Auditory System EXAM 2

50-16,000 Hz

What is the typical hearing frequency range for humans?

100-8,000 Hz

What is the standard frequency range for human speech?

50 dB

What is the approximate intensity of a normal conversation in decibels?

120-130 dB

At what decibel range does sound become painful to the human ear?

>150 dB

What intensity level or repeated exposure in the painful range causes permanent auditory damage?

pinna

auditory meatus

what constitutes the outer ear (2 things)

pinna

The visible part of the outer ear that passively channels airwaves and helps determine sound direction

Monaural localization difficulty

What clinical condition occurs when there is damage to the pinna in only one ear?

difficulty with localization in that ear but if the other ear is functioning well then you can still localize sound

what does damage to the outer ear result in/lead to difficulty with

tympanic membrane (eardrum)

Which structure serves as the anatomical border between the outer ear and the middle ear?

conduction deafness

Damage to the external ear typically results in which general type of deafness?

• tympanic membrane

• deafness

Conduction Deafness of the External Ear

• No (or altered) transformation of sound to _____

• Decreased hearing or total ____

otitis externa

What is the clinical name for "swimmer's ear," an infection of the external auditory canal?

It causes conduction deafness by obstructing sound wave transformation

How does excessive cerumen (wax) in the external auditory canal affect hearing?

Malleus (hammer)

Incus (anvil)

Stapes (stirrup)

List the 3 bony ossicles located in the middle ear

malleus

Which ossicle is directly connected to the tympanic membrane?

oval window

Into which structure does the stapes fit to transmit vibrations to the inner ear?

To amplify sound waves and transmit vibrations to the cochlea

What is the primary function of the ossicular chain in the middle ear?

ossicles

oval window

cochlea

Sound waves traveling through middle ear

• Ear drum membrane is stretched tightly & vibrates → ____ amplify sound waves → transmit vibration → vibration to the stirrup which is at the ________ → send sound into the _____

inner

tympanic membrane

Ossicles transmit sound to the ____ ear and reduce magnitude of ______ movement

acoustic reflex

An involuntary muscle contraction in the middle ear that reduces the magnitude of vibrations in response to high-intensity sound

Tensor tympani (CN V)

Stapedius (CN VII)

What 2 muscles are activated by the acoustic reflex of the middle ear to Stiffness of the chain

CN V (Trigeminal nerve)

Which cranial nerve innervates the tensor tympani muscle?

CN VIII (facial nerve)

Which cranial nerve innervates the stapedius muscle?

stapedius

Which muscle of the middle ear is considered more dominant in the acoustic reflex?

talking

chewing

swallowing

Besides loud external noises, what self-induced actions activate the acoustic reflex?

malleus

what ossicle is stiffened by the tensor tympani muscle

stapes

what ossicle is stiffened by the stapedius muscle

Cochlear hair cells → Cochlear nucleus → Ipsi and Contra Superior olivary complex → Facial motor nucleus → bilateral signal to Stapedius muscle

Trace the pathway of the acoustic reflex starting from the cochlear hair cells picking up a loud signal

Otosclerosis

A middle ear condition, often inherited, involving the fixation of the stapes on the oval window

otitis media

Inflammation of the middle ear that may involve an accumulation of pus or exudate

By directly damaging the ossicles or causing bleeding into the middle ear

How can a fracture of the temporal bone cause conduction deafness?

There is mostly air in the middle ear and when you put fluid… that would change the mechanics of that process

why does otitis media (which may have accumulation of pus or exudate) result in Conduction Deafness of the Middle Ear

- bony labyrinth
- membranous labyrinth
- 3 fluid filled chambers

what are the 3 parts of the inner ear that make up the Cochlea

perilymph

Structure of the bony labyrinth of the cochlea

• Contains membranous labyrinth

• Filled with _____

• osseous cochlea

• saccule

• endolymph

Structure of the membranous labyrinth of the cochlea

• Coiled portion encased in the ______

• 3 spiraling chambers (2 + 2/3 turns)

• Base connected to the ____

• Filled with ____

endolymph

what type of fluid is found in the scala media

cochlear duct

what is another name for the scala media

perilymph

what type of fluid is found in the scala vestibuli

perilymph

what type of fluid is found in the scala tympani

saccule

what structure found within the cochlea detects linear acceleration

CSF (high in Na+)

what fluid in the body is perilymph similar to

endolymph

what helps hair cells remain very active at not much energy cost

8th CN

Hearing transmitted through the cochlea

• Afferent nerve fibers from hair cells in the cochlea pick up vibration which then causes depolarization of hair cells signaling the ____ nerve

Vibrations from oval window reach scala vestibuli → along cochlea to end → scala tympani → round window

how does sound travel through the cochlea as vibration passes from the stapes to the oval window (entrance to the cochlea)

• scala vestibuli

• scala tympani

Sound travel through the cochlea as vibration passes from the stapes to the oval window

• Vibrations from oval window reach _____ → along cochlea to end → ____ → round window

basilar membrane

Sound waves enter through the oval window and vibration passes through the lymph fluid around the ____ and back around to the round window

• oval window

• apex of cochlea

Tonotopic representation

• Higher frequency sounds activate hair cells near the _____

• Lower frequency sounds activate hair cells near apex of ____

Damage to cochlea or cochlear root of VIII

What is Sensorineural Deafness or Nerve Deafness damage of?

- Prolonged exposure to loud noise
- Certain antibiotics, infections, rubella, mumps, bacterial meningitis, tumor
- Labyrinthitis or otitis interna

what are possible causes of Sensorineural Deafness or Nerve Deafness

Sensorineural Deafness or Nerve Deafness

Prolonged exposure to loud noise, Certain antibiotics, infections, rubella, mumps, bacterial meningitis, tumor, and Labyrinthitis or otitis interna can result in ________

• Deafness on affected side

• Tinnitus (perception of ringing in ears)

what are the 2 symptoms of Sensorineural Deafness or Nerve Deafness

inflammation of the ear

what does otitis mean

air conduction > bone conduction

normal Rinne test result

air conduction > bone conduction (have to compare both sides)

Sensorineural deafness Rinne test result

bone conduction > air conduction

Conduction deafness Rinne test result

tone sounds equal on both sides

normal Weber test result

tone louder in healthy ear

Sensorineural deafness Weber test result

tone louder in affected ear

Conduction deafness Weber test result

damaged

bone

cochlea and nerve

Conduction Deafness

• You're going to perceive sound on the _____ side because you’re stopping the conduction through air BUT through the ____ you are still able to hear the sound.

• This is because the ____ and ____ are not affected, vibrating skull and causing hair cells to be activated

contralateral

Monaural information processing

• Monaural processing starts on 1 side, then is processed over on the ____ side

• acoustic stria

• lateral lemniscus

• inferior colliculus

• medial geniculate

Pathway sound travels via monaural processing

• Cochlear nucleus → decussates in posterior _____ → _____ → _____ → ____ nucleus of thalamus → auditory cortex

lateral aspect of inferior cerebellar peduncle at pontomedullary junction

where is cochlear nucleus found in the brainstem

lateral lemniscus

important ascending auditory pathway in pons/lower midbrain

• trapezoid body/medial lemniscus

• superior olivary

• lateral lemniscus

• inferior colliculus

• medial geniculate nucleus

Pathway sound travels via Binaural processing

• Cochlear nucleus → some information decussates in _____ → ____ complex → _____ → some will cross over in posterior tegmental commissure → ____ → _____ nucleus → auditory cortex

trapezoid body

white matter structure formed by crossing auditory fibers

Binaural processing example

You hear a sound like a fire truck siren; The sound takes a certain amount of time to get to the other side due to the sound being deflected and slightly different due to it traveling. The Brain is able to tell those small differences between the sound waves that arrived from the same source

review

Primary pathway taken by Ascending Monaural & Binaural Pathways

• posterior and anterior Cochlear Nucleus → superior olive → inferior colliculus → medial geniculate nucleus → primary & association auditory cortex

restiform body

Cochlear nuclei in the rostral medulla are located lateral and posterior to the _____

spatial awareness

inferior colliculus

• Multisensory integration, auditory-motor reflex

• Processing sound information and localizing it for ______

thalamus

Superior Colliculus

Medial Geniculate Nucleus is located at posterior end of _____, & adjacent to _____

transverse gyri of Heschl (sylvian fissure)

Primary Auditory Cortex (AI) location

sound localization

Primary Auditory Cortex (AI) function

bilaterally

contralateral

Lesion to the Primary Auditory Cortex

• Impaired sound localization in space

• Decrease hearing ____, but primarily _____

- ipsilateral secondary auditory cortex
- contralateral auditory association areas
- S1 sensory cortex
- frontal eye fields
- Broca's area of speech (frontal lobe)
- MGN

what areas of the brain are connected to the Primary Auditory Cortex

primary auditory cortex

cortical-cortical

Language is usually first perceived by _____ in the superior temporal lobe. Information is then relayed through ____-____ association fibers to other areas

prefrontal cortex

corpus callosum

Connections of the Secondary Auditory Cortex

• via anterior commissure with _____

• via ______ with prefrontal, premotor, parietal and cingulated cortices

41

Auditory and Related Association Cortices

• Area __: Primary auditory cortex

42

Auditory and Related Association Cortices

• Area ___: Secondary auditory cortex

22

39

40

Auditory and Related Association Cortices

• Area __, __, and __: Wernicke's areas for receptive speech and language

44

45

Auditory and Related Association Cortices

• Area __ and __: Broca's area for expressive speech and languag

22

39

40

what 3 Brodmans areas are the auditory association areas

39 and 40

what are the 2 higher association Brodman’s areas for hearing

important in aspects of language, e.g. reading and writing (Areas can be included in the Wernicke area)

what are the functions of the higher auditory association areas

Important for reading/writing and receptive speech

what are the 1⁰ & 2⁰ Auditory Cortices and Wernicke's Area important for

area 22

what area is Wernicke's area

• speech receptive

• primary auditory cortex

Function of area 22 Wernicke's area

• _____ area

• Receives input from ______, visual, and somatosensory information

middle cerebral artery damage

What can cause Wernicke's aphasia (speech comprehension deficit)

middle cerebral artery

what artery supplies Wernicke's area

wernicke’s aphasia

- Receptive or fluent aphasia
- Comprehension of speech sounds is impaired
- Discrimination of nonverbal sounds is primarily unaffected

the language centers are mostly on the L side of the brain except for L handed people

for the majority of people what side of the brain is the language centers mostly on

44 and 45

what 2 areas make up Broca's area

expressive speech and language area

what is the function of Broca's area (44 and 45)

broca’s aphasia

- Expressive or non-fluent aphasia
- Comprehension of verbal & non-verbal sounds is largely unimpaired

insular and opercular

damage to ____ and ___ branches of the Middle Cerebral artery can cause Broca’s aphasia

middle cerebral artery

what primary cerebral vasculature supplies Broca's area

- May alter perception of sound, not deafness in ear
- Temporal lobe seizures or lesions → auditory cortices damage

effects of a central lesion to the auditory system

may not be able to understand or comprehend the sound that you are hearing

what are the effects of a central lesion to the auditory system resulting in altered perception

- Cranial nerve/tract deficits
- Perceived auditory events (Buzzing insects, strands of music)

Pontine Auditory Hallucinosis caused by a central lesion to auditory system is due to…