Flashcards in Auditory Deck (22)
What are the major landmarks of the auricle?
Helix & Antihelix
Tragus & Antitragus
Concha & Lobule
Where are the ceruminous glands and what do they produce?
Outer third of external auditory meatus.
Ear wax is a mix of cerumen, sebaceous gland secretions, and shed meatal cells.
What nerves innervate the inner and outer surfaces of tympanic cavity? (6 nerves)
Upper outside: Lesser occipital
Lower outside: Greater auricular
Upper inside: Auriculotemporal branch of V3
Inside concha: Facial
Middle ear: Glossopharyngeal
Describe the eustacian tube and what muscles open it.
Cartilaginous tube connecting tympanic cavity to nasopharynx.
Cartilage opened by levator palati, tensor palati, and salpingopharyngeus.
How does swallowing equalize pressure in the middle ear?
Levator palati (assisted by tensor palati) raises the soft palate during swallowing to prevent reflux into nasopharynx. They also tug on the auditory tube during swallowing or yawning.
Salpingopharyngeus raises pharynx and larynx during swallowing and opens the pharyngeal orifice of auditory tube.
The three muscles work at the same time and allow air pressure to be equalized between middle ear and the environment.
Describe the ossicles, their attachments, and their significance in transmission of sound.
Three small bones in the tympanic cavity that convert sound waves into vibrations, which are transmitted to the fluid of the inner ear.
Malleus is attached to the tympanic membrane, stapes is attached to the oval window of the vestibule, and the incus is suspended between them.
Where are the tensor tympani and stapedius muscles and what do they do?
Tensor tympani attaches to the malleus and stapedius attaches to the stapes. They dampen ossicle vibration in extreme intensity sound to prevent damage.
Describe the chorda tympani: source, passage through tympanic cavity, and function.
The chorda tympani is a branch of the facial nerve that travels backward through the middle ear, passing between the tympanic membrane and malleus, to join V3.
It contains sensory afferents (anterior 2/3 of tongue) and parasympathetic efferents to salivary glands.
What is otitis media?
Infection/inflammation of the middle ear.
What is the tegmen tympani, and what is its significance in spread of infection?
It is the thin plate of bone separating the tympanic cavity from the meninges and brain. It is thin enough that bad ear infections can spread through the bone to cause meningitis or brain abscess.
Describe the spaces in the cochlea, including the important membranes and the fluid in the cochlear duct.
The bony canal of the cochlea is divided into three spaces by membranes that run its length:
Scala tympani and scala vestibuli with scala media (the cochlear duct) between them.
The cochlear duct is separated from scala vestibule by the vestibular membrane and from scala tympani by the basilar membrane.
The cochlear duct is filled with endolymph.
What is the difference between perilymph and endolymph?
Perilymph (think peripheral) is in scala v & t) and around the semicircular ducts in the semicircular canals.
Endolymph (think inside) is in the cochlear duct and semicircular ducts and is rich in potassium ions.
Describe the organ of Corti in terms of location, cell types, and relation to the tectorial membrane.
The organ of Corti is a layer of epithelium on the basilar membrane, which is covered by the tectorial membrane (like a flap).
It consists of modified epithelial cells (non-neural cells) called inner and outer hair cells embedded among support cells.
What is the difference between inner and outer hair cells in terms of location, function, innervation, and impact on sound reception?
The cochlear duct is a tube shaped like a wedge. The inner hair cells are closer to the point (deeper under the tectorial membrane).
The function of the inner hair cells is to detect sound information and convert it into electrical signals via the auditory (cochlear) nerve. Thus, they are innervated by 95% of its sensory neurons.
The function of the outer hair cells is to amplify the sound signal to the inner cells. They do this by contracting in response to vibration of the basilar membrane, which results in increased amplitude of vibration so that the signal to the inner cells is essentially louder. Since they have little sensory function, they receive only 5% of sensory innervation.
Without amplification by the outer hair cells, we can't really hear.
How does the cochlea encode sound frequencies?
Regions of the organ of corti are sensitive to different frequencies of sound due to variable thickness and pliability of the basilar membrane.
Describe the path of auditory information from the inner ear to the cortex.
Basilar membrane ->
Inner hair cells ->
Cochlear nerve via spiral ganglion ->
Ventral and dorsal nuclei ->
Superior olivary complex (except some fibers from dorsal nucleus) ->
Inferior colliculus ->
Medial geniculate nucleus ->
Primary auditory cortex in temporal lobe.
How does the superior olive localize sound?
Unless the source of a sound is equidistant between both ears (directly in front or behind you), the sound will reach each ear at a different time and different intensity.
Time difference is important for low-frequency sounds.
Intensity difference is important for high-frequency sounds.
Describe the anatomy and impact of superior olivary feedback to the organ of Corti.
Efferent fibers from the superior olive travel via the cochlear nerve to the inner and outer hair cells to control their sensitivity to sound--raising or lowering their threshold, essentially. This allows you to block out background noise or otherwise attend to specific sounds while ignoring others.
Describe the location and function of the primary auditory cortex.
Superior temporal lobe (inside lateral fissure)
Sensitivity to frequencies is laid out tonotopically (like basilar membrane).
Frequencies synthesized into sound forms.
What is tinnitus? Compare subjective and somatic varieties.
Hearing sounds that don't exist in the world, just in your brain.
Subjective: no external stimulation, phantom perception originating in the brain (often due to hearing loss, just like a phantom limb)
Somatic: Subtype of subjective, seems to be a problem with relaying information from nerves to brain. Usually triggered by synergistic effects of multiple causes.
What are the dorsal and ventral streams of cortical processing of auditory information?
Dorsal: Up to the parietal lobes. Involves Broca's area and speech production. "Say it." Think parietal--proprioception, sense of body.
Ventral: To temporal lobes. Involves Wernicke's area and language comprehension. "Understand it." Think temporal--memory, context, etc.