2- Ear / Vestibular

Question 1

Outer ear

Answer 1

Auricle / Pinna + externa auditory canal
(anything you can touch with a Q tip)
-Anything before eardrum

Question 2

Middle ear

Answer 2

• starts at tympanic membrane, which vibrates
• Ossicles: Malleus (hammer), incus (anvil), stapes (stirrup)
• stapes touches oval window, which is gateway to inner ear
• also connects to nasal cavity via Eustachian tube- equalize pressure b/w middle ear and environment

Question 3

Inner ear

Answer 3

• 2 functions: Hearing + Vestibular sense (balance; where our head is located- how our head is moving, if it’s rotating, etc)
• Semicircular canals (above) and cochlea (snail shaped)
• Vestibule (chamber/open space/cavity) in front of the 3 semicircular canals
• Vestibulocochlear nerve (CN 8)
• Stapes @ oval window
• Endolymph (K+ rich)- fills cochlea, vestibule, semicircular canals of inner ear “membranous labyrinth”
• Perilymph surrounds membranous labyrinth - transmits vibrations from outside world & cushions inner ear structures
• Round window

Question 4

More specifics of inner ear

Answer 4

Basilar membrane - at base b/w perilymph and endolymph; it’s the base that everything else sits on; b/w scala tympani and cochlear duct (vs vestibuli)
Organ of Corti- transduction, hair cells sense vibrations as move, process info
Nerves- take info to brain

Organ of corti overlaid by tectorial membrane; hair cells
-Higher frequency noises produced at window (lower wavelength, higher pitch- wired backwards; at the base there’s the treble noises)
PLACE THEORY

Tectorial membrane over hair cells- amplifies sounds
TECTORIAL MEMBRANE AMPLIFIES SOUND

Question 5

Tonotopic map

Answer 5

location of sounds in space
(comparable to retinotopic map of eye/visual cortex)

hearing- MGN, inferior colliculus, auditory cortex, superior olive (localize)

vision- LGN, superior colliculus, visual cortex

Question 6

Vestibule

Answer 6

fluid-filled cavities in bony labyrinth (outside, vs membranous)
VESTIBULE IN BONY LABYRINTH
-contain utricle and saccule (info about linear acceleration)– contain modified hair cells covered with OTOLITHS which bend hair which signal brain
-UTRICLE: HORizontal acc
-SACCULE- VERticle acc

Semicircular canals- rotational acc
-perpendicular to e/o, running from ampulla, where hair cells are

Question 7

MGN

Answer 7

LGN (lateral geniculate nucleus) for LIGHT
MGN (medial) for MUSIC = hearing

LGN and MGN are in thalamus
LGN on left and right
MGN in middle

MGN, like LGN, repackages info- frequency, intensity, location (2 ears get different info- lag time tells where in space sound came from)
-Then go to temporal lobe
Right ear = left temporal lobe
Left ear = right temporal lobe

Inferior colliculus - sensory reflexes- startle reflex & keeps eyes fixed on point when head is turned (vestibulo-ocular reflex)
(superior colliculus = eyes)

Some info also sent to superior olive- localizes sound (also in thalamus)

Question 8

Hair cells

Answer 8

• hair cells are the receptor cells for hearing [inner]
• hair cells in clusters/tufts
• stereocilia at tops of surface
• signal transduction at inner hair cells- to organ of corti- to signaling brain
• stereocilia sway w/in endolymph as vibrations reach basilar membrane underlying organ of corti
• outer hair cells are directly connected to immobile tectorial membrane (amplify incoming sound)
• hair cells in ear allow nerve cells to fire if they vibrate at the distance of a width of an atom- slight disturbances
• get less sensitive w/ age = age-caused hearing loss
• to them, loud noises don’t get softer, but soft noises get much softer for hard-of-hearing
• speaking loudly to them doesn’t help

-low sounds/back of cochlea lost first- so speak HIGHER, not louder

Hearing aids don’t amplify all sounds; they compress the range of sounds so softer sounds get closer to louder sounds