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Weber Test

Weber test

In the Weber test of hearing, a tuning fork is struck and placed on the patient's forehead. The patient is asked to report in which ear the sound is heard louder. A normal patient would report that the sound is heard equally in both ears. A patient with a conductive hearing loss would hear the sound louder in the affected ear. This is because the affected ear cannot hear ambient noises as well because of its conductive hearing loss and so is effectively masked to these noises and able to focus more on the sound conducted through the skull. You can replicate this yourself by plugging one ear with your finger (i.e. mimicking a conductive hearing loss) and performing the Weber test on yourself. A patient with a sensorineural hearing loss would hear the sound louder in the normal ear, because the affected ear is less effective at picking up sound even if is transmitted directly by conduction into the cochlea. Category:Otolaryngology Category:Eponymous medical signs

Hearing (sense)

Hearing, or audition, is one of the traditional five senses, and refers to the ability to detect sound. There is a common misconception that listening and hearing are the same thing. Hearing is an involuntary process of sound waves striking the ear drum. Hearing requires no effort. Listening, however, is purely voluntary and it requires effort. Listening requires one to: 1) Attend - hear and pay attention to the signal 2) Understand - make sense of the message 3) Respond - give feedback to the speaker 4) Remember In human beings, hearing is performed by the ears, which also perform the function of balance, a sense in itself but not one of the traditional list (due to Aristotle). This is in common with most mammals. Many other organisms also have some form of hearing, either by some sort of ear, or by other structures, or by a combination. A common rule of thumb used to describe human hearing is that human hearing is sensitive in the range of frequency of 20 Hz to 20 kHz, though this varies significantly with age, occupational hearing damage, and gender; some individuals are able to hear up to 22 kHz and perhaps beyond, while others are limited to about 16 kHz. Frequencies capable of being heard by humans are called audio or referred to as sonic. Frequencies higher than audio are referred to as ultrasonic, while frequencies below audio are referred to as infrasonic. Some organisms are able to hear ultrasound and/or infrasound. Some bats use ultrasound for echo location while in flight. Dogs are able to hear ultrasound, which is the principle of 'silent' dog whistles. Snakes sense infrasound through their bellies, and there is evidence that whales and elephants may use it for communication. See sound for hearing ranges of various organisms. The hearing can be tested using a device or computer program called audiometer. One should bear in mind that, as Arthur Reber says, 'Explaining hearing adequately has proven a singularly difficult task. One would almost ensure oneself a Nobel prize by presenting a theory explaining satisfactorily no more than the perception of pitch and loudness.' (A. S. & E. S. Reber, The Penguin Dictionary of Psychology (3rd Edn., 2001))

Localization of Sound

Humans can hear the direction of the source of a sound, sometimes with surprising accuracy. Two mechanisms are known to be used.
- The nervous system can resolve time differences as small as the time it takes sound to pass one ear and reach the other.
- For high frequencies, frequencies with a wavelength shorter than the listener's head, more sound reaches the nearer ear. Neither of these mechanisms work as well in water, in which the speed of sound is faster than in air. The arrival time of a sound to a particular ear is given greater weight when localizing than relative intensity, according to an observation known as the Law of the First Wavefront.

From the Ear to the Primary Auditory Cortex

Axons of the vestibulocochlear nerve (auditory nerve) synapse in the cochlear nucleus of the same side. Projections lead from the cochlear nuclei to the superior olives, and the olivary nuclei continue on passing through the lateral lemniscus towards the inferior colliculi, where they synapse again on neurons that project to the medial geniculate nuclei of the thalamus, which in turn projects toward the primary auditory cortex. This Primary Auditory Cortex is located slightly below the lateral fissure between the frontal and the temporal lobes.

External links

- [http://www.sensaura.co.uk/whitepapers/index.php Sensaura white papers] on human hearing and emulating hearing in 3D
- [http://www.med.uwo.ca/physiology/courses/sensesweb/L9Auditory/L9Auditory.swf flash demonstration on hearing] (664 KB)
- [http://communication-skills-4confidence.com/listening-skills.html Listening Skills] How to develop listening skills. Category:Sound ja:聴覚

Tuning fork

A tuning fork is a simple metal two-pronged fork with the tines formed from a U-shaped bar of elastic material (usually steel). A tuning fork resonates at a specific constant pitch when set vibrating by striking it against a surface or with an object, and after waiting a moment to allow some high overtones to die out. The pitch that a particular tuning fork generates depends on the length of the two prongs, with two nodes near the bend of the U. Currently, the most common tuning fork used by musicians sounds the note of A (440 HZ), but they are commercially made in all keys. This is because the Key of A is the standard concert pitch used by most orchestras standard concert pitch The tuning fork was invented in 1711 by John Shore, Sergeant Trumpeter to the court, who had parts specifically written for him by both George Friderich Handel and Henry Purcell. When struck, it gives out a very faint note which is barely audible unless held close to the ear. For this reason, it is sometimes struck and then pressed down on a solid surface such as a desk which acts as a sounding board and greatly amplifies the note. Well-known manufacturers of tuning forks include Ragg and John Walker, both of Sheffield, England. They are commonly used to tune musical instruments, although electronic tuners also exist, and some musicians have perfect pitch. Tuning forks can be tuned by grinding material off the tines (filing the ends of the tines to raise it or filing inside the base of the tines to lower it) or by sliding weights attached to the prongs. Once tuned, a tuning fork's frequency varies only with changes in the elastic modulus of the material; for precise work, a tuning fork should be kept in a thermostatically controlled enclosure. Large forks are often made to be driven electrically, like an electric bell or buzzer, and can vibrate for an indefinite time. A number of keyboard musical instruments have been made which use tuning forks as their sound source. None of them have ever been popular, although the Rhodes piano, which has hammers hitting constructions working on the same principle as tuning forks, is widely used. Rhodes piano A tiny quartz tuning fork is used in crystal oscillators, the most notable use of which are quartz digital watches. The piezoelectric properties of quartz crystals cause a quartz tuning fork to generate a pulsed electrical current as it resonates, which is used by the computer chip in the watch to keep track of the passage of time. In today's watches, they generally resonate at

2^=32,768

Hz. (See quartz clock.) Tuning forks are sometimes used by medical practitioners to assess a patient's hearing. They are also used therapeutically in sonopuncture. John Beaulieu, a researcher on the therapeutic benefits of tuning forks, has recorded an album of music made entirely with tuning forks, called Calendula. Category:Musical instruments ja:音叉

Forehead

In human anatomy, the forehead or brow is the bony vertical part of the head above the eyes. Muscles of the forehead include the frontalis, which moves and contracts the forehead's scalp.
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Conductive hearing loss

Conductive hearing loss is a failure in the efficient conduction of sound waves through the outer ear, typanic membrane (eardrum) or middle ears (ossicles). This type of hearing loss may occur in conjunction with sensorineural hearing loss or alone. When a Weber test is carried out, sound localizes to the ear affected by the conductive loss. A Rinne test, in which air conduction is normally greater than bone conduction, is usually negative (abnormal), and shows higher greater bone conduction than air conduction. Table 1. A table comparing sensorineural hearing loss to conductive Category:deaf culture

Skull

A skull, or cranium, is a bony structure of Craniates which serves as the general framework for a head. The skull supports the structures of the face and protects the brain against injury.

Humans

brain brain In humans, the adult skull is normally made up of 28 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, rigid articulations permitting very little movement. Eight bones form the neurocranium (braincase), a protective vault of bone surrounding the brain and medulla oblongata. Fourteen bones form the splanchnocranium, the bones supporting the face. Encased within the temporal bones are the six ear ossicles of the middle ear. The hyoid bone, supporting the larynx, is usually not considered as part of the skull, as it does not articulate with any other bones.

Development of the skull

The skull is a complex structure; its bones are formed both by intramembranous and endochondral ossification. The bones of the splanchnocranium and the sides and roof of the neurocranium are formed by intramembranous (or dermal) ossification, while the bones supporting the brain (the occipital, sphenoid, temporal, and ethmoid) are largely formed by endochondral ossification. At birth, the human skull is made up of 45 separate bony elements. As growth occurs, many of these bony elements gradually fuse together into solid bone (for example, the frontal bones). The bones of the roof of the skull are initially separated by regions of dense connective tissue called "sutures". There are five sutures: the frontal suture, sagittal suture, lambdoid suture, coronal suture, and squamosal suture. At birth these regions are fibrous and moveable, necessary for birth and later growth. This growth can put a large amount of tension on the "obstetrical hinge," which is where the squamous and lateral parts of the occipital bone meet. A possible complication of this tension is rupture of the great cerebral vein of Galen. Larger regions of connective tissue where multiple sutures meet are called fontanelles. The six fontanelles are: the anterior fontanelle, the posterior fontanelle, the two sphenoid fontanelles, and the two mastoid fontanelles. As growth and ossification progress, the connective tissue of the fontanelles is invaded and replaced by bone. The posterior fontanelle usually closes by eight weeks, but the anterior fontanelle can remain up to eighteen months. The anterior fontanelle is located at the junction of the frontal and parietal bones; it is a "soft spot" on a baby's forehead. Careful observation will show that you can count a baby's heart rate by observing his or her pulse pulsing softly through the anterior fontanelle.

Pathology

If the brain is bruised or injured it can be extremely serious. Normally the skull protects the brain from damage through its hard unyieldingness, but in some cases of head injury, there can be raised intracranial pressure through mechanisms such as a subdural haematoma. In these cases the raised intracranial pressure can cause herniation of the brain out of the foramen magnum ('coning') because there is no space for the brain to expand;this can result in significant brain damage or death unless an urgent operation is performed to relieve the pressure. This is why patients with concussion must be watched extremely carefully. In earlier times, a skull operation called trepanation was often performed for semi-mystical reasons and not only as an attempted life-saving technique. The skull also contains the sinus cavities. The meninges are the membranes that separate the brain from the skull.

Craniometry and morphology of human skulls

Like the face of a living individual, a human skull also can tell to a certain degree his or her life history and origin. Forensic scientists and archaeologist uses metric and nonmetric traits to estimate what the bearer of the skull looked like. When a good amount of bones are found, such as at Spitalfields in the UK and Jomon shell mounds in Japan, osteologists can use such traits, such as proportions of length, height, width, to know the relationships of population of the study, with living or extinct ones.

Sexual differences

In general, male skulls tend to be larger and more robust than female skulls. Male skulls typically have more prominent supraorbital ridges, a more prominent glabella, and more prominent temporal lines. Male skulls typically have larger, broader palates, squarer orbits, larger mastoid processes, larger sinuses, and larger occipital condyles than do females. Male mandibles typically have squarer chins and thicker, rougher muscle attachments than female mandibles. All of these features vary considerably within human populations, making it difficult to identify the sex of a skull without knowledge of the population it came from. The pelvis is considered the best skeletal indicator of sex.

Ancestry

Although persons' descents are occasionally stereotyped as different from other ethnic groups on the basis of a variety of traits like eye, hair and skin color, all such characters are not discrete nor preserved in bones. Among archaeologists and forensic scientists, it is well-known that the most consistent and unique trait of ancestry in skeleton is skull shape.

Bones of the human skull

Cranial bones

- frontal bone
- parietal bone (2)
- temporal bone (2)
- occipital bone
- sphenoid bone
- ethmoid bone

Facial bones

- mandible
- maxilla (2)
- palatine bone (2)
- zygomatic bone (2)
- nasal bone (2)
- lacrimal bone (2)
- vomer bone
- inferior nasal conchae (2)

Ear ossicles

- malleus (2)
- incus (2)
- stapes (2)

Wormian bones

In addition to the usual centers of ossification of the cranium, others may occur, giving rise to irregular isolated bones termed sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, but are occasionally seen at the fontanelles, especially the posterior. One, the pterion ossicle, sometimes exists between the sphenoidal angle of the parietal bone and the great wing of the sphenoid bone. They have a tendency to be more or less symmetrical on the two sides of the skull, and vary in size. Their number is generally limited to two or three; but more than a hundred have been found in the skull of an adult hydrocephalic subject. Note: Ole Worm, Professor of Anatomy at Copenhagen, 1624–1639, was erroneously supposed to have given the first detailed description of these bones.

Other features of the skull

Foramina of skull base

The following is a list of holes, or foramina, in the base of the skull and what goes through each of them. Arranged from anterior to posterior:
- foramen caecum - emissary veins to superior sagittal sinus
- foramina of cribriform plate - olfactory nerve bundles
- posterior ethmoidal foramen - posterior ethmoidal artery, vein and nerve
- optic canal - optic nerve (II), ophthalmic artery
- superior orbital fissure
- oculomotor nerve (III)
- trochlear nerve (IV)
- lacrimal, frontal and nasociliary branches of ophthalmic nerve (V₁)
- abducens nerve (VI)
- superior ophthalmic vein
- foramen rotundum - maxillary nerve (V₂)
- foramen ovale
- mandibular nerve (V₃)
- accessory meningeal artery
- lesser petrosal nerve (occasionally)
- foramen spinosum
- middle meningeal artery and vein
- meningeal branch of mandibular nerve
- foramen lacerum
- internal carotid artery
- internal carotid nerve plexus
- hiatus of canal of lesser petrosal nerve
- hiatus of canal of greater petrosal nerve
- internal acoustic meatus
- facial nerve (VII)
- vestibulocochlear nerve (VIII)
- labyrinthine artery
- jugular foramen
- inferior petrosal sinus
- glossopharyngeal nerve (IX)
- vagus nerve (X)
- accessory nerve (XI)
- sigmoid sinus
- posterior meningeal artery
- internal jugular vein
- hypoglossal canal - hypoglossal nerve (XII)
- foramen magnum
- medulla oblongata
- vertebral arteries
- meningeal branches of vertebral arteries
- spinal roots of accessory nerves

Notable sutures

Most sutures are named for the bones they articulate, but some have special names of their own.
- Sagittal - along the midline, between parietal bones
- Coronal - between the frontal and parietal bones
- Lambdoidal - between the parietals and the occipital bone
- Squamosal - between the parietal and the temporal bone
- Metopic - between the two frontal bones, prior to the fusion of the two into a single bone

External links

- [http://www.skullsunlimited.com/ Site with pictures of various animal skulls]
- [http://www.wtamu.edu/~rmatlack/Mammalogy/lab1.htm Skull terminology site by Texas A&M]

References

- White, T.D. 1991. Human osteology. Academic Press, Inc. San Diego, CA. Category:Head and neck Category:Skeletal system Category:Skull ja:頭蓋骨 simple:Cranium

Sensorineural hearing loss

Sensorineural hearing loss is a type of hearing loss in which the root cause lies in the vestibulocochlear nerve (Cranial nerve VIII), the inner ear, or central processing centers of the brain.
The Weber test, in which a tuning fork is touched to the head, localizes to the normal ear in people with this condition. The Rinne test, which tests air conduction vs. bone conduction is positive (normal), though both bone and air conduction are reduced equally. Sudden sensorineural hearing loss is an otologic emergency, and must be treated with a high dose of steroids.

Differential diagnosis

Sensorineural hearing loss may be congenital or acquired.

Congenital

- lack of development (aplasia) of the cochlea
- Chromosomal syndromes (rare)
- Congenital cholesteatoma - squamous epithelium from the ear canal invades the middle ear, which is normally covered by respiratory epithelium. The squamous epithelium behaves like an invasive tumour and destroys middle ear structures if not removed
- Delayed familial progressive

Acquired

- Inflammatory
- Suppurative labyrinthitis
- Meningitis
- Mumps
- Measles
- Viral
- Syphilis
- Ototoxic drugs
- Aminoglycosides (most common cause; e.g., tobramycin)
- Loop diuretics (e.g., Furosemide)
- Anti-Metabolites (e.g., Methotrexate)
- Salicylates (e.g., Aspirin)
- Physical trauma - either due to a fracture of the temporal bone affecting the cochlea and middle ear, or a shearing injury affecting cranial nerve VIII.
- Noise-induced - prolonged exposure to loud noises (>90dB) causes hearing loss which begins at 4000Hz (high frequency). The normal hearing range is from 125 Hz to 8,000 Hz.
- Presbyacusis - age-related hearing loss that occurs in the high frequency range (4000Hz to 8000Hz).
- Sudden hearing loss
- Idiopathic
- Vascular ischemia of the inner ear or CN 8
- Perilymph fistula, usually due to a rupture of the round or oval windows and the leakage of perilymph. The patient will most likely also experience vertigo or imbalance. A history of an event that increased intracranial pressure or caused trauma is usually present).
- Autoimmune - a prompt injection of steroids into ear is necessary.
- Cerebellopontine angle tumour (junction of the pons and cerebellum) (the cerebellopontine angle is the exit site of both CN7 and CN8. Patients with these tumours often have signs and symptoms corresponding to compression of both nerves)
- Acoustic neuroma (Vestibular schwannoma) - this is a schwannoma (benign neoplasm of Schwann cells)
- Meningioma - benign tumour of the pia and arachnoid maters
- Meniere's disease - causes sensorineural hearing loss in the low frequency range (125 Hz to 1000 Hz). Meniere's disesase is characterized by sudden attacks of vertigo lasting minutes to hours preceded by tinnitus, aural fullness, and fluctuating hearing loss. Table 1. A table comparing sensorineural to conductive hearing loss

Treatment

At present, sensorineural hearing loss is treated with hearing aids, which amplify sounds at pre-set frequencies to overcome a sensorineural hearing loss in that range; or cochlear implants, which stimulate the cochlear nerve directly.

References

- [http://www.med.uwo.ca/UME/Diane/Year2Postings2004-2005/Trimester%202/CNS/SensorineuralHearingLossPowerpointDrParnes.ppt Sensorineural Hearing Loss] - Powerpoint presentation slides for a presentation on sensorineural hearing loss (FDL).
- [http://www.med.uwo.ca/UME/Diane/Year2Postings2004-2005/Trimester%202/CNS/SensorineuralHearingLossDrParnes.pdf Sensorineural Hearing Loss] - Lecture notes for a presentation on sensorineural hearing loss (FDL). category:deaf culture

Cochlea

Named after the Latin word for snail shell, the cochlea is a coiled, tapered tube containing the auditory branch of the mammalian inner ear. Its core component is the Organ of Corti, the sensory organ of hearing.

Anatomy

The cochlea consists of three fluid-filled chambers - scala tympani and scala vestibuli (both of which contain perilymph), and scala media (which contains endolymph). The scala tympani and the scala vestibuli are contiguous with each other, merging at the tip of the "snail's shell" - the helicotrema. The stapes transmits vibrations to the fenestra ovalis (oval window) on the outside of the cochlea, which vibrates the perilymph in the scala vestibuli. This in turn vibrates the endolymph in the scala media, thus causing movements of the hair bundles of the hair cells, which are acoustic sensor cells that convert vibration into electrical potentials. The hair cells are arranged in four rows in the Organ of Corti along the entire length of the cochlear coil. Three rows consist of outer hair cells (OHCs) and one row consists of inner hair cells (IHCs). The IHCs provide the main neural output of the cochlea. The outer hair cells, instead, mainly receive neural input from the brain, which influences their motility as part of the cochlea’s mechanical pre-amplifier.x

Comparative physiology

The coiled form of cochlea is unique for mammals. In birds and in other non-mammalian vertebrates the compartment containing the sensory cells for hearing is occasionally also called “cochlea”, although it is not coiled up. Instead it forms a blind-ended tube, also called the cochlear duct. This difference apparently evolved in parallel with the differences in frequency range of hearing and in frequency resolution between mammals and non-mammalian vertebrates. Most bird species do not hear above 4-5 kHz, the currently known maximum being ca 11 kHz in the barn owl. Some marine mammals hear up to 200 kHz. The superior frequency resolution in mammals is due to their unique mechanism of pre-amplification of sound by active cell-body vibrations of outer hair cells. A long coiled compartment, rather than a short and straight one, provides more space for frequency dispersion and is therefore better adapted to the highly derived functions in mammalian hearing.

References

- Vater M, Meng J, Fox RC. Hearing organ evolution and specialization: Early and later mammals. In: GA Manley, AN Popper, RR Fay (Eds). Evolution of the Vertebrate Auditory System, Springer-Verlag, New York 2004, pp 256-288. See also: Cochlear implant Category:Auditory system

Category:Otolaryngology

Category:Medical specialties ko:분류:이비인후과

Category:Eponymous medical signs

These are medical signs that have been named after a person, usually the physician who first described them. Also see: List of eponymous medical signs Category:Eponymous medical terms Category:Sign (medicine)

Richard Trevithick

Richard Trevithick, född 13 april 1771 i Illogan, Cornwall i Storbritannien, död 22 april 1833, engelsk ingenjör som anses ha uppfunnit världens första fungerande lok för järnvägsdrift. Richard Trevithicks lok presenterades den 21 februari 1804. Detta lok anses vara förebilden till de allra flesta ånglok som sedan skulle tillverkas i mer än 100 år framåt i tiden. Loket var konstruerat vid ett järnbruk i Wales. Richard Trevithick har även byggt bland annat ångbåtar. Kategori:Engelska uppfinnare ja:リチャード・トレビシック

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