Special Senses (II)

Hearing and Equilibrium

outer ear

auricle, auditory canal, and tympanic membrane

auricle

detects sound waves into the auditory canal

auditory canal

secretes ear wax (ceremen) which helps clean and lubricate the ear canal and prevent the entry of bacteria, water, and foreign objects

tympanic membrane

also known as the ear drum, it vibrates in response to sound waves

sound

originates from vibrating object and travels in waves created by the back and fourth vibration of the surronding air molecules

middle ear

malleus, incus, stapes, and oval window

Ossicles

malleus, incus, and stapes - vibrations are amplified across ossicles, the force is transferred from the eardrum to the stapes to increase pressure - need to amplify the sounds because the inner ear is liquid

oval window

separates middle ear and inner ear

muscles that attenuate sound levels

tensor tympani and stapedius

Inner Ear

membranous labyrinth and the bony labyrinth

bony labyrinth

bony cavities within the temporal lobe, 3 semicircular canals, vestibule, and cochlea

perilymph

filled with CSF

endolymph

intracellular fluid

membranous labyrinth

utricle, saccule, and cochlear duct

cochlea

snail like structure that contains the organ for hearing

scala vestibuli

top part - perilymph

scala media

middle part, only one filled with endolymph

scala tympani

bottom part - perilymph

vestibular mb

between scala vestibuli and scala media

tectorial mb

on top of organ of corti

basilar mb

separates scala media and scala tympani

organ of corti

receptor organ for hearing, it is a sensory epithelium

outer hair cells

they receive descending inputs from the brain to assist with the modulation of IHC function

Inner Hair cells

~3,500 cells for hearing

mechanotransduction in the hair cell

1. positive mechanical deformation of the hair bundle toward the longer stereovilli

2. More opening of mechanosensitive channels at the tips of the stereovilli, which allows K+ influx, leading to depolarization

3. the depolarization activates voltage-sensitive Ca2+ channels, causing release of synaptic vesicles with NT - stimulation of the adjacent sensory neurons

auditory projection pathway

1. CN VIII

2. cochlear nucleus (medulla)

3. superior olive (Pons)

4. inferior colliculus (midbrain)

5. medial geniculate (thalamus)

6. primary auditory cortex (Temporal lobe)

vestibular apparatus system

sensory epithelium: crista, 3 semicircular ducts filled with endolymph, utricle and saccule contain a sensory epithelium: macula

macula

static equilibrium and the sense of linear acceleration

otolithic organs

utricle and sacculus

utricle

detects linear accelerations and head tilts in the horizontal plane

saccule

detects linear acceleration and head tilts in the vertical plane