Lecture 05 - Ears 2 Flashcards
Auditory/Spiral ganglion
cochlear output via ANF in auditory/spiral ganglion
- from temporal bone into middle cranial fossa via internal acoustic meatus along with CN8 and 7
- 7up, coke down
- ANF enter and terminate on IPSI dorsal and ventral cochlear nuclei at pons/medulla border
- lesion DCN/VCN = IPSI hearing loss
Superior Olive
cells of cochlear nucleus project BILATERALLY to superior olive in the pons via trapezoid body
- information from both ears can influence a cell at the brainstem superior olive level
- a lot of preprocessing goes on in auditory CNS before info reaches auditory cortex
- SOC cells compare timing or intensity of info from 2 ears to localize sound in space (responds to sounds from either ear)
Inferior Colliculus
some cells of cochlear nucleus bypass SOC and go directly to inferior colliculus via lateral lemniscus
- SOC also sends axons bilaterally via LL to the IC
- IC cells project either across midline to other IC or IPSI to auditory thalamus (medial geniculate)
- cells in auditory thalamus also responds to sounds in both ears despite getting input only from IPSI IC (IC already has binaural inputs)
- both medial geniculates carry auditory info from both ears
Medial Geniculate (MGB)
MGB projects to IPSI primary auditory cortex (superior surface of temporal lobe), surrounded by 2ndary auditory cortical areas
- cells organized TONOTOPICALLY (just like in cochlea)
- frequency mapped in order from low to high
- not auditory map of space, just freq
Auditory Pathway
VCN/DCN –> SOC/IC via trapezoid body/LL –> MGB –> Auditory cortex
Wernicke’s area
2ndary cortical structure in sup. post. temporal cortex near TPO junction
- language comprehension and proper word selection
- input from primary auditory and visual cortices and other cerebral cortex
- axons project to many areas, especially Broca’s area via Arcuate fasciculus
***lesion = language comprehensive deficits, can speak
Arcuate fasciculus
connects Wernicke’s to Broca’s
-role in language repetition
***lesion = understand and produce speech, but can’t repeat heard phrases
Broca’s area
2ndary cortical structure
- inf part of lateral frontal cortex, ant. to face of primary motor cortex
- language production
- input from Wernicke’s via arcuate fasciculus + other cerebral cortex
- output to primary motor cortex for communication
***lesion = problems with production of language
Conductive hearing loss
occurs when conduction of sound waves are prevented from passing from air to fluid-filled inner ear
- buildup of earwax, infection, fluid in middle ear, punctured ear drum, fixation of ossicles, scarring, ear canal narrowing, middle ear tumors
- hearing can be restored
Sensorineural hearing loss
occurs when sensory cells or neural components of system are damaged
- nerve deafness
- Presbycusis/age-related hearing loss (usually bilateral)
Weber test
testing unilateral hearing loss
- place vibrating tuning fork on patients forehead
- stimulus will bypass external and mid ear and stim hair cells directly bilaterally –> bone conduction
- sound louder in ok ear (patient indicated) = sensorineural
- sound louder in bad ear = conduction
Rinne test
test one ear at a time for conductive hearing loss
- air conduction is much more efficient/better than bone conduction
- Part1: tuning fork put on mastoid process and patient indicates when sound disappears
- Part2: as soon as patient responds, place tuning fork in front of ear but not touching
- normal ear will hear sound because air>bone
- conductive = air slightly better/same as bone
Audiograms
graph showing hearing threshold as function of frequency
3 variables:
1. sound frequency presented (Hz)
2. sound intensity presented (dB)
3. sound presentation (air or bone conduction)
0dB hearing level represents lowest sound level (threshold)
-ask patient to indicate when hear tone
-decrease threshold for that freq until patient stops signal
Normal = with 20-25 dB of normal
bone conduction test can be performed simultaneously
-combined test indicates sensorineural loss if both air and bone conduction both have increased threshold
Presybycusis
age-related sensorineural hearing loss
- speech banana represents diff speech sounds, frequencies and normal conversational dB level
- high threshold = can’t hear as well
Auditory brainstem responses (ABRs)
assess physiology of auditory pathway
- scalp electrodes applied to head and EEG for thousands of brief auditory stimuli recorded and averaged
- as neural signal travels thru auditory pathway, electrical activity generated at each side
- auditory evoked response = record of these waves of electrical activity generated by stations in auditory pathway
- divide into early, middle and long-latency components
Tinnitus
- perception of sound in ears or head where no external source is present
- mostly caused by damage to hair cells/CN8
Meniere’s Disease
endolymph hydrops - disorder of inner ear that causes spontaneous episodes of vertigo, imbalance, nausea/vomiting, ringing ear, ear pressure, flucutating hearing loss
-rupture of membrane –> mix endolymph and perilymph, disturbs solution balance
