Final

• The site of transduction is the cochlea
• Transduction occurs when hair cells rub against tectorial membrane
• The first synapse of the spiral ganglion is the cochlear nuclei
• Three subregions of the cochlear nuclei:

  1. Dorsal
  2. Anteroventral
  3. Posteroventral
• The dorsal cochlear nucleus is the only neuron that projects directly to the inferior colliculus
• The lemniscal part of inferior colliculus is the central nucleus (ICC, CIC)
• The lemniscal pathway of the IC is:

  1. Short latency responses
  2. responds well to tones
  3. precise tonotopy
• The non-lemniscle pathway of the inferior includes:

  1. dorsal inferior colliculus
  2. external nucleus of the inferior colliculus
• Properties of the non-lemniscal pathway:

  1. More complex auditory responses
  2. longer latency
  3. not responsive to pure tones
  4. often not tonotopic
  5. receives and projects to non-auditory areas
• There is a segregation of lemniscal and non-lemniscal pathways from the midbrain to the thalamus
• The ICC projects to the dorsal medial geniculate body
• The ICD projects to the dorsal division of the medial geniculate body
• The ICx projects to the medial division of the medial geniculate body
• Sound is quantified by its amplitude (dB) and frequency (Hz)
• cochlea is the sight of transduction
• Hair cells do not fire action potentials, spiral ganglion cells do
• Sound wave causes fluid wave in cochlea
• Scala vestibuli and tympani: contain perilymph
• Scala media: contains endolymph
• Low frequencies are detected at the apex of the basilar membrane
• higher frequencies are detected at the base of the basilar membrane
• Auditory system: Massive divergence from cochlea to brainstem. Massive convergence from brainstem to midbrain
• MRI Gradient Coils - spatial localization of protons
• MRI Radio Frequency coil - transmit and recieve signals
• Diffusion weighted imaging shows white matter pathways
• Resting state functional MRI shows functional connectivity.
• Task-based functional MRI shows brain activation
• Freesurfer: automated cortical parcellation of MRI scans
• MRI area measurement: voxel
• Vestibular system informs the brain on current position and movement of the head relative to gravity
• Vestibular system is Responsible for conscious perception of position and movement
• vestibular apparatus: semicircular canals that detect rotational or angular motion.
• Horizontal (lateral) semi circular canal: detect head rotation in the horizontal plane
• Anterior (superior) semi circular canal: detect head rotation in the sagittal plane
• Posterior semi circular canal: detect head rotation in the coronal plane (tilt head toward left or right shoulder)
• Two otolith organs: detect linear motion

  1. saccule
  2. utricle
• Saccule: detect linear movement in the vertical plane
• Utricle: detect linear movement in the horizontal plane
• The Vestibulocochlear Nerve : Cranial Nerve VIII
• Neurons in the vestibular ganglion project mostly to the vestibular nuclei