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 Vestibulocochlear nerve (VIII) EXTERNAL EAR MIDDLE EAR INNER EAR Auricle Auditory ossicles Semicircular canals Petrous part of temporal bone Facial nerve (VII) Bony labyrinth of inner ear To pharynx Tympanic membrane Cartilage External acoustic canal Cochlea Vestibule Round 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

The Auditory Ossicles The collection of the three tiny bones in the middle ear. The malleus, the incus, and the stapes Stapedius muscle Malleus attached to tympanic membrane Inner surface of Stapes (b) (a) External acoustic canal Tympanic Auditory tube Tensor tympani Footplate of stapes in oval window Incus Branch of cranial nerve VII (cut) Round window Connections to mastoid air cells Temporal bone Tendon of tensor tympani muscle Footplate of stapes at 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. Tensor tympani muscle, stiffens the tympanic membrane, this increased stiffness reduces the amount of movement possible. 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 Lateral Semicircular canal Cristae within ampullae Maculae Endolymphatic sac Cochlea Vestibular duct Cochlear duct Organ of Corti Tympanic duct Posterior (a) (b) Anterior Semicircular ducts Vestibule Saccule Utricle Endolymph Perilymph Membranous labyrinth Bony labyrinth

The state of physical balance 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

Vestibular branch (VIII) Endolymphatic duct sac Vestibular branch (VIII) Semicircular ducts Utricle Ampulla Saccule Maculae (a) Right semicircular ducts, anterior view Direction of duct rotation relative endolymph movement At rest (c) Hair cells Crista Cupula Supporting cells Sensory nerve (b) Cross section through the ampulla Stereocilia Kinocilium Hair cell ending (d) Hair cell Displacement in this direction stimulates hair cell Displacement in this direction inhibits hair cell Supporting cell Anterior Posterior Lateral 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 Process 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 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 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 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 External acoustic canal Movement of sound waves Malleus Incus Stapes Oval window Cochlear branch of cranial nerve VIII Vestibular duct (perilymph) Cochlear duct (endolymph) Tympanic duct Round window Tympanic membrane Vestibular membrane Basilar membrane 1 2 3 4 5 6 Sound waves arrive at tympanic membrane. Movement of tympanic membrane causes displacement of the auditory ossicles. Movement of the stapes at the oval window establishes pressure waves in the perilymph of the vestibular duct. The pressure waves distort the basilar membrane on their way to the round window of the tympanic duct. Vibration of the basilar membrane causes vibration of hair cells against the tectorial Information about the region and the intensity of stimulation is relayed to the CNS over the cochlear branch of cranial nerve VIII.

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.