14 - Auditory System

Question 1

Endolymph

Answer 1

• High K+ solution found in the scala media
  
  • Runs in the membranous labyrinth
  • +80 mV potential compared to perilymph
• Secreted by stria vascularis

Question 2

Perilymph

Answer 2

• High-sodium solution (Similar to CSF)
• Present in two cochlear compartments separated by the scala media (endolymph):
  
  • Scala vesibuli
  • Scala tympani
• Runs outside of the membranous labyrinth

Question 3

Middle ear ossicles (bones)

Answer 3

1. Malleus
2. Incus
3. Stapes

Question 4

Human audible range

Answer 4

20-20,000 Hz (best is 3,000)

Question 5

Helicotrema

Answer 5

passage located at the end of the basilar membrane so the scala vestibuli and scala tympani can communicate

Question 6

Cochlear Root Neurons

Answer 6

• 2nd order neurons off the central projection of the cochlear nerve
• Send axons to SC for auditory startle reflex

Question 7

Olivocochlear Bundle

Answer 7

• Efferent fibers
• Run from superior olivary complex to the outer hair cells
• Origin is in the periolivary nuclei

Question 8

Dorsal Cochlear Nucleus Path

Answer 8

• Immediately decussate in the dorsal acoustic striate
• Fibers ascend in the contralateral lateral lemniscus
• Completely bypass the olivary complex
• Terminate in the inferior colliculus

Question 9

Ventral Cochlear Pathway

Answer 9

1. Terminate in the ipsilateral superior olivary complex
   
   • Fibers leave SOC to run in the ipsilateral lateral lemniscus to the inferior colliculus
2. Decussate via the trapezoid body
   
   • Terminate in the contralateral SOC
   • Fibers leave SOC to run in the contralateral lemniscus to the inferior colliculus

Question 10

Conductive Hearing Loss

Answer 10

• Mechnical problem
• Middle, inner ear
• Infections, diseases cause ossicle rigidity
• Loss of conduction = simple attenuation

Question 11

Sensorineural hearing loss

Answer 11

• Damage to inner ear (hair cells, cochlear nerve, central auditory systems)

Question 12

Dorsal Acoustic Striate

Answer 12

Point of decussation of dorsal cochlear nucleus pathway

Question 13

Inferior quadrigeminal brachium

Answer 13

Path from inferior colliculus to the medial geniculate body of the thalamus