Sensory System - Special Senses: Ear, Taste, Smell

Three components of sound waves

Pitch of sound - depends on frequency of air waves

Intensity (loudness) - depends on amplitude of air waves

Timbre (quality) - determined by overtones (overlayed sound waves of diff frequencies)

Pinna

Outer ear

Visible ear

External auditory meatus

Outer ear

Ear canal - carries sound waves to tympanum

Tympanum

Outer ear

Ear drum, entry to middle ear

Converts vibrations from sound waves into mechanical vibrations to be sent to ossicles

Ossicles

Middle ear

Amplifies sounds by 20-30x after receiving from tympanum then transmits vibrations to oval window

Small bones called malleus, incus, and stapes

Eustachian tube

Middle ear

Equalizes ear pressure

Oval window

Middle ear

Transmits vibrations from ossicles to cochlea

Cochlea (what it contains and its function)

Inner ear

Contains organ of corti, endolymph, and perilymph

Transduction from waves to AP’s

Organ of corti

In cochlear duct

Receptors - hair cells

Basilar Membrane - contains hair cells

Tectorial membrane - stiff, tips of hair cells imbedded here

Basilar Membrane

Bulges with sound waves (oscillating) creating the sound wave pattern that determines the pitch

Transmission of sound (Entering ear to oval window)

Sound waves hit tympanic membrane, membrane oscillates, moves ear ossicles (amplified waves), oval window moves in and out (sets perilymph in motion)

Transmission of sound (in cochlea)

Standing waves form in perilymph, transfer into endolymph

Basilar membrane oscillates - pushes hair cells against tectorial membrane, hair cells bend creating AP’s down auditory nerve

Location of bent cells determine pitch

Conduction Deafness

Problem with amplification of sound (outer/middle ear)

• ear ossicles, tympanic membrane

• Hearing aids help

• Eg. Ear infection or otosclerosis

Sensory Deafness

Problem with hair cells or auditory nerve (inner ear)

• hearing aids don’t help - need cochlear implants

• Eg. Loud music damage - higher amplitude = more hair cells bending and can case breakage

Vestibular Apparatus

Inner ear

Balance and body position

Consists of semicircular canal (rotation), utricle and saccule (linear motion)

Equilibrium

Bending/movement of hair cell created by body movement (hair cell in gelatinous fluid)

Vestibular nerve

• to cerebellum

• Balance and posture

• Motion and orientation

• Eye movement

Semicircular canals

Sense acceleration and deceleration

Uses endolymph and hair cells - in all planes

As body accelerates; hair cells move with skull, endolymph lags behind and bends hair cells in after skull is stopped, ion gates altered (creates AP’s)

Deceleration

Hair cells stop - endolymph continues

Bends hair cells in other direction

Utricle and Saccule

Detects linear motion

Endolymph contains otoliths (calcium “stones”)

As head moves

• heavier endolymph moves forwards

• Bends hair cells (triggers AP’s)

Chemoreceptors (function and nerves associated with smell and taste)

Binding of molecules (chemicals) will trigger GP’s and AP’s

Smell: olfactory nerve

Taste: facial and glossopharyngeal nerve

Smell

Memory and emotional response - depends on pattern of scent receptors

Closely related to taste

Scent molecules must be dissolved in mucous (allows for stronger scent)

140+ scent receptors identified

• 2 month lifespan then replaced

Taste receptors

Taste buds - life span is ten days

5 types - salty, sweet, sour, bitter, umami

Supported by mucous cells which trigger taste buds after substance is being dissolved

Nerve taste bud map

Facial nerve - front 2/3 of tongue, possibly salty and sweet

Glossopharyngeal nerve - back 1/3 of tongue, possible sour and bitter

Umami - central concentration - some in periphery

Some people show regions of sensitivity and others do not