This document discusses the anatomy and functions of the ear. It describes the external, middle, and inner ear in detail. The external ear includes the pinna, external auditory canal, and eardrum. The middle ear contains three small bones called ossicles that transmit sound from the eardrum to the inner ear. The inner ear includes the cochlea for hearing and semicircular canals for balance. The eustachian tube connects the middle ear to the throat and helps equalize pressure. The ear has important functions of hearing sound waves and maintaining balance.
5. The ear is divided
into:
1. External ear
2. Middle ear
3. Internal ear or
the labyrinth.
6. THE EXTERNAL EAR
Consists of the:
(i) auricle or pinna.
(ii) external acoustic canal.
(iii) tympanic
membrane(Eardrum).
7. PINNA/AURICLE
• Visible part.
• Made up of yellow elastic
cartilage and skin(except
lobule).
• There is no cartilage between
the tragus and crus of the helix,
and this area is called the
incisura terminalis.
8. BOXER’S EAR
• Stripping of the
perichondrium from the
cartilage as occurs following
injuries that cause
hematoma can lead to ear
necrosis and so called boxer’s
ear.
9. External Acoustic (Auditory) Canal
• Extends from the bottom of the concha to the tympanic
membrane.
• 24mm long
• 2 parts: cartilaginous and bony.
oCartilaginous (outer 1/3rd):
- 8 mm long.
- Presence of skin and has hair( furuncle prone; staphylococcal
infection of hair follicles).
- 2 glands: ceruminous and pilosebaceous (makes wax).
10. oBony ( inner 2/3rd):- 16mm long.
- No hair or glands.
- Common site of foreign body dislodgement.
•EAR WAX (काने गुजी):- Mixture of cerumen, sebum,
desquamated cells.
•ISTHMUS:- 5mm lateral to tympanic membrane, bony
meatus is narrow (so called isthmus) and is site for
foreign body lodgement.
•Arterial supply of EAC:- External carotid artery.
•Nerve supply of EAC:- Auriculotemporal nerve, Arnold
nerve(Auricular branch of vagus nerve).
11. Tympanic Membrane or Drumhead
• Partition between the external acoustic canal and the
middle ear.
• Obliquely placed.
• 9-10 mm tall, 8-9 mm wide and 0.1 mm thick.
• Pearl grey in colour.
• two parts: Pars tensa and Pars flaccida.
• UMBO: most reliable landmark in Otoscopy.
• CONE OF LIGHT: is seen in antero-inferior quadrant of TM.
16. THE MIDDLE EAR
• The middle ear together with the eustachian tube, aditus, antrum,
middle ear (tympanic cavity) and mastoid air cells is called the middle
ear cleft.
• It is lined by mucous membrane and filled with air.
17. Like a 6 sided box with roof, floor, medial, lateral part,
anterior posterior parts
18. •Roof – formed by a thin bone from the petrous
part of the temporal bone. It separates
the middle ear from the middle cranial fossa.
•The Floor of the middle ear is the jugular wall; it
separates the tympanic cavity from the internal
jugular vein.
19. Parts of Middle ear
• Middle ear
• Eustachian tube
• Aditus
• Antrum
• Mastoid ear cells
20. Middle ear
- 3 ossicles: maleus, incus, stapes.
- 2 muscles: tensor tympani and stapedius.
- 2 nerves: chorda tympani and tympanic plexus.
- Vessels supplying/ draining middle ear ( Anterior tympanic
branch of maxillary artery, Stylomastoid branch of posterior
auricular artery , Veins drain into pterygoid venous plexus
and superior petrosal sinus, Lymphatics from the middle ear
drain into retropharyngeal and parotid nodes while those of
the eustachian tube drain into retropharyngeal group)
- Ligaments of ear ossicles.
- Air.
23. EUSTACIAN TUBE
• Like a canal.
• Also called auditory or pharyngotympanic tube.
• Connects Nasopharynx with the tympanic cavity(Middle ear).
• About 36 mm long.
• It is divided into two parts: bony, forms one-third (12 mm) and
fibrocartilaginous, forms two-thirds (24 mm).
• FUNCTION:-
- Controls the pressure within the middle ear, making it equal with the
air pressure outside the body.
- Clearance of middle ear secretions.
25. Mastoid air cells
• Protect the delicate structures of the ear.
• Regulate ear pressure.
• Protect the temporal bone during trauma.
26. THE INTERNAL EAR / Labyrinth
• Important organ for hearing and balance.
• 2 parts: bony and membranous.
• Bony labyrinth:- vestibule, semicircular canals and cochlea.
• Membranous labyrinth:- cochlear duct, utricle and saccule,
Semicircular ducts, Endolymphatic ducts and sac.
• There are two main fluids in the inner ear:- perilymph and
endolymph (Both contains sodium, potassium, glucose, proteins).
• The membranous labyrinth is filled with a clear fluid called
endolymph while the space between membranous and bony
labyrinths is filled with perilymph.
31. Sound waves arrive
to the auricle
Channelled through EAC
to reach Tympanic
membrane
Strikes TM
Due to wave TM
vibrates
Vibration on
the ossicles
Sound that reaches TM
has to be increased in
power before reaching
middle ear
Increase pressure
so much that it
causes fluid of
inner ear to
vibrate
In cochlea
converted into
periodic
movements
Initiate nerve
impulse in fibres
of acoustic nerve
Goes to
midbrain
Auditory
cortex
Perceived
as sound
