Structure and function of Ear-3

Physiology of Hearing

The vibration of matter, such as air, water, or solid material, produces sound. The vocal cords vibrate when someone speaks, which causes the air leaving the lungs to vibrate as well. As sound waves, this vibration travels through the atmosphere. The auricle gathers sound waves, which are then carried by the external auditory meatus to the tympanic membrane.

The tympanic membrane vibrates when sound waves hit it. Three middle ear ossicles vibrate as a result of this vibration. The malleus, which also begins to vibrate, is connected to the center of the ear drum. The malleus sends the vibration to the incus, which subsequently sends it to the stapes. The vibrating stapes causes the oval window's membrane to move in and out and vibrate. Waves in the scala vestibuli's perilymph are created by the oval window membrane vibrating. The round window expands outward into the middle ear as a result of pressure waves traveling from the scala vestibuli to the scala tympani.

Pressure waves are produced in the endolymph inside the cochlear duct as a result of the vestibular membrane being pushed along with the walls of the scala vestibuli and scala tympani. The basilar membrane is vibrated by the endolymph pressure waves. Since the basilar membrane supports the organ of Corti, changes to the basilar membrane cause changes to the hair cells. Cochlear neurons receive nerve signals as a result of hair cell bending. The nerve impulses are subsequently carried by the cochlear nerve to the auditory region of the cerebral cortex of the central nervous system, where sound perception takes place.

In essence, the external auditory meatus directs sound waves that the auricle has collected toward the ear drum. When sound waves hit the tympanic membrane, they cause a vibration that travels to the middle ear's three ossicles. The membrane of the oval window thus experiences vibration as a result of the mechanical linkage between the ossicles. In the cochlea's perilymph, the oval window's vibration creates pressure waves. The cochlea's various structures, including the scala vestibuli, scala tympan, round window, and vestibular membrane, then transmit pressure waves. Finally, pressure waves are sent through the cochlear duct's endolymph. It causes the basilar membrane to vibrate, which in turn bends the specialized hair cells on the organ of Corti and causes cochlear nerve impulses to be produced. The nerve impulses are then carried to the central nervous system by the vestibular branch and cochlear nerve.

Physiology of Balance and Equilibrium

The organs of balance are the saccule, utricle, and semicircular ducts. The maintenance of the head's position involves the utricle and saccule. The semicircular ducts are responsible for sustaining head movements like rotation. The vestibule and the three semicircular canals contain the specific sensors for balance and equilibrium. When we move our heads, a specific receptor called a cristae ampullaris produces a nerve impulse. The sensory cells in the cristae ampullaris have extensions dangling in the endolymph that resemble hair. When the head moves, causing the endolymph to move and the hairs to bend, the sensory cells are activated. The nerve impulse is produced by the hair's bending. The vestibular nerve, a branch of the vestibulocochlear nerve, is made up of nerves from the vestibule's receptors joining those from the semicircular canals. The cerebellum and medulla are eventually reached by nerve impulses traveling along this nerve.

The Taste or Gustation

The taste buds are the sensory organs that recognize flavor or gestation. Because the sensations are the result of chemical molecules interacting with taste or smell receptors, taste and smell are also considered chemical senses. Gustatory cells, which are specialized cells found on taste buds, are responsible for producing nerve impulses from saliva-dissolved food molecules. On the tongue, there are around 10,000 taste buds. A few are dispersed on the larynx's epiglottis, pharynx, and soft palate. Age causes a reduction in taste buds.

The majority of taste buds are located in papillae, which are elevations on the tongue that give the upper half of the tongue a slightly rough surface. The four main varieties of papillae are identified by their shapes.

• Circumvallates papillae: (surrounded by a groove), The gr go papillae are the largest but fewest in number; at the back of the tongue, 7 to 12 of them form an inverted V.
• Fungiform papillae (Mushroom-shaped) The entire dorsal surface of the tongue is covered in an erratic distribution of them.
• Foliate papillae (Leaf-shaped) They are dispersed along the tongue's sides. They increase with age and are most prevalent in young children.
• Filiform papillae (Thread-shaped) Despite having no taste buds, they are the most numerous papillae on the tongue's surface.

The stimulation of taste buds only produces the four flavors of sweet, sour, bitter, and salty. The stimulation of both taste buds and olfactory receptors results in the production of all other flavors. In other words, the countless tastes that are identified are not just tastes but also scents. Because of this, the stimulation of the olfactory receptors by the scents of meals in the mouth is interfered with by a cold, which significantly dulls taste perceptions. The two cranial nerves (VII and IX) are the primary pathways used by nerve impulses produced when taste buds are stimulated to reach the cerebral cortex's specialized taste area.

Smell or Olfaction

Odors that enter the nasal cavity trigger olfaction, or the sense of smell. The olfactory epithelium, a small area of epithelial tissue in the upper part of the nasal cavity, houses the chemical receptors that are in charge of smell. Millions of olfactory receptors are found in the olfactory epithelium, which covers the superior nasal concha on either side of the nasal septum. Three types of cells make up the olfactory epithelium: olfactory receptors, supporting cells, and basal cells.

Olfaction, or the sense of smell, is triggered by odors that enter the nasal cavity. The chemical receptors responsible for smell are housed in the olfactory epithelium, a small region of epithelial tissue in the upper section of the nasal canal. The olfactory epithelium, which covers the superior nasal concha on either side of the nasal septum, contains millions of olfactory receptors. The olfactory epithelium is composed of olfactory receptors, supporting cells, and basal cells.

Following odor-producing chemicals' stimulation of the olfactory cells, the ensuing nerve impulse passes through the olfactory nerves in the olfactory bulb and tract before entering the thalamic and olfactory centers of the brain, where it is interpreted as a particular odor.