Lectures 18 + 19 ( hearing + lang)

middle ear

1. eardrum (tympanic membrane)

2. 3 tiny bones (malleus, inucs, stapes)

3. oval window (membrane)

4. round window = release valve of cochlear fluid pressure

5. tympanic reflex msucles - damp the vibrations to protect ear from damagne

inner ear

bony labyrinth filled with endolumph

1. semicircular canneals (vestibular organs)

2. cochlea = haering organ that senses sound vibrations

   1. subdivided nto 3 cnalas (scala media, tympani, and vestibuli)

   2. scala tympani = has soft flexible membrane (basilar membrane) to separate it from media

   3. oval winodw sensds waves of fluid pressure into the cochlea, the B membrane vibratestoo

   4. have the organ of corti on tp of B membrane with tectorial memrbane (gelatin) on top

hair cells

• primary sensory neurons of the inner ear (for both hearing and vestibular sensation)

• stereocilia = transduce mechanicla movemtns into nerve signals (mehcanorepctors)

• the tallest stereocilia on the hair cell =kiinocilium

• tip links = tiny protein strands

• tip links are anchored to mehcnaically gated K+ channels

• depolarizes the cell, bc concentration of K+ high here

• triggers NT release —> binds to receptors on the afferent (incoming) vestibular or cochlear nerve

afferent and efferent

• Afferent: Carries signals or fluids toward a central point or organ.

• Efferent: Carries signals or fluids away from a central point or organ

inner vs outer hair cells

• inner = release GLU onto auditory nerve fibers, which recieve Ach inputs

• outer = relase Ach and receve GABA from brain

tonotopic strucutral of basilar membrane

different parts o the membrane vibrate in respoonse to different soudn freq, high near its base, low freq near the apex (furtherest point)

auditoroy pathway to the brain

spinal ganglion —> cochlear nucleus —> superior olive —> inferior colliculus —> MGN thalamus —> auditory cortex

• Spinal = cochlear

  • spinal gang contains somata for bipolar sensroy neurosn taht form the auditory nerve (these are the first neurons taht fire Aps)

• cochlear nuclues

  • bilateral projection to olive

  • some cochlear nucleus axons target the ipsilateral superior olive, some cross the midline

  • therefore, superior olvie recievs binaural input (input form both ears)

  • which helps infereir colliculus to perfrom auditory localization by comparing the sounds loudness and the arrival time at each eear

• superior olvie

  • inferior colliculus = has tonotopic map of sound frequences = nueorns that are near each other in the inferior colliculus prefer similar sound infrequneces

    • also has spatiotopic maps of the sounds source = the adjacent nuerons respond to sounds from nearby locations

  • the inferior and superior colliculi together formt he tectum of the midbrain, which are imporatnt strucutres that ocntrol orietning towards evnriotmal stimuli such as sounds, visual stimuli, etc

• after the inferior colliculus => MGN => aud cortex

  • medial geniculate nucleus of hte thalamus, which is the auditory region of teh thalamus

  • thalamus is gateway to the neocortex

  • aud cortex. = the lateral part of the temporal lobes

lateral vs medial

lateral = toward the side or away from the midline of the body

medial = twoard the middle or closer to the midline of teh body

auditory cortex

• primary auditory cortex resides largely on the inner surface of the lateral sulcus

• higher aud areas are nearby along the adjacent superior temporal gyrus

semicirculate canals are designed so that hair cells can sense movment and position

• 3 translation degres (linera motion)

• 3 rotational degrees (turning motion)

• utricle = horizontal plane (x,y)

• saccule = vertical plane = z axis

macula of the utricle

the saccula and utricle both contain a motion sensing organ called the macula

3 layers

• bottom = somata of hair cells

• middle = otolithic membrane = stereocilia embedded + gelatinous

• top = crust of calcium carbonate crystals called otoliths (ear rocks)

sensing head tilt and linear acceleration

• hair cells in the utricle are depolarized by backward head tilts / forward accelaratin

• hari cells in the utricle are hyper polarized by forward head tilts/ backward acceleration