““If a tree falls…”If a tree falls…”

If a tree falls in the forest and there is

nobodyaround to hear it…

Does it make a noise?

NO…Sound (like colour) is all in your head!

HearingHearing

What is Sound?What is Sound?Compression & Rarefaction

of air molecules.

Sound WavesSound WavesAmplitude (Loudness)

Strength or height of thewave

Frequency (Pitch)Distance twixt consecutive

peaks

Mix (Timbre)Interaction of different

waves

1 Hertz = 1 Cycle/Sec1 Hertz = 1 Cycle/Sec Human HearingHuman Hearing20 - 20k Hz20 - 20k Hz

Perceiving PitchPerceiving Pitch

Georg von Békésy1899-1972

Place Theory - pitch determined bypoint of maximal vibration on

basilar membraneTraveling Wave Theory 1957Traveling Wave Theory 1957

Frequency Theory - pitch determined by the rateat which the hair cells fire (i.e., 1KHz tone cause

hair cells to fire 1k times/sec) Volley PrincipleVolley Principle

The EarThe Ear

Houses two senses

Hearing

Equilibrium (balance)

Receptors are mechanoreceptors

Anatomy of the EarAnatomy of the Ear

Slide 8.21

The ear is divided into three areas Outer

(external) ear

Middle ear

Inner ear

Figure 8.12

The External EarThe External Ear

Slide 8.22

Involved in hearing only

Structures of the external ear Pinna

(auricle)

External auditory canal

Figure 8.12

The External Auditory CanalThe External Auditory Canal

Slide 8.23

Narrow chamber in the temporal bone

Lined with skin

Ceruminous (wax) glands are present

Ends at the tympanic membrane

malleus

cochlea

incus

pinnapinna

auditory canalauditory canal

tympanic membranetympanic membrane

auditory/8th nerve

Outer EarOuter Ear

Tympanic MembraneTympanic Membrane - collect “sound” &

vibrate ossicles

PinnaPinna - collect and direct “sound” into auditory canal

Auditory CanalAuditory Canal - amplify & funnel “sound” totympanic membrane

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

Slide 8.24a

Air-filled cavity within the temporal bone

Only involved in the sense of hearing

Middle EarMiddle Ear

MalleusMalleus - vibrate & move the IncusIncusIncus - vibrate & move the StapesStapesStapes - vibrate against Oval Window of Cochlea

malleusmalleus incusincus

handleof malleus

long processof incus

stapesstapes

The Middle Ear or Tympanic CavityThe Middle Ear or Tympanic Cavity

Slide 8.24b

Two tubes are associated with the inner ear

The opening from the auditory canal is covered by the tympanic membrane

The auditory tube connecting the middle ear with the throat

Allows for equalizing pressure during yawning or swallowing

This tube is otherwise collapsed

Bones of the Tympanic CavityBones of the Tympanic Cavity

Slide 8.25a

Three bones span the cavity

Malleus (hammer)

Incus (anvil)

Stapes (stirrip)

Figure 8.12

Bones of the Tympanic CavityBones of the Tympanic Cavity

Slide 8.25b

Vibrations from eardrum move the malleus

These bones transfer sound to the inner ear

Figure 8.12

Inner Ear or Bony LabyrinthInner Ear or Bony Labyrinth

Slide 8.26a

Includes sense organs for hearing and balance

Filled with perilymph

Figure 8.12

Inner Ear or Bony LabrynthInner Ear or Bony Labrynth

Slide 8.26b

A maze of bony chambers within the temporal bone

Cochlea

Vestibule

Semicircular canals

Inner EarInner Ear

lateralsemicircular

canal

posteriorsemicircular

canal

vestibule

anteriorsemicircuar

canal

cochleacochlea

CochleaCochlea - filled with fluid & contains receptorsfor hearing (Hair Cells)(Hair Cells)

Basilar MembraneBasilar Membrane - divides length of cochlea & holdsthe hair cells

Auditory PathwayAuditory Pathway

Organs of HearingOrgans of Hearing

Slide 8.27a

Organ of Corti

Located within the cochlea

Receptors = hair cells on the basilar membrane

Gel-like tectorial membrane is capable of bending hair cells

Cochlear nerve attached to hair cells transmits nerve impulses to auditory cortex on temporal lobe

Organs of HearingOrgans of Hearing

Slide 8.27b

Mechanisms of HearingMechanisms of Hearing

Slide 8.28

Vibrations from sound waves move tectorial membrane

Hair cells are bent by the membrane

An action potential starts in the cochlear nerve

Continued stimulation can lead to adaptation

Mechanisms of HearingMechanisms of Hearing

Slide 8.29Figure 8.14

Organs of EquilibriumOrgans of Equilibrium

Slide 8.30a

Receptor cells are in two structures

Vestibule

Semicircular canals

Figure 8.16a, b

Organs of EquilibriumOrgans of Equilibrium

Slide 8.30b

Equilibrium has two functional parts

Static equilibrium – sense of gravity at rest

Dynamic equilibrium – angular and rotary head movements

Figure 8.16a, b

Static EquilibriumStatic Equilibrium

Slide 8.31

Maculae – receptors in the vestibule Report on the position of the head

Send information via the vestibular nerve

Anatomy of the maculae Hair cells are embedded in the otolithic

membrane

Otoliths (tiny stones) float in a gel around the hair cells

Movements cause otoliths to bend the hair cells

Function of MaculaeFunction of Maculae

Slide 8.32

Figure 8.15

Dynamic EquilibriumDynamic Equilibrium

Slide 8.33a

Crista ampullaris – receptors in the semicircular canals

Tuft of hair cells

Cupula (gelatinous cap) covers the hair cells

Figure 8.16c

Dynamic EquilibriumDynamic Equilibrium

Slide 8.33b

Action of angular head movements

The cupula stimulates the hair cells

An impulse is sent via the vestibular nerve to the cerebellum

Figure 8.16c

Chemical Senses – Taste and Chemical Senses – Taste and SmellSmell

Slide 8.34

Both senses use chemoreceptors

Stimulated by chemicals in solution

Taste has four types of receptors

Smell can differentiate a large range of chemicals

Both senses complement each other and respond to many of the same stimuli

Olfaction – The Sense of SmellOlfaction – The Sense of Smell

Slide 8.35

Olfactory receptors are in the roof of the nasal cavity

Neurons with long cilia

Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex

Olfactory EpitheliumOlfactory Epithelium

Slide 8.36

Figure 8.17

The Sense of TasteThe Sense of Taste

Slide 8.37

Taste buds house the receptor organs

Location of taste buds Most are on

the tongue

Soft palate

Cheeks Figure 8.18a, b

Structure of Taste BudsStructure of Taste Buds

Slide 8.39a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Gustatory cells are the receptors

Have gustatory hairs (long microvilli)

Hairs are stimulated by chemicals dissolved in saliva

Structure of Taste BudsStructure of Taste Buds

Slide 8.39b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Impulses are carried to the gustatory complex by several cranial nerves because taste buds are found in different areas

Facial nerve

Glossopharyngeal nerve

Vagus nerve

Anatomy of Taste BudsAnatomy of Taste Buds

Slide 8.40Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 8.18

Taste SensationsTaste Sensations

Slide 8.41Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Sweet receptors Sugars Saccharine Some amino acids

Sour receptors Acids

Bitter receptors Alkaloids

Salty receptors Metal ions

Developmental Aspects of the Developmental Aspects of the Special SensesSpecial Senses

Slide 8.42Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Formed early in embryonic development

Eyes are outgrowths of the brain

All special senses are functional at birth