ear

• The auricle, or PINNA, is what most people call the “ear”- the shell-shaped structure surrounding the auditory canal opening.

   
• The external acoustic meatus is a short, narrow chamber carved into the temporal bone of the skull;
• in its skin-lined walls are the CERUMINOUS GLANDS, which secrete waxy, YELLOW CERUMEN or EARWAX, which provides a sticky trap for foreign bodies and repels insects.
• Tympanic membrane. 

  Sound waves entering the auditory canal eventually hit the tympanic membrane, or EARDRUM, and cause it to vibrate;
• The tympanic cavity is flanked laterally by the eardrum and medially by a bony wall with two openings, the OVAL WINDOW AND THE INFERIOR, membrane-covered round window.
• The pharyngotympanic tube runs obliquely downward to link the middle ear cavity with the throat, and the mucosae lining the two regions are continuous.
• The TYMPANIC CAVITY is spanned by the three smallest bones in the body, the ossicles, which transmit the vibratory motion of the eardrum to the fluids of the inner ear;
• these bones, named for their shape, are the hammer, or MALLEUS, the anvil, or INCUS, and the stirrup, or STAPES
• Subdivisions.

   The three subdivisions of the bony labyrinth are THE SPIRALING, pea-sized cochlea, THE VESTIBULE, and THE SEMICIRCULAR CANALS.
• The bony labyrinth is filled with a plasma-like fluid called perilymph.
• Suspended in the perilymph is a membranous labyrinth, a system of membrane sacs that more or less follows the shape of the bony labyrinth.
•  The membranous labyrinth itself contains a thicker fluid called endolymph.
• The thousands of olfactory receptors, receptors for the sense of smell, occupy a postage stamp-sized area in the roof of each nasal cavity.
• The olfactory receptor cells are neurons equipped with OLFACTORY HAIRS, long cilia that protrude from the nasal epithelium and are continuously bathed by a layer of mucus secreted by underlying glands.
•  When the olfactory receptors located on the cilia are stimulated by chemicals dissolved in the mucus, they transmit impulses along the olfactory filaments, which are bundled axons of olfactory neurons that collectively make up the olfactory nerve.
•  The olfactory nerve conducts the impulses to the olfactory cortex of the brain.
• The taste buds, or specific receptors for the sense of taste, are widely scattered in the oral cavity; of the 10, 000 or so taste buds we have, most are on the tongue.
• The dorsal tongue surface is covered with small peg-like projections, or papillae.
•  The TASTE BUDS are found on the sides of the large round circumvallate papillae and on the tops of the more numerous fungiform papillae.
• The specific cells that respond to chemicals dissolved in the saliva are epithelial cells called gustatory cells.
• •  Their long microvillithe gustatory hairs- protrude through the taste pore, and when they are stimulated, they depolarize and impulses are transmitted to the brain.
• The facial nerve (VII) serves the anterior part of the tongue.
• The other two cranial nerves– the glossopharyngeal and vagus- serve the other taste bud-containing areas.
• TASTE BUD CELLS are among the most dynamic cells in the body, and they are replaced every seven to ten days by basal cells found in the deeper regions of the taste buds.