Audition Flashcards
List the structures that makeup the outer ear
- pinna
- external auditory canal
- tympanic membrane (eardrum)
List the structures that makeup the middle ear
ossicles (malleus -> incus -> stapes)
List the structures that makeup the inner ear
- oval window of cochlea
- cochlea
- semicircular canal
List the structures of the hearing pathway from outer ear to brain
- pinna
- external auditory cortex
- tympanic membrane
- malleus
- incus
- stapes
- oval window
- perilymph in cochlea
- basilar membrane
- hair cells
- vestibulocochlear nerve
- brainstem
- medial geniculate nucleus of thalamus
- auditory cortex in temporal lobe
What is the range (in Hz) that humans hear sounds?
20-20,000 Hz
What is the main function of the pinna?
channel sound waves into the external auditory canal
Where are sound waves directed to from the external auditory canal?
tympanic membrane
Tympanic Membrane
- eardrum
- divides the outer ear from the middle ear
- vibrates in phase with the incoming sound waves
- frequency of sound wave determines the rate at which this membrane vibrates: moves back and forth at high rate for high frequency sounds and slowly for low frequency sounds
- louder sounds have greater intensity – increased amplitude of vibration
Ossicles
- the three smallest bones in the ear (and body)
- help transmit and amplify the vibrations from the tympanic membrane to the inner ear
- malleus is affixed to tympanic membrane and acts on the incus which acts on the stapes (baseplate of this bone rests on the oval window of the cochlea)
Eustachian Tube
- connects the middle ear to the nasal cavity
- helps equalize pressure between the middle ear and the environment
Bony Labyrinth
- what the inner ear sits within
- contains the cochlea, vestibule, and semicircular canals
What fills the structures in the bony labyrinth?
membranous labyrinth
Membranous Labyrinth
- bathed in K+ fluid called endolymph
- suspended within the bony labyrinth by a thin layer of another fluid called perilymph
Perilymph
- simultaneously transmits vibrations from the outside world
- cushions the inner ear structures
Cochlea
-spiral-shaped organ divided into 3 parts called scalae
Organ of Corti
- located in the middle scala
- hearing apparatus
- rests on a thin flexible membrane (basilar membrane)
- on top of the organ is a relatively immobile structure called the tectorial membrane
What is the Organ of Corti composed of?
thousands of hair cells that are bathed in endolymph
Describe the other two scalae
- filled with perilymph
- surround the hearing apparatus
- continuous with the oval and round windows of the cochlea
What happens to sound entering the cochlea through the oval window? (describe processes from oval window to auditory nerve)
it causes vibrations in perilymph which are transmitted to the basilar membrane which pushes on the tip of each kinocilium (filaments that make up hair bundles) which are connected by tip links attached to the gate of K+ channels which are pushed and stretch allowing for K+ to enter the hair cell which then activates Ca2+ channels inside the hair cells to cause an AP in spiral ganglion cell which then activates the auditory nerve
Round Window
- located in cochlea
- membrane-covered hole that permits the perilymph to move within the cochlea
Hair cells in the organ of corti convert the ____ stimulus into ____ signal which is carried to the CNS by the ____ _____.
- physical
- electrical
- auditory (vestibulocochlear) nerve
What does the vestibule refer to?
the portion of the bony labyrinth that contains the utricle and saccule
What type of acceleration are the utricle and saccule sensitive to?
linear acceleration (part of balancing apparatus, determine one’s orientation in 3D space)
Otoliths
- contained in the uticle and saccule
- resist motion as the body accelerates which causes bending of them and stimulation of the underlying hair cells which send a signal to the brain
Semicircular Canals
- sensitive to rotational acceleration
- 3 of them that are arranged perpendicularly to each other
- end in a swelling called an ampulla (location of hair cells)
- rotation of head causes endolymph in these canals to resist the motion which bends the underlying hair cells leading to a signal being sent to the brain
Medial Geniculate Nucleus (MGN)
- processes sound
- located in the thalamus
- receives signals from brainstem
- projects to the auditory cortex in the temporal lobe
Superior Olive
- receives some signals from MGN
- localizes the sound
Inferior Colliculus
- involved in startle reflex
- helps keep the eyes fixed on a point while the head is turned (vestibulo-ocular reflex)
Hair Cells
- have long tufts of sterocilia on their top surface
- certain cells are directly connected to the immobile tectorial membrane and are involved in amplifying the incoming sound
Place Theory
-location of a hair cell on the basilar membrane (changes thickness depending on its location) determines the perception of pitch when that hair cell is vibrated
Explain the Tonotopical organization of the Cochlea
- highest frequency pitches cause vibrations of the basilar membrane very close to the oval window
- low frequency pitches cause vibrations at the apex away from the oval window
