sense organs

1. UNIT 3:
SENSE ORGANS –
NOSE AND EARS
• Chemical senses
•Sense of hearing and balance
Campbell et.al, 2010 –
CHAPTER 50

2. 1. SENSE OF SMELL
Receptor cells of smell are OLFACTORY
CELLS
Olfactory cells are located within olfactory
epithelium high in the roof of the nasal
cavity.

3. SENSE OF SMELL

4. PERCEPTION OF SMELL
The gas molecules in the air dissolves in the
mucus of the nasal cavity.
It stimulates the microvilli of olfactory cells
where it bonds to the odorant receptors
This cause an impulse to be send from
olfactory cell through the sensory nerve
fibers, to the olfactory bulb and then to the
temporal lobe of the cerebrum.
Smell is integrated and perceived.

5. PERCEPTION OF SMELL

6. 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.

7. THE HUMAN EAR

8. FUNCTIONS OF
DIFFERENT
PARTS OF THE
EAR
OUTER EAR
MIDDLE EAR
INNER EAR

9. THE OUTER EAR
Pinna – 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)

10. THE OUTER EAR
Tympanic membrane
– A thin membrane that covers the opening
between the inner- and middle ear.
- Converts soundwaves into vibrations.
(starts to vibrate)

11. MIDDLE EAR
3 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).

12. MIDDLE EAR

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

14. 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.

15. 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.

16. COCHLEA
Cross section through
cochleaCochlear
unrolled

17. 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.

18. 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.

19. CRISTAE

20. 4. INNER EAR: UTRICULUS AND
SACCULUS
Enlarged 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.

21. 4. INNER EAR: UTRICULUS AND
SACCULUS
If 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.

22. MACULA FOUND IN SACCULUS AND
UTRICULUS

23. PROCESS OF HEARING

24. PROCESS OF HEARING

25. PROCESS OF HEARING

26. Fig. 50-8
Hair cell bundle from
a bullfrog; the longest
cilia shown are
about 8 µm (SEM).
Auditory
canal
Eustachian
tubePinna
Tympanic
membrane
Oval
window
Round
window
Stapes
Cochlea
Tectorial
membrane
Incus
Malleus
Semicircular
canals
Auditory nerve
to brain
Skull
bone
Outer ear
Middle
ear Inner ear
Cochlear
duct
Vestibular
canal
Bone
Tympanic
canal
Auditory
nerve
Organ of Corti
To auditory
nerve
Axons of
sensory neurons
Basilar
membrane
Hair cells

27. SENSE OF BALANCE

28. Fig. 50-11
Vestibular nerve
Semicircular canals
Saccule
Utricle Body movement
Hairs
Cupula
Flow of fluid
Axons
Hair
cells
Vestibule