Life Sciences Glossary: Ear, Defects of Ear, Nose and Basic Modalities of Taste

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  • Ears are the stat acoustic organs meant for both balancing and hearing. Ears are paired structures attached to the skull posterior- laterally in all vertebrates.
  • There are three regions of ear: external, middle and internal.
  • External ear consists of pinna (auricle) and auditory canal (external auditory meatus) . Pinna is provided with voluntary muscles in many animals; but voluntary muscles are absent in man. In man pinna is supported by elastic fibrocartilage and it is designed to collect sound waves.
  • Auditory canal conducts sound waves to middle ear. Auditory canals contains few hairs and specialized sebaceous glands called calumnious glands. Calumnious glands secrete crewmen (earwax) . The combination of hairs and crewmen helps to prevent foreign particles from entering the ear.
  • Tympanic membrane (eardrum) separates middle ear from external ear. Three auditory icicles in the middle ear are malleus, incus and stapes. The passage connecting the middle ear with pharynx is Eustachian tube. The function of Eustachian tube is to equalize air pressure in both sides (external and middle ear) of tympanic membrane.

The internal or inner ear is called the labyrinth, and it consists of two main divisions:

  • Bony labyrinth and
  • A Membranous labyrinth.

Bony labyrinth is filed with a fluid called perilymph. Membranous labyrinth contains a fluid called end lymph. Membranous labyrinth is called stat acoustic organ because it is concerned with both blanking and hearing Membranous labyrinth is divided into three parts:

  • Body proper (Utricles and Succubus)
  • Semicircular canals and
  • Cochlea.

Three semi-circular canals are anterior vertical, posterior vertical and horizontal.

  • Cochlea is a long coiled, tubular and bling outgrowth of succubus. Cochlea makes turns in man and is filled with end lymph and perilymph.
  • The perception of sound by a mammal involves the stimulation of mechanoreceptors located on organ of Corte.
  • There are two types of equilibrium, static equilibrium and dynamic equilibrium. Static equilibrium refers to orientation of the body (mainly head) relative to gravity. Dynamic equilibrium is the maintenance of the body position in response to sudden movements. The receptor organs for equilibrium are the succubus, utricles and semicircular canals. All of these are known as vestibular apparatus. Vestibular apparatus is a type of proprioceptor. Utricles and succubus are considered to be sense organs of static equilibrium the three semicircular canals maintain dynamic equilibrium.
  • Hearing is controlled by auditory area of the temporal lobe of cerebral cortex. Human ear is sensitive to sound frequency 50 - 20,000 cycles/sec. The measuring unit of sound intensity is decibel.

Defects of Ear

  • Labyrinthine disease: Malfunction of inner ear.
  • Meniere՚s disease: Loss of hearing due to defect in cochlea.
  • Otitis media: Acute infection of middle ear.
  • Eustachitis: Inflammation of Eustachian tube.
  • Meningitis (Tympani is) : Inflammation of eardrum.
  • Nostalgia: Earache (pain in ear) .


Nose may be called the sense organ for smell or olfaction. Olfactory epithelium lines the nasal cavity. Olfactory epithelium (Schneider Ian membrane) is a pseudo stratified epithelium consisting of three types of cells, viz. , olfactory receptor cells, sustencular or supporting cells and basal cells. Olfactory receptor cells function as chemoreceptors; they are stimulated by specific chemical substances. Olfactory receptor cells are bipolar neurons, their cell bodies lie between the supporting cells. The unmyelinated axons of the olfactory cells unite to form the olfactory nerve (cranial nerve I) . Olfactory stimuli such as pepper, ammonia and chloroform are irritating and may cause tearing because they stimulate the lacrimal and nasal receptors. Dogs have an acute olfactory sense. They can track people because they can distinguish between the odors of different persons.


Tongue is a Gusstaoreceptors or receptor for taste. Receptors for gustatory sensations are located in the taste buds. Taste buds are most numerous on the tongue. But they are also found on the soft palate, pharynx and epiglottis. Human tongue bears about 10,000 taste buds in its papillae. The papillae give the upper surface of the tongue its rough appearance. Circumvallate papillae, the largest type, are circular and form an inverted V- shaped row at the posterior portion of the tongue. Fungiform papillae are knob- like found on the top and sides of the tongue. Fusiform papillae are pointed thread- like structures that cover the anterior two- thirds of the tongue. All circumvallate and most fungiform papillae contain taste buds.

Taste Buds

The taste buds are oval bodies consisting of two types of cells: Supporting cells and gustatory cells. The supporting cells are a specialized epithelium that forms a capsule. Inside each capsule are four to twenty gustatory cells. Each gustatory cell contains a hair-like process (gustatory hair) that projects to the external surface through an opening in the taste bud called the taste poorer. Gustatory cells make contact with taste stimuli through taste pore.

Basic Modalities of Taste

Four fundamental sensations of taste are sweet, salt, sour and bitter. All other ‘tastes’ such as chocolate, pepper and coffee are actually odors. Each of the four tastes is due to a different response to different chemicals. Tip of the tongue is highly sensitive to sweet, anterior margin to salt, posterior margin to sour and posterior central portion to bitter substances. Sweet taste is evoked mainly by organic substances such as sugars. Dextrin՚s, glycerol, chloroform, saccharine and aspartame. Saccharine and aspartame are widely used as artificial sweetening agents by patients of diabetics. Salty taste results mainly from some captions like Na + of inorganic salts. Sour taste is evoked by H + ions produced by the ionization of acids. Bitter taste is evoked by many organic substances like quinine, morphine, caffeine, nicotine and urea. Bitter is also produced by the actions of many inorganic salts like magnesium salts.

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