UNIT 3: SENSE ORGANS – NOSE AND EARS

• Chemical senses•Sense of hearing and balance

Campbell et.al, 2010 – CHAPTER 50

1. SENSE OF SMELLReceptor cells of smell are OLFACTORY

CELLSOlfactory cells are located within

olfactory epithelium high in the roof of the nasal cavity.

SENSE OF SMELL

PERCEPTION OF SMELLThe gas molecules in the air dissolves

in the mucus of the nasal cavity.It stimulates the microvilli of olfactory

cells.This cause an impulse to be send from

olfactory cell through the sensory nerve fibers, to the olfactory bulb in the temporal lobe of the cerebrum.

Smell is integrated and perceived.

PERCEPTION OF SMELL

2. THE SENSE OF HEARING AND BALANCE

The ear has two sensory functions: Hearing and Balance.

The sensory receptors for both of these is located in the inner ear, and each consist of hair cells and cillia which are sensitive to mechanical stimulation. They are called machanoreceptors.

THE HUMAN EAR

FUNCTIONS OF

DIFFERENT PARTS OF THE EAR

OUTER EARMIDDLE EAR

INNER EAR

THE OUTER EARPinna – Concentrate sound waves in the

direction of the external auditory canal.External Auditory canal – Transport sound waves from the pinna to the

tympanic membrane. - Contain fine hairs and cerumin glands that

secrete cerumin (earwax) to help guard the ear against foreign material and insects. (smell)

THE OUTER EARTympanic membrane – A thin membrane that covers the opening

between the inner- and middle ear.- Converts soundwaves into vibrations.

(starts to vibrate)

MIDDLE EAR3 Bony ossicles e.g.: (start to vibrate):

- Malleus – transmit vibration to incus- Incus – transmit vibrations to stapes- Stapes – transmit vibrations to oval

window (fenestra ovalis)Oval window – start to vibrate and cause

waves in liquid (perilymph) in cochlea.Eustachian tube – Equalize the pressure

between the atmosphere and the inside of the ear. (Connected with the pharynx).

MIDDLE EAR

INNER EAR

Cochlea: - Snail shaped canal.- Divided in 3 canals separated by membranes1. Vestibular canal (scale vestibuli) – top canal, filled with perilymph. Receives vibration from oval window, form waves in perilymph, causes Reissner membrane to form waves.

2. Cochlear canal (Scala media) – middle canal, filled with endolymph.

Form waves in endolymph, that causes Basilar membrane to wave up and

down. Contains the receptor cells for hearing:

Organ of Corti - which pushes the stereocilia against the tectorial

membrane, causes an impulse which is send through the cochlear nerves to the temporal lobe of the brain for integration.

3. Tympanic canal (Scala tympani)– bottom canal, filled with perilymph. Form

waves which are carried to the round window (fenestra rotunda).

Round Window: absorb excess sound waves to prevent echoing in the ear.

COCHLEACross section

through cochleaCochlear unrolled

3. INNER EAR: SEMI CIRCULAR CANALS

Contain machanorecepters (cristae) – detect rotational or angular movement of the head.

Cristae- located in the ampulla (enlarged base of semi circular canals)in the endolymph found in the semi circular canals.

- Consist of hair cells, supporting cells, stereocillia imbedded in a gelatin capsule called cupula, and nerve fibers.

INNER EAR: SEMI CIRCULAR CANALS

Movement of the head causes the endolymph to move around in the

ampulla, the cupula moves, bending the stereocilia, causing an impulse send through the

vestibular nerve to the cerebellum of the brain for integration.

CRISTAE

4. INNER EAR: UTRICULUS AND

SACCULUSEnlarged area below the semi circular canals.Contain mechanoreceptors (macula) – that

detects straight line movement of the head in any direction – gravitational equilibrium.

Macula: Consist of hair cells with stereocilia embedded

in a gelatin membrane called otolithic membrane with otoliths (crystals) ontop, supporting cells and vestibular nerves.

4. INNER EAR: UTRICULUS AND

SACCULUSIf a person stops suddenly, the endolymph in the utriculus and

sacculus move around, the otolithic membrane moves, bending the stereocilia, which sends an impulse through the

vestibular nerves to the cerebellum of the brain to maintain

balance.

MACULA FOUND IN SACCULUS AND UTRICULUS

PROCESS OF HEARING

PROCESS OF HEARING

PROCESS OF HEARING

Fig. 50-8

Hair cell bundle froma bullfrog; the longestcilia shown areabout 8 µm (SEM).

Auditorycanal

EustachiantubePinna

Tympanicmembrane

Ovalwindow

Roundwindow

Stapes

Cochlea

Tectorialmembrane

IncusMalleus

Semicircularcanals

Auditory nerveto brain

Skullbone

Outer earMiddle

ear Inner ear

Cochlearduct

Vestibularcanal

Bone

Tympaniccanal

Auditorynerve

Organ of Corti

To auditorynerve

Axons ofsensory neurons

Basilarmembrane

Hair cells

SENSE OF BALANCE

Fig. 50-11

Vestibular nerve

Semicircular canals

Saccule

Utricle Body movement

Hairs

Cupula

Flow of fluid

Axons

Haircells

Vestibule