Lec 6: Vestibulocochlear Nerve Cochlear Division/Nerve

the vestibular nerve and cochlear nerve are

2 Nerves in 1

what is vestibular nerve

• Monitors head position and movement\

• – Sensory Signals from Semicircular Canals and Vestibule

• – Monitors head position and movement

what is Cochlear Nerve

• Responds to sound stimulation

• – From Cochlea

• – Responds to sound stimulation

what is vestibular nerve receptors?

• Hair cells in:

  • Semicircular Canals

    • Anterior

    • Posterior

    • Lateral

• Vestibule

  • Utricle

  • Saccule

what is the receptors of cochlear nerve?

Hair cells of the Spiral Organ (Organ of Corti) – in the Cochlea

Structure of the Ear

The Cochlea

Cochlear nerve formed by sensory afferents with their nerve cell bodies in the Spiral Ganglion

Spiral Organ in the Cochlea

• Hairs (stereocilia) bend and activate Hair Cell receptors

• Sensory signals produced in the cochlear nerve

Hair cells of the Spiral Organ

Route of Sound Waves Through the Ear

High Pitch Vs Low Pitch

• __ (low frequency) sound waves are detected near the base/beginning of the cochlea

• – __ detection declines with age

high pitch 

(low frequency) sound waves are detected towards the end/apex of the cochlea

low pitch

Impulses from cochlea pass via __

spiral ganglion to cochlear nuclei of medulla

From spiral ganglion to cochlear nuclei of medulla, impulses sent

• To superior olivary nucleus

  • Sound Localization

• – Via lateral lemniscus to Inferior colliculus

  • Auditory Reflex Center

• From there, impulses pass to __ of thalamus, then to primary auditory cortex

• Auditory pathways decussate so that both cortices receive input from both ears

medial geniculate nucleus

Cochlear Nucleus:

• the most central site in which a lesion can produce deafness in the ipsilateral ear

  • receives a projection from only the ipsilateral ear

• Only receives unilateral info

• Every other “higher” brainstem nuclei in the auditory pathway

  • receives bilateral (Binaural) inputs (from both ears)

• lesions of the other higher auditory nuclei do not produce deafness

• produce partial hearing loss that is more prominent contralaterally, because more second-order axons decussate

supplies the cochlear nuclei
• unilateral occlusion can produce deafness in one ear.

Anterior Inferior Cerebellar Artery

what is Superior Olivary Nucleus?

integrates sound from both ears to precisely localize sound in three-dimensional space

When a sound comes from one side:

• The ear closest to the sound receives a slightly louder stimulus than the ear further away

• there is a delay in activating auditory neurons such that the cochlear nucleus nearer the source is activated first

• Loss of hearing impairs the ability to localize sound in space

what is Inferior Colliculus?

• Sound location data becomes fully integrated by the inferior colliculus
• Produces the Startle Response
• Turns Head to Threatening/Interesting Sounds
• Also controls the Vestibuloocular Reflex (VOR

sends information to other brain areas to interpret sounds and to respond to them

Primary Auditory Cortex

Upon hearing a loud noise:

• temporal lobe 

• parietal lobe 

• frontal lobe 

what is temporal lobe?

identifies the sound
• Sorts through all your sound memories

what is parietal lobe

figures out how is was produced and where is came from

what is frontal lobe

produces a motor response

Upon hearing Spoken Language:

• Signals sent from Auditory cortex to Wernicke’s Area
• From Wernicke’s Area to Broca’s Area
• Broca’s Area to Primary Motor Cortex
• Spoken response produced