The Ear PDF

The Ear Dr. Jessa Mayet A. Sumatra-Mabalot M.P.H The Ear Maintains the balance of the body (vestibular) Perceives sound (auditory)  Consists of the : external ear middle ear (tympanic cavity) internal ear (labyrinth) External Ear External Ear Comprised of the au...

The Ear Dr. Jessa Mayet A. Sumatra-Mabalot M.P.H The Ear Maintains the balance of the body (vestibular) Perceives sound (auditory)  Consists of the : external ear middle ear (tympanic cavity) internal ear (labyrinth) External Ear External Ear Comprised of the auricle , external auditory meatus Auricle Has a characteristic shape Collects air vibration Consist of a thin plate of elastic cartilage covered by skin Possesses both extrinsic and intrinsic muscles supplied by facial nerve Auricle Superior portion: skeleton of elastic cartilage Inferior portion (lobule): no cartilage Auricle Helix Outermost curved rim of the auricle Continuous anteriorly to blend with the head at the crus of helix Auricle antihelix Portion of cartilage that follows along the helix from the inside Auricle Scaphoid fossa Depressed area between the helix and antihelix Auricle Concha Demarcated by the antihelix Depressed area that leads to the external acoustic meatus Auricle Tragus Extends from the face into the concha Auricle Antitragus Extends from the inferior portion of the antihelix into the concha and is separated from the tragus by the intertragic notch External Auditory meatus Curved tube that leads from the auricle to the tympanic membrane About 2.5cm in length Conducts sound waves from the auricle to the tympanic membrane Lined by skin and its outer third is provided with hairs, sebaceous and ceruminous glands External Auditory meatus outer third - elastic cartilage Inner two thirds- bone (osseous); formed by the tympanic, squamous, and petrous portion of the temporal bone External Ear External auditory meatus Sensory nerve supply of the skin auriculotemporal nerve auricular branch of the vagus nerve Lymphatic drainage super cial parotid mastoid super cial cervical lymph nodes fi fi Tympanic Membrane Most medial portion of the external ear that separates it from the middle ear Lies in a groove on the tympanic part of the temporal bone A connective tissue structure that is covered with skin on the outside and mucous membrane on the outside Tympanic Membrane A thin semitransparent, 3-layered membrane External layer Derived from the skin; composed of strati ed squamous epithelium Middle layer Fibrous, with bers attaching to the malleus Inner layer Continuous with the mucous membrane of the middle ear cavity Composed of columnar epithelium with cilia fi fi Tympanic Membrane Translucent ; allows the structure within the middle ear to be observed during otoscopy malleus attaches to the umbo of tympanic membrane. Tympanic Membrane handle/manubrium of malleus continues superiorly, and at its highest point, a small projection called the lateral process of the malleus can be seen The parts of the tympanic membrane moving away from the lateral process are called the anterior and posterior malleolar folds. Tympanic Membrane Pars accida a.k.a Shrapnell's membrane Flaccid portion of the tympanic membrane located superiorly fl Tympanic Membrane Pars tensa Tense portion of the TM Main portion of the membrane extends from the anterior and posterior malleolar folds to the inferior extent of the tympanic membrane at its attachment Clinical Correlate Tympanic membrane examination Facilitated by rst straightening the external auditory meatus by : pulling the auricle upward and backward in adult Backward and downward in infants fi Middle Ear Middle Ear Transmits sound vibrations from the tympanic membrane to the inner ear via the ear ossicles: Malleus Incus Stapes Located mainly within the petrous portion of temporal bone Resembles a biconcave lens in shape Middle Ear Composed of the tympanic cavity that connects anteriorly with the nasopharynx via the auditory tube (eustachian tube) and mastoid air cells posteriorly Middle Ear Contents: Ear ossicles Muscles: tensor tympani and stapedius muscles Nerves: chorda tympani, tympanic branch CN IX, lesser petrosal nerve Tympanic plexus : parasympathetic (CN IX), sympathetics (superior cervical ganglion via carotid plexus) Malleus Ear Ossicles Largest ossicle possesses head neck long process/handle anterior process lateral process Malleus Auditory Ossicles Head Rounded; articulates with the incus Neck Constricted part below the head Handle Passes downward and backward to attach to the TM Anterior process Bony spicule connected to the anterior wall of tympanic cavity Lateral process Projects laterally ; attached to anterior and posterior malleolar folds of TM Incus Auditory Ossicles Possesses a large body and two processes Body Rounded; articulates anteriorly with the head of malleus Long process Descends behind and parallel to the handle of malleus Short process Projects backward and is attached to the posterior wall of the tympanic cavity by a ligament Stapes Auditory Ossicles Head Small; articulates with the long process of the incus Neck Narrow and receives insertion of the stapedius muscle 2 limbs Diverge from the neck and are attached to the oval base Base Muscles of the Ossicles Auditory Tube a.k.a eustachian tube connects the anterior wall of the tympanic cavity to the nasal pharynx Its posterior third is bony, and its anterior two thirds is cartilaginous It serves to equalize air pressures in the tympanic cavity and the nasal pharynx Mastoid Antrum Lies behind the middle ear in the petrous part of the temporal bone Communicates with the middle ear by the aditus  Relations of the Mastoid Antrum Anterior wall: related to the middle ear; contains the aditus Posterior wall: separates the antrum from sigmoid venous sinus and cerebellum Lateral wall: forms the oor of the suprameatal triangle Medial wall: related to the posterior semicircular canal fl Inner Ear Inner Ear a.k.a labyrinth situated in the petrous part of the temporal bone, medial to the middle ear Consists of the bony labyrinth and the membranous labyrinth Bony (Osseous) Labyrinth Located in the petrous portion of the temporal bone Surrounds the membranous labyrinth Contains perilymph Connects to the middle ear via the fenestra vestibuli and the fenestra cochlae 3 parts: vestibule, cochlea, and semicircular canals Bony (Osseous) Labyrinth Vestibule Middle portion of the osseous labyrinth Contains the saccule and utricle of the membranous labyrinth Contains an opening for the vestibular aqueduct containing the endolymphatic duct Bony (Osseous) Labyrinth Cochlea Anterior portion of the osseous labyrinth Contains the cochlear duct of the membranous labyrinth Spirals around a central point (modiolus), which carries branches of the cochlear nerve to the cochlear duct Functions to transform the vibrations of the cochlear liquids and associated structures into a neural signal Bony (Osseous) Labyrinth Semicircular Canal Posterior portion of the osseous labyrinth 3 parts: anterior, posterior, lateral Anterior and posterior semicircular canals have a common crus Ampulla: dilated end of each part Membranous labyrinth Located within the osseous labyrinth Contains endolymph Divided into 4 parts: cochlear duct, saccule, utricle, semicircular ducts Membranous labyrinth Cochlear Duct a.k.a scala media Spiral structure located within the cochlea Triangular in shape, with a base created by the endosteum of the canal known as the spiral ligament and the stria vascularis  Stria vascularis Structure composed of 3 layers of cells- marginal, intermediate and basal Responsible for maintaining the ionic composition of endolymph  Membranous labyrinth Cochlear Duct Its roof is formed by the vestibular membrane that separates the cochlear duct from the Scala vestibuli Its oor is formed by the basilar membrane on which lies the organ of Corti; separates the duct from the Scala tympani fl Membranous labyrinth Saccule Small structure located within the vestibule of the osseous labyrinth Connected to the utricle via the utriculosaccular duct and the endolymphatic duct Where the sensory receptors (maculae) are located Otolith organ that is sensitive to vertical accelration Membranous labyrinth Utricle Located within the vestibule of the osseous labyrinth Sensory receptors are also present Otolith organ that is sensitive to horizontal accelration Membranous labyrinth Semicircular Ducts Correspond to the semicircular canals of the osseous labyrinth (anterior, posterior, and lateral) Open into the utricle via 5 openings Sensory receptors known as crista are located in its ampullae Sensory Innervation to the External Ear Nerve Innervation: skin over the mastoid process, posterior portion of the auricle, and the concha Great Auricular Nerve and lobule Lesser occipital nerve skin posterior to the auricle Skin in the region of the tragus, crus, helix, anterior portion of EAM, and outer Auriculotemporal nerve surface of the tympanic membrane Auricular branch of the vagus Skin of the back of the auricle, and posterior portion of the EAM nerve Preganglionic parasympathetic bers to the parotid gland Tympanic branch of Postganglionic sympathetic bers to the parotid gland Glossopharyngeal nerve Sensory bers to the middle ear cavity including the TM and auditory tube fi fi fi Sensory Innervation to the Middle Ear Nerve Innervation: Preganglionic parasympathetic bers to the parotid gland Tympanic Plexus Postganglionic sympathetic bers to the parotid gland Sensory bers to the middle ear cavity including the TM and auditory tube Stapedius muscle Facial Nerve Chorda tympani carries preganglionic parasympathetic bers to the submandibular ganglion of the oral cavityand taste bers to anterior 2/3 of tongue fi fi fi fi fi Sensory Innervation to the Inner Ear Vestibulocochlear Nerve Nerve Innervation: Superior branch- maculae of the saccule and utricle and ampulla of the anterior and Vestibular lateral semicircular ducts Inferior branch- macula of the saccule and ampulla of the posterior semicircular duct transfers auditory information from the cochlea (auditory area of the inner ear) to the Cochlear brain.  Vascular Supply of the External Ear Artery Supplies the: Auricle and external acoustic meatus Super cial temporal Auricle and external acoustic meatus Posterior Auricular Inner surface of tympanic membrane TMJ Deep Auricular Outer surface of tympanic membrane Anterior tympanic Inner surface of tympanic membrane fi Vascular Supply of the Middle Ear Artery Supplies the: Outer surface of TM and anterior portion of tympanic cavity Anterior tympanic Medial walls of the tympanic cavity Inferior tympanic Superior tympanic Tensor tympani and its bony canal Caroticotympanic branch of Middle ear the internal carotid Vascular Supply of the Internal Ear Artery Supplies the: Cochlear and vestibular structures Labyrinthine Auricle and external meatus Internal surface of the TM, and posterior portion of the tympanic cavity and helps Posterior Auricular supply the inner ear