Lecture 7: Auditory and Balance Flashcards
Describe the main functions of the ear.
The ear is responsible for hearing and equilibrium (balance).
Explain how fluids in the ear contribute to hearing and balance.
Fluids must be moved to stimulate the mechanoreceptors located in the internal ear, which are essential for both hearing and equilibrium.
Define the three major areas of the ear and their functions.
The ear has three major areas: the external ear (hearing only), the middle ear (tympanic cavity, hearing only), and the internal ear (hearing and equilibrium).
How are the receptors for hearing and balance activated?
Receptors for hearing and balance respond to separate stimuli and are activated independently.
What are the components of the external ear?
The external ear consists of the auricle (pinna), helix, lobule, and the external acoustic meatus (auditory canal).
Explain the function of the auricle (pinna).
The auricle (pinna) is a shell-shaped structure that functions to funnel sound waves into the auditory canal.
What happens if the tympanic membrane is subjected to unequal pressure?
If pressures on both sides of the tympanic membrane are not equal, it cannot vibrate efficiently, leading to distorted sounds.
Describe the structure and function of the tympanic membrane (eardrum).
The tympanic membrane is a thin, translucent connective tissue membrane that vibrates in response to sound and transfers sound energy to the bones of the middle ear.
What is the role of the pharyngotympanic (auditory) tube?
The pharyngotympanic tube connects the middle ear to the nasopharynx and helps equalize pressure in the middle ear cavity with external air pressure.
How do the auditory ossicles function in hearing?
The auditory ossicles (malleus, incus, stapes) transmit vibratory motion from the eardrum to the oval window, facilitating sound transmission.
Describe the role of the tensor tympani and stapedius muscles in hearing.
The tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to hearing receptors.
Identify the three small bones in the tympanic cavity and their names.
The three small bones in the tympanic cavity are the malleus (hammer), incus (anvil), and stapes (stirrup).
Explain the significance of the epitympanic recess in the middle ear.
The epitympanic recess is the superior portion of the middle ear, contributing to the overall structure and function of the tympanic cavity.
What is the function of the mastoid antrum?
The mastoid antrum is a canal that allows communication with mastoid air cells in the mastoid process.
How does the trigeminal nerve relate to the ear’s function?
Motor input from the trigeminal nerve (V) is involved in the reflexive contraction of the tensor tympani muscle in response to loud sounds.
Define the role of the saccule and utricle in the inner ear..
The saccule and utricle are membranous sacs within the bony labyrinth that house equilibrium receptor regions called maculae, which respond to gravity and changes in head position.
Explain the function of the membranous labyrinth.
The membranous labyrinth consists of a series of membranous sacs and ducts contained within the bony labyrinth, filled with potassium-rich endolymph. It plays a crucial role in balance and hearing.
Describe the bony labyrinth and its components.
The bony labyrinth is a system of tortuous channels and cavities within the bone, divided into three regions: vestibule, semicircular canals, and cochlea. It is filled with perilymph fluid, which is similar to cerebrospinal fluid.
How are the semicircular canals oriented in relation to each other?
The three semicircular canals are oriented in three planes of space: the anterior and posterior canals are at right angles to each other, while the lateral canal is horizontal.
What is the function of the ampulla in the semicircular canals?
The ampulla is the enlarged area of the ducts of each semicircular canal that houses the equilibrium receptor region called the crista ampullaris, which responds to angular (rotational) movements of the head.
Describe the structure and function of the cochlea.
The cochlea is a small spiral, conical, bony chamber that extends from the vestibule and coils around a bony pillar called the modiolus. It contains the cochlear duct, which houses the spiral organ (organ of Corti) responsible for hearing.
Explain the significance of the scalae in the cochlea.
The cochlea is divided into three chambers: scala vestibuli, scala media (cochlear duct), and scala tympani. The scala vestibuli and scala tympani contain perilymph, while the scala media contains endolymph, playing essential roles in sound transmission.
What is the role of the basilar membrane in sound processing?
The basilar membrane vibrates in response to sound waves, with different areas resonating at specific frequencies. This mechanical processing occurs before signals reach the hair cell receptors.
How do hair cells in the cochlea convert mechanical energy into neural signals?
Movement of the basilar membrane deflects the stereocilia of inner hair cells, which project into the potassium-rich endolymph. This mechanical deflection transforms mechanical energy into neural signals.
Explain the concept of resonance in the basilar membrane.
Resonance refers to the movement of different areas of the basilar membrane in response to specific sound frequencies, with shorter, stiffer fibers near the oval window resonating with high frequencies and longer, floppier fibers near the apex resonating with lower frequencies.
Describe the pathway of sound waves from the tympanic membrane to the cochlea.
Sound waves enter the external acoustic meatus, strike the tympanic membrane causing it to vibrate, and this vibration is transferred through the auditory ossicles to the oval window, creating wave motions in the perilymph of the cochlea.
What is the function of the stria vascularis in the cochlear duct?
The stria vascularis is the external wall of the cochlear duct composed of mucosa that secretes endolymph, essential for maintaining the ionic composition of the fluid in the cochlear duct.
How does the tympanic membrane contribute to hearing?
The tympanic membrane vibrates when sound waves strike it, and the intensity of the sound affects the degree of vibration, which is then transferred to the auditory ossicles.
Define the role of the cochlear branch of nerve VIII.
The cochlear branch of nerve VIII runs from the spiral organ to the brain, transmitting auditory information from the cochlea.
What happens to sound waves with frequencies below the threshold of hearing?
Sound waves with frequencies below the threshold of hearing travel through the helicotrema and scala tympani to the round window, where they cause it to bulge outward into the middle ear cavity.
Describe the role of otoliths in the vestibular system.
Otoliths increase the weight and inertia of the membrane, helping to detect changes in head position.
Explain the anatomy of a macula.
Each macula is a flat epithelial patch containing hair cells and supporting cells, with hair cells featuring stereocilia and a true stereocilium called kinocilium.
Describe the role of outer hair cells in the auditory system.
Outer hair cells can contract and stretch, changing the stiffness of the basilar membrane, which increases the responsiveness of inner hair cells and protects them from loud noises.
Explain how the ascending auditory pathway functions.
The ascending auditory pathway transmits auditory information primarily from cochlear receptors (inner hair cells) to the cerebral cortex, with some nerve fibers crossing over to the other side of the brain.
Define the perception of pitch in relation to hair cells.
The perception of pitch is based on impulses from hair cells in different positions along the basilar membrane, which the brain interprets as specific pitches.
How is loudness detected by the brain?
Loudness is detected by the brain as an increase in the number of action potentials (frequency) that result when hair cells experience larger deflections.
Describe the factors that contribute to sound localization.
Sound localization depends on the relative intensity and timing of sound waves reaching both ears; if timing is increased on one side, the brain interprets the sound as coming from that side.
Explain the function of the vestibular apparatus.
The vestibular apparatus contains equilibrium receptors in the semicircular canals and vestibule, which help maintain balance and spatial orientation.
How do stereocilia contribute to the function of maculae?
Stereocilia are embedded in the otolith membrane, a jelly-like mass that responds to changes in head position and linear acceleration.
Describe the relationship between frequency of action potentials and loudness.
The frequency of action potentials correlates with loudness, where a higher frequency indicates a louder sound measured in decibels (dB).
What is the difference between static and dynamic equilibrium?
Static equilibrium is monitored by vestibular receptors that detect the position of the head in space, while dynamic equilibrium is monitored by semicircular canal receptors that respond to head movements.
Define maculae and their role in equilibrium.
Maculae are sensory receptor organs located in the saccule and utricle walls that monitor static equilibrium and respond to linear acceleration forces.
How do utricle maculae respond to head movements?
Utricle maculae are horizontal with vertical hairs and respond to changes along a horizontal plane, such as tilting the head.
What stimulates the utricle maculae?
Forward and backward movements stimulate the utricle.
Describe the orientation and function of saccule maculae.
Saccule maculae are vertical with horizontal hairs and respond to changes along a vertical plane, such as up and down movements.
How do hair cells communicate with the vestibular nerve?
Hair cells release neurotransmitters continuously, and changes in acceleration or deceleration affect the amount released, altering the action potential frequency sent to the brain.
Explain the mechanism of hair cell activation in a macula.
When hair cells bend towards the kinocilia, they depolarize, increasing neurotransmitter release and impulse generation to the brain.
What happens when hair cells bend away from kinocilia?
Bending away from kinocilia hyperpolarizes the receptors, reducing neurotransmitter release and decreasing impulse generation.
Define the crista ampullaris and its function.
Crista ampullaris is a receptor for rotational acceleration located in the ampulla of each semicircular canal, excited by head acceleration and deceleration.
How do semicircular canals contribute to balance?
Semicircular canals detect rotational movements of the head, with cristae responding to changes in velocity.
What is the role of the ampullary cupula in the vestibular system?
The ampullary cupula is a gel-like mass that hair cells extend into, and it helps detect changes in head rotation by bending hair cells.
Explain the process of depolarization in cristae during head rotation.
Inertia in the ampullary cupula causes endolymph to move opposite to the body’s rotation, bending hair cells and leading to depolarization.
What is the significance of complementary semicircular ducts?
The axes of hair cells in complementary semicircular ducts are opposite, allowing one ear to depolarize while the other hyperpolarizes during head rotation.
How does the brain process equilibrium information?
Equilibrium information is sent to reflex centers in the brain stem, allowing for fast, reflexive responses to maintain balance.
What are the three modes of input for balance and orientation?
The three modes of input are vestibular receptors, visual receptors, and somatic receptors.
Describe sensorineural deafness and its treatment.
Sensorineural deafness can be treated with cochlear implants that convert sound energy into electrical signals, effective for congenital or age/noise-related cochlear damage.
How are cochlear implants inserted?
Cochlear implants are inserted into a drilled recess in the temporal bone.
What is the outcome of cochlear implants for deaf children?
Cochlear implants are so effective that deaf children can learn to speak.
