Ear Anatomy PDF

Anatomy of the Ear Dr. David Hopper Ear Divided into 3 Parts The ear is made of 3 parts: the external, middle and inner ear External ear helps to focus and direct air pressure waves (sounds) through the external auditory meatus to the middle ear. The tympanic membrane forms the boundary between t...

Anatomy of the Ear Dr. David Hopper Ear Divided into 3 Parts The ear is made of 3 parts: the external, middle and inner ear External ear helps to focus and direct air pressure waves (sounds) through the external auditory meatus to the middle ear. The tympanic membrane forms the boundary between the external and middle ear. Middle ear and its associated ossicles and muscles fine tune and amplify the vibrations of the air. Vibrations of the tympanic membrane are converted to mechanical energy by the vibrations of the ossicles. This is necessary in order to stimulate the movement of the fluid contained in the inner ear’s bony and membranous labyrinths. The membranes covering the oval and round windows mark the boundary between the middle and inner ear. Inner ear contains the organs of hearing and balance. The cochlea transduces vibrations of the basilar membrane into action potentials, which are then relayed to the cortex and perceived as sound/hearing. The vestibular system (semicircular canals, saccule & utricle) similarly transduces acceleration forces of the fluids (endolymph) into action potentials, which are relayed to the cortex and perceived as movement/balance. External Ear - Auricle Auricle (pinna) - The auricle is composed of elastic cartilage covered by a thin skin extending into the external acoustic meatus. The auricle is held to the skull by ligaments and muscle. This shape pulls in sound in the range of human speech, 2-5mHz. The parts of the auricle are: 1. Helix - the rim of the auricle on the superior and posterior free margin. 2. Antihelix - internal to the helix. A semicircular prominence located anterior and inferior to the helix. Its superior portion divides into the crura. 3. Concha – Deep fossa anterior to the antihelix. 4. Tragus - Small projection immediately anterior to the external opening of the ear. It may have a tuft of hair on its surface. 5. Antitragus - A small tubercle located opposite the tragus. 6. Intertragic notch - Located between the tragus and the antitragus. 7. Lobule - inferior to the intertragic notch. Composed of areolar and adipose tissue. Ear Shape & Sound -Connected with eyes, look lateral and ears move -Locate where sound is coming from -Brain calculates which ear heard first -Same time = directly in front -Below or above locate too Ear Size Predicts Biological Age Subject's age = 1.96 x (Ear circumference in millimeters - 88.1). SENSORY INNERVATION OF THE EXTERNAL EAR 1. Lesser occipital nerve (C2,3) - posterior, superior surface 2. Great auricular nerve (C2,3) - anterior, inferior surface 3. Auriculotemporal nerve (branch of V3 ) - anterior surface 4. Vagus (CN X) - posterior surface, concha (Nausea as a symptom) Vagus Nerve innervation to Ear • Posterior Auricle - Concha - Part of external acoustic meatus - Part of tympanic membrane Venous Drainage of External Ear Blood Supply to External Ear Injury to External Ear Cartilage of the ear has no other blood supply except that supplied by the overlying skin. Cauliflower ear happens when the skin is pulled from the cartilage, and/or separated from the cartilage by blood. Piercings, wrestling, boxing, and martial arts are causes. External Acoustic Meatus • A canal which extends from the external opening of the ear to the tympanic membrane • Approximately 2.5 cm in length ~1 inch • Direction- inward, forward and upward then backward and downward. • During an examination, the meatus can be straightened somewhat by pulling the auricle in an up-out-backward direction • Outer _______ is cartilage and inner ________osseous • Lined by skin -even tympanic membrane • Ceruminous glands (modified sweat) and hair • Excessive hair and/or wax can cause conductive loss Hypertrichosis! Tympanic Membrane • Circular structure on the lateral wall of the middle ear • Separates the outer and middle ear. • Highly sensitive for pain. COMPOSED OF THREE LAYERS: 1. Outer - modified skin continuous with the external acoustic meatus; innervated primarily by the Auriculotemporal n. (V3) and the auricular branch of the Vagus n. (X). 2. Intermediate/middle - fibrous tissue (radial and circular fibers). Gives strength to the mucous membrane. Innervated by a sensory component of the Facial n. (VII). 3. Inner - mucous membrane of the tympanic cavity; innervated primarily by the Glossopharyngeal n. (IX). These 3 layers are derived from ectoderm, mesoderm, and endoderm Tympanic Membrane Tympanic Membrane Middle Ear The Middle Ear is divided into the: 1. Tympanic cavity proper - directly medial to the tympanic membrane. Contains the ossicles: malleus, incus and stapes bones. • True synovial membranes – the smallest in the human body. • The stapes vibrates fluid (the perilymph) in the inner ear via the oval window 2. Epitympanic recess – superior to the tympanic cavity proper. • Tegmen tympani, the superior wall, separates the middle ear from the cranial cavity. • Continuous with the mastoid antrum. • The floor of the antrum and associated mastoid air cells are lined with mucous membrane that is continuous with that lining the middle ear cavity. • Possible pathway for spread of infection Pharyngotympanic Tube • Also known as Auditory Tube, Eustachian Tube • Connects the middle ear to the pharynx (nasopharynx) • Equalizes pressure on both sides of the tympanic membrane • The tube is 2/3rds cartilaginous (pharynx side) and 1/3rd osseous (tympanic side). The osseous portion is the narrowest. • The resting position is closed • Eustachian tube opens with swallowing and yawning • Infants and children horizontal, after 6-7 yrs. more vertical • Eustachian Tube Dysfunction – tube doesn’t equalize pressure when should, (air flight, scuba diving) • Valsalva maneuver – pinch nose and gently exhale • Toynbee maneuver – add swallowing • Dysfunction can lead to retracted eardrum, fluid build-up, infection Pharyngotympanic Tube Pharyngotympanic Tube – Muscles Acting On _____________________ – opens the tube when swallowing Levator veli palatini -contracts longitudinally, thickening of the muscle (due to shortening) pushes against the wall of the tube Tensor veli palatini – simultaneously pulls on the opposing wall THE AUDITORY OSSICLES In the middle ear, there are three small bones - malleus, incus and stapes - Joined by true synovial (diarthrodial) articulations -Covered by the mucous membrane lining the tympanic cavity (NO periosteum) -Suspended in the tympanic cavity by ligaments -Function to convert vibrations of air (sound waves) reaching the tympanic membrane into mechanical energy -Results in the oscillation of the stapes at the oval (vestibular) window -Perilymph of the cochlea is displaced, stimulating the sensory endings on the hair cells of the spiral organ (of Corti) -This does not affect the vestibular organ The ossicles are fixed in position by: -Attachment of the malleus to the tympanic membrane -Stapes in the oval window. -Various other ligaments also connect the ossicles to the walls of the tympanic cavity. Pressure Wave Ossicles Malleus is the largest, handle attaches to the inner tympanic membrane Incus – body articulates with the head of the malleus and the small lenticular process articulates with the stapes head Stapes – the base fits in the Oval window of the inner ear Ossicles – Muscles Acting On _____________________ 0: Cartilagenous portion of auditory tube and adjacent part of the greater wing of the sphenoid bone I: “Handle” of the malleus bone F: Increase tension on the tympanic membrane (in loud environments) by pulling the handle of the malleus medially, thus reducing the amplitude of oscillations at the tympanic membrane N: Mandibular branch (V3) of the trigeminal nerve Ossicles – Muscles Acting On ________________: 0: Pyramidal eminence (posterior wall) I: Neck of the stapes bone F: Lessen vibrations of the stapes bone (typically during explosive sounds) by pulling the stapes posteriorly, thus tipping the bone away from the oval window. N: Facial nerve (VII) - Nerve to Stepedius FACIAL NERVE CANAL Stapedius muscle Middle Ear – Boundaries and Connections ROOF (Tegmental wall) - Tegmen tympani separates the middle ear from the middle cranial fossa. (If bone erodes, then infection can spread from throat to ear to brain, usually leading to meningitis) FLOOR (Jugular wall) - Thin piece of bone separates the middle ear from the jugular fossa . LATERAL (Membranous wall) – The tympanic membrane separates the external ear from the middle ear. This multi-layered membrane is composed of skin and mucus membranes, and is innervated by four cranial nerves (V, VII, IX and X). It can be damaged from either side, thus affecting hearing. MEDIAL (Labyrinthine wall) - Promontory - a rounded bony eminence formed by the cochlea. Above the promontory is the oval (vestibular) window and below it is the round window. ANTERIOR (Carotid wall) - Thin layer of bone separates the middle ear from the carotid canal. POSTERIOR (Mastoid wall) - Pyramidal eminence. Also on the posterior wall the entrance to the mastoid antrum and air cells - can also become infected. VERY difficult to treat due to isolated location. Roof Lateral Wall Floor Medial Wall Middle Ear - Otitis Media • Inflammation of the middle ear • ________________ (build up of fluid or mucus) Otitis Media with Effusion (OME) Also known as “glue ear” or serous otitis media • Can be an infection due to bacteria or virus Acute Otitis Media (AOM) • Symptoms can include pain, dizziness, nausea, loss of hearing or muffled hearing, retracted eardrum, pulling on ear, and fever (AOM) Middle Ear - Otitis Media ■ ■ ■ ■ Tympanic Plexus - innervates the mucous membrane lining the walls and the contents of the middle ear This plexus lies over the promontory in the medial wall. Formed by: ■ tympanic branch of glossopharyngeal (CN IX), ■ branches of the carotid plexus that are in the mucous membrane covering the promontory. This plexus gives off the ___________________ Nerve, which carries preganglionic parasympathetics to the otic ganglion Otitis Media Pain – Will be transmitted by the plexus but most pain is from the tympanic membrane Rupture- less pain INNER EAR ■ ■ ■ ■ Consists of a series of bony cavities/canals (bony labyrinth) and membranous ducts & sacs (membranous labyrinth - suspended within the bony labyrinth). All these structures are in the petrous part of the temporal bone between the middle ear laterally and the internal acoustic meatus medially Inner ear contains the vestibular and cochlear structures: Organ of hearing - cochlear duct (organ of Corti). Organ of balance/equilibrium - semicircular canals (dynamic equilibrium), utricle (horizontal movements), and saccule (vertical movements). Vestibulocochlear n. (CN VIII) supplies both components. Equilibrium • Also involves Vestibulocochlear nerve and the inner ear (NOT the outer or middle ear) • 2 areas of the inner ear are involved 1. __________________ – senses change in linear motion and gravity, otolithic organ -Utricle – horizontal -Saccule – vertical -Otoliths are embedded in a gelatinous material on top of stereocilia of receptor cells -Static information is provided as well as linear or gravitational movements 2. Semicircular canals – sense change in angular acceleration or rotation of the head -Canals are paired with each other, ex: right superior w left inferior -Canals widen at ampulla, crista are ridges where the receptors are located -Cupula is a gelatinous material where the receptor hairs are embedded Otoliths – Utricle and Saccule Semicircular Canals – Crista Ampullaris with Cupula – NO otoliths Vertigo • Otoliths can become dislodged and end up in a semicircular canal • Benign paroxysmal positional vertigo BPPV • Most common cause of dizziness, vertigo • Maneuver to cure Manual treatments for BPPV – Epley, Semont