Lecture 05 - Ears 2 Flashcards Preview

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Flashcards in Lecture 05 - Ears 2 Deck (17):
1

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

2

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)

3

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

4

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

5

Auditory Pathway

VCN/DCN --> SOC/IC via trapezoid body/LL --> MGB --> Auditory cortex

6

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

7

Arcuate fasciculus

connects Wernicke's to Broca's
-role in language repetition

***lesion = understand and produce speech, but can't repeat heard phrases

8

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

9

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

10

Sensorineural hearing loss

occurs when sensory cells or neural components of system are damaged
-nerve deafness
-Presbycusis/age-related hearing loss (usually bilateral)

11

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

12

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

13

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

14

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

15

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

16

Tinnitus

- perception of sound in ears or head where no external source is present
-mostly caused by damage to hair cells/CN8

17

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