Lecture 7: Auditory Pathway Flashcards
Injury to what area in the ascending pathway of the auditory system will result in unilateral sensorineural hearing loss?
- Cochlear nucleus
- Cochlear nerve
- The only 2 structures that if damagd will result in unilateral sensorineural hearing loss!
What is the location of the first-order neurons in the auditory system, what nerve do they travel on and where do they synapse first?
- Spiral ganglion inside the Cochlea
- Leave via Cochlear nerve (CN VIII)
- Terminate in the Cochlear nucleus
What are the different nuclei located within the Cochlear nucleus?
- Dorsal Cochlear Nucleus
- Ventral Posterior Cochlear Nucleus
- Anterior Ventral Cochlear Nucleus
What are the axons sent from the dorsal cochlear nucleus and describe their route?
- Dorsal acoustic stria
- Decussate in the upper medulla and ascend in the contralateral, lateral lemniscus
What are the axons from the ventral posterior cochlear nucleus and describe their route?
- Intermediate acoustic stria
- Decussate in the upper medulla, and ascend in the contralateral, lateral lemniscus
What are the axons from the anterior ventral cochlear nucleus, what do they form and where do they go?
- Ventral acoustic stria
- Form the trapezoid body
- Terminate bilaterally in the superior olivary nucleus
What is the only way that auditory information can get to the inferior colliculus?
Via the lateral lemniscus
What is the connection between the cochlear nucleus and the superior olivary nucleus?
Ventral Acoustic Stria
What nucleus of the auditory pathway contains axons from the 2nd, 3rd, and 4th order neurons?
Nucleus lateral lemniscus
How are 2nd, 3rd, and 4th order neurons all able to reach the inferior colliculus in the auditory pathway?
- They can bypass the nucleus lateral lemniscus and go straight to the inferior colliculus via the lateral lemniscus tract
- Axons also go to the nucleus lateral lemniscus and can be housed there
What are the locations of the 1st, 2nd, 3rd, 4th, and 5th order neurons in the auditory pathway?
1st = Spiral ganglion of Cochlea
2nd = Cochlear nucleus
3rd = Superior Olivary nucleus
4th = Nucleus lateral lemniscus
5th = Inferior colliculis
E COLI
How do fibers get from the inferior colliculus to the medial geniculate nucleus?
Brachium of the inferior colliculus
How do fibers get from the medial geniculate nucleus to the auditory cortex?
Sublenticular (auditory) radiations
Where is the primary auditory cortex located?
Transverse and superior temporal gyri (AKA transverse gyrus of Heschl)
Where is the auditory association cortex for processing and integration of sounds located?
Parieto-occipito-temporal (POT) association cortex and Wernicke’s area
What is the direct link between the auditory association cortex (Wernicke’s) and Broca’s speech area in the frontal lobe?
Arcuate fasciculus
What is Wernicke’s aphasia vs. Broca’s aphasia?
Wernickes: is a fluent apahasia where the patient can talk but give no meaning to what they are saying and will also have trouble comprehending spoken or written word
Broca’s: you can understand what people are saying to you, but will have trouble forming the words you want to say due to damage in the motor area of brain
What is conduction aphasia?
- Patient can comprehend speech and is able to talk
- Have trouble repeating phrases
What part of the auditory cortex is for high frequencies and which is for low frequencies?
- High frequencies are heard on the interior (medially)
- Low frequencies are heard more exteriorly (laterally)
What are the functions of the medial and lateral portions of the Superior Olivary nucleus?
Medial SON: allows us to localize sound based off timing
Lateral SON: allows us to understand the intensity/loudness of sound
What is Olivocochlear bundle and its function?
- Projection of efferent fibers from the SON which can dampen sound
- Connects to the outer hair cells in the organ of corti and can elongate them, in turn, pushing the tectorial membrane further away from inner hair cells and decreasing our ability to hear sounds
- Protective mechanism
Which nucleus is the superior olivary nucleus able to send fibers to which directly controls muscles of the inner ear?
- Facial nucleus
- Fibers from the facial nucleus go to the inner ear to control the action of the stapedius m. (Stapedius = Seventh CN)
What occurs with unilateral lesion of the central auditory pathway?
- Bilateral diminution of hearing
- Structures include: lateral lemniscus, inferior colliculus and brachium, and the medial geniculate body
Lesions of the Primary Auditory Cortex result in what; are there hearing deficits?
- Difficulty localizing sounds and tone discrimination
- Does NOT result in hearing deficits
Auditory agnosia is caused by lesions where; results in?
- Lesions in the auditory association cortex (POT)
- Inability to comprehend auditory information in general
Which Brodmann’s area is Wernicke’s located in?
Brodmann’s area 22
Which Brodmann’s area is Broca’s located in?
Area 44 and 45
Although similar, what is the difference between Wernicke’s aphasia and auditory agnosia?
- In Wernicke’s a person is unable to comprehend the spoken or written word. Their speech patterns will demonstrate numerous word substitutions, new word creations, and talking a lot.
- In auditory agnosia a person has difficulty distinguishing speech from non-speech sounds (auditory information in general). Spoken and written language may remain intact.
