Hearing and the Ears
The Anatomy of the Ear
The ear consists of 3 different sections1. The External Ear2. The Middle Ear
- The Auditory Ossicles3. The Inner Ear
Anatomy of the Ear
Vestibulocochlear nerve (VIII)
EXTERNAL EAR MIDDLE EAR INNER EAR
Auricle
Auditory ossicles Semicircularcanals
Petrous partof temporal
bone
Facial nerve (VII)
Bony labyrinth of inner ear
To pharynx
Tympanicmembrane
Cartilage
Externalacoustic
canal
Cochlea
VestibuleRound window
Oval window
Auditory tube
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_OEt8
• *Warning*real ear endoscopy! Don’t get grossed out!
The Auditory Ossicles
Stapediusmuscle
Malleusattached to
tympanicmembrane
Innersurface of tympanic
membrane
Malleus
Stapes
(b)(a)
Externalacoustic
canal
Tympanicmembrane
Auditory tube
Stapedius muscle
Stapes
Tensor tympani muscle
Footplate of stapes in oval window
IncusMalleus
Branch ofcranial
nerve VII(cut)
Round window
Connectionsto mastoid
air cellsTemporal
bone
Tendon of tensortympani muscle
Footplateof stapes at
oval window
Incus
The Auditory Ossicles • The collection of the three tiny bones in the middle ear. The
malleus, the incus, and the stapes
•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 EarKEY
Lateral
Semicircular canal
Cristae within ampullae
Maculae
Endolymphatic sac
Cochlea
Vestibular duct
Cochlear duct Organ of
CortiTympanic
duct
Posterior
(a)
(b)
AnteriorSemicircular
ductsVestibule
Saccule
Utricle
Endolymph
Perilymph
Membranouslabyrinth
Bony labyrinth
Membranous labyrinth
Bony labyrinth
EquilibriumThe 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
Endolymphaticduct
Endolymphaticsac
Vestibular branch (VIII)
Semicircularducts
Utricle
Ampulla
Ampulla
Saccule Maculae(a) Right semicircular ducts, anterior view
Direction of duct rotation
Direction ofduct rotation
Direction ofrelative
endolymphmovement
Semicircularduct
Ampulla
At rest
(c)
Hair cells
Crista
Cupula
Supporting cells
Sensory nerve
(b) Cross section through the ampulla
StereociliaKinocilium
Hair cell
Sensory nerve ending
(d) Hair cell
Displacement in thisdirection stimulates
hair cell
Displacement in this direction inhibits hair cell
Supporting cell
Anterior
PosteriorLateral Cochlea
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 Process1. 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 Process2. 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 Process3. 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 Process4. 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 Process5. 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 Process6. 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
Externalacoustic
canal
Movementof sound
waves
Malleus Incus Stapes Oval window
Cochlear branch of cranial nerve VIII
Vestibular duct (perilymph)
Cochlear duct (endolymph)
Tympanic duct (perilymph)
Roundwindow
Tympanicmembrane
Vestibular membrane
Basilar membrane
1
2
3
4
5
6
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.