Special Senses: Hearing & Balance

Special Senses: Hearing & Balance

• Transcripts are auto-generated lecture captions, not edited
• The lecture covers hearing and balance
• Starts by looking at the anatomy of the external, middle, and inner ear
• Explores how sound waves are converted to electrical signals for the brain
• Examines inner ear structures related to balance, head position, and acceleration/deceleration
• Discusses motion sickness

Slide 1: Cochlea

• The cochlea structure is highlighted in the picture
• It's located within the temporal bone
• The image shows the cochlea's membranous structure within the temporal bone

Slide 2: Sound

• Sound is a vibration in air, causing compressed and less compressed air bands (sound waves)
• Sound waves are depicted in the images
• Sound volume depends on wave amplitude
• Sound pitch depends on the frequency of the waves

Slide 3: External Ear

• The auricle (pinna) collects sound waves from the environment
• The external auditory canal directs these waves toward the middle ear
• Ear wax (cerumen) protects the middle and inner ear from dust, water, and insects
• The tympanic membrane (eardrum) is the boundary between the external and middle ear

Slide 3: Middle Ear

• An air-filled cavity containing three tiny bones (auditory ossicles): malleus, incus, and stapes
• The malleus is connected to the tympanic membrane
• The incus transfers vibrations from the malleus to the stapes
• The stapes vibrates the oval window, triggering fluid waves in the inner ear (cochlea)
• The eustachian tube equalizes pressure between the middle ear and the external environment

Slide 3: Inner Ear

• Includes the cochlea (fluid-filled) and structures for balance (vestibule and semicircular canals)
• Vibrations from the stapes cause fluid waves in the cochlea
• The cochlea contains the spiral organ (organ of Corti) with sensory hair cells for hearing

Slide 4: Inner Ear Anatomy

• Inner Ear's structure includes the oval window and round window as entry/exit points for cochlear waves
• The vestibule and semicircular canals are for balance (static and dynamic)

Slide 5

• The bony labyrinth is the outer part of the inner ear
• The membranous labyrinth is inside the bony, containing fluid (endolymph and perilymph)
• The membranous labyrinth will divide the bony labyrinth into three chambers
• Special receptor cells detect sound and balance

Slide 6 & 7: Cochlea Details

• The cochlea has three chambers (scala vestibuli, scala media, scala tympani) filled with fluids (endolymph, perilymph)
• The basilar membrane inside the cochlea holds the specialized receptor cells (hair cells) of the spiral organ
• Hair cells/Stereocilia and tip links are involved in sound detection
• Potassium ions enter the cells if waves vibrate the basilar membrane

Slide 8

• Microvilli (stereocilia) on hair cells are arranged in rows (outer, inner)
• Tip links connect stereocilia to ion channels
• Movement of stereocilia opens ion channels for potassium entry

Slide 9

• Tip links are also known as "gating springs" as they move stereocilia
• Sound waves move basilar membranes which move hair cells
• Potassium enters hair cells creating depolarization
• This triggers signals to the central nervous system

Slide 10: Hearing Process

• Sound waves enter the external auditory canal
• Vibrate tympanic membrane
• Move ossicles
• Vibrate oval window
• Fluid waves in cochlea
• Vibrate basilar membrane (mechanoreceptors)

Slide 11-12: Pitch and Volume

• High-pitch sounds stimulate hair cells near the oval window
• Low-pitch sounds stimulate hair cells at the helicotrema
• Louder sounds stimulate more hair cells
• Location and number of activated hair cells determine pitch and volume

Slide 13: Vestibular System

• Vestibular system consists of the vestibule and semicircular canals
• Involved in static (head position) and dynamic (head movement) balance

Slide 14: Balance Process

• Otoliths (crystals) in the otolithic membrane are pulled by gravity
• Movement of the membrane changes hair cell stimulation
• Signals sent to vestibular nuclei

Slide 15: Dynamic Equilibrium

• Semicircular canals' fluid moves when the head moves
• Cupula inside fluid deflects hair cells
• Stimulates sensory receptors to signal movement to the brain

Slide 16: Brain's Processing

• Vestibular nuclei process vestibular signals
• Signal sent to cerebellum regulates balance
• Cerebellum coordinates movement and posture
• Signals can be routed to the eye muscles for movement correction

Slide 17: Crista and Cupula

• Crista ampullaris found in semicircular canals, hair cells and cupula inside
• Movement in the semicircular canals stimulates hair cells, moves cupula
• Movement is detected and sent to the central nervous system
• The brain interprets this movement to know when we are accelerating
• When the head is in a still position, the fluids are not moving and the cupula is upright

Slide 18 & 19: Brain Integration

• Vestibular nuclei process information about head movement
• Information sent to the cerebellum for coordination and posture
• The cerebellum ensures appropriate actions in response to vestibular signals
• The brain integrates vestibular signals with other sensory cues; this leads to motion sickness when sensory information is contradictory