Term
| What structures are in the external ear and what are their functions? |
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Definition
| The pinna and external auditory meatus, to gather and conduct sound waves to the tympanic membrane |
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Term
| What separates the external and middle ear? |
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Definition
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Term
| What are the three bones in the middle ear? What is their function |
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Definition
The malleus, incus, and stapes
Their function is to amplify sound (20 times) so that the liquid inner ear can hear it |
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Term
| What connects the middle and inner ear? |
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Definition
| The oval window and the round window |
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Term
| What connects the middle ear with the pharnyx? |
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Definition
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Term
| What is the vestibular apparatus? |
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Definition
| Important in equilibrium, includes the semicircular canals, utricle, and saccule |
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Term
| What nerve carries afferents for hearing and equilibrium? |
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Definition
| The vestibulochlear nerve (cranial nerve 8) |
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Term
| What in a sound wave determines volume? |
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Definition
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Term
| What in a sound wave determines pitch? |
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Definition
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Term
| What is the point at the end of the cochlea spiral? |
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Definition
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Term
| What seperates the scala vestibuli and the scala media? |
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Definition
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Term
| What seperates the scala media and the scala tympani? |
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Definition
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Term
| What membrane is on the organ of corti? |
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Definition
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Term
| What is another name for the scala media? |
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Definition
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Term
| Where is the perilymph fluid? |
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Definition
| Scala vestibule and scala tympani (connected at the helicotrema) |
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Term
| Where is the endolymph fluid? |
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Definition
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Term
| What are the concentrations in the endolymph? |
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Definition
| High potassium, low sodium |
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Term
| What are hair cells embedded into? |
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Definition
| The basilar membrane and (if outer hair cells) the tectorial membrane |
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Term
| What is the result of bending toward the tallest cilia? |
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Definition
| More K+ channels open, depolarization |
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Term
| What is the result of bending away from the tallest cilia? |
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Definition
| Elastic fibers go slack, K+ channels close, and hyperpolarization |
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Term
| What does the brain stem do with auditory input? |
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Definition
| Uses the information for alertness and arousal |
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Term
| What does the medial geniculate nucleus of the thalamus do with auditory info? |
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Definition
| Sorts and relays the information to the higher brain |
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Term
| What specifically in the cerebrum detects sound quality? |
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Definition
| The primary auditory cortex |
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Term
| What in the thalamus sorts and relays information to the cerebrum? |
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Definition
| The medial geniculate nucleus of the thalamus |
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Term
| What kind of deafness is conductive deafness? |
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Definition
Sound wave disruption through external and middle ear
(ear wax, fluid, perforation of tympanic membrane, otosclerosis) |
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Term
| What kind of deafness is sensorineural deafness? |
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Definition
The sound waves reach the inner ear, but are not converted into electrical signals
(noise, drugs (ototoxicity), presbycusis, tumor) |
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Term
| What is the function of the tympanic membrane |
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Definition
| Conducts sound waves to the middle ear, and converts sound energy to mechanical displacements. |
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Term
| Describe the attenuation (tympanic) reflex |
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Definition
Two muscles in the inner ear (the stapedius and the tympani) are activated during loud sounds to diminish the movement of middle ear bones, reducing damage to hair cells
Doesn't work for sudden or high pitched sounds
Also can help filter out ambient low tones in an ambient environment |
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Term
| Describe the transmission of sound from the middle to inner ear |
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Definition
Piston-like action of the stapes on the oval window converts a mechanical displacement to a hydraulic displacement (movement of perilymph).
Movement of fluid pushes against the round window and displaces the basilar membrane, ultimately resulting in action potentials |
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Term
| Where do high frequencies displace the basilar membrane? |
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Definition
| The base (stiff and narrow) |
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Term
| Where do low frequencies displace the basilar membrane? |
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Definition
| The apex (floppy and wide) |
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Term
| Define tonotopic organization, as it has to do with the basilar membrane |
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Definition
| Different frequencies are coded at different places along the basilar membrane. For example, a hair cell located at the site on the basilar membrane that moves best to a frequency of 4000 Hz will respond best (more depolarization and hyperpolarization) to 4000 Hz. |
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Term
| What immediately causes neurotransmitter release from hair cells? |
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Definition
| The amount of Ca++ that enters the cell is proportional to the degree of depolarization. Ca++ causes the neurotransmitter, glutamate, to be released onto the sensory neurons that innervate the hair cell. |
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Term
| Describe the sensory neurons for sound |
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Definition
Consist of bipolar neurons with their cell bodies in the spiral ganglion (located within the bony part of the cochlea) and their peripheral processes forming synapses with the hair cells.
The central processes comprise the cochlear portion of the vestibulocochlear nerve |
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Term
| Which hair cells (inner or outer) transmit more auditory information? |
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Definition
Inner hair cells
95% of neurons innervate inner hair cells, 5% outer hair cells
Outer hair cells act to amplify the sound signal by enhancing the movement of the basilar membrane |
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Term
| Describe "characteristic frequency" |
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Definition
Auditory neurons have a characteristic frequency at which they respond with the greatest intensity; thus, neurons are "tuned" to different frequencies.
The characteristic frequency of a neuron depends on the hair cells that the neuron innervates. |
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Term
| How is frequency neuronally coded? How is loudness? |
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Definition
Frequency of sound is mainly encoded by which neurons are excited.
Loudness is coded by the frequency of action potentials and number of neurons activated by the sound. |
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Term
| Describe the path of auditory projections past the cochlear nuclei |
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Definition
All auditory projections past the cochlear nuclei are bilateral. This means that a person will not become
deaf as a result of a brain lesion above the level of the cochlear nuclei. |
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Term
| Describe the auditory pathway for (horizontal) sound |
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Definition
| ventral cochlear nucleus → superior olivary nucleus → inferior colliculus (via the lateral lemniscus) → medial geniculate nucleus → primary auditory cortex |
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Term
| Where is the primary nucleus where horizontal sound localization occurs? |
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Definition
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Term
| Describe how horizontal sound is localized |
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Definition
| Because of the arrangement of neurons in the superior olivary nucleus, there are neurons that discharge in response to the particular delay between stimuli reaching each ear. |
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Term
| How is vertical sound localized? |
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Definition
The ear somehow uses a comparison of direct sound vs. reflected sound to determine relative altitude of
sound. Because of the shape of the pinna, sounds arriving from different vertical levels will vary in both the direct and reflected pathways. |
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Term
| Where is the primary auditory complex located? |
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Definition
| The superior portion of the temporal lobe |
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Term
| What is the function of the secondary auditory complex? |
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Definition
| Secondary auditory cortex, surrounding the primary auditory cortex, processes input from the primary cortex and provides interpretation of complex sounds. |
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Term
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Definition
| An area partly in the secondary auditory cortex, important for understanding speech |
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Term
| Describe what lesions in the central pathways would cause |
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Definition
| With injuries up to the cochlear nuclei, there will be degrees of deafness on the ipsilateral side. Past the cochlear nuclei, deafness does not occur because the pathways are bilateral. Some lesions do produce difficulties in localizing sounds, however. |
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Term
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Definition
| Ringing in the ears, or perception of sound without a stimulus. This can be caused by a number of CNS deficits, not just auditory problems. |
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Term
| How do hearing aids work? |
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Definition
| With an intact auditory system but with inadequate numbers of hair cells, hearing aids simply amplify the incoming sounds. |
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Term
| How do cochlear implants work? |
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Definition
| If hair cells are dead, a cochlear implant has a series of electrodes that directly stimulate the cochlear nerve. |
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