Lecture 6: Auditory Pathways Flashcards
(22 cards)
What is the receptor for the central auditory pathway?
Inner and outer hair (neuroepithelial) cells in the spiral organ of corti
Inner hair cells = pitch discrimination
Outer hair cells = loudness discrimination
Describe the general central auditory pathway
- Hair cells are innervated by peripheral processes of spiral ganglion
- Central processes of these nerves form cochlear N which exits base of modiolus and courses in internal auditory meatus with vestibular N and terminates in cochlear nuclei
- Fibers from cochlear nuclei ascend to inf. Colliculus
- Inf colliculus projects to medial geniculate body
- Medial geniculate body projects to primary auditory cortex via sublenticuar (auditory) neurons
On the posterolateral aspect of the upper medulla the cochlear nerve passes over the inferior cerebellar peduncle and terminates on neurons in the dorsal and ventral cochlear nucleus. Axons from these neurons form the dorsal, intermediate and ventral acoustic striae. What course do fibers from the dorsal and intermediate acoustic striae take?
Decussate in upper medulla and ascend in contralateral lateral lemniscus -> lateral lemniscus terminates upon neurons in the inferior colliculus
On the posterolateral aspect of the upper medulla the cochlear nerve passes over the inferior cerebellar peduncle and terminates on neurons in the dorsal and ventral cochlear nucleus. Axons from these neurons form the dorsal, intermediate and ventral acoustic striae. What course do fibers from the ventral acoustic striae take?
As they cross the medial lemniscus they form the trapezoid body -> these fibers terminate bilaterally in the superior olivary nucleus which projects fibers to the inferior colliculus primarily thorugh the ipsilateral lateral lemniscus
Where is the primary auditory cortex located?
In the transverse and superior temporal gyri and is typographically organized according to high and low frequencies
Where is the auditory association cortex located?
In the parieto-occipital-temporal association cortex and Wernicke’s area
**The superior longitudinal fasciculus directly links the auditory association area with Broca’s speech area in the frontal lobe
What is the superior olivary nuclear complex and what is its function?
Represents a collection of nuclei dispersed along the ascending auditory pathway
Play a role in modifying auditory information
What is the function of the medial superior olivary nucleus?
Important in localizing sounds
Neurons in the lateral superior olivary nucleus give rise to most of the ____________ efferents. What is the function of these?
Olivocochlear efferents, which exert inhibitory influences upon the hair cells of the organ of corti
- peripherally these fibers pass through the vestibular division and cross over to the cochlear divison via the vestibulocochlear anastomosis
Where is the nucleus of the trapezoid body located, where does it send fibers and what is its function?
Located at jnx of medial lemniscus and ventral acoustic stria
Sends fibers bilaterally to inf colliculus and nucleus of lateral lemniscus
Important in central processing of auditory information
What are the symptoms of a unilateral lesion of the cochlear nerve?
Ipsilateral complete deafness
What are the symptoms of a unilateral lesion of the central auditory pathway?
Bilateral diminution of hearing which is more prominent in contralateral ear
What structures are involved in a unilateral lesion of the central auditory pathway?
Lateral lemniscus
Inferior colliculus and brachium
Medial geniculate body
What are the symptoms of lesions of the primary auditory cortex?
Results in difficulty in localizing sounds and tone discrimination -> it does NOT result in hearing deficits
T/F: Lesions of the primary auditory cortex results in hearing deficits
False; Results in difficulty in localizing sounds and tone discrimination -> it does NOT result in hearing deficits
What causes auditory agnosia and what are the symptoms?
Lesions in the auditory association cortex
Inability to comprehend auditory information; spoken and written language as well as other sensory modalities may remain in tact
What is Wernicke’s aphasia?
Damage to Wernicke’s area post to primary auditory cortex in dominant hemisphere
Inability to comprehend the spoken or written work -> pt can speak fluently but makes no sense
What is Broca’s aphasia?
Lesion to Broca’s area in frontal lobe of dominant hemisphere
Pt is unable to speak bc they cant select the appropriate grammar or words
**Brocas area is critically important in the initiation of motor speech activity
What is conduction aphasia?
Damage to the superior temporal gyrus &/or supramarginal gyrus of the dominant hemisphere
Pt comprehends and has fluent speech but has poor speech repetition -> cant repeat back phrases
***Complete deafness of the right ear indicates involvement of which of the following? A. Lateral lemniscus B. Cristae ampullaris C. Inferior geniculate body D. Vestibular nuclei E. Vestibulocochlear N
E. Vestibulocochlear N
***A 64yo male with 12yr Hx of HTN was examined for sudden loss of hearing. PE revealed bilateral diminution of hearing that was more pronounced in the left ear indicates involvement of which of the following? A. Brachium of the superior colliculus B. Cochlear nucleus C. Lateral lemniscus D. Primary auditory cortex E. Vestibulocochlear N
C. Lateral lemniscus
An 83yo femal had a brief syncopal episode with a fall. Since she had a Hx of minor strokes, a head MRI was performed. The mental status exam indicated she couldn’t comprehend spoken commands. Her ability to speak and write was intact. No motor findings were noted. This condition is best described as which of the following? A. Agraphia and alexia B. Auditory agnosia C. Broca’s aphasia D. Conduction aphasia E. Fluent paragrammatical aphasia
E. Fluent paragrammatical aphasia
**This is another name for Wernicke’s aphasia!
