4.  External Ear
› Auricle/ Pinna: Flap of elastic cartilage
shaped like flared end of a trumpet and
covered by skin

5.  External Auditory Canal:
› Curved tube about 2.5 cm (1 in.)
› Lies in the temporal bone and lead from the auricle
to the eardrum
› Contains a few hair and ceruminous glands
(specialized sebaceous glands)
 Tympanic membrane:
› A thin, semitransparent partition between the
external auditory canal and middle ear
› Consists of a connective tissue core lined with skin on
the outside and mucous membrane on the inside
› Covered by epidermis and lined by simple cuboidal
epithelium

7.  Small, air-filled cavity in the temporal bone
that is lined by epithelium.
 Contains two small membrane-covered
openings:
› Oval window
› Round window
 Contains the three smallest bones in the
body
› Malleus (hammer)
› Incus (anvil)
› Stapes (stirrup)
 Joints: synovial joints

8.  Malleus: attached to the internal surface
of the eardrum
 Incus: the middle bone; articulates with
the head of the stapes
 Stapes: its base fits into the oval window
(which is right above the round window)

10.  Tensor Tympani muscle: inserts into the
handle of the malleus. It reduces the
vibrations of malleus that could
potentially harm the tympanic
membrane (i.e. loud noise)
 Stapedius muscle: Reduces the
vibrations of stapes

12.  An opening on the anterior wall of the
middle ear
 Consists of both bone and hyaline cartilage
 Connects middle ear with the nasopharynx
 Functions to equalizes the pressure within
middle ear and the atmospheric pressure
(between tympanic cavity and
nasopharynx)
 A route where pathogens may travel from
the nose and throat to the middle ear

14.  Called a labyrinth because of its
complicated series of canals
 Two main divisions:
› Bony Labyrinth: lined with periosteum and
contains perilymph (similar to CSF)
› Membranous Labyrinth: surrounded by the
CSF. A series of sacs and tubes inside the
bony labyrinth and having the same general
form

16. › Bony Labyrinth: series of cavities in the
temporal bone. Divided into three areas:
 Semicircular Canals: projects posteriorly and
superiorly from the vestibule. Consists of an
anterior, posterior and lateral semicircular
canal.
 Ampulla: swollen enlargement at the end of each
canal
 Semicircular ducts: allows communication between
the utricle and the vestibule

17.  Vestibule:
 contains receptors for equilibrium
 Oval central portion of the bony labyrinth
 Communicates anteriorly with the cochlea and
posterosuperiorly with the SCC
 The membranous labyrinth in the vestibule consists of:
 Utricle
 Saccule

18.  Cochlea: contains receptors for hearing
› Anterior to the vestibule
› A bony spiral canal that resembles a snail
shell and makes almost three turns around a
central bony core (modiolus). It is divided
into three channels
 The partitions that separate the channels are
shaped like a letter Y
 Scala vestibuli: channel above the bony partition and
ends at the oval window
 Scala Tympani: channel below and ends at the round
window

19.  Cochlea:
› Adjoins the wall of the vestibule (where the
scala vestibuli opens)
› It has two membranes: basilar membrane
and vestibular membrane (which separates
the cochlear duct from the scala vestibuli)
› Spiral Organ of Corti: Rests on the basilar
membrane and contains hair cells, which
are receptors for hearing

20.  Lodged within bony labyrinth
 Filled with endolymph
 Surrounded by perilymph

23.  Sense of equilibrium---- provides
orientation with respect to gravity
 Forms the inner ear along with the
cochlea
 Consists of two parts:
› Otolith Organs: utricle and saccule
› Semicircular canals

25.  The sensory structures of both the
vestibular apparatus and cochlea are
located within the membranous
labyrinth (which is filled with a fluid called
endolymph) which is located within the
bony cavity in the skull, bony labyrinth.
 Perilymph is the fluid between the
membranous labyrinth and the bone

26.  Utricle and Saccule: provide information
about linear acceleration
› Refers to the changes in velocity when
traveling horizontally or vertically (i.e. riding in
a car)
 Semicircular Canals: provides a sense of
rotational and angular motion It helps
maintain balance when turning the
head, spinning, or tumbling.
› Refers to the changes in direction

27.  Receptors for equilibrium; modified
epithelial cells
 Named as they are because each cell
contains twenty to fifty hairlike extensions
› Stereocilia: processes containing filaments of
protein surrounded by part of the cell
membrane
› Kinocilium: larger extension that has the
structure of a true cilium

30. 1. When the stereocilia are bent in the direction
of the kinocilium, the cell membrane is
depressed and becomes depolarized.
2. The hair cell releases a synaptic transmitter,
thus stimulating the dendrites of sensory
neurons that are part of the vestibulocochlear
nerve.
3. When the stereocilia are bent in the opposite
direction, the membrane of the hair cell
becomes hyperpolarized, which causes the
release of a less amount of synaptic transmitter.

31.  In this way, the frequency of action
potentials in the sensory neurons that
innervate the hair cells carries
information about movements that
cause the hair cell processes to bend.

32.  Utricle and Saccule have a patch of
specialized epithelium called a macula
that consists of hair cells and supporting
cells.
› The hair cells project into the membranous
labyrinth, with their hairs embedded in a
gelatinous otolithic membrane
 Contains microscopic crystals of calcium
carbonate, these increase the mass of the
membrane, and increase the resistance to
change in the movement

33.  Utricle is more sensitive to horizontal
acceleration
› Otolithic membrane lags behind the hair
cells
› Hair cells are pushed backward
 Saccule is more sensitive to vertical
acceleration
› Causes the hairs of the saccule to be
pushed upward

36.  Semicircular duct: inner extension of the
membranous labyrinth in each canal
› Ampulla
 Crista ampullaris: elevated area of the
ampulla where the sensory hair cells are
located.
 Cupula: gelatinous membrane where the processes
of the hair cells are embedded. It can be pushed in
several directions because of the endolymph.

37.  Endolymph:
› Provides inertia so that the sensory processes
will be bent in a direction opposite to that of
the angular acceleration.
 Through this, it stimulates the hair cells

38. The Semicircular Canals:
 Anterior Semicircular canal: hair cells are
stimulated when doing a somersault.
 Posterior Semicircular canal: stimulated
when performing a cartwheel.
 Lateral Semicircular canal: stimulated when
spinning around the long axis of the body.

40.  Stimulation of hair cells in the vestibular
apparatus activates sensory neurons of
Vestibulocochlear nerve (CN VIII)
 These fibers transmit impulses to the
cerebellum and to the vestibular nuclei
of the medulla oblongata
 The vestibular nuclei then send fibers to
the oculomotor center of the brain stem
and to the spinal cord

42.  During a spin, the bending of the cupula
produces smooth movements of the eyes in
a direction opposite to that of the head
movement so that a stable visual fixation
point is maintained.
 When the spin is abruptly stopped, the eyes
continue to smoothly in the previous
direction of the spin, and then are jerked
rapidly back to the midline position
 This produces involuntary oscillations of the
eyes called vestibular nystagmus.

45. • Loss of equilibrium as a result of spinning
• May be caused by anything that alters
the firing rate of one of the CN VIII
compared to the other
 Usually due to a viral infection causing
vestibular neuritis
• Severe vertigo is accompanied by
dizziness, pallor, sweating, nausea, and
vomiting due to involvement of ANS,
which is activated by vestibular input
tothe brain stem

46.  Involuntary movement of the eye
resulting from abnormal stimuli to the
inner ear.
 One of the symptoms of an inner-ear
disease called Ménière's disease
› Early symptom: “ringing in the ears” or
tinnitus
 Vestibular symptoms of vertigo and
nystagmus accompany hearing
problems in this disease

47.  Types
› Central
 produce one-way or two-way eye movement
› Peripheral
 exhibits only one-way eye movement.
 Treatment
› Botulinum toxin, the substance that causes
botulism, is sometimes injected to reduce
eye movement
› Surgery is also necessary in some cases

49.  Sound causes vibrations of the tympanic
membrane, and they produce movements
of the middle-ear ossicles, which press
against a membrance called the oval
window in the cochlea.
 Movements of the oval window produce
pressure waves within the fluid of the
cochlea, causing movements of the basilar
membrane.
› Bending of the sensory hair cells follows
› Stimulation of action potentials transmitted to
the brain in sensory fibers and interpreted as
sound

50.  Alternating zones of high and low
pressure traveling in a medium (air or
water)
 Are characterized by:
› Frequency (Hz)
 cycles per second (cps)
 Pitch
› Intensity (dB)
 Amplitude of the sound waves

51.  Sound waves are funneled by the pinna
(auricle) into the external auditory
meatus, and these 2 form the outer ear.
 External auditory meatus channels the
sound waves (while increasing the
intensity) to the eardrum, or tympanic
membrane
 Sound waves in the EAM produce
extremely small vibrations of the
tympanic membrane.

53.  The cavity between the tympanic
membrane on the outer side and the
cochlea on the inner side
 3 middle-ear ossicles – protection
› Malleus (hammer)
 attached to the tympanic m.
 vibrations are transmitted via the malleus and incus
to the stapes
› Incus (anvil)
› Stapes (stirrup)
 attached to the oval window in the cochlea
 vibrates in response to the vibrations of the
tympanic m.

54.  Stapedius muscle
› Attaches to the neck of the stapes
› Increases protective function
› Helps prevent nerve damage within the
cochlea in very loud sounds as it contracts
and dampens the movements of the stapes
against the oval window

56.  Auditory (eustachian) tube
› A passageway leading from the middle ear to the
nasopharynx
› Is usually collapsed; to prevent debris and infectious
agents from traveling from the oral cavity to the
middle ear.
› Tensor tympani muscle
 Must contract to open the auditory tube
 Occurs during swallowing, yawning, sneezing
 “popping” sensation in swallowing when driving up to a
higher altitude
 The auditory canal opening allows air to move from the
region of higher pressure (middle ear) to the region of
lower pressure (nasopharynx)

60. • cochlea which serves as the body's
microphone, converting sound pressure
impulses from the outer ear into electrical
impulses which are passed on to the brain via
the auditory nerve.
• The inner ear structure called the cochlea is a
snail-shell like structure.

63.  The pressure changes in
the cochleacaused by sound entering
the ear travel down the fluid filled
tympanic(scala tympani) and
vestibular canals(scala vestibuli) which
are filled with a fluid called perilymph.
This perilymph is almost identical to
spinal fluid and differs significantly from
the endolymph which fills the cochlear
duct(scala media) and surrounds the
sensitive organ of Corti.

65. • Receptor organ of hearing
• It contains four rows ofhair cells which
protrude from its surface. Above them is
the tectoral membrane which can move
in response to pressure variations in the
fluid- filled tympanic and
vestibularcanals. There are some 16,000 -
20,000 of the hair cells distributed along
the basilar membrane which follows the
spiral of the cochlea.

66.  The place along the basilar
membrane where maximum
excitation of the hair cells occurs
determines the perception
of pitch according to the place
theory. The perception
of loudness is also connected with
this organ.

67.  Tiny relative movements of the
layers of the membrane are
sufficient to trigger the hair cells.
Like other nerve cells, their response
to stimulus is to send a tiny voltage
pulse called an "action potential"
down the associated nerve fiber
(axon). These impulses travel to
the auditory areas of the brain for
processing.

70. Prepared by: Chris Carlo M.
Galeno

71.  Sensory neurons in the vestibulocochlear
nerve (VIII) synapse with neurons in the
medulla oblongata that projects to the
inferior colliculus of the midbrain.
 Neurons in this area project to the
thalamus thats sends axons to the
auditory cortex of temporal lobe.
 Neurons in different regions of basilar membrane
stimulate neurons in corresponding areas in auditory
cortex.

73.  Each area of the
auditory cortex thus
represents a different
part of the basilar
membrane and a
different pitch.

74.  The cochlea acts like a frequency
analyzer, in different frequencies
(pitches) of sound stimulate different
sensory neurons that project to different
places in the auditory cortex
 The analysis is based on which hair cells
activate the sensory neurons
 It is related to the position of the hair cells on the
basilar membrane. This is known as the PLACE THEORY
OF PITCH.

75.  Since the different sensory neurons
project to different places in the auditory
cortex, the organization of this cortex is
said to be tonotopic.
 tone frequencies are transmitted separately along
specific parts of the structure.

76.  Able to recognize that a given sound
frequency (such as 400 Hz) is the same
regardless of whether it is played by
violin or piano
 In harmonics, can vary, depending on
their amplitudes. However, if the
fundamental frequency is the same, the
pitch is recognized being the same on
the different instruments

78.  Conduction Deafness
› Transmission of sound waves through the
middle ear to the oval window is impaired
 Sensorineural or Perceptive Deafness
› Transmission of nerve impulses anywhere
from the cochlea to the auditory cortex is
impaired

80.  Caused by middle–ear damage from
otitis media or otosclerosis
 Impairs hearing at all sound frequencies
 Can be helped by Hearing Aids
 Device that amplify sounds and conduct the
sound waves through bone to the inner ear.

82.  Result from a wide variety of
pathological processes and from
exposure to extremeley loud sounds
 Unfortunately, the hair cells in the inner ears cannot
regenerate once destroyed.
 Impairs the ability to hear some pitches
more than others.
 This may be due to pathological processes or to
changes that occur during aging.

83.  Can be corrected by Cochlear Implants
 It consists of elctrodes threaded into the
cochlea, a receiver implanted in the temporal
bone, and an external microphone, processor
and transmitter.

85.  Age-related hearing impairment
 Begins after age 20 when the ability to
hear high frequencies (18000-20000 Hz)
diminishes
 Men are affected to greater degree
than women, but the progression is
variable
 Deficits may gradually extend to 4000-
8000 Hz range

86.  Impairment can be detected by
Audiometry
 A technique in which threshold intensity of
different pitches is determined.
 The ability to hear speech is particularly
affected by hearing loss in the higher
frequencies