Auditory System

Question 1

primary neuron in the auditory pathway

Answer 1

• located in the spiral ganglion in the modiolus
• cochlear division of VIII N is formed by the central processes of bipolar neurons
  
  • central processes terminate in the dorsal (acoustic tubercle) and ventral cochlear nuclei–in the upper medulla

Question 2

dorsal and intermediate acoustic striae

Answer 2

• visible as the stria medullaris acoustic
• both decussate in the upper medulla and ascend in the lateral lemniscus
  
  • LL terminates upon neurons in the inferior colliculus

Question 3

ventral acoustic stria

Answer 3

• cross the medial lemniscus and form the trapezoid body
• fibers terminate bilaterally in the superior olivary nucleus (SON)
  
  • SON projects fibers to the inferior colliculus primarily thru the ipsilateral lateral lemniscus

Question 4

inferior colliculus and medial geniculate body

Answer 4

inferior colliculus–>brachium of inferior colliculus–>medial geniculate body–>sustentacular auditory radiations–>primary auditory cortex

Question 5

primary auditory cortex

Answer 5

• located in the transverse and superior temporal gyri

- has a general tonotropic organization according to high freq in the caudal aspect and low freq in the rostral aspect

Question 6

auditory assoc cortex

Answer 6

• for processing and integration of sounds
• located in the parieto-occipito-temporal assoc cortex and Wernicke’s area
• superior longitudinal fasciculus links the auditory assoc area to Broca’s speech area in the frontal lobe

Question 7

superior olivary nuclear complex

Answer 7

• represents a collection of nuclei dispersed along the ascending auditory pathway
• play a role in modifying auditory info
• medial superior olivary nucleus–needed for localizing sounds
• neurons in the lateral superior olivary nucleus–gives rise to olivocochlear efferents which exert inhibitory influences upon the organ of Corti
  
  • peripherally the fibers cross over to the cochlear division via the vestibulocochlear anastomosis

Question 8

pathway for auditory information

Answer 8

primary neuron in spiral ganglion–>central processes of bipolar neurons form the cochlear N of VIII–>

1. dorsal (acoustic tubercle) acoustic stria–>decussate in upper medulla–>ascend in contralateral lateral lemniscus–>inferior colliculus
2. ventral acoustic stria–>cross the medial lemniscus and form the trapezoid body–>terminate bilaterally in superior olivary nucleus–>lateral lemniscus–>inferior colliculus
   - ->brachium of inf colliculus–>medial geniculate body–>sustenticular auditory radiations–>primary auditory cortex

Question 9

unilateral lesion of the cochlear N

Answer 9

results in ipsilateral complete deafness

Question 10

unilateral lesion of the central auditory pathway

Answer 10

• results in bilateral diminution of hearing which is more prominent in the contralateral ear
• involves structures like the lateral lemniscus, inf colliculus, brachium of inf colliculus, and medial geniculate body

Question 11

lesions of primary auditory cortex

Answer 11

result in difficulty localizing sounds and tone discrimination
-no hearing deficits

Question 12

conduction aphasia

Answer 12

• lesion of the arcuate fasciculus
• results in conduction aphasia
• fluent language disorder
• characterized by severe impairment of repetition, difficulty reading aloud, marked paraphasia, severe anomia, and normal auditory comprehension
• right hemiparesis and hemianopsia, orofacial and bilateral limb apraxia may be presetn

Question 13

auditory agnosia

Answer 13

• lesion in the auditory association (POT) cortex
• characterized by inability to comprehend auditory info
• spoken and written language and other sensory modalities in tact

Question 14

fluent paragrammatical aphasia

Answer 14

• Wernicke’s Aphasia
• due to damage to Wernicke’s area of dominant hemisphere
• phasic zone appears to be an assembly area for the critical components of language
• characterized by pt’s inability to comprehend the spoken or written word
• pt’s speak fluently and their speech patterns have word substitutions, new word creations, and circumlocution of language
• also a receptive aphasia