Auditory Receptors

Stimulus

• Longitudinal waves -- compressions and rarefactions
• Frequency response 20-20,000 cps - (middle age: upper range decreases 80 Hz every 6 months; vonBekesy, 57).
• Amplitude - intensity or loudness.
• Tympanic Membrane - hammer - anvil - stirrup - oval window.

• Organ of Corti (traveling wave)
  • Tectorial membrane
  • Basilar membrane
  • Hair cells

Two Types of Auditory Pathways

1. Dorsal cochlear nucleus
   • More primitive function (reflex and activation)
   • Noncrossing fibers - lateral lemniscus and Reticular Formation
   • Others cross - form lateral lemniscus
   • Superior olivary nuclei
   • Some uncrossed fibers and some crossed
   • Smaller cells
   • Serves more generalized hearing

2. Ventral cochlear nucleus (VCN)(lemniscal)
   • Fibers bifurcate--to each nucleus
   • Dual nature maintained
   • Bipolar cells in VCN
   • Serves pitch discrimination
   • Stotler (1961)- Connections for different pitches localized here (hi - dorsal).

Structures in the Ventral Cochlear (VCN) Pathway

1. Cochlear nerve--bipolar cells
2. Spiral ganglion - at base of spiral lamina.
3. Ventral cochlear nucleus (lemniscal)
4. Superior olivary nucleus--reflex
   • Tensor tympani muscle--to malleus
   • Stapedius muscle--to stapes
5. Trapezoid body--sound localization
6. Lateral lemniscus and nuclei
7. Reticular formation, cerebellar vermis
8. Inferior colliculus
9. Brachium of inferior colliculus
10. Medial geniculate
11. Auditory radiations
12. Auditory cortex -- Pattern discrimination

Auditory Coding

• Some frequency coding.
• Cochlear microphonic - generator potential from hair cells.
• On, off, on-off fibers at all levels.
• Tuning curves for cells.
  • Both frequency and intensity.
  • Sharpens as get closer to cortex.

General Functions

• Two ascending pathways
  • Ventral cochlear nucleus--pitch discrimination
  • Dorsal cochlear nucleus--more primitive function (reflex and activation)
• Medial Geniculate Nucleus--frequency discrimination
• Cortex - Pattern discrimination
• Trapezoid body - Sound localization

TERMS to Know

Links to Associated Areas

LINK Sense of Hearing

LINK Physiology of Hearing