THE POWER POINT PRESENTATION OF ANATOMY AND PHYSIOLOGY OF THE EAR (SENSE OF HEARING) IS JUST TO EQUIP READERS WITH SOME BASIC UNDERSTANDING ON THE ORGAN. HOW IT OPERATES AND CONNECTED TO THE CENTRAL NERVOUS SYSTEM IN ORDER TO PERCEIVE SOUND AND AID IN BALANCE.

1. EAR
BY
MR. MWELWA JORDAN

2. INTRODUCTION
The ear is the organ of hearing (Hearing is the ability to perceive
sounds). It is an engineering marvel because its sensory receptors can
transduce sound
vibrations with amplitudes as small as the diameter of an atom of gold
(0.3 nm) into electrical signals 1000 times faster than photoreceptors
can respond to light. The ear also contains receptors for equilibrium,
the sense that helps you maintain your balance and be aware of your
orientation in space.

3. INTRO CONT’
• The ear is supplied by the 8th cranial nerve, i.e. the cochlear part of
the vestibulocochlear nerve which is stimulated by vibrations caused
by sound waves.
• With the exception of the auricle(pinna), the structures that form the
ear are encased within the petrous portion of the temporal bone.

4. GENERAL OBJECTIVES
At the end of the lecture, students should be able to acquire
knowledge and have the understanding on the anatomy and physiology
of the Ear.

5. SPECIFIC OBJECTIVES
At the end of the lecture learners should be able to: -
• Describe the structures of the Ear.
• Explain the physiology of hearing.
• State the role of sense of hearing in balance.

6. STRUCTURE
The ear is divided into three distinct parts:
•outer ear
•middle ear(tympanic cavity)
•inner ear.

7. STRUCTURE CONT’

9. STRUCTURE CONT’
EXTERNAL EAR (OUTER EAR)
(A) External ear consists of:
• Auricle (pinna)
• External auditory canal
• Tympanic membrane (ear drum)

10. STRUCTURE CONT’
(1) AURICLE/ PINNA
• It is flap of elastic cartilage
• It is covered by skin
• Rim of auricle is called HELIX
• Inferior portion is called LOBULE.
• Plays important role in localization of sound
• It opens into External Auditory Canal

12. STRUCTURE CONT’
(2) EXTERNAL AUDITORY CANAL/ EXTERNAL AUDITORY MEATUS
• Curved tube, extends from pinna to ear drum.
• 2.5 cm long
• Near the external opening the external auditory canal contains a few
hairs and ceruminous glands.
• Ceruminous glands secrete the cerumen (ear wax)
• Combination of hairs and cerumen helps prevent dust and foreign
objects from entering the ear.

13. STRUCTURE CONT’
(3) TYMPANIC MEMBRANE/ EAR DRUM
• External auditory canal ends at the TYMPANIC MEMBRANE also
known as ear drum.
• It is a thin, semitransparent portion between external auditory canal
and middle ear.
• It is covered by epidermis
• Lined by simple cuboidal epithelium

14. STRUCTURE CONT’
(B) MIDDLE EAR
Middle ear is small, air filled cavity in temporal bone. It is lined by
epithelium. The middle ear is separated from external ear by ear drum.
It is separated from the inner ear by the oval window.
The structures of middle ear are:
• Auditory ossicles
• Oval window
• Eustachian tube

15. MIDDLE EAR

16. STRUCTURE CONT’
(1) AUDITORY OSSICLES:
These are the smallest three bones of the body connected by synovial
joints. These are malleus (Hammer), incus (Anvil), Stapes (Stirrup)

17. STRUCTURES CONT’
(A) MALLEUS:
• Word malleus is latin for hammer.
• It is the first bone of the middle ear.
• The handle of malleus is attached with internal surface of eardrum.
• Head of malleus is attached with the body of incus.
• The primary function of the malleus is to transmit sound waves or
vibrations from the eardrum to the incus.

18. STRUCTURE CONT’
• (B) INCUS (ANVIL)
• It is a second bone located in between the malleus and the stapes.
• The incus transmits vibrations from the malleus to the stapes

19. STRUCTURES CONT’
(C) STAPES
• Stapes is the third final bone of the middle ear.
• It is the smallest and lightest bone of the human body.
• The stapes connects to the incus on the outward side and to the oval
window.
• The primary function of the stapes is to transmit sound waves from
the incus to the membrane of the inner ear.
• The base or footplate of stapes fits into oval window.

21. STRUCTURE CONT’
(2) OVAL WINDOW:
• It is a membrane-covered opening that leads from the middle ear to
the vestibule of the inner ear.
• The oval window is the intersection of the middle ear with the inner
ear and is directly contracted by the Stapes;
• By the time vibrations reach the oval window, they have been
amplified over 10 times from what they were when they contacted
the tympanic membrane.

24. STRUCTURE CONT’
(3) EUSTACHIAN TUBE
• The middle ear is an air-filled space.
• It consists of both bone and hyaline cartilage.
• This runs from the middle ear to the naso-pharynx behind the nose.

25. • It is normally closed at pharyngeal end.
• During swallowing, chewing and yawing it opens.
• It helps maintaining equal air pressure on the two sides of eardrum.
• If pressure disturbed hinders clear and normal hearing.

27. STRUCTURE CONT’
INNER EAR:
• It is also called as labyrinth
• There are two main divisions of labyrinth: -
• Outer bony labyrinth: is a series of cavities in the temporal bone. It is
divided into three regions: Semicircular canals; vestibule; cochlea. Bony
labyrinth is lined with periosteum and contains fluid PERILYMPH which
is similar to CSF.

28. • Inner membranous labyrinth: It is series of sacs and tubes inside of
bony labyrinth. Membranous labyrinth is lined with epithelium. It
contains endolymph. The level of potassium ions is high in endolymph.
Potassium ions generates the auditory signals. Membranous labyrinth
consists of two sacs (Utricle, saccule).

31. STRUCTURE CONT’
OUTER BONY LABYRINTH
(i) SEMICIRCULAR CANALS
• They are named: Anterior semicircular canals; posterior semicircular
canals; lateral semicircular canals.
• Anterior and posterior are vertically oriented.
• Lateral is horizontally oriented.
• They contain cristae, site of hair cells, maintain static equilibrium.
• AMPULE: one end of each canal is swollen enlargement is called AMPULA.

32. STRUCTURE CONT’
(ii) VESTIBULE:
• It is the central part. Lies between cochlear in front and semicircular
canal behind.
• It contains utricles and saccule which are part of membranous
labyrinth.
• The walls of both saccule and utricle contain small thickened region
called MACULA.

33. • Contains receptor for static equilibrium
• Maintains poster and balance
• Maculae contains two types of cells
• -Hair cells
• -Supporting cells

34. STRUCTURE CONT’
(iii) COCHLEA
• It is a snail shaped, bony spiral canal.
• It is divided into three channels:-
• Cochlear duct
• Scala vestibule
• Scala tampani

37. STRUCTURE CONT’
Organ of CORTI
• It is also known as spiral organ
• It is a coiled sheet of epithelial cells, with two main cells:-
• Supporting cells
• Hair cells
• There are two groups of hair cells
• Inner hair cells
• Outer hair cells

38. STRUCTURE CONT’
• It consists of neurons called HAIR CELLS; their axons form CN VIII.
• The stapes is attached to the OVAL WINDOW, and vibrations cause
the perilymph to vibrate; the hair cells here transmit this vibration.
• Therefore, the HAIR CELLS in this region are receptors for HEARING.

39. • The VESTIBULAR COCHLEAR NERVE, which takes the signals to the
brain.
• Therefore, the cochlea is where the hearing receptors are located, so
the cochlea is responsible for all of the hearing of sounds.
• However, the ear does more than just hear; it is also responsible for
balance and equilibrium.

40. PHYSIOLOGY OF HEARING
• Auricle/ pinna directs sound waves into external auditory canal.
• When sound waves strike eardrum that cause eardrum to vibrate.
• The central area of EAR drum is connected to malleus which starts to
vibrate. The vibration is transmitted from malleus to incus then to
stapes.
• As a stapes moves back and forth it pushes the membrane of oval
window in and out.

41. PHYSIOLOGY CONT’
• The movements of the oval window sets-up fluid pressure waves in
the perilymph.
• Then the vibrations are transmitted to “organ of corti” through
perilymph and endolymph.
• From the organ of corti, the impulses (produced by vibrations) are
carried to brain through 8th cranial nerve to auditory centers of brain
which is present in temporal lobe.

43. BALANCE
VESTIBULAR SYSTEM
• This system regulates balance.
• It is also within the inner ear.
• SEMI-CIRCULAR CANALS (Three of them, all in different planes)
determine movement in three planes.
• Within each semi-circular canal is endolymph and hair cells, which
connect to nerves that go to the cerebellum.

44. BALANCE
UTRICLE AND SACCULE
• Attached to the semi-circular canals are two joined structures called
the UTRICLE and the SACCULE.
• These also contain HAIR CELLS and ENDOLYMPH.

45. • Within the endolymph here are OTOLITHS (“ear rocks”) which are
calcium deposits.
• When you stand perfectly upright, these otoliths fall directly down
and bend the HAIR CELLS, in this region are receptors for equilibrium
and the OTOLITHS are an essential component of this process.

46. BALANCE

47. APPLIED ANATOMY

49. SUMMARY
• The ear is the sense organ of hearing. It is divided in three parts;
outer ear, middle ear and inner ear. The outer ear has the pinna
(outer part), the auditory canal and ear drum (tympanic membrane).
• The middle ear has the auditory bones (malleus, incus and stapes),
Eustachian tube and oval window.

50. • The inner ear has the outer bony labyrinth and inner membranous
labyrinth.
• The physiology of hearing is achieved by vibrations which are
transmitted to the “organ of cort” through perilymph and endolymph
from the outer and middle ear. Then the impulses are transmitted to
the brain for interpretation. The sense of hearing also plays a role in
balance through the vestibular system.

51. REFERENCES
• A.M.Agur & A.F.Dalley, (2013), Grants Atlas of Anatomy, 13th Ed,
Lippincott Williams & wilkins.
• Vlerie C. Scanlon, Tina Sauders, (2007), Essentials of Anatomy and
Physiology, 5th Ed, F.A. Davis company.
• Waugh.A & Grant. A, (2009),Ross and Wilson: Anatomy and
physiology in Health and Illness, 11th Edition, Churchill Livingston.