final exam- the ear and hearing and equilibrium

4. Describe the sound conduction pathway from the auricle to the fluids of the inner ear and the path of the nerve impulses from the spinal organ (Corti) to various parts of the brain

1. Sound waves enter the external ear canal and cause vibrations of the tympanic membrane 2. As the drum vibrates, it causes the auditory ossicles to oscillate (move forward and backwards). 3. The movement of stapes in and out of the oval window causes pressure changes (waves) in the perilymph of scala vestibuli and scala tympani (the two canals filled with perilymph) 4. Perilymph movements cause vibrations of the basilar membrane (up and down) 5. Vibrations of the basilar membrane embed the hair cells in the tectorial membrane (immobile) and bends them 6. Bending generates a graded potential (depolarization) which causes a release of NT at the base of the hair cell 7. NT causes an action potential in the dendrites of cochlear nerve which then sends it to the brain (temporal lobe)

1. Distinguish between static and dynamic equilibrium

Static - The special sense which interprets the position of the head permitting the CNS to maintain stability and posture when the head and body are not moving; Ex: chair is not moving. Dynamic - The special sense which interprets balance when one is moving, or at least the head is moving. Ex: bicycle is moving.

2. Describe the structure of the maculae and their function in static equilibrium

Static equilibrium is detected by mechanoreceptors in the vestibule of the inner ear, the utricle and saccule, which each contain a macula with the receptors for static equilibrium; when the head moves with reference to gravity, the otolithic membrane shifts and the mechanoreceptors (hair cells) in the macula detect this movement and send the information along the vestibular nerve to the brain for interpretation ("which way is up"). Macula (meaning "spot") is a patch of hair cells topped by a membrane (otolithic membrane) that has small, calcium carbonate crystals called otoliths. The saccule and utricle lie at 90 degrees to each other. Thus, with any position of the head, gravity will bend the cilia of one patch of hair cells, due to the weight of the otoliths to which they are attached by a gelatinous layer. This bending of the cilia produces afferent activity going through the seventh nerve to the brainstem. The utricle is most sensitive to tilt when the head is upright. The saccule is most sensitive to tilt when the head is horizontal. Unlike the semicircular ducts, the kinocilia of hair cells in the maculae are NOT oriented in a consistent direction. The kinocilia point toward (in the utricle) or away from (in the saccule) a middle line. Because hair cells are oriented in different directions, tilts in any direction will activate some afferents.

what are the functions of the cochlea in the inner ear during the process of hearing

The function of cochlea in hearing depends on the organ of Corti that has hair cells responsible for hearing. The cochlea is a snail like structure divided into 3 ducts: superior called scala vestibuli (vestibular canal)-attached to oval window; middle called cochlear duct (scala media) that has the organ of Corti and inferior called scala tympani (tympanic canal)-attached to round window. The vestibular and tympanic canals are filled with perilymph and function to transmit pressure, while the cochlear duct is filled with endolymph and has sensory function as it houses the organ of Corti (detects pressure impulses). A vestibular membrane separates the vestibular canal from the cochlear duct and the BASILAR membrane separates the cochlear duct from tympanic canal. The basilar membrane is the membrane where the organ Corti attaches and it plays a critical role in hearing. The organ of Corti has two components: 1. hair cells (inner and outer) with stereocilia and 2. Tectorial membrane (it is anchored and does not move and sits atop the hair cells).

3. Describe the structure of the crista ampullaris and its function in dynamic equilibrium

The semicircular canals contain the receptors for dynamic equilibrium; within each semicircular canal is a complex mechanoreceptor called a crista ampullaris which contains the mechanoreceptors (hair cells) for dynamic equilibrium; when the perilymph in one of the semicircular canals moves, the hair cells in the crista ampullaris are stimulated to send nerve impulses to the brain; this advises the brain of whether or not a person has their balance during body movements or if their body is in motion, e.g, riding in a car or turning one's head from side to side. The semicircular canals are the body's balance organs, detecting acceleration in the three perpendicular planes. There are three pairs of semicircular ducts, which are oriented roughly 90 degrees to each other for maximum ability to detect angular rotation of the head. Each slender duct has one ampulla. crista ampullaris is a patch of innervated hair cells found at the base of the ampulla. The crista contains hair cells with stereocilia oriented in a consistent direction. The cupula, sits atop this crest, filling the lumen of the semicircular duct. The stereocilia of the hair cells are embedded in the gelatinous cupula. When the head turns, fluid in one or more semicircular ducts pushes against the cupula and bends the cilia of the hair cells. Fluid in the corresponding semicircular duct on the opposite side of the head moves in the opposite direction.

inner

consists of passageways in the temporal bone (bony and membranous labyrinth). These passageways start at the oval window and have 3 parts: cochlea (with receptors for hearing), vestibule and 3 semicircular ducts (with receptors for balance). Inner ear is filled with fluid: perilymph which surrounds the membranous labyrinth and endolymph that fills the membranous labyrinth.

outer ear

fleshy auricle, external auditory meatus (the external opening into auditory canal in temporal bone), external auditory canal with ceruminous glands and the tympanic membrane at the inner end.

middle

starts at the tympanic membrane (lateral boundary), has 3 auditory ossicles (in sequence from the tympanic membrane to inner ear: malleus, incus, stapes) and ends medially at the oval window (where the inner ear begins). Auditory ossicles are the smallest bones in the human body and are connected with synovial joints, which allow them to move freely during vibrations of tympanic membrane and to transmit these vibrations to the inner ear. Middle ear cavity is filled with air. (In middle ear infections, fluid accumulates in middle ear and interferes with hearing)

1. Describe the functions of the ceruminous glands

•Exocrine glands located in external ear canal. Produce cerumen (ear wax) to prevent foreign particles from entering the auditory canal. It also coats the tympanic membrane and protects from water.

how does the various structures of the Outer ear function in hearing

•Fleshy auricle - directs sound into the external auditory canal. External auditory meatus is the external opening into the auditory canal in the temporal bone. Tympanic membrane vibrates in response to sound waves and transmits vibrations from air to ossicles (malleus first, then incus, then stapes).

how does the various structures of the Middle ear function in hearing

•Located in the air-filled tympanic cavity of the temporal bone. It is continuous posteriorly with the air cells in the mastoid process and communicates with the pharynx through the auditory tube. The 3 auditory ossicles amplify (increase) and conduct vibrations from the tympanic membrane to the oval window of the inner ear

5. Explain how the structures of the ear enable differentiation of pitch and loudness of sounds

•Pitch is determined by the frequency of the sound. High frequency=high pitch; low frequency=low pitch. Measured in Hertz (Hz). Flexibility of basilar membrane varies along its length, so different frequencies affect different parts. Much as on a piano, high frequencies are at one end and low frequencies at the other. High frequencies are transduced at the base of the cochlea (near the oval window) whereas low frequencies are transduced at the apex. •The intensity (amplitude) determines the loudness of the sound. Measured in decibels. Soft sounds stimulates few hair cells. Loud sounds stimulate more hair cells. The louder the sound, the more basilar membrane moves and the more hair cells are stimulated. So the number of responding cells identifies the loudness of sound.

2. Describe the role of the auditory tube in drainage and equalization of pressure in the middle ear

•The auditory tube connects the middle ear (normally filled with air) with the pharynx (throat). It is usually closed, but opens when swallowing or yawning occurs. This allows air to enter or leave the middle ear cavity and equalize pressure on both sides of the tympanic membrane-this is why when you fly, swallowing can help pop the ears. When the middle ear is inflamed and filled with fluid, some fluid can drain through the tube. Usually though, in frequent middle ear infections, surgeons can place a tube in the tympanic membrane to drain the cavity better.

how do the various structures of the Inner ear function in hearing?

•The bony labyrinth in temporal bone. Has fluid filled cavities. Houses the organ of hearing called organ of Corti in the cochlea. Cochlea is like a microphone: it converts sound pressure impulses into electrical impulses that will travel through the (vestibule) cochlear nerve to the brain.