the speed of the wind if the sound and wind are moving in the same direction. If the sound and wind are moving in opposite directions, the speed of the sound wave will be decreased by the speed of the wind; the viscosity of the medium.
Medium viscosity determines the rate. For many media, such as air or water, attenuation due to viscosity is negligible; when sound is moving through a medium that does not have constant physical properties, it may be refracted. The mechanical vibrations that can be interpreted as sound can travel through all forms of matter: gases, liquids and plasmas; the matter that supports the sound is called the medium. Sound cannot travel through a vacuum. Sound is transmitted through gases and liquids as longitudinal waves called compression waves, it requires a medium to propagate. Through solids, however, it can be transmitted as transverse waves. Longitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction, while transverse waves are waves of alternating shear stress at right angle to the direction of propagation. Sound waves may be "viewed" using parabolic objects that produce sound; the energy carried by an oscillating sound wave converts back and forth between the potential energy of the extra compression or lateral displacement strain of the matter, the kinetic energy of the displacement velocity of particles of the medium.
Although there are many complexities relating to the transmission of sounds, at the point of reception, sound is dividable into two simple elements: pressure and time. These fundamental elements form the basis of all sound waves, they can be used to describe, in every sound we hear. In order to understand the sound more a complex wave such as the one shown in a blue background on the right of this text, is separated into its component parts, which are a combination of various sound wave frequencies. Sound waves are simplified to a description in terms of sinusoidal plane waves, which are characterized by these generic properties: Frequency, or its inverse, wavelength Amplitude, sound pressure or Intensity Speed of sound DirectionSound, perceptible by humans has frequencies from abou
The oval window is a membrane-covered opening that leads from the middle ear to the vestibule of the inner ear. Vibrations that contact the tympanic membrane travel through the three ossicles and into the inner ear; the oval window is the intersection of the middle ear with the inner ear and is directly contacted by the stapes. It is a reniform opening leading from the tympanic cavity into the vestibule of the internal ear, it is occupied by the base of the stapes, the circumference of, fixed by the annular ligament to the margin of the foramen. Round window This article incorporates text in the public domain from page 1040 of the 20th edition of Gray's Anatomy Diagram at Washington University The Anatomy Wiz. Oval Window
Vestibule of the ear
The vestibule is the central part of the bony labyrinth in the inner ear, is situated medial to the eardrum, behind the cochlea, in front of the three semicircular canals. The name comes from the Latin vestibulum an entrance hall; the vestibule flattened transversely. In its lateral or tympanic wall is the oval window, closed, in the fresh state, by the base of the stapes and annular ligament. On its medial wall, at the forepart, is a small circular depression, the recessus sphæricus, perforated, at its anterior and inferior part, by several minute holes for the passage of filaments of the acoustic nerve to the saccule; this ridge bifurcates below to enclose a small depression, the fossa cochlearis, perforated by a number of holes for the passage of filaments of the acoustic nerve which supply the vestibular end of the ductus cochlearis. The orifice of the aquæductus vestibuli is the hind part of the medial wall, it transmits a small vein and contains a tubular prolongation of the membranous labyrinth, the endolymphatic duct, which ends in a cul-de-sac between the layers of the dura mater within the cranial cavity.
On the upper wall or roof, there is a transversely oval depression, the recessus ellipticus, separated from the recessus sphæricus by the crista vestibuli mentioned. The pyramid and adjoining part of the recessus ellipticus are perforated by a number of holes; the apertures in the pyramid transmit the nerves to the utricle. Behind, the five orifices of the semicircular canals can be found. In the frontal view, there is an elliptical opening which communicates with the scala vestibuli of the cochlea; this article incorporates text in the public domain from page 1047 of the 20th edition of Gray's Anatomy Vestibular system
An anvil is a metalworking tool consisting of a large block of metal, with a flattened top surface, upon which another object is struck. Anvils are as massive as is practical, because the higher their inertia, the more efficiently they cause the energy of striking tools to be transferred to the work piece. In most cases the anvil is used as a forging tool. Before the advent of modern welding technology, it was a primary tool of metal workers; the great majority of modern anvils are made of cast or forged steel, heat treated. Inexpensive anvils have been made of cast iron and low quality steel, but are considered unsuitable for serious use as they deform and lack rebound when struck; because anvils are ancient tools and were at one time commonplace, they have acquired symbolic meaning beyond their use as utilitarian objects. They have found their way into popular culture including episodes of Looney Tunes, the name of a heavy metal band, usage by blacksmiths as well as jewelers and metal smiths.
The primary work surface of the anvil is known as the face. It is made of hardened steel and should be flat and smooth with rounded edges for most work. Any marks on the face will be transferred to the work. Sharp edges tend to cut into the metal being worked and may cause cracks to form in the workpiece; the face is hardened and tempered to resist the blows of the smith's hammer, so the anvil face does not deform under repeated use. A hard anvil face reduces the amount of force lost in each hammer blow. Hammers and work pieces of hardened steel should never directly strike the anvil face with full force, as they may damage it; the horn of the anvil is a conical projection used to form various round shapes and is unhardened steel or iron. The horn is used in bending operations, it is used by some smiths as an aid in "drawing down" stock. Some anvils European, are made with two horns, one square and one round; some anvils are made with side horns or clips for specialized work. The step is that area of the anvil between the "horn" and the "face".
It is used for cutting. The hardie hole is a square hole into which specialized forming and cutting tools, called Hardy tools, are placed, it is used in punching and bending operations. The pritchel hole is a small round hole, present on most modern anvils; some anvils have more than one. It is used for punching. At times, smiths will fit a second tool to this hole to allow the smith more flexibility when using more than one anvil tool. An anvil needs to be placed upon a sturdy base made from an fire resistant material, it requires being fastened to the base, so it will not move when struck with a hammer. A loose anvil is unsafe, as it can fall off the base and is an ineffective forging tool. Common methods of attaching an anvil are spikes, steel or iron straps, bolts where there are holes provided, cables. A smith would use whatever was at hand, as long as it held the anvil in place; the anvil is placed as near to the forge as is convenient no more than one step from the forge to prevent heat loss in the work piece.
The most common base traditionally was a hard wood log or large timber buried several feet into the floor of the forge shop floor. This was done to make the anvil immobile when heavy bending were done upon the anvil. In the industrial era cast iron bases became available, they had the advantage of adding additional weight to the anvil, making it more stable while making the anvil movable. These bases are sought after by collectors today; when concrete became available, there was a trend to make steel reinforced anvil bases by some smiths, though this practice has been abandoned. In more modern times many anvils have been placed upon bases fabricated from steel a short thick section of a large I-Beam. In addition, bases have been made from dimensional lumber bolted together to form a large block or steel drums full of oil-saturated sand to provide a damping effect. In recent times tripod bases of fabricated steel have become popular with some smiths. There are many designs for anvils, which are tailored for a specific purpose or to meet the needs of a particular smith.
For example, there were anvils made for farriers, general smiths, chain makers, saw tuners, coach makers and many other types of metal workers. Such designs have originated in diverse geographic locations; the common blacksmith's anvil is made of either forged or cast steel, forged wrought iron with a hard steel face or cast iron with a hard steel face. Cast iron anvils are not used for forging as they are incapable of standing up to the impact and will crack and dent. Cast iron anvils without a hard steel face do not have the rebound that a harder anvil would and will tire out the smith; some anvils have been made with a smooth top working face of hardened steel welded to a cast iron or wrought iron body, though this manufacturing method is no longer in use. At one end, the common smith's anvil has a projecting conical bick used for hammering curved work pieces; the other end is called the heel. The other end is provided with a bick rectangular in section. Most anvils made since the late 18th century have a hardy hole
Ossicles are small calcareous elements embedded in the dermis of the body wall of echinoderms. They provide rigidity and protection, they are found in different forms and arrangements in sea urchins, brittle stars, sea cucumbers, crinoids. The ossicles and spines are the only parts of the animal to be fossilized after an echinoderm dies. Ossicles are created intracellularly by specialised secretory cells known as sclerocytes in the dermis of the body wall of echinoderms; each ossicle is composed of microcrystals of calcite arranged in a three-dimensional lattice known as a stereom. Under polarized light the ossicle behaves as if it were a single crystal because the axes of all the crystals are parallel; the space between the crystals is known as the stroma and allows entry to sclerocytes for enlargement and repair. The honeycomb structure is light but tough and collagenous ligaments connect the ossicles together; the ossicles are embedded in a tough connective tissue, part of the endoskeleton. When an ossicle becomes redundant, specialised cells known as phagocytes are able to reabsorb the calcareous material.
All the ossicles those that protrude from the body wall, are covered by a thin layer of epidermis but functionally they act more like an exoskeleton than an endoskeleton. Ossicles have a variety of forms including flat plates, spines and crosses, specialised compound structures including pedicellariae and paxillae. Plates are tabular ossicles, they form the main skeletal covering for sea urchins and sea stars. Spines are ossicles that project from the body wall and articulate with other ossicles through ball and socket joints mounted on tubercles, they are formed from crystals of calcite and can be solid or hollow, long or short, thick or thin and sharp or blunt. The spines serve a protective function and are used for locomotion. Pedicellariae are compound ossicles that articulate with other ossicles and protrude from the aboral surface of some sea stars, they have short fleshy stalks and either two or three moveable ossicles forming a set of pincer-like jaws. They may be grouped around spines.
Their function is to pick off debris so as to keep the surface clean and to prevent larvae of other invertebrates from settling and growing there. Paxillae are small pillar-shaped ossicles with flat tops sometimes found covering the aboral surface of sea stars such as Luidia and Goniaster that live underneath sediment, their stalks emerge from the body wall and their tops, each fringed with short spines, abut each other to form a protective external false skin. Beneath this is a water-filled cavity which contains the madreporite and delicate gill structures known as papullae. Sea urchins are covered with plates which are fused together to give a rigid test, but in the order Echinothurioida, the test is leathery because the plates are separate; the test is divided into five segments. Each contains two ambulacral rows of plates alternating with two interambulacral rows; the ambulacral plates are each pierced by a pair of pores through which the active tube feet are connected to the water vascular system.
Ossicles in the form of spines connect to tubercles on some of the plates. Sea urchins have several types of pedicellariae. A ring of specialised plates surround the aboral pole consisting of five genital plates, one of, the madreporite, five smaller ocular plates. Other large specialist plates surround the mouth in a set of jaws known as Aristotle's lantern. Sea stars have separate plates giving flexibility to arms, they are arranged into interambulacral and ambulacral regions and the arms have an ambulacral groove on the underside from which the tube feet project. Other ossicles that may be present include paxillae. There is a large row of marginal plates adjoining the ambulacral groove, sometimes bearing spines. Brittle stars do not have pedicellariae, the plates that cover their surface are known as shields. On the arms these are in four rows with each segment having an aboral and oral shield and two lateral shields with fringing spines. Other ossicles include spines, small scales and vertebrae.
The large central vertebrae in each arm segment provides the articulating element that joins it to the next. Several types of small ossicles are found in the body wall of sea cucumbers. Baskets are cup-shaped and have four projections. Buttons may be smooth or knobbed. Perforated plates are sieve-like and widely distributed and rods provide support for the tube feet and tentacles. In the order Apodida, members of which lack tube feet, there are anchor-shaped ossicles attached to anchor plates; the flukes provide traction. Crinoids are supported by jointed stalks containing substantial compound ossicles; the crown has ossicles scattered throughout the connective tissue. The arms contain columns of well-developed vertebrae-like ossicles; each joint has limited movement but the whole arm can be coiled and uncoiled. Ruppert, Edward E.. Invertebrate Zoology, 7th edition. Cengage Learning. ISBN 81-315-0104-3
A stirrup is a light frame or ring that holds the foot of a rider, attached to the saddle by a strap called a stirrup leather. Stirrups are paired and are used to aid in mounting and as a support while using a riding animal, they increase the rider's ability to stay in the saddle and control the mount, increasing the animal's usefulness to humans in areas such as communication and warfare. In antiquity, the earliest foot supports consisted of riders placing their feet under a girth or using a simple toe loop. A single stirrup was used as a mounting aid, paired stirrups appeared after the invention of the treed saddle; the stirrup appeared in China in the first few centuries AD and spread westward through the nomadic peoples of Central Eurasia. The use of paired stirrups is credited to the Chinese Jin Dynasty and came to Europe during the Middle Ages; some argue that the stirrup was one of the basic tools used to create and spread modern civilization as important as the wheel or printing press.
The English word "stirrup" stems from Old English stirap, Middle English stirop, styrope, i.e. a mounting or climbing-rope. Compare Old English stīgan "to ascend" and rap "rope, cord"; the stirrup, which gives greater stability to a rider, has been described as one of the most significant inventions in the history of warfare, prior to gunpowder. As a tool allowing expanded use of horses in warfare, the stirrup is called the third revolutionary step in equipment, after the chariot and the saddle; the basic tactics of mounted warfare were altered by the stirrup. A rider supported by stirrups was less to fall off while fighting, could deliver a blow with a weapon that more employed the weight and momentum of horse and rider. Among other advantages, stirrups provided greater balance and support to the rider, which allowed the knight to use a sword more efficiently without falling against infantry adversaries. Contrary to common modern belief, however, it has been asserted that stirrups did not enable the horseman to use a lance more though the cantled saddle did.
The invention of the stirrup occurred late in history, considering that horses were domesticated in 4500 BC, the earliest known saddle-like equipment were fringed cloths or pads with breast pads and cruppers used by Assyrian cavalry around 700 BCThe earliest manifestation of the stirrup was a toe loop that held the big toe and was used in India late in the second century BC, though may have appeared as early as 500 BC. This ancient foot support consisted of a looped rope for the big toe, at the bottom of a saddle made of fibre or leather; such a configuration was suitable for the warm climate of south and central India where people used to ride horses barefoot. A pair of megalithic double bent iron bars with curvature at each end, excavated in Junapani in the central Indian state of Madhya Pradesh have been regarded as stirrups although they could as well be something else. Buddhist carvings in the temples of Sanchi and the Bhaja caves dating back between the 1st and 2nd century BC figure horsemen riding with elaborate saddles with feet slipped under girths.
In this regard archaeologist John Marshall described the Sanchi relief as "the earliest example by some five centuries of the use of stirrups in any part of the world". Some credit the nomadic Central Asian group known as the Sarmatians as developing the first stirrups; the invention of the solid saddle tree allowed development of the true stirrup. Without a solid tree, the rider's weight in the stirrups creates abnormal pressure points and make the horse's back sore. Modern thermography studies on "treeless" and flexible-tree saddle designs have found that there is considerable friction across the center line of a horse's back. A coin of Quintus Labienus, in service of Parthia, minted circa 39 BC depicts on its reverse a saddled horse with hanging objects. Smith suggests they are pendant cloths, while Thayer suggests that, considering the fact that the Parthians were famous for their mounted archery, the objects are stirrups, but adds that it is difficult to imagine why the Romans would never have adopted the technology.
In Asia, early solid-treed saddles were made of felt. These designs date to 200 BC One of the earliest solid-treed saddles in the west was first used by the Romans as early as the 1st century BC, but this design did not have stirrups, it is speculated. Stirrups were used in China at the latest by the early 4th century AD. A funerary figurine depicting a stirrup dated AD 302 was unearthed from a Western Jin dynasty tomb near Changsha; the stirrup depicted is a mounting stirrup, only placed on one side of the horse, too short for riding. The earliest reliable representation of a full-length, double-sided riding stirrup was unearthed from a Jin tomb, this time near Nanjing, dating to the Eastern Jin period, AD 322; the earliest extant double stirrups were discovered in the tomb of a Northern Yan noble, Feng Sufu, who died in AD 415. Stirrups have been found in Goguryeo tombs dating to the 4th and 5th centuries AD, but these do not contain any specific date; the stirrup appeared to be in widespread use across China by AD 477.
The appearance of the stirrup in China coincided with the rise of armoured cavalry in the region. Dated to 357 AD, the tomb of Dong Shou shows armoured riders as well as horses. References to "iron cavalry"