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Anatomy of the Ear

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Anatomy of the Ear Anatomy of the Ear Neuroanatomy block-Anatomy-Lecture 10 Editing file Objectives At the end of the lecture, students should be able to: ● List the parts of the ear: External, Middle (tympanic cavity) and Internal (labyrinth). ● Describe the parts of the external ear: auricle and external auditory meatus. ● Identify the boundaries of the middle ear : roof, floor and four walls (anterior, posterior, medial and lateral). ● Define the contents of the tympanic cavity: I. Ear ossicles (malleus, incus, and stapes) II. Muscles (tensor tympani and stapedius III. Nerves (branches of facial and glossopharyngeal) ● List the parts of the inner ear,bony part filled with perilymph (cochlea, vestibule, and semicircular canals), in which is suspended the membranous part that is filled with Color guide endolymph ● Only in boys slides in Green ● List the organs of hearing and equilibrium ● Only in girls slides in Purple ● important in Red ● Notes in Grey The External Ear Formed By The External Auditory The Auricle Canal ● It has a characteristic shape ● is a curved S-shaped tube about and it collects air vibrations 2.5 cm, that conducts & collects ● It consists of a thin plate of sound waves from the auricle to elastic cartilage covered by a the tympanic membrane. Its double layer of skin outer 1/3rd is elastic cartilage, ● It receives the insertion of Tympanic while its inner 2/3rds are bony extrinsic muscles which are membrane ● Its lined by skin, and its outer supplied by the facial nerve. External 1/3rd is provided with hairs, Sensation is carried by acoustic meatus sebaceous and ceruminous greater auricular & glands (modified sweat glands auriculotemporal nerves that secrete a yellowish brownish substance called ear wax) * The auricle is also called pinna * The external auditory canal is also called the external auditory (acoustic) meatus 3 Middle Ear (Tympanic Cavity) ● The middle ear is a narrow, oblique slit-like cavity (air-filled) in the petrous temporal bone & lined with mucous membrane. ● It contains the auditory ossicles, which transmit vibrations of the tympanic membrane (eardrum) to the internal ear ● The middle ear communicates anteriorly with the nasopharynx through the auditory tube (it's also known as the pharyngotympanic tube or eustachian tube) ● which extends from the anterior wall downard, forward and medially to the nasopharynx. ● The posterior 1/3rd of the canal is bony and its anterior 2/3rds are cartilaginous Floor ● its function is to equalize the pressure of both sides of the eardrum It Has Medial Wall Lateral Wall Anterior Wall Posterior Wall Roof Formed by a thin plate of bone Floor called tegmen tympani which is part of the petrous temporal Formed by a thin plate of bone bone It separates the tympanic which separates the middle ear cavity from the temporal lobe from the bulb of the internal of the brain jugular vein 4 Middle Ear (Tympanic Cavity) Posterior Wall Anterior Wall ● The posterior wall has in ● The anterior wall is its upper part a large formed below by a thin irregular opening,which is plate of bone that the aditus to mastoid separates the tympanic antrum a cavity behind cavity from the internal the middle ear, within carotid artery mastoid process, it ● There are 2 canals at the contains air cells) upper part of the anterior ● Below, a small, hollow, wall: conical projection, the - Upper smaller, which pyramid, which houses is the canal for the the stapedius muscle and tensor tympani muscle its tendon - Lower larger, which is ● The tendon emerges from for the auditory tube the apex of the pyramid 5 Middle Ear (Tympanic Cavity) The Lateral Wall Tympanic Membrane ● It is largely formed by the ● It is concave laterally, & at the tympanic membrane. depths of its concavity there is ● The membrane is obliquely a small depression, “the umbo” placed, facing downward, , which is produced by the tip forward, & laterally. of the handle of the malleus. ● It’s extremely sensitive to pain. ● When the membrane is ● Nerve supply of the eardrum: illuminated through an - Outer surface: otoscope, the concavity ● Auriculotemporal produces a “cone of light”, nerve which radiates anteriorly & ● Auricular branch of inferiorly from the umbo. vagus nerve ● Most of the membrane is tense - Inner surface: and is called the Pars Tensa. ● Tympanic branch of the ● A small triangular area on its glossopharyngeal upper part is slack and is nerve called the Pars Flaccida. 6 Middle Ear (Tympanic Cavity) The Medial wall The medial wall is formed by the lateral wall of the inner ear. The greater part of the medial wall shows a rounded projection, called the promontory, that results from the underlying 1st turn of the cochlea. Above & behind the promontory lies the oval window (Fenestra Vestibuli), which is closed by the base of the stapes. Below & behind the promontory lies the round window (Fenestra Cochleae), which is closed by the secondary tympanic membrane. 7 Middle Ear (Tympanic Cavity) ● They transmit sound waves from the tympanic membrane to the perilymph of the internal ear ● They are covered by mucous Auditory Ossicles membrane & are articulated by synovial joints. Stapes( Stirrup) Incus (Anvil) Malleus (Hammer) 8 Middle Ear (Tympanic Cavity) Muscles of the Ossicles Tensor Tympani Stapedius (the smallest voluntary muscle) Internal walls of the hollow Cartilage of the auditory tube & Origin Origin pyramid the bony walls of its own canal The tendon emerges from the Insertion Into the handle of the malleus apex of the pyramid and is Insertion inserted into the neck of the stapes Nerve Mandibular Nerve Supply Nerve Facial Nerve Supply Contracts reflexly in response to loud sounds to limit the Action Reflexly damps downs the excursion of the tympanic Action vibrations of the stapes by membrane pulling on the neck of that bone 9 Nerves in Middle Ear Tympanic Nerve Tympanic Plexus The tympanic nerve is a branch of the glossopharyngeal 1 nerve 2 It gives the Tympanic plexus on the promontory The tympanic plexus gives the lesser petrosal nerve which 3 relays in the otic ganglion The lesser petrosal nerve gives secretomotor supply to the Tympanic Nerve 4 parotid gland 10 Nerves in Middle Ear Facial Nerve The facial nerve enters through the internal acoustic 1 meatus with the 8th nerve. 1 2 It expands to form the geniculate ganglion 2 3 It passes vertically behind the pyramid & leaves the middle ear through the stylomastoid 3 foramen Branches: 4 - Greater petrosal nerve: arises from the geniculate ganglion & carries preganglionic parasympathetic to supply Lacrimal, nasal, & palatine glands. 3 - Nerve to stapedius - Chorda tympani: arises just before the facial nerve exits 11 Internal Ear (Labyrinth) Consists of The labyrinth is situated in the petrous part of the temporal bone, medial to the middle ear. Bony Labyrinth Membranous Labyrinth A series of bony chambers lined by endosteum. They Consists of a series of contain a clear fluid, the membranous sacs & ducts perilymph, in which is within the bony labyrinth, its suspended the membranous filled with endolymph labyrinth 12 Internal Ear (Labyrinth) The Bony Labyrinth consists of Semicircular Vestibule Cochlea Canals -The vestibule is the -There are 3 central part of the semicircular canals: bony labyrinth Superior (anterior) -It contains the utricle canal -The first turn of the & saccule (parts of the Posterior canal cochlea produces the membranous Lateral canal promontory on the labyrinth) -Each canal has a medial wall of the -In the lateral wall of swelling at one end tympanic cavity the vestibule are the called the ampulla -It contains the fenestra vestibuli, -The canals open into cochlear duct (part of which is closed by the the vestibule by five the membranous base of the stapes, & orifices, one of which is labyrinth) the fenestra cochleae, common to two canals which is closed by the -Lodged within the secondary tympanic canals are the membrane. semicircular ducts 13 Internal Ear (Labyrinth) Membranous Labyrinth The membranous labyrinth consists of four ducts & two sacs, which freely communicate with one another. Sacs Ducts Three semicircular ducts (lie within the bony semicircular canals) Utricle & Saccule (lodged in the bony vestibule) Cochlear duct (lies within the bony cochlea). The cochlear duct divides the bony cavity into Scala Vestibuli & Scala Tympani *only in boys slides - The perilymph within the scala vestibuli is separated from the middle ear by the base of stapes at the fenestra vestibuli (oval window) - The perilymph within the scala tympani is separated from the middle ear by the secondary tympanic membrane at the fenestra cochleae (round window) 14 Internal Ear (Labyrinth) Equilibrium & Hearing ● Located on the walls of the utricle & saccule are specialized sensory receptors, which are sensitive to the orientation of the head to gravity or other acceleration forces. ● The utricle, saccule, & semicircular ducts are concerned with maintenance of equilibrium ● The highly specialized epithelium on the floor of the cochlear duct forms the spiral organ of corti that contains sensory receptors for hearing. 15 Practice Q5: The auditory ossicles are articulated by which type of joint? Q1: The outer 1/3rd of the external auditory canal is: A. Synovial A. Bony B. Fibrous B. Elastic cartilage C. Cartilaginous C. Fibrous cartilage D. None of the above D. Hyaline cartilage Q6: The tensor tympani muscle is inserted into the: Q2: The auditory ossicles are found in: A. Lateral process of malleus A. External Ear B. Handle of stapes B. Middle Ear C. Handle of malleus C. Internal Ear D. Neck of stapes D. Labyrinth Q7: Which of the following is responsible for the maintenance of equilibrium? Q3: Which wall in the middle ear contains the aditus to mastoid antrum? A. Utricle A. Medial Wall B. Saccule B. Lateral Wall C. Semicircular ducts C. Anterior Wall D. All of the above D. Posterior Wall Q8 : Each of the semicircular canals has a swelling at one called: Q4: The tympanic cavity communicates with the nasopharynx via the: A.
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