Download Hearing and the Ears

Hearing and the Ears
The Anatomy of the Ear
The ear consists of 3 different sections
1. The External Ear
2. The Middle Ear
- The Auditory Ossicles
3. The Inner Ear
Anatomy of the Ear
EXTERNAL EAR
MIDDLE EAR
Auditory ossicles
INNER EAR
Semicircular
canals
Auricle
Petrous part
of temporal
bone
Facial nerve
(VII)
Vestibulocochlear
nerve (VIII)
External
acoustic
canal
Bony labyrinth
of inner ear
Tympanic
membrane
Oval window
Cartilage
Round window
Vestibule
To pharynx
Auditory tube
Cochlea
The External Ear
The External Ear
• Made up of fleshy and cartilaginous auricle,
which surrounds the external acoustic canal
• Sounds coming from the back of the head are
blocked by auricle, and sounds coming from
the sides of the head are collected and
channeled into the external acoustic canal.
• The external acoustic canal ends where the
tympanic membrane is located.
The External Ear
• Tympanic Membrane
- separates the external ear from the middle
ear
-is very delicate, and is protected by external
acoustic canal and the auricle
• Foreign objects are denied access by the
ceruminous glands which secrete a waxy
secretion, cerumen.
The Middle Ear
The Middle Ear
• Air filled chamber
• Communicates with the nasopharynx through the
auditory tube and mastoid air cells
• The auditory tube permits the equalization of
pressures on either side of the tympanic
membrane
-On the down side, the auditory tube can also
let in microorganisms causing an unpleasant
middle ear infection, aka otitis media.
Video!!!!!!
• http://www.youtube.com/watch?v=M3znkf_O
Et8
• *Warning*real ear endoscopy! Don’t get
grossed out!
The Auditory Ossicles
The Auditory Ossicles
• The collection of the three tiny bones in the middle ear. The
malleus, the incus, and the stapes
Temporal
bone
Connections
to mastoid Malleus
air cells
Tendon of tensor
tympani muscle
Incus
Footplate of
stapes in
oval window
Tensor
tympani
muscle
Branch of
cranial
nerve VII
(cut)
Stapes
Tympanic
membrane
Stapedius
muscle
Round
window
External
acoustic
canal
Auditory tube
(a)
Incus
Footplate
of stapes at
oval window
Malleus
Malleus
attached to
tympanic
membrane
Stapes
Inner
surface of
tympanic
membrane
Stapedius
muscle
(b)
•Vibration of the tympanic membrane converts arriving sound
waves into mechanical movements, the auditory ossicles acts
as a lever for these vibrations to arrive to the inner ear.
The Auditory Ossicles
• There are two muscles located in the middle ear
that protect the tympanic membrane and ossicles
from violent movements under noisy conditions.
1. Tensor tympani muscle, stiffens the tympanic
membrane, this increased stiffness reduces the
amount of movement possible.
2. Stapedius muscle, contraction of the stapedius
pulls the stapes, reducing movement of the
stapes at the oval window
The Inner Ear
The Inner Ear
• Provides senses of equilibrium and hearing
• The superficial contours are made up of a
dense bone layer called the bony labyrinth,
which can be subdivided into the vestibule,
three semicircular canals and the cochlea.
The Inner Ear
• The Vestibule
- Consists of two membranous sacs: the uricle
and the saccule
- The receptors in the uricle and the saccule
provide sensations of gravity and linear
acceleration
The Inner Ear
•
•
-
Semicircular canals
Enclose semicircular ducts
Are stimulated by the rotation of the head
The cochlea
Senses within the cochlear duct provide the
sense of hearing
- Looks like a snail shell
The Inner Ear
KEY
Semicircular canal
Membranous
labyrinth
Anterior
Semicircular
ducts
Bony labyrinth
Lateral
Posterior
Vestibule
Cristae within
ampullae
Maculae
Endolymphatic sac
Cochlea
Perilymph
(a)
Utricle
Bony labyrinth
Saccule
Endolymph
Vestibular duct
Membranous
labyrinth
Cochlear duct
(b)
Tympanic
duct
Organ of
Corti
Equilibrium
The state of
physical balance
Equilibrium
• Equilibrium sensations are provided by
receptors of the vestibular complex
• Semicircular ducts convey information about
rotational movements of the head
• The saccule and utricle convey information
about your position with respect to gravity,
this also stimulated by rapid acceleration
Equilibrium
• The anterior, posterior, and lateral semicircular ducts are
continuous with the utricle
• Each semicircular duct contains
– an ampulla: the expanded region that contains the
receptors
– Crista: area where receptors are located in the
ampulla. Each crista is bound to a cupula
– A cupula being a gelantinous structure that extends
the entire ampulla
• Semicircular Ducts:
– Contain sensory receptors and hair cells
– Active during movement
– Are quite when motionless
Semicircular
ducts
Endolymphatic
duct
Anterior
Endolymphatic
sac
Vestibular branch
(VIII)
Posterior
Cochlea
Lateral
Ampulla
Utricle
(a) Right semicircular ducts, anterior view
Saccule
Maculae
Displacement in this
direction stimulates
hair cell
Ampulla
Displacement in
this direction
inhibits hair cell
Cupula
Kinocilium
Stereocilia
Hair cells
Crista
Supporting cells
Hair cell
Sensory nerve
(b) Cross section through the ampulla
Direction of
duct rotation
Direction of
relative
endolymph
movement
Direction of
duct rotation
Sensory nerve
ending
Supporting cell
Semicircular
duct
Ampulla
At rest
(c)
(d) Hair cell
Introduction
to Sound
Introduction to
Sound
• The sound we hear consists of pressure waves
through the air
• Each pressure wave consists of a certain
wavelength and each wavelength has a certain
frequency (# of waves that pass a fixed
reference point in given time)
Sound
• Sound is measures in hertz (Hz)
• Amplitude of sounds determines how
loud something seems to be.
–Greater the energy = Greater the
amplitude
Sound
• When sounds waves strike an object, their
energy is a physical pressure
• For you to be able to hear any sound, your
thin tympanic membrane must vibrate in
resonance
– Resonance is the phenomenon that with the right
combination of frequencies and amplitudes,
objects will vibrate at the same frequency.
The Hearing Process
The Hearing Process
1. Sound waves arrive at the tympanic
membrane
– Sound waves have direct access to the tympanic
membrane on the side of the head they enter
The Hearing Process
2. Movement of the tympanic membrane
causes displacement of the auditory ossicles
–
the tympanic membrane provides a surface to
collect sound
– It vibrates in resonance to sound waves with
frequencies between 20 and 20,000 Hz
The Hearing Process
3. Movement of the stapes at the oval window
establishes pressure waves in the perilymph
of the vestibular ducts
– When the stapes moves inward, the round
window bulges outward into the middle ear
– Stapes move in and out, vibrating at the
frequency of sound arriving at the tympanic
membrane
– This creates pressure waves within the perilymph
The Hearing Process
4. The pressure waves distort the basilar
membrane on their way to the round
window of the tympanic duct
– The louder the sound = the more the basilar
membrane moves
The Hearing Process
5. Vibration of basilar membrane causes
vibration of hair cells against the tectorial
membrane
– Movement of hair cells causes there to be a rush
of ions to be sent to neurotransmitters causing
the simulation of neurons
– More intense sound= hair cells become more
active
– Hair cells are located on the organ of Corti
The Hearing Process
6. Information about the region and intensity of
stimulation is relayed to the CNS over the cochlear
branch of the vestibulocochlear nerve (VIII)
– bipolar sensory neurons that monitor cochlear
hair cells are located at the center of the bony
cochlea, the spiral ganglion
– From there information is carried to the cochlear
nuclei of the medulla oblongata for distribution to
other centers of the brain
The Hearing Process
Cochlear branch
of cranial nerve VIII
External
acoustic
canal
Malleus
Incus
Stapes
Oval window
6
Vestibular duct
(perilymph)
3
Movement
of sound
waves
Vestibular membrane
2
Cochlear duct
(endolymph)
1
Basilar membrane
4
5
Tympanic
membrane
Round
window
Tympanic duct
(perilymph)
Professions
• Audiologist- Help people with hearing or
balance problems
• Otolaryngologists (ENT)- treat anything wrong
with the ears, nose, or throat
• Pediatrician- treat children with ear infections.
Children are more likely to contract an ear
infection
Diseases
• Middle Ear Infection- In the pocket of air behind
the eardrum, if germs get into the middle ear, it
fills with germ-fighting fluid called pus. The build
up this fluid is what causes pain.
Diseases
• Nystagmus- The inner part of the ear senses
movement and position helps control eye
movements, if injured it can cause eyes to
shake. If the shaking is so bad, then it can
prevent the person from having 20/20 vision.
Diseases
• Deafness- occurs when sound vibrations don't go from the air
around a person to the moving bones of the inner ear as well
as they should. Causes: hereditary disorders, genetic
disorders, prenatal exposure to disease, prolonged exposure
to loud noises, trauma
• Swimmers Ear- Germs get into the outer part of the ear and
cause an outer ear infection. Can often be brought on by
water sitting in the outer ear, allowing for bacteria to grow.