Auditory Tracts

Question 1

• Primary afferents carrying auditory information to the brain come from which cranial nerve? Which part?
• Where do they enter the brainstem?
• Where do these primary afferents synapse

Answer 1

• VIII (Vestibulocochlear)-Specifically the cochlear part
• Enter brainstem @ pontomedullary junction
• Primary afferents descend or ascend to synapse on ventral or dorsal cochlear nuclei in the brainstem

Question 2

• What is the function of the dorsal cochlear nucleus?
• It is part of what auditory tract?

Answer 2

• Receives primary afferent fibers containing information on:
  
  • Identifying sound source elevation
  • Identifying complex spectral characteristics of sounds
• Monaural (Dorsal and Monaural both have an O)

Question 3

• What is the function of the ventral cochlear nucleus?
• It is part of what auditory tract?

Answer 3

• Receives primary afferent fibers from the cochlear portion of CN VII
  
  • Horizontal localization of sound
  • Anterior and posterior subdivisions (see physio)
• Binaural

Question 4

• Describe the monaural tract

Answer 4

1. Primary afferents from cochlear portion of CN VIII travel to the dorsal cochlear nucleus where they will synapse
2. FIbers then CROSS and ascend in the lateral lemniscus
3. These fibers will synapse on the inferior colliculi
4. Axons from the inferior colliculi will travel through the brachium of the inferior colliculi to the medial geniculate nucleus (remember SLIM mnemonic for superior and inferior colliculi)
5. Fibers from MGN will ascend thru the sublenticular limb of the internal capsule and travel to the primary auditory cortex

Question 5

• Describe the binaural tract

Answer 5

• Primary afferent fibers of cochlear portion of CN VIII synapse in ventral cochlear nucleus
• Axons project BILATERALLY by passing thru the trapezoid body to the superior olivary complex (pons)
• Cell bodies from medial and lateral olivary nucleus ascend in lateral lemniscus to the inferior colliculus
• Axons from inferior colliculus will travel through the brachium of the inferior colliculus to the MGN (medial geniculate nucleus) of the thalamus
• Axons from MGN will travel through SUBLENTICULAR LIMB of the internal capsule and synapse on cells of primary auditory cortex

Question 6

• What layer of the primary auditory cortex do cells from the MGN synapse in?
• What is another name for the primary auditory cortex?

Answer 6

• Layer IV
• Heschl’s gyrus

Question 7

• What are two rules to consider when discussing monaural and binaural auditory tracts?

Answer 7

1. All nerve fibers from cochlea will synapse in one of the cochlear nuclei (ventral or dorsal or both)
2. Fibers in brainstem cross multiple times
3. ALL fibers will synapse in the following areas
   
   1. Inferior colliculus
   2. MGN
   3. Primary Auditory Cortex

Question 8

• Lesions that occur in the brainstem and damage the vestibulocochlear n will or will not cause deafness?

Answer 8

• Will not.
  
  • Fibers cross too many times at that point
  • Will have issues localizing sounds but will still be able to hear

Question 9

• Where are three places that auditory nerve fibers cross?

Answer 9

1. Trapezoid body (between medial and lateral superior olivary nuclei)
2. Lateral lemniscus
3. Brachium of inferior colliculus

Question 10

• Conduction deafness versus
• Sensorineural deafness versus
• Central deafness

Answer 10

• Conduction deafness
  
  • ​Problems with external or middle ear
  • Can’t conduct sound from the outside world into the inner ear
  • Transformation of sound to the tympanic membrane or thu ossicle chain
• Sensorineural (Nerve) deafness
  
  • ​Damage to cochlea
  • Damage to cochlear part of CN VII or cochlear nuclei
  • Ipsilateral nerve deafness (fibers have not crossed yet)
• Central
  
  • ​Damage to the central pathways (aka areas in the brainstem)

Question 11

• What does the basilar a. supply?

Answer 11

• Cochlear
• Auditory nuclei of pons and medulla

Question 12

• What does the labyrinthe (internal auditory) a. supply?
• What is it a branch of?

Answer 12

• Branch of AICA
  
  • Supplies inner ear and cochlear nuclei (esp in medulla)

Question 13

• What happens if there is an occlusion of the AICA

Answer 13

• Monaural hearing loss (supplying cochlear nuclei in medulla before they have had the opportunity to cross?)
• Can also damage facial nerve (Bell’s Palsy-ipsilateral facial paralysis) and pontine gaze center (inability to look towards side of lesion)

Question 14

• What do short circumferential branches of the basilar a supply?

Answer 14

• Superior olivary complex
• Lateral lemniscus

Question 15

• What do the superior cerebellar and quadrigeminal a’s supply?

Answer 15

• Inferior colliculus

Question 16

• What do the thalamogeniculate arteries supply?

Answer 16

• Medial geniculate bodies of thalamus

Question 17

• What does M2 supply?

Answer 17

• M2=branch of middle cerebral a.
• Supplies primary auditory and association cortices

Question 18

• What makes up Wernicke’s area and what is its function?
• On what side is it most common (AKA dominant side)?

Answer 18

• Wernicke’s area:
  
  • Supramarginal gyrus (part of parietal)
  • Angular gyrus (part of parietal)
  • Parts of superior temporal gyrus
• Function
  
  • Comprehension of spoken language
• Most people-LEFT hemisphere

Question 19

• What makes up Broca’s area? What is the function of this area?
• What lobe is it dominant in?

Answer 19

• Broca’s area
  
  • Opercular gyrus
  • Triangular gyrus
  • Both of these gyri are parts of the inferior frontal gyrus
• Function
  
  • Instruction for language output
  • Planning movements to produce speech
  • Grammatical function of words (no ifs, ands or buts)
• LEFT hemisphere

Question 20

• What is the function of non-dominant lobe Wernicke area?

Answer 20

• Interpreting nonverbal signals
  
  • EX: Shrugging shoulders means IDK

Question 21

• What is the function of the non-dominant Broca’s area

Answer 21

• Instructions for producing non-verbal communication
  
  • Emotional gestures (flipping someone off)
  • Intonation of speech (George is here. vs George is here?)

Question 22

• What is the pathway of auditory information from the primary auditory cortex to the action of producing actual speech?

Answer 22

1. Auditory discrimination (Primary auditory Cortex)
2. Classifying sounds (Auditory association cortex)
3. Auditory comprehension (Wernicke’s)
4. Linking understanding area (Wernicke’s) to speech area (Broca’s) via Arcuate fibers
5. Instruction for language output (Broca’s)
6. Cortical output to speech muscles (Oral and throat region of sensorimotor cortex)

Question 23

• Visual word form area is important for what activity?
• Lateral temporal cortex is important for _

Answer 23

• Reading
• Semantic knowledge (reading/seeing the word cat and knowing what that means)

Question 24

• Auditory agnosia

Answer 24

• Inability to describe a sound that has been heard
• LESION IS UNIMODAL SENSORY ASSOCIATION CORTEX B/L (B/L TEMPORAL LESIONS REQUIRED TO DEVELOP AUDITORY AGNOSIA)
• Damaging transverse temporal gyrus of Heschl

Question 25

* ***Broca's Aphasia (Expressive aphasia/Non-Fluent Aphasia)*** * ***​****Where is the lesion?* *Are the following functions intact?**​* * *Fluent?* * *Grammar?* * *Comprehension?* * *Naming?* * *Repitition?*

Answer 25

* Lesion in **left inferior frontal gyrus (Broca's area)** * Non-fluent (impaired word formation) * Impaired grammar * Comprehension impaired for complex sentences * Naming is preserved * Repitition impaired for complex sentences These people can understand what you are saying, but have a difficult time responding to what you are saying d/t inability to produce affluent speech

Question 26

* ***Wernicke's aphasia (Receptive or Fluent Aphasia)*** * ***​Where is the lesion?*** * ***Are the following functions present?*** * ***​Fluency*** * ***Grammar*** * ***Comprehension*** * ***Naming*** * ***Repitition***

Answer 26

* **Lesion in left superior temporal gyrus, inferior parital lobule, posterior middle temporal gyrus** * Are fluent * Grammar may be normal * Comprehension _impaired even for single words_ * Naming is impaired * Repetition impaired for single words

Question 27

* ***Conduction Aphasia*** * ***​Where is the lesion?*** * ***Are the following functions present/absent?*** * ***​Fluency*** * ***Grammar*** * ***Comprehension*** * ***Naming*** * ***Repitition***

Answer 27

* **Lesion of arcuate fasciculus** * Non-fluent * Grammar is preserved * Comprehension is normal * Naming is preserved * **Repitition is preserved**

Question 28

* ***Transcortical motor lesions*** * ***​Where is the lesion located?*** * ***Are the following functions absent/present:*** * ***​Fluency*** * ***Grammar*** * ***Comprehension*** * ***Naming*** * ***Repitition***

Answer 28

* **Lesion in ACA-MCA watershed area** * Nonfluent * Grammar is preserved * Comprehension is normal * Naming is preserved * Repitition is preserved

Question 29

* ***Transcortical sensory lesions*** * ***​Where is the lesion located?*** * ***Are the following functions present/absent:*** * ***​Fluency*** * ***Grammar*** * ***Comprehension*** * ***Naming*** * ***Repitition***

Answer 29

* **Lesion in MCA-PCA watershed regions** * Fluency is normal * Grammar preserved * Comprehension is impaired * Naming is impaired * **Repitition is preserved**

Question 30

***Global lesions***

Answer 30

* **Type of non-fluent aphasia** * **LESION OF LATERAL SULCUS (hitting both Broca's and Wernicke's)** * **Usually MCA issue** *

Question 31

* Transcortical lesions

Answer 31

* Sensory or motor * Can repeat

Question 32

* **Conduction aphasia**

Answer 32

* Type of fluent aphasia * Lesion of supramarginal gyrus and arcuate fasciculus * Can't repeat