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17 Cards in this Set

  • Front
  • Back

By what age can hearing decrease from


20-20,000Hz in children to 50-8000Hz ?

Middle Age

Perceived loudness of a sound is a function of?

Amplitude and of pressure wave and Frequency

Human ear is most sensitive to sounds between what range?

250-4000Hz Speech fits into category

Travel of Sound in Ear

Ext Ear --> Canal --> Drum- -> Vibrate




Midd;e Ear --> Air filled Tympanic Cavity --> MIS --> Transmits vibrations to Oval Window (fenestra vestibuli) --> Converts & magnifies sound into fluid in inner ear

Inner Ear Pathway?

Sound waves --> Perilymph from oval window --> Helicotrema --> to Round window.


Sound waves deform the tectorial membrane at a location along its length.


Depending where on membrane determines frequency

Inner Hair Cell Properties?

- Principal sensory cells.


- Contain stereo cilia that bend from shear forces generated by vibration of basilar & tectorial membranes.


- Depolarise & activate bipolar neurone in spiralcochlear ganglion

Outer Hair Cells?

- Amplify Vibrations of basilar membrane.


- Increases our sensitivity to faint sounds.


- Receive inhibitory input from neurones in Superior Olivary Nucleus.


- Has effect of raising threshold of excitation of inner hair cells which helps to sharpen the perception of pitch.


- Gets rid of noise.

Auditory Pathway (Tract)

- Inner Hair Cell (IHC) send axons to...


- Spiral Ganglia (Which has bipolar neurons)


- They Travel along Cranial Nerve VIII (cochlear).


- Terminates in 2 nuclei (Cochlear Nuclei = Dorsal & Ventral)


- Cells in Cochlear Nuclei send their Axons through Brainstem to thalamus where they cross the midline(not all) (in pons) runs through LM pathways.


- They both terminate in Inferior Colliculus in MidBrain


- The other remaining neurons cross over at this point to same side as the main tract to...


- Medial Geniculate Nucleus in thalamus


- Auditory Cortex(temporal)

If we had a lesion in brainstem will you be deaf in one or both ears?

You would still have hearing in both ears but you wont hear as well. Roughly cut by half.

True or False




Organ of corti transduces into action potentials

True

Tectorial membrane

- Stiff at the base of cochlear and less rigid at apex.


Base = High Frequency


Apex = Low Frequency

Ventral Cochlear Nucleus

Location of sound




- Axon that divide!


- Axons synapse tightly on neurons in Ventral CNVIII allowing timing of the signal to preserve.


- One branch goes to Ipsilateral Sup Oliv Nucleus


- Other branch goes to Contraleteral Sup Oliv Nucleus.



Dorsal Cochlear Nucleus

Quality of sound


Compares Small Differences in sound


Axons from Auditory nerve branch to synapse on DORSAL cochlear nuclues.


Straight to Inf Colliculus


BYPASSING SUP OLIV NUCLEUS




e.g. "Bet" or "Bat"



Inferior Colliculus

Integrates Auditory information to make 3D sound


then


3D Visual , Vestibule and Tactile maps to enable us to orient and respond to sound




Info then goes to MGN Thalamus as a Relay Point (no other known reasoning)

Auditory Cortex

Transverse gyri of Heschi from Prim A1




2 Parts




Primary - A1 Recieves auditory radiations from MGN via Int Capsule




Secondary - A2 (Brodmans area) recieves auditory information from A1 & the MGN




NEW Studies SHOWS MANY AREAS NOT JUST ABOVE due to soo many variables laterelisation/discrimination/temporal analysis/localisation etc

Wernickes


&


Brocas

Wernicke - Comprehension of Speech(usually left hemishpere)




Broca - Performing speech

At Level of Superior Olivary Nuclie

Auditory pathway contain input from both ears at these levels so damage to one side will cause BILATERAl mild Loss of hearing