Human Ear Anatomy and Functions

Special Senses: Hearing and Balance

• Transcribes lecture captions, not edited for grammar or spelling
• Lecture 22, Video 1

Introduction

• Special senses of hearing and balance are discussed
• Anatomy of external, middle, and inner ear explained
• Turning sound waves into electrical signals for the brain
• Structures for balance: head position, acceleration/deceleration
• Motion sickness explained

Slide 1

• Textbook material: Chapter 15, Section 15.4
• Cochlea highlighted: structure within the inner ear, deep within the temporal bone
• Temporal bone is shown in the image, with the cochlea showing membranous structures
• Specific structure's function discussed later in lecture

Slide 2

• Sound defined: vibration in air, causing compressed and less compressed air bands (sound waves)
• Sound wave graphs shown, depicting compressed and less compressed bands
• Volume: dependent on wave amplitude, higher amplitude = higher volume
• Pitch: dependent on wave frequency, higher frequency = higher pitch

Slide 3

• External, middle, and inner ear regions of hearing and balance
• External ear: auricle (pinna) collects sound waves, external auditory canal directs towards middle ear
• Ear wax (cerumen): protection from dust, insects, and water
• Middle ear: tympanic membrane (eardrum) vibrates with sound waves, auditory ossicles (malleus, incus, stapes) amplify vibrations
• Auditory tube (eustachian tube): connects to pharynx to equalize pressure on tympanic membrane
• Pressure equalization: needed for tympanic membrane function
• Chewing, swallowing, yawning: actions that open the auditory tube for pressure equalization

Slide 4

• Inner ear structures highlighted: oval window transmits vibrations from stapes, round window is an exit point for vibrations
• Cochlea: fluid-filled cavity; discussed
• Vestibule (static balance): involved in head position in the upright position
• Semicircular canals (dynamic balance): involved in head acceleration/deceleration

Slide 5

• Membranous labyrinth (inside the bony labyrinth): contains endolymph (high potassium, low sodium)
• Perilymph (around the membranous labyrinth): high sodium, low potassium
• Specialized cells in membranous labyrinth: detect hearing/balance signals
• Cochlear duct, important for hearing

Slide 6

• Cross section of the cochlea: 3 chambers (scala vestibuli, cochlear duct, scala tympani) with different fluids
• Basilar membrane: divides the cochlear duct into 2 parts; hair cells & associated structures for hearing found here
• Tectorial membrane: gelatinous membrane on top of the hair cells
• Important: ion concentration differences in fluids (endolymph, perilymph)

Slide 7

• Hair cells in hearing and balance (outer hair cells, inner hair cells)
• Hair bundle and stereocilia: how sound waves are sensed
• Tectorial membrane role: important in activating the hair cells

Slide 8

• Microvilli (stereocilia), how they're arranged in progressively taller order, and how they're linked with tip links (gating springs)
• Tip links/gating springs : role in causing depolarization and signal generation

Slide 9

• Resting hair cells, gating springs and how they respond to sound
• How basilar membrane movements stimulate hair cells and cause depolarization

Slide 10

• Sound waves, tympanic membrane, and ossicles
• How sound waves cause vibrations in the cochlea
• Cochlea pathway discussed

Slide 11-12

• Matching of numbers to steps in the pathway
• Details on movement of sound through the inner ear (how sound waves travel from tympanic membrane-- oval window--cochlea)
• Basilar membrane function, pitch and volume perception
• Matching numbers to steps of auditory pathway

Slide 13

• Explanation of how hair cells generate signals to the auditory cortex; role of specialized cells (cochlear nerve, vestibular nerve)
• Motion sickness: sensory conflict between the visual and vestibular systems; conflicting information from the two

Slide 14

• Information to the vestibular nuclei (cerebellum, eye muscles)
• Brain receives multiple auditory inputs, balance information too

Slide 15

• Otolithic membrane (mass) and otoliths (crystals)
• Macula (specialized region of hair cells): used in static equilibrium (or position relative to gravity)
• How position of the head is detected when it is upright or tilted in the macular region
• How information is sent (to brain)

Slide 16

• Semicircular canals involved in dynamic balance (detecting acceleration/deceleration of head)
• Crista ampullaris (in the ampulla of each semicircular canal): structure that detects acceleration/deceleration of head
• Endolymph: fluid in semicircular canals, and how head movement moves endolymph and causes hair cell movement and depolarization, relative to head movement

Slide 17

• Crista, cupula, and hair cells in semicircular canals
• How movements affect fluid and causing hair cell movement
• Explain how head motion is related to fluid movement/ how fluid movement results in hair cell stimulation

Slide 18

• How head movement affects sensory information
• Motion sickness: sensory conflict results in nausea

Slide 19

• Action potentials on vestibular nerve
• Different parts of the brain receive the vestibular signals, for posture control/balance
• Vision's role, how balance and vision information works together