PMCY 4050 - Hearing and Balance

external ear

• collects sound; localization of sound; each individual’s pinna collects distinctive sound imprint

• protection

• earlobe detects sensations

external meatus (auditory canal)

• extends from pinna to tympanic membrane

• size and shape varies between individuals

• functions: protects ear drum, resonator

cerumen (ear wax)

• repel water

• traps dust, particulate matter, microbes, debris

• moisturize epithelium of ear canal

• odor discourages insects

• cleans ear canal

tympanic membrane (ear drum)

• thin, semitransparent membrane

• covered by epidermis

middle ear

• air-filled cavity

• ear drum separates it from external ear

• oval window separates it from inner ear

• contains auditory ossicles, oval window, eustachian tube

ossidcles

malleus (hammer), incus (anvil), stapes

malleus (hammer)

• attached to ear drum

• transfers vibrations (sound waves) to incus

incus (anvil)

transfers vibrations to stapes

stapes

• smallest bone in body

• transmits vibrations to membrane of inner ear

• base fits into oval window

oval window

• intersection of middle ear and inner ear

• vibrations have been amplified > 10x

eustachian tube

• extends from middle ear to naso-pharynx behind the nose

• normally closed at pharyngeal

  • opens during swallowing, chewing, and yawning

• aids in maintaining equal pressure on either side of ear drum

inner ear

labyrinth: outer bony labyrinth and inner membranous labyrinth

outer bony labyrinth

• series of cavities in temporal bond

• three regions:

  • semicircular canals

  • vestibule

  • cochlea

• lined with periostem

• contains perilymph (similar to CSF)

inner membranous labyrinth

• series of sacs and tubules inside bony labyrinth

• lined with epithelium

• contains endolymph

  • high potassium content

  • potassium generates auditory signals

• two sacs

  • utricle (vertical)

  • saccule (horizontal)

semicircular canals

• anterior (vertical orientation)

• posterior (vertical orientation)

• lateral (horizontal orientation)

• contains criste, hair cells

• maintain static equilibrium

ampula

enlargement at end of each canal

vestibule

• central portion of outer bony labyrinth

• contains utricles and saccule

• contains receptor for static equilibrium

• maintains posture and balance

• maculae contains hair cells and supporting cells

cochlea

• snail shaped

• bony spiral canal

• three channels

  • cochlea duct

  • scala vestibuli

  • scali tampani

organ of corti

• coiled sheet of epithelial cells (spiral organ)

• 2 groups of hair cells (neurons from cranial nerve VIII)

  • inner and outer hair cells

• hair cells = hearing receptors

vestibular system

• regulates balance

• semicircular canals determine movement in 3 diff planes

• endolymph and hair cells present in each semi-circular canal

• motion results in movement of endolymph which results in movement of hair cells

• utricle and saccule are attached to semi-circular canals which also contain endolymph and hair cells

• otoliths (Ca deposits) are contained in endolymph

• when standing, otoliths fill on hair cells on bottom

• movement stimulates the hair cells on the side

• hair cells are receptors for balance